WO2011139964A1

WO2011139964A1 - Improved heat exchanger system and methods

Info

Publication number: WO2011139964A1
Application number: PCT/US2011/034785
Authority: WO
Inventors: Martin David Smalc; Gregory P. Kramer; Robert A. Reynolds; Bradley E. Reis; Joseph Paul Capp; Lawrence K. Jones
Original assignee: Graftech International Holdings Inc.
Priority date: 2010-05-04
Filing date: 2011-05-02
Publication date: 2011-11-10
Also published as: KR20130002812U; CN203349354U; JP3183582U

Abstract

A heat exchanger for radiant heating and cooling applications provides a graphite heat spreader attached to a liner. The liner includes a groove, or recess, shaped for accommodating a thermal element. The heat spreader extends into and conforms to the groove. In one embodiment a snap tab is integrally molded on the liner and protrudes into the groove for retaining the thermal element in the groove. In one embodiment the snap tab extends through a clearance void in the heat spreader for engaging the thermal element. Methods of forming a heat exchanger, a heat spreader and a liner are also provided.

Description

IMPROVED HEAT EXCHANGER SYSTEM AND METHODS

BACKGROUND SUMMARY

TECHNICAL FIELD

[0001] The present disclosure relates to an improved heat exchanger for distributing thermal energy. More particularly, the present disclosure relates to a heat exchanger of the type used for distributing or absorbing heat between a thermal element and a floor or a wall.

BACKGROUND ART

[0002] Heat exchanger systems for radiant heating and cooling applications are known in the art. Radiant heating systems are alternatives to the conventional heating systems such as forced hot air, discrete radiators, and baseboards, and can be either electric (i.e., use a resistance element) or hydronic (i.e., use heated or cooled fluid, especially water). The typical electric radiant heating system consists of a resistance element with the appropriate wiring and associated circuitry. The typical hydronic radiant heating system consists of a boiler for heating water, a pump, a supply pipe, a flexible heating pipe embedded throughout the floor of a room to be heated, a return pipe, and a thermostat for regulating the boiler. Hydronic systems have been designed for applications such as slab-on-grade, thin-slab, underfloor staple-up, etc., as can be seen in the Radiant Panel Association web site (as www.radiantpanelassociation.org). Heated water is pumped from the boiler, through the supply pipe, the heating pipe, and the return pipe back to the boiler. As noted, these systems have several advantages over other heating systems, and provide uniform heat to a room. Because the source of the heat in radiant hydronic heating systems is not localized, such as with a forced hot air, discrete radiator, or baseboard systems, the heating water only has to be heated to a temperature that is slightly above the desired room temperature. For example, if the desired room temperature is 70°F, the water may only have to be heated to about 90°F, depending upon the outside temperature, as opposed to about twice that for other conventional heating systems. [0003] As noted, conventional radiant heating systems known in the art utilize a heating element within a floor or wall structure to carry and distribute heat without any visible radiators or heating grills. They generally do so by embedding the heating element such as tubing, especially a strong, flexible plastic tubing such as cross-linked polyethylene, referred to as PEX tubing, in a material such as a flooring intermediary substrate. For example, in a conventional radiant floor heating system, the tubing can be embedded in a single continuous horizontal concrete slab poured below the finished flooring, although applications using lighter weight materials like polystyrene foam materials have also been employed. Warm water is circulated through the tubing and the heat in the circulated fluid flowing through the tubing is transferred to the concrete slab by conduction. The concrete stores and radiates the heat, thereby warming the air as well as people and objects in the room, rather than only the air in the room, and thus can be more cost effective and can reduce heat loss. Further, such systems may be used for cooling wherein colder or cool water is run through the system; such cooling systems may be embedded in walls or ceilings, for example.

[0004] Some conventional radiant heating systems are formed by providing a subfloor, running tubing over the subfloor, and then pouring a single continuous concrete or gypsum slab, such as Maxxon Corporation's THERMA-FLOOR® material, around and over the tubing. A synthetic material is generally used for the tubing, such as polyethylene or polybutylene, which has the advantage of not expanding and contracting with fluctuations in temperature. When the concrete or gypsum hardens, it acts as the thermal mass for the system. The concrete or gypsum underlayment or slab is poured in liquid form across the entire surface area and cures to encase the tubing.

[0005] What is needed then is an improved heat exchanger apparatus for radiant temperature control of a room or an environment that improves heat transfer performance and provides a desirable temperature gradient between thermal elements. Also needed is a method of manufacturing a heat exchanger apparatus exhibiting improved thermal performance characteristics.

BRIEF DESCRIPTION

[0006] One aspect of the present disclosure provides a heat exchanger for transferring heat between a thermal element and a structural assembly. The structural assembly can include a floor, a wall, a ceiling or any other boundary surface for an environment, particularly for a room in a building. The heat exchanger includes a heat spreader comprising at least one sheet of compressed particles of exfoliated graphite having a density of at least about 0.6 grams per cubic centimeter (g/cc) and a thickness of less than about 10 millimeters (mm). In certain embodiments, the heat spreader defines a spreader recess. A liner is attached to the heat spreader, and an extended tab protrudes from the liner toward the heat spreader. The extended tab is shaped for retaining the thermal element in the spreader recess.

[0007] Another embodiment of the present disclosure provides a heat exchanger for transferring heat between a thermal element and a structural assembly. The heat exchanger includes a heat spreader comprising at least one sheet of compressed particles of exfoliated graphite having a density of at least about 0.6 g/cc and an in-plane thermal conductivity of at least about 140 watts per meter-Kelvin (W/m*K). The heat spreader includes a first side and a second side. A liner is attached to the first side, and a sheet layer is attached to the second side. The sheet layer includes a thickness between about ten microns and about fifty microns. In one embodiment, the sheet layer is polyethylene.

[0008] Yet another embodiment of the present disclosure provides a heat exchanger for distributing thermal energy from a thermal element to an environment. The heat exchanger includes a panel having a thermal conductivity less than about 1.0 W/m*K. The panel includes a panel groove shaped for receiving the thermal element. A heat spreader is disposed on the panel. The heat spreader includes at least one sheet of compressed particles of exfoliated graphite having an in-plane thermal conductivity of greater than about 140 W/m*K. The heat spreader defines a spreader groove shaped for mating with the panel groove. A thermoplastic liner is positioned between the panel and the heat spreader. The liner includes an extended tab protruding toward the spreader groove.

[0009] Yet another embodiment of the present disclosure provides a foldable heat exchanger panel apparatus for transferring heat from a thermal element to an environment. The heat exchanger panel includes a first base including a first surface groove defined therein. A second base is pivotally attached to the first base. A first liner is disposed on the first base, and a heat spreader is disposed on the first liner and second liner. The heat spreader includes at least one sheet of compressed particles of exfoliated graphite.

[0010] Yet another embodiment of the present disclosure provides a heat exchanger including at least one flexible graphite sheet having an in- plane thermal conductivity greater than about 250 W/m*K and a thickness less than about 2 millimeters. A thermoplastic liner includes a U-shaped groove defined therein. The flexible graphite sheet extends into the U-shaped groove between the thermal element and the thermoplastic liner. At least one snap tab is integrally molded on the thermoplastic liner and protrudes into the U-shaped groove.

[0011] Yet another embodiment of the present disclosure provides a method of forming a thermoplastic liner for a heat exchanger apparatus. The method includes the steps of: (a) providing a thermoplastic liner blank having a first thickness and a second thickness, the second thickness being greater than the first thickness; (b) positioning the thermoplastic liner blank on a mold having a liner recess channel formed therein, wherein the region of the thermoplastic liner blank having the second thickness is aligned with the liner recess channel; and (c) forcing the thermoplastic liner blank into the liner recess channel to deform the thermoplastic liner blank into a thermoplastic liner, wherein the thermoplastic liner forms a groove having substantially the same shape as the liner recess channel.

[0012] Yet another embodiment of the present disclosure provides a method of forming a graphite heat spreader, the method comprising the steps of: (a) providing a heat spreader blank including a sheet of compressed particles of exfoliated graphite positioned between a male vacuum die and a matching multipart female die, wherein the male vacuum die includes a spreader groove former and the female die includes a center die, an inner tube former and an outer tube former; (b) pressing the center die against the male vacuum die; (c) pressing the first inner tube former against the male vacuum die partially aligned with the spreader groove former; and (d) pressing the outer tube former against the male vacuum die partially aligned with the spreader groove former.

[0013] Yet another embodiment of the present disclosure provides a method of forming a heat exchanger, comprising the steps of: (a) thermoforming a liner blank comprising a thermoplastic material in a female thermoforming die, wherein the mold defines at least one liner recess channel, thereby forming a thermoformed liner retained on the female thermoforming die; (b) pre-forming a spreader blank comprising a sheet of compressed particles of exfoliated flexible graphite, thereby forming a preformed heat spreader retained on the male vacuum die; and (c) pressing the male vacuum die with pre-formed heat spreader positioned thereon against the female thermoforming die with the thermoformed liner positioned thereon, such that the preformed heat spreader engages and bonds to the thermoplastic liner.

[0014] Yet another embodiment of the present disclosure provides heat exchanger panel apparatus including a base panel, a base panel heat spreader disposed on the base panel, the heat spreader including at least one sheet of compressed particles of exfoliated graphite having a density greater than about 0.6 g/cc and a thickness less than about 10 millimeters. A channel panel is disposed on the heat spreader, the channel panel defining a channel panel gap.

[0015] Numerous other features and advantages of the present disclosure will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1A illustrates an exploded partial perspective view of one embodiment of heat exchanger apparatus.

[0017] FIG. IB illustrates a detail exploded partial perspective view of the embodiment of a heat exchanger apparatus seen in FIG. 1A.

[0018] FIG. 1C illustrates a detail partial perspective view of one embodiment of a heat exchanger apparatus.

[0019] FIG. 2 illustrates a detail partial perspective view of one embodiment of a heat exchanger apparatus including a thermal element.

[0020] FIG. 3A illustrates a perspective view of one embodiment of a heat exchanger apparatus.

[0021] FIG. 3B illustrates a detail partial plan view of the embodiment of a heat exchanger apparatus seen in FIG. 3A.

[0022] FIG. 4 illustrates a partial cross-sectional view of one embodiment of a heat exchanger apparatus in a below-subfloor application.

[0023] FIG. 5A illustrates a partial exploded cross-sectional view of one embodiment of a heat exchanger apparatus.

[0024] FIG. 5B illustrates a partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0025] FIG. 6 illustrates a partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0026] FIG. 7 illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0027] FIG. 8 illustrates an exploded partial perspective view of one embodiment of a heat exchanger apparatus.

[0028] FIG. 9 illustrates a partial cross-sectional view of Section B - B seen in FIG. 8.

[0029] FIG. 10 illustrates an exploded partial perspective view of one embodiment of a heat exchanger apparatus.

[0030] FIG. 11 illustrates a partial perspective view of one embodiment of a floor assembly including one embodiment of a heat exchanger apparatus. [0031] FIG. 12 illustrates an exploded partial perspective view of one embodiment of a heat exchanger apparatus.

[0032] FIG. 13 illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0033] FIG. 14 illustrates a plan view of one embodiment of a heat exchanger apparatus.

[0034] FIG. 15 illustrates a partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0035] FIG. 16 illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0036] FIG. 17A illustrates a plan view of one embodiment of a heat exchanger apparatus.

[0037] FIG. 17B illustrates a detail corner view of the embodiment of a heat exchanger apparatus seen in FIG. 17 A.

[0038] FIG. 18A illustrates a partially exploded detail partial cross- sectional view of one embodiment of a heat exchanger apparatus.

[0039] FIG. 18B illustrates a detail partial cross-sectional view of the one embodiment of a heat exchanger apparatus seen in FIG. 18A.

[0040] FIG. 19A illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus including a thermal element.

[0041] FIG. 19B illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus including a thermal element.

[0042] FIG. 19C illustrates a detail partial cross-sectional view the one embodiment of a heat exchanger apparatus seen in FIG. 19B.

[0043] FIG. 20A illustrates a detail partial perspective view of one embodiment of spreader recess of a heat exchanger apparatus.

[0044] FIG. 20B illustrates a detail partial cross-sectional view of the heat exchanger apparatus of FIG. 20A.

[0045] FIG. 20C illustrates a detail partial perspective view of one embodiment of a heat exchanger apparatus.

[0046] FIG. 20D illustrates a detail partial cross-sectional view of the heat exchanger apparatus of FIG. 20C. [0047] FIG. 20E illustrates a detail partial perspective view of one embodiment of a heat exchanger apparatus including a thermal element.

[0048] FIG. 20F illustrates a detail partial cross-sectional view of the heat exchanger apparatus of FIG. 20E.

[0049] FIG. 21A illustrates a detail partial perspective view of one embodiment of a heat exchanger apparatus.

[0050] FIG. 2 IB illustrates a detail partial cross-sectional view of the heat exchanger apparatus of FIG. 21 A.

[0051] FIG. 21C illustrates a detail partial perspective view of one embodiment of a heat exchanger apparatus.

[0052] FIG. 2 ID illustrates a detail partial cross-sectional view of the heat exchanger apparatus of FIG. 2 ID.

[0053] FIG. 2 IE illustrates a detail partial perspective view of one embodiment of a heat exchanger apparatus including a thermal element.

[0054] FIG. 2 IF illustrates a detail partial cross-sectional view of the heat exchanger apparatus of FIG. 2 IE.

[0055] FIG. 22A illustrates a perspective view of one embodiment of a heat exchanger apparatus.

[0056] FIG 22B illustrates a detail partial cross-sectional view of the heat exchanger apparatus of FIG. 22A.

[0057] FIG. 22C illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0058] FIG. 22D illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0059] FIG. 22E illustrates a detail partial cross-sectional view of one embodiment of a heat exchanger apparatus.

[0060] FIG. 22F illustrates a perspective view of one embodiment of a heat exchanger apparatus.

[0061] FIG. 23 illustrates an exploded partial perspective view of one embodiment of an exemplary step of a method of pre-forming a heat spreader.

[0062] FIG. 24 illustrates an exploded partial perspective view of one embodiment of a multipart female die for pre-forming a heat spreader. [0063] FIG. 25 illustrates a partial perspective view of one embodiment of an exemplary step of a method of pre-forming a heat spreader.

[0064] FIG. 26 illustrates a partial perspective view of one embodiment of a pre-formed heat spreader on a male vacuum die.

[0065] FIG. 27 illustrates an exploded partial perspective view of one embodiment of a female thermoforming die for thermoforming a liner.

[0066] FIG. 28A illustrates a detail partial perspective view of one embodiment of a female thermoforming die for thermoforming a liner.

[0067] FIG. 28B illustrates a detail partial perspective view of one embodiment of a female thermoforming die with a moveable tab former.

[0068] FIG. 29 illustrates a partial perspective view of one embodiment of a thermoformed liner.

[0069] FIG. 30 illustrates an exploded partial perspective view of one embodiment of a female thermoforming die for thermoforming a liner.

[0070] FIG. 31 illustrates the die setup for performing the thermal bonding method between the heat spreader and the thermoplastic liner.

[0071] FIG. 32 illustrates a partial cross-sectional view of one embodiment of a heat exchanger panel apparatus.

[0072] FIG. 33 illustrates a partial cross-sectional view of one embodiment of a heat exchanger panel apparatus.

DETAILED DESCRIPTION

[0073] The following disclosure generally describes a heat exchanger having a heat spreader including a sheet of compressed particles of exfoliated graphite.

[0074] Compressed exfoliated graphite materials, such as graphite sheet and foil, are coherent, with good handling strength, and are suitably compressed, e.g. by roll pressing, to a thickness of about 0.05 mm to 3.75 mm and a typical density of about 0.4 to 2.2 g/cc or higher. Indeed, in order to be consider "sheet," the compressed particles of exfoliated graphite should have a density of at least about 0.6 g/cc, and to have the flexibility required for the present disclosure, it should have a density of at least about 1.1 g/cc, more preferably at least about 1.5 g/cc. From a practical standpoint, the graphite sheet has a density of no greater than about 2.1 g/cc. While the term "sheet" is used herein, it is meant to also include continuous rolls of material, as opposed to individual sheets.

[0075] The graphite sheet(s) which make up the disclosed heat spreader should have a thermal conductivity parallel to the plane of the sheet (referred to as "in-plane thermal conductivity") of at least about 140 W/m*K for effective use. More advantageously, the thermal conductivity parallel to the plane of the graphite sheet(s) is at least about 220 W/m*K, most advantageously at least about 300 W/m*K. Of course, it will be recognized that the higher the in-plane thermal conductivity, the more effective the heat spreading characteristics of the inventive heat spreader. From a practical standpoint, sheets of compressed particles of exfoliated graphite having an in- plane thermal conductivity of up to about 800 W/m*K are all that are necessary. The expressions "thermal conductivity parallel to the plane of the sheet" and "in-plane thermal conductivity" refer to the fact that a sheet of compressed particles of exfoliated graphite has two major surfaces, which can be referred to as forming the plane of the sheet; thus, "thermal conductivity parallel to the plane of the sheet" and "in-plane thermal conductivity" constitute the thermal conductivity along the major surfaces of the sheet of compressed particles of exfoliated graphite. The through-plane thermal conductivity, that is, the thermal conductivity through the thickness of the sheet, should be less than about 12 W/m*K, more preferably less than about 9 W/m*K, and need not be any less than 0.1 W/m*K.

[0076] Referring now to FIG. 1A, a heat exchanger 10 for transferring heat between a thermal element and a structural assembly includes a heat spreader 18 and a liner 22. Heat spreader 18 is generally disposed on the surface of liner 22. In some embodiments, a structural assembly can include any boundary surface of an indoor or outdoor room, enclosure or environment, for example a floor, a wall, a ceiling, driveway, a sidewalk, etc. In some embodiments, heat exchanger 10 is positioned in contact with a structural assembly, i.e. below a subfloor, above a subfloor, behind a wall or above a ceiling in a room of a building, for improving heat transfer, and specifically heat flux, between a thermal element and the wall assembly. In other embodiments, heat exchanger 10 may be used in an outdoor application, for example to improve heat flux between a thermal element and a ground surface. It is also understood that heat exchanger 10 can be used in vertical, horizontal or angular orientations. It will be appreciated that heat exchanger 10 can have various dimensions, and will typically be sized as required for a given application.

[0077] In contrast to the graphite sheets disclosed herein, conventional heat spreaders formed of aluminum generally do not exhibit anisotropic thermal conductivity, and typically have in-plane and cross-plane thermal conductivities ranging between about 160 - 220 W/m*K. Additionally, conventional aluminum heat spreaders typically include a density of about 2.7 g/cc.

[0078] Additional characteristics of the graphite sheet used in some embodiment of heat spreader 18 include a sheet having a thickness between about 0.020 mm and about 10.0 mm. In some embodiments, the graphite sheet of heat spreader 18 has a thickness less than about 1.5 mm. It is understood that flexible graphite sheet of heat spreader 18 can be also provided in rolls that can be unrolled to a desirable length and can be cut to a desired shape. Additionally, the graphite sheet of heat spreader 18 in some embodiments is non-toxic, is RoHS-compliant and complies with Underwriters Laboratories UL-94-VO flammability standard, rendering the graphite sheet suitable for many residential and commercial building applications.

[0079] Referring again to FIG. 1A, heat spreader 18 is attached to liner 22. It is understood that liner 22 can be attached to heat spreader 18 using an adhesive or can be directly boned to liner 22 using a thermal bonding process. Liner 22 in some embodiments includes a thermoplastic or thermosetting material, including, for example, polyester, polystyrene, polyethylene, or mixtures thereof. Typically, liner 22 is given its shape using a thermoforming process during which heat and pressure are applied to a liner blank in a mold, or die. In another embodiment, liner 22 can be extruded into the desired shape. Liner 22 defines a liner recess 24. In some embodiments, liner 22 includes a plurality of liner recesses 24, seen for example in FIG. 10. Although liner recess 24 seen in FIG. 1A is shown with a linear orientation and a curved cross-sectional profile, it is understood that liner recess 24 can include numerous other longitudinal shapes, including non-linear or curved longitudinal shapes, for example U-shaped orientations, and can include various other cross-sectional provides not shown.

[0080] Liner recess 24 is generally shaped to accommodate a thermal element. The thermal element can include an electronic resistance heating element. In other embodiments, particularly for radiant hydronic heating and cooling applications, the thermal element can include a tube for transporting a heated or cooled fluid or gas medium for transferring heat to or absorbing heat from heat spreader 18.

[0081] Also seen in FIG. 1A, heat spreader 18 can include at least one spreader groove, or spreader recess 26. In some embodiments, heat spreader 18 includes a plurality of spreader recesses 26. Spreader recess 26 is generally shaped to mate with liner recess 24. In some embodiments, heat spreader 18 is flexible and is pressed into liner recess 24 to contour to the shape of liner recess 24. It is understood that in some embodiments spreader recess 26 will define a protruding region in heat spreader 18 that extends into liner recess 24, substantially contouring to and engaging the surface of liner 22 in liner recess 24. In other embodiments, the protruding region of heat spreader 18 extending into liner recess 24 will only partially engage to the surface of liner recess 24.

[0082] Referring now to FIGS. 1A and IB, liner 22 can include a snap tab, or extended tab 30, protruding from liner 22 generally toward heat spreader 18. More particularly, as seen in one embodiment in FIG. IB, extended tab 30 protrudes into liner recess 24. In some embodiments heat spreader 18 defines a tab clearance void 32 generally aligned with tab 30. Tab clearance void 32 can include interior corners 34 each having a radius of curvature for relieving stress concentration during installation, packaging, shipment and/or use. Rounded interior corners 34 can also prevent crack propagation between adjacent tab clearance voids 32 positioned along spreader recess 26. In some embodiments, interior corners 34 include a radius of curvature between about one mm and about five mm. In some embodiments, when heat spreader 18 is positioned on liner 22, as seen in FIG. 1C, extended tab 30 protrudes through tab clearance void 32 at least partially into spreader recess 26. In one embodiment, extended tab 30 extends outward from liner 22 a maximum distance between about 1 and about 20 mm. In yet another embodiment, extended tab 30 extends outward from liner 22 between about 1 and about 5 mm. It is understood that extended tab 30 can have a variety of other shapes and positions on liner 22. It is noted that extended tab 30 does not extend along the entire length of liner recess 24, but rather includes a tab width. In some embodiments, the tab width is between about 5 and about 50 mm. In other embodiments tab width is between about 10 and about 25 mm.

[0083] Referring now to FIG. 2, a thermal element 14 is positioned in heat exchanger 10. Thermal element 14 in one embodiment is a plastic or polymer tube. Especially in radiant hydronic applications, thermal element 14 can include cross-linked polyethylene, or PEX, tubing. Extended tab 30 engages thermal element 14, thereby retaining thermal element in spreader recess 26. In some embodiments, extended tab 30 applies a compressive force on thermal element 14, pushing thermal element 14 into spreader recess 26 and providing additional surface area contact between heat spreader 18 and thermal element 14 as thermal element 14 is pushed against heat spreader 18. It is understood that improved surface area contact between thermal element 14 and heat spreader 18, especially along spreader recess 26, improves heat flux between thermal element 14 and heat spreader 18. In some embodiments, the compressive force applied by extended tab 30 against thermal element 14 is sufficient to secure heat spreader 18 to liner 22 without any requiring any other bonding or attachment means present between liner 22 and heat spreader 18.

[0084] Referring now to FIG. 3A, one embodiment of heat exchanger apparatus 10 includes heat spreader 18 positioned on a liner 22 includes a plurality of extended tabs, or snap tabs 30, protruding from liner 22 generally toward heat spreader 18. Heat spreader 18 includes a plurality of tab clearance voids 32 generally aligned with the plurality of extended tabs 30. Each extended tab 30 can be thermoformed or integrally molded on liner 22. Each extended tab 30 extends into spreader recess 26 for securing thermal element 14 (not shown) in liner recess 26. In one embodiment, seen in FIG. 3B, adjacent tab clearance voids 32 are separated by void separation distance 38. Each tab clearance void 32 also includes a void length 40. In some embodiments, seen in FIG. 3A and 3B, void separation distance 38 is less than void length 40. In other embodiments (not shown), void separation distance 38 is equal to or greater than void length 40. In some applications, it is desirable to include a heat exchanger 10 having tab clearance voids 32 spaced at even intervals along spreader recess 26, wherein each void separation distance 38 is equal and is greater than each void length 40. Such a configuration can prevent the development and propagation of cracks in heat spreader 18 between adjacent tab clearance recesses 32. For example, heat spreader 18 may be thermoformed to include spreader recess 26 prior to attaching to liner 22. In some embodiments, tab clearance voids 32 are formed in heat spreader 18 prior to thermoforming spreader recess 26. Evenly-spaced tab clearance voids 32, as seen in FIG. 3C can prevent crack development during thermoforming of heat spreader 18. Evenly-spaced tab clearance voids can also improve heat transfer from thermal element 14 to heat spreader 18 and can prevent local hot or cold spots, providing a more uniform floor temperature gradient. Additionally, evenly-spaced tab clearance voids 32 can provide greater ease of installation as thermal element 14 is pushed into spreader recess 26 by hand, i.e. even spacing reduces lateral bending moment applied on thermal element 14 as it passes over and between adjacent tabs.

[0085] In some embodiments, seen in FIG. 3A, liner 22 together with spreader 18 forms a modular panel that can be used in above-subfloor or below-subfloor radiant hydronic thermal control applications. Generally, heat exchanger 10 is installed such that liner 22 is on the side of heat spreader 18 opposite the direction of desired heat flux. For example, heat exchanger 10 could be placed between joists 116 underneath a subfloor so that heat spreader 18 is between the subfloor and liner 22, as seen generally FIG. 4. In this embodiment, the direction of desired heat flux is from heat spreader 18 toward subfloor 118. In similar configurations, heat exchanger 10 can be positioned between beams in wall or rafters in a ceiling such that the direction of desired heat flux is toward the room or environment surrounded by the wall or ceiling. In the configuration shown in FIG. 4, heat exchanger 10 can be secured to subfloor 118, or similarly a wall board or ceiling, by a variety of fastening means, including stapling, nailing, screwing or gluing heat exchanger 10 directly to subfloor 118. In some embodiments, liner 22 includes a flexible thermoplastic material, wherein the flexibility facilitates efficient installation between joists, support beams or rafters.

[0086] As seen in FIG. 5A, heat exchanger 10 can include a liner 22 having multiple liner recesses 26 and a heat spreader 18 having multiple spreader recesses 26 for accommodating multiple thermal elements 14, or multiple passes of one continuous thermal element 14. In some embodiments of a heat exchanger 10 having multiple thermal elements 14, or multiple passes of one thermal element 14, it is desirable to provide spreader recesses 26 at intervals spaced sufficiently to allow adequate heat transfer between adjacent thermal elements 14. One advantage of using graphite as a heat spreader material includes improving in-plane thermal conductivity of heat spreader 18. Generally, by improving in-plane thermal conductivity of heat spreader 18 over conventional heat spreaders, the spacing between thermal elements 14 can be increased, reducing material, labor and operation costs. The inter-groove spacing between spreader grooves 26, and thus thermal elements 14, can be chosen based on several factors, i.e. heat spreader thickness, heat spreader thermal conductivity, convective medium flow rate and temperature and thermal element inner diameter, for preventing undesirable local variations in the temperature distribution achieved in the wall assembly. In one embodiment, inter-groove spacing between spreader grooves 26 is between about five inches and about twenty inches for providing the desired temperature field for a heat spreader 18 having a density at least about 0.6 grams per cubic centimeter and a thickness less than about ten millimeters across a wide range of operating conditions.

[0087] Referring now to FIG. 6, heat exchanger 10 includes a heat spreader 18 generally having a spreader width 140 and a liner 22 generally having a liner width 146. As seen in FIG. 6, liner width 146 can be less than spreader width 140 in some embodiments. In the embodiment seen in FIG. 6, heat exchanger 10 is installed in a below-subfloor configuration with heat spreader 18 positioned between subfloor 118 and liner 22, and the direction of desired heat flux is toward subfloor 118. It is understood that a similar configuration could be installed behind a wall, above a ceiling, or along other types of boundary interfaces used to separate spaces such that the desired direction of heat flux is oriented toward the space desired to be heated or cooled, and such that subfloor 118 as indicated in FIG. 6 represents a wall, ceiling, or other boundary surface. In the embodiment seen in FIG. 6, heat spreader 18 includes a spreader width 140 substantially equal to the distance between adjacent floor joists 116. It will be appreciated that spreader width 140 could be less than the distance between floor joists and still be greater than liner width 146. In some applications, reducing liner width 146 to a size less than spreader width 140 facilitates ease of installation and reduces material costs without adversely affecting thermal performance. In some embodiments, a liner 22 having liner width 146 less than spreader width 140 also includes one or more extended tabs 30 protruding from liner 22 toward liner recess 24, as seen in FIGS. IB and 1C, for securing thermal element 14 in spreader recess 26. Referring to FIG. 7, heat exchanger 10 can also include multiple liners 22 positioned on one heat spreader 18 having multiple spreader recesses such that each liner width is less than the spreader width. This configuration allows the removal of unnecessary liner material between adjacent liners 22, thereby reducing material costs without significantly affecting thermal performance characteristics of heat spreader 10. It is appreciated that in some embodiments heat exchanger 10, as seen in FIG. 6 and FIG. 7 can be provided in modular panels having liner 22 bonded to heat spreader 18 such that the panel is ready for installation. Such panels can be cut to a pre-determined length. Because liner 22 and heat spreader 18 in some embodiments include flexible graphite and a thermoplastic material, each having a thickness less than about 1.5 millimeters, a user may cut the panel to a desired length using conventional hand tools, thereby facilitating relatively quick and inexpensive installation as compared to conventional heat exchanger systems.

[0088] Referring now to FIG. 8, a heat exchanger 10 in some embodiments can include a heat spreader 18, a liner 22 and an insulation layer 154. The insulation layer 154 is generally attached to the liner 122 on the side opposite the direction of desired heat flux for improving directional heat flux away from insulation layer 154. In one embodiment, insulation layer 154 includes an expanded polystyrene (EPS) foam material having a thermal conductivity less than the thermal conductivity of heat spreader 18. For example, insulation layer 154 can be formed from a material having a thermal conductivity less than about 2.0 W/m*K. In other embodiments, insulation layer 154 has a thermal conductivity less than about 0.5 W/m*K. While there is no technical lower limit to the thermal conductivity of insulation layer 154, a practical lower limit is reached at about 0.025 W/m*K. Insulation layer 154 in some embodiments includes a surface shaped to contour to heat exchanger 10. Insulation layer 154 in some embodiments includes at least one insulation recess, or insulation groove 158, longitudinally aligned with liner recess 24 and spreader recess 26 and generally shaped to receive thermal element 14. Insulation panel 154 can have a thickness ranging between about 5 mm and about 500 mm. While there is no technical upper limit to the thickness of insulation layer 154, a practical limit is reached around 200 mm. It is noted, however, that in some industrial applications, thickness of insulation layer 154 may exceed five- hundred millimeters. In one embodiment, insulation layer 154 comprises expanded polystyrene foam (EPS) having a thickness between about twenty and about thirty millimeters. Liner 22 can be bonded to insulation layer 154 adhesively or thermally, and in some embodiments liner 22 is not bonded to insulation layer 154 at all, but merely rests against insulation layer 154.

[0089] Referring now to FIG. 9, a partial cross-sectional view, along Section B - B from FIG. 8, is generally illustrated. As seen in FIG. 9, liner 22 is positioned between heat spreader 18 and insulation layer 154. A heat exchanger 10 having this configuration can be used in a variety of applications, including either above-subfloor or below-subfloor radiant hydronic heating and cooling applications. For example, as seen in FIG. 10, one embodiment of a flooring assembly 150 having an above-subfloor configuration is generally illustrated. In this embodiment, an insulation layer 154 is positioned on subfloor 118. Subfloor 118 can be any building or material surface, for example but not limited to particle board, wood composite, plywood, concrete, gravel, metal or other types of interior or exterior structural and building materials. Insulation layer 154 in one embodiment is an insulation panel made of expanded polystyrene sheet (EPS) having insulation recesses 158 formed therein. It is understood that in some embodiments each insulation recess 158 can be formed by discrete sections of expanded polystyrene foam whose edges do not touch but rather define a gap therebetween (not shown). Heat exchanger 10 is generally positioned on insulation layer 154. Heat exchanger 10 includes a heat spreader 18 and a liner 22. Liner 22 includes at least one liner recess 24 shaped for receiving a thermal element 14. Each liner region surrounding a liner recess 24 is housed in an insulation recess 158, such that liner 22 generally conforms to the surface of insulation layer 154. Heat spreader 18 includes at least one sheet of graphite material and is positioned against liner 22. In some embodiments, heat spreader 18 is bonded, either adhesively or thermally, to liner 22. Heat spreader 18 defines spreader recesses 26 shaped for receiving thermal elements 14. Thermal element 14 is inserted into spreader recess 26. Outer surface 152 is positioned on heat spreader 18. In some embodiments, additional layers are positioned between outer surface 152 and heat spreader 18. For example, in one embodiment heat spreader 18 is carpet or wood flooring material, and an additional foam cushioning layer can be positioned between outer surface 152 and heat spreader 18. Outer surface 152 in some applications can any boundary surface of a room or environment, i.e. a wall, a ceiling, a driveway, a sidewalk, etc. As also seen in FIG. 10, in some embodiments extended tab 30 is aligned with tab clearance void 32 for securing thermal element 14 in spreader recess 26. Outer surface 152 can include various materials, including but not limited to flooring material such as tile, wood, carpet, concrete, stone, marble, etc., or wall material such as drywall, gypsum board, wood paneling, textiles, paperboard, etc. Each component can be combined to form a flooring, or wall, or ceiling assembly 150, as seen in the partial cutaway perspective view of FIG. 11.

[0090] Liner 22 included in floor assembly 150, as seen in one exemplary embodiment in FIG. 10 includes a single liner 22 formed of a thermoplastic material substantially backing the entire heat spreader surface. It is understood that in other embodiments, liner 22 includes not one continuous sheet of thermoplastic material, but instead includes multiple elongated liners 22, as seen previously in FIG. 6 and FIG. 7 and as seen in FIG. 12. Each liner 22 in this embodiment includes a liner width less than spreader width, and includes a liner recess 24 formed therein. In some embodiments, liner recess 24 is thermoformed in liner 22. In other embodiments, liner 22 can be extruded in a shape including liner recess 24. Liner 22 includes an elongated, strip-like shape including liner recess 24 shaped to engage the recessed region of heat spreader 18. In some embodiments, as seen in FIG. 13, liner flange 142 extends laterally outward a flange width 144 from each liner recess 24. In one embodiment, flange width 144 ranges between about 5 and about 200 mm. In another embodiment, flange width 144 is between about 15 and about 40 mm. Using this configuration, excess liner material extending between individual liner recesses 24 can be eliminated, reducing both liner material cost and overall system cost. The liner region forming liner recess 24 generally fits into insulation recess 158 on insulation layer 154. Insulation layer 154 in some embodiments includes insulation grooves 160 adjacent each side of each insulation recess 158, seen in FIG. 12. Each insulation groove is shaped to accommodate liner 22, and specifically liner flange 142, such that liner 22, when inserted into each liner recess 158 and liner groove 160, rests substantially flush with the mounting surface 148 of insulation layer 154. By providing liner grooves 160 for accommodating each liner 22, the insulation panel 154 and liners 22 when combined form a substantially flat substrate for positioning heat spreader 18, as seen in FIG. 13. This configuration creates a substantially even heat spreader surface for uniformly mounting a flooring or other outer surface or engaging a wall assembly.

[0091] Referring now to FIG. 14, in one embodiment, heat exchanger apparatus 10 includes a sheet layer, or encapsulation layer 50 disposed over heat spreader 18. In some embodiments, particulate graphite material, including dust or flakes, are present on the surface or edges of heat spreader 18. This particulate material can, in some applications, create debris or dust that may undesirably contaminate an environment in which the heat spreader is installed. Sheet layer 50 can be disposed on the surface of heat spreader 18 to prevent contamination or pollution of the environment by particulate graphite material during installation or use of heat exchanger 10. In this embodiment, heat spreader 18 includes a first side 102 and a second side 104, as seen in FIG. 16. Liner 22 is attached to the first side 102 of heat spreader 18, and sheet layer 50 is attached to the second side 104 of heat spreader 18. Sheet layer 50 includes a sheet layer thickness 52. In one embodiment, sheet layer thickness 52 is between about ten and about fifty microns. In yet another embodiment, sheet layer thickness 52 is equal to or greater than about 12 microns. In some embodiments, a sheet layer thickness 52 of about 12.7 microns is the minimum thickness suitable for providing adequate encapsulation for containing particulate debris on heat spreader 18 without sacrificing structural integrity. Sheet layer 50 in some embodiments includes a substantially transparent, or clear, polyester (PET) sheet, or film. Sheet layer 50 extends substantially coextensively with second side 104 of heat spreader 18, defining a sheet layer recess 106 extending in some embodiments into heat spreader recess 26, seen in FIG. 15. Sheet layer recess 106 is generally shaped for receiving thermal element 14. In other embodiments not shown, sheet layer 50 can extend across spreader recess 26, encapsulating both thermal element 14 and heat spreader 18.

[0092] Sheet layer 50 can be sealed against liner 22 to fully encapsulate heat spreader 18 between liner 22 and sheet layer 50. In one embodiment, heat spreader 18 includes a first outer perimeter edge 60, seen in FIG. 17A. Liner 22 includes a second outer perimeter edge 62 extending beyond first outer perimeter edge 60 by a distance A, seen in FIGS. 17B and 18A. Sheet layer 50 also includes a third outer perimeter edge 64 extending beyond first outer perimeter edge 60 a distance B, seen in FIGS. 17B and 18A. In some embodiments, distance A is greater than distance B. Third outer perimeter edge 64 extends over second outer perimeter edge 62, and can be pressed downward against liner surface 48 to seal sheet layer 50 against liner 22. In one embodiment, sheet layer 50 is adhesively bonded to liner 22 by an adhesive placed on liner surface 48 and/or sheet layer surface 70. Additionally, a vacuum can be used in one embodiment to evacuate the space between liner 22 and sheet layer 50, resulting in an improved seal around heat spreader 18. In other embodiments, sheet layer 50 is thermally bonded to liner 22 during a thermoforming process. In some embodiments, distance A is between about 5 and about 8 mm, and distance B is between about 3 and about 6 mm. In yet another embodiment, the ratio of distance A divided by distance B is between about 1.1 and about 1.4. In some embodiments, layer 50 forms a continuous seal surrounding heat spreader 18.

[0093] Referring now to FIG. 19A, one embodiment of an improved heat exchanger 10 including a heat spreader 18 and a liner 22 is generally illustrated. Heat spreader 18 includes a spreader recess 26. A thermal element 14 is disposed in spreader recess 26. Thermal element 14 defines a diameter D. In some embodiments, diameter D is the outer diameter of thermal element 14, especially where thermal element 14 is a polymer or metal tube. Spreader recess 26 defines a height H extending from the interior bottom of spreader recess 26 to the outer surface 104 of heat spreader 18. Heat exchanger 10 generally defines a recess interference ratio equal to diameter D divided by height H, or D/H. In the embodiment seen in FIG. 19A, recess interference ratio is less than one, and the outer surface of thermal element 14 does not extend above the outer surface 104 of heat spreader 18. In this embodiment, when a substrate or other material (not shown) is positioned against outer surface 104 of heat spreader 18, the substrate does not directly contact thermal element 14. In another embodiment, recess interference ratio D divided by H equals about 1.0, and an applied substrate (not shown) engages in line contact with thermal element 14. In yet another embodiment, seen in FIG. 19B, height H of spreader recess 26 is less than diameter D of thermal element 14, defining a recess interference ratio D divided by H which is greater than 1.0. In this embodiment, thermal element 14 extends above outer surface 104 of heat spreader 18 by vertical offset distance 88. In one embodiment, vertical offset distance 88 is between about 0.25 and about 1.5 mm. In yet another embodiment, recess interference ratio is between about 15 and about 30.

[0094] A heat exchanger 10 having a recess interference ratio D divided by H being greater than 1.0 generally causes thermal element 14 to be compressed by any additional layer positioned on surface 104. For example, in one embodiment, seen in FIG. 19C, a substrate 110 is positioned on surface 104 of heat spreader 18 having a recess interference ratio greater than 1.0. Substrate 110 can be a wall assembly, a floor panel in an above-subfloor configuration wherein heat exchanger 10 is positioned above the subfloor. In other embodiments, substrate 110 can be a subfloor in a below-subfloor, or staple-up, configuration wherein the heat exchanger 10 is positioned below a subfloor between floor joists. In yet other embodiments, substrate 110 can be an intermediate layer, such as a foam cushioning layer, between heat exchanger 10 and a floor layer. Thermal element 14 is compressed by substrate 110 from an initial position 112 to a compressed position 114, seen in FIG. 19C. Compression of thermal element 14 is possible in embodiments where thermal element 14 is a deformable tube, i.e. a plastic or polymer tube, and is compressible. Compression of thermal element 14 by substrate 110 can improve heat transfer between thermal element 14 and heat spreader 18 by pressing thermal element 14 against heat spreader 18. For example, in some embodiments, thermal element 14 does not coextensively contour to spreader recess 26 along the entire length of thermal element 14, but may instead have local gaps or separation areas (not shown) caused by local variations in the geometries of either thermal element 14 or spreader recess 26. However, compression of thermal element 14 by substrate 110 due to recess interference ratio greater than 1.0 can push, or compress, thermal element 14 into any vacant gaps or separations areas, thereby increasing surface area contact between thermal element 14 and heat spreader 18. Increased surface area contact improves heat spreader performance by at least enhancing heat flux between thermal element 14 and heat spreader 18. Additionally, compression of thermal element 14 will increase surface area contact between thermal element 14 and substrate 110, further enhancing heat transfer in the desired direction of heat flux.

[0095] In some embodiments a heat spreader 18 is positioned on liner 22 wherein liner 22 includes an extended tab 30 but heat spreader 18 does not include the tab clearance recess seen in FIG. IB. Instead, in some embodiments, heat spreader 18 is inserted into liner recess 22 to generally conform to heat spreader 18. One possible reason for inserting heat spreader 18 into liner recess 22 without including a tab clearance void on heat spreader 18 is to provide heat transfer between thermal element 14 and heat spreader 18 while also providing a securement means for retaining thermal element in spreader recess. For example, the one embodiment seen in FIG. IB and FIG. 2, which includes tab clearance void 32, requires removing a section of heat spreader 18 where tab clearance void 32 is defined to allow passage of extended tab 30. The removal of part of heat spreader 18 can locally reduce heat transfer from thermal element 14 to heat spreader 18 in some applications. What may be desired then, in some applications, is an extended tab 30 protruding from liner 22 for securing thermal element 14, but without removing such a large portion of heat spreader 18 to provide clearance for extended tab 30. Referring now to FIG. 20A, a heat spreader 18 includes a heat spreader recess 26 positioned to conform to liner recess. Extended tab underneath heat spreader 18 pushes heat spreader 18 out toward spreader recess 26, forming a spreader tab 28. As seen in the cross- sectional profile of Section C - C from FIG. 20A, FIG. 20B illustrates a gap 130 defined between heat spreader 18 and liner 22 because heat spreader 18 cannot completely fill liner recess 22 in the vicinity of tab 30. To remove gap 130, a longitudinal slot, or incision 46, can be defined in heat spreader 18 in spreader recess 26. As seen in FIG. 20C, slot 46 allows heat spreader 18 to more completely contour to liner 22. A slot gap 86 is defined when heat spreader 18 is locally pushed back against liner 22 in the vicinity of tab 30, as seen in FIG. 20C and seen in cross-sectional view of Section D - D from FIG. 20C, shown in FIG. 20D. The slot gap exposes a small region of liner 22, as seen in FIG. 20C. As seen in FIG. 20E, thermal element 14 can be inserted in spreader recess 26 while heat spreader 18 maintains contact with liner 22 in the vicinity of spreader tab 28. Referring to the view of Section E - E of FIG. 20E illustrated in FIG. 20F, when thermal element 14 is positioned in spreader recess 26, heat spreader 18 is sandwiched between thermal element 14 and liner 22 in the region below extended tab 30 and spreader tab 28. As such, heat spreader 18 maintains thermal contact with thermal element 14 in the region around extended tab 30, thereby improving heat exchanger performance in some applications.

[0096] Similarly, referring now to the embodiment shown in FIG. 21A -

2 IF, a U-shaped incision 42 can be defined in the region of heat spreader 18 that overlaps the extended tab. In this embodiment, the U-shaped incision 42 extends around extended tab 30, with the longitudinal part of the U-shaped incision 42 positioned interior spreader recess 26. The U-shaped incision 42 defines a flap 44 attached to heat spreader 18 and overlapping extended tab 30, as seen in FIGS. 21C and the partial cross-sectional view of Section G - G from FIG. 21C illustrated in FIG. 2 ID. As seen in FIG. 2 IE, when thermal element 14 is positioned in spreader recess 26, flap 44 is sandwiched between thermal element 14 and liner 22. As seen in the partial cross-sectional view of Section H - H from FIG. 2 IE illustrated in FIG. 2 IF, a flap gap 84 is defined in spreader recess 26, partially exposing liner 22 when thermal element 14 is inserted. In this configuration, as seen in FIG. 2 IF, heat spreader 18 maintains thermal contact with thermal element 14 in the vicinity of extended tab 30, thereby improving thermal performance of the heat exchanger in some applications. It is noted that slot 46 and U-shaped incision 42 can be formed in some applications by a user during installation. It is also understood that the embodiments of a heat exchanger configuration described herein or seen in FIGS. 20A - 20F or FIGS. 21A - 2 IF can interchangeably be used with any of the previously described or illustrated embodiments of a heat exchanger, including those embodiments illustrated in FIGS. 4 - 19C.

[0097] Referring now to FIG. 22 A, one embodiment a heat exchanger panel 200 is generally illustrated. Heat exchanger panel 200 includes a first base 202 including a first surface groove 206 defined therein. In some embodiments, first base 202 comprises a wood or a wood composite material. In other embodiments, first base 202 can include other solid materials, including but not limited to laminated plywood, plastic or polystyrene foam. First surface groove 206 can be cut into first base 202 using a router, saw, or other chipping or cutting tool. It is further understood that base 202 can form surface groove 206 by including two base members positioned on a wider base member such that the two base members define a gap therebetween, wherein the gap between base members defines the first surface groove 206. First surface groove 206 in one embodiment includes a rectangular cross-sectional groove profile, as seen in FIGS. 22 A and 22B. It is understood that other first surface groove profiles, including rounded or curved shapes, can be used, for example first surface groove 206 does not have to contour to heat spreader 18.

[0098] As seen in FIG. 22A, in certain embodiments, a first liner 204 is disposed on first base 202. First liner 204 in some embodiments is a thermoformed plastic sheet having a thickness between about 0.25 mm and about 5 mm. First liner 204 includes a first protruding region 208 extending into first surface groove 204 on first base 202. First protruding region 208 in some embodiments only partially fills first surface groove 206, as seen in FIG. 22B. First protruding region 208 defines a first liner recess 210 in first liner 204. [0099] A first heat spreader 212 is disposed on first liner 204. First heat spreader 212 includes at least one sheet of compressed particles of exfoliated graphite. In one embodiment, first heat spreader 212 includes a flexible graphite sheet having a density greater than about 0.6 g/cc and a thickness less than about 10 mm. In some embodiments, first heat spreader 212 includes first and second encapsulation layers positioned on each side of heat spreader 212. In some embodiments, each encapsulation layer includes a polyethylene terephthalate (PET) film having a thickness between about ten and about one-hundred microns and laminated to each side of first heat spreader 212. In yet another embodiment, first and second encapsulation layers each include a PET sheet having an average thickness of about 25 microns. Heat spreader 212 can be adhesively bonded to first liner 204. As seen in FIG. 22B, Heat spreader 212 includes a second protruding region 214 extending into first liner recess 210. In some embodiments, second protruding region 214 is shaped to substantially conform to the shape of first liner recess 210. In other embodiments, second protruding region 214 may not completely fill first liner recess 210, allowing separation gaps to exist between first heat spreader 212 and first liner 204. Second protruding region 214 defines a first spreader recess 216, seen in FIG. 22A. First spreader recess 216 is generally shaped for receiving thermal element 14, seen in FIG. 22B. In some embodiments, first liner 204 does not completely contact first base 202, especially in the region adjacent to surface groove 206, creating a gap between first liner 204 and first base 202. In some embodiments, first liner 204 can include a resilient thermoplastic material such that when a flooring surface is positioned on heat spreader 212, first liner 204 is pressed downward against first base 202, and the resilient force of first liner 204 presses heat spreader 212 away from base 204 and improves thermal contact between heat spreader 212 and the flooring surface positioned thereon. Heat spreader 212 and first liner 204 can be attached to base 202 by a variety of fastening means, including for example by nailing, stapling, screwing or gluing. [00100] One aspect of heat exchanger panel 200 provides a first base 202 made of a wood or similar material that can support a structural load. In one application, heat exchanger panel 200 provides a modular panel that can be attached directly to floor joists to form a subfloor having a heat exchanger mounted directly thereon. In yet another embodiment, heat exchanger panel 200 can be attached directly to an existing subfloor in an above-subfloor configuration. Because heat exchanger panel 200 can be provided in modular assembly with a first base 202 providing a structural load-bearing member, savings in time and installation costs can be realized using such an apparatus.

[00101] Referring again to FIG. 22A, in some embodiments at least one snap tab 218 is integrally formed on first liner 204. In some embodiments, snap tab 218 is a thermoformed plastic integrally molded on first liner 204. Snap tab 218 protrudes outward from first liner 204 toward heat spreader 212. In one embodiment, heat spreader 212 defines a first tab clearance void 220 aligned with snap tab 218 and snap tab 218 extends through tab clearance void 220 into first spreader recess 216. Snap tab 218 is generally shaped to secure thermal element 14 in first spreader recess 216. It is understood that, in some embodiments, a slot 42 or U-shaped incision 46 can be used in place of at least one first tab clearance void 220. Similarly, in some embodiments at first tab clearance void 220 can be used in conjunction with a U-shaped incision 46 or slot 42.

[00102] Referring further to FIG. 22A, second base 228 can be pivotally attached to first base 202 to form a foldable heat exchanger panel 200. Second base 228 in some embodiments can be made of any similar materials comprising first base 202, discussed above. Second base 228 in one embodiment is foldable relative to first base 202, as seen in FIG. 22F, by a bridge extending between first and second bases 202, 228. A folding heat exchanger panel can be used for a variety of applications, including both above-subfloor and below-subfloor hydronic radiant heating and cooling applications. Folding of the heat exchanger panel 200 can provide improved shipping, handling and installation by reducing the overall size of the panel apparatus. The first and second bases 202, 228 are foldable relative to each other by a hinge, or bridge, extending between the first and second bases 202, 228. In one embodiment, seen in FIG. 22C, heat spreader 212 extends across a gap between first and second bases 202, 228, forming a heat spreader bridge 224. Heat spreader bridge 224 in some embodiments includes the flexible graphite sheet of heat spreader 212. In some embodiments, the graphite sheet is pre-bent in the region between first and second bases 202, 228 to better facilitate folding and unfolding of the panel 200. Also, in some embodiments first and second layers of polyethylene terephthalate (PET) sheeting (not shown) are positioned on each side of first heat spreader 212 to add additional flexibility or strength. Also seen in FIG. 22C, a second liner 226 can be positioned on second base 228 between second base 228 and first heat spreader 212. In this embodiment, first heat spreader 212 extends continuously across first and second bases, 202, 228. In some embodiments, second base 228 defines a second surface groove 234 into which second liner 226 extends. A second spreader recess 232 extends into second surface groove 234 generally shaped for accommodating a thermal element. Referring now to FIG. 22D, in another embodiment a hinge layer 222 extends between first and second bases 202, 228. Hinge layer 222 in some embodiments includes a flexible fabric, or cloth, material. In the embodiment seen in FIG. 22D, hinge layer 222 is positioned beneath spreader bridge 224, or between first heat spreader 212 and first and second bases 202, 228. In another embodiment, seen in FIG. 22E, a second heat spreader 230 is positioned on second base liner 226 on second base 228, and hinge layer 222 provides the pivoting connection between first and second bases 202, 228. In this embodiment, first heat spreader 222 does not provide a continuous bridge between first and second bases 202, 228. In yet another embodiment (not shown), hinge layer 222 is glued to first and second liners 204, 226 to provide a foldable connection between first and second bases 202, 228. As seen in FIG. 22D, heat exchanger panel 200 is foldable relative to itself. One aspect of the folding panel configuration seen in FIG. 22D is that, when folded, the first and second bases 202, 228 form the exterior surfaces of the folded panel. This configuration can protect heat spreader 212 during packaging, shipping, storage and/or installation. One embodiment of heat exchanger panel 200 provides first heat spreader 212 on top of first base 202, thereby maximizing the thickness of base 202 and further improving the insulative effect of first base 202 when first base 202 comprises at thermally-insulative material. It is understood that additional bases can be pivotally connected by additional hinge layers between bases in an accordion-style configuration such that each layer can be folded over on an adjacent layer for improved ease of transport, handling and/or installation.

Method of Pre-forming Heat Spreader

[00103] Another embodiment of the present disclosure provides a method of manufacturing a heat spreader for use in a heat exchanger apparatus. In one embodiment, a graphite sheet is pre-formed into the shape of a heat spreader as described above prior to attachment to a thermoplastic liner. The graphite sheet, or spreader blank, in one embodiment includes a sheet of compressed particles of exfoliated graphite. The graphite sheet in some embodiments includes a thickness less than about ten millimeters, and in other embodiments less than about five millimeters. In one embodiment, the graphite sheet is less than about two millimeters in thickness. The graphite sheet, or spreader blank 312, is generally positioned between a male vacuum die 314 and a matching female die 316, as seen generally in FIG. 23. It is noted that the illustration in FIG. 23 represents only a partial perspective view, and the actual spreader blank and molding apparatus can have a greater longitudinal and/or lateral dimension as the exemplary illustrated embodiment.

[00104] Male vacuum die 314 generally includes one or more spreader groove formers 318 extending outward from the body of male vacuum die 314. Male vacuum die 314 also generally includes one or more vacuum, or pressure, ports positioned on the side of the die from which spreader groove formers 318 extend. Each vacuum port includes an orifice from which a suction force, or reduced pressure, can be locally applied against spreader blank 312 for retaining spreader blank 312 to the surface of male vacuum die 314. As seen in FIG. 23, spreader blank 312 in one embodiment includes preformed tab clearance voids 332 defined in spreader blank 312 prior to the preforming process. Referring now to FIG. 24, one embodiment of a female die 316 used to preform a graphite heat spreader is generally shown in an exploded, or separated position. The female die 316 includes five sections: a center die 320, a first inner tube die 322, a second inner tube die 324, a first outer tube die 326 and a second outer tube die 328. Each section is moveable relative to male vacuum die 314, generally in a direction normal to the surface of male vacuum die from which each spreader groove former 318 extends. Each piece of female die 316 moves generally vertically, but does not move horizontally. In one embodiment, each piece of female die 316 is moveable using a hydraulic cylinder and/or a compression spring.

[00105] A method of forming a graphite heat spreader provides several steps. A spreader blank 312 is positioned between male vacuum die 314 and female die 316, as seen in FIG. 23. In one embodiment, the spreader blank 312 is a precut, flat sheet of knurled graphite spreader material. The spreader blank 312 includes cutouts, or tab clearance voids 332 defined therein. In one embodiment, alignment pins, located along the center line of the center die 320 (not shown) are used to align the spreader blank 312 to each die. The dies are then moved together such that each die generally contacts the surface of spreader blank 312. The center die 320, which is substantially flat in some embodiments but may include a curved profile or other geometrical features defined thereon in other embodiments, moves upwards and presses the spreader blank 312 against the male vacuum die generally between spreader groove formers 318. As the center section is pressed flat, the free ends are drawn into the die space, as seen in FIG. 25. In a separate step, the two inner tube dies 322, 324 move upward and press the spreader blank 312 against the sides and bottom of each spreader groove former 318, causing the free ends to be drawn further into the die space. In a separate step, each outer tube die 326, 328 moves toward male vacuum die 314, compressing spreader blank 312 and forming graphite heat spreader and completing the pre-forming process. Next, a vacuum, or reduced pressure, is applied through the one or more ports on male vacuum die 314 to retain heat spreader against male vacuum die 314, and each section of female die 316 is disengaged from the heat spreader surface, resulting in a pre-formed heat spreader 334 secured to male vacuum die 314 by a releasable vacuum seal, as seen in FIG. 26. Also seen in FIG. 26, pre-formed heat spreader 334 includes tab clearance voids 332 defined therein. In one embodiment, male vacuum die 314 also includes a cutout clearance aligned with each tab clearance void 332 for allowing clearance of each extended tab during subsequent steps.

Method of Thermoforming Liner

[00106] Yet another embodiment of the present disclosure provides a method of forming a liner for use in the disclosed heat exchanger. Referring generally to FIG. 27, process for forming a liner provides placing a liner blank 402 over a female thermoforming die 404. The female thermoforming die 404 in some embodiments includes one or more vacuum, or pressure, ports positioned thereon. Each vacuum port includes an orifice through which a suction, or reduced pressure, force can be applied to liner blank 402 for releasably retaining liner blank 402 on the surface of female thermoforming die 404. Female thermoforming die 404 also includes one or more liner recess channels 406. Each liner recess channel 406 is generally shaped to have the desired shape of the liner recess 24 seen in FIG. 1A. Female thermoforming die 404 in some embodiments also includes one or more tab formers 408 shaped for forming each extended tab 30, seen for example in FIG. IB.

[00107] A method of forming a liner provides a step of positioning liner blank 402 against female thermoforming die 404. Liner blank 402 is held in position by a reduced pressure applied thorough one or more vacuum ports (not shown) on the surface of female thermoforming die 404. In one embodiment of a liner forming process, a separate mold structure, or press, can be pressed against liner blank 402, forcing liner blank material into each mold recess 82 to form the desired shape of a liner for a heat exchanger. In another embodiment of a liner forming process, the applied negative pressure between liner blank 402 and female thermoforming die 404 can be further reduced to deform, or pull, liner blank 402 into each liner recess channel 406, thereby forming a liner having a desired shape including one or more liner recesses shaped for accommodating a thermal element. In some embodiments, liner blank 74 can be heated to a predetermined material softening temperature prior to or during the thermoforming process to facilitate plastic deformation of liner blank 402 into the desired shape. Liner blank 402 can include any of the previously discussed liner materials, including but not limited to polystyrene, polyethylene or other thermoplastic materials. In one embodiment, the liner blank 402 is pre-heated to a molding temperature between about 60°C and about 180°C prior to the deformation step, wherein the molding temperature represents the softening point of the liner blank material. In yet another embodiment, the liner blank 402 is preheated to a molding temperature between about 100°C and about 150°C.

[00108] The female thermoforming die 404 used in one embodiment of a method of forming a thermoplastic liner includes tab formers 408, seen in FIG. 27. Generally, when liner blank 402 is plastically deformed to fill liner recess channel 406, liner blank material envelops tab former 408, integrally forming, or integrally molding, an extended tab 30 in liner 22, as seen in FIG. IB. As liner blank material contours to the underside of tab former 408, a finished liner can be difficult to remove from liner recess channel 406 because tab former 408 extends into the backside of extended tab 30. To overcome this problem, a female thermoforming die having a moveable tab former 408 is disclosed herein. Referring to FIG. 28A, a tab former 408 extends through a tab former slot 414 in female thermoforming die 404. Tab former 408 includes a first, or molding, position, seen in FIG. 28A. In the molding position, tab former 408 extends into the liner recess channel 406. Upon thermoforming of a liner, tab former 408 can be rotated away from liner recess channel 406, as seen in FIG. 28B for removing a liner or a heat exchanger apparatus having a liner with an integrally molded extended tab 30 formed therein. Tab former 408 in some embodiments is resiliently positioned in the molding position in tab former slot 414 by a spring, and returns to molding position seen in FIG. 28A upon removal of the thermoformed liner or heat exchanger. [00109] Referring again to FIG. 27, in one embodiment, liner blank 402 is a thermoplastic material having a uniform liner blank thickness 416. When liner blank 402 is thermoformed in female thermoforming die 404, the uniformly flat liner material is deformed under pressure to form each thermoformed liner recess 424, seen in FIG. 29. In one embodiment where a substantially flat liner blank 402 having a uniform thickness between about 0.25 millimeters and about 2.0 millimeters is thermoformed to produce a thermoformed liner 422, each liner recess 424 defines a minimum liner recess thickness 426 less than the substantially flat liner body thickness 416. For example, in one embodiment, uniform thickness 416 of the substantially flat liner blank 402 is between about 1.0 and about 1.5 mm and minimum recess thickness 426 is between about 0.5 and about 0.9 mm after the liner thermoforming process.

[00110] Generally, the minimum liner recess thickness 426 must be sufficient for supporting heat spreader and a thermal element. Thus, to achieve an appropriate minimum liner recess thickness 426, it may be necessary to include more liner material than necessary in the substantially flat regions of thermoformed liner 424. Because the flat regions can form a relatively large percentage of the liner material used in the liner (up to 90% of total liner material in some embodiments), it is understood that in some applications it is desirable to reduce the thickness of the substantially flat liner body while also providing an adequate minimum liner recess thickness 426 for supporting a heat spreader and a thermal element.

[00111] Referring to FIG. 30, a liner blank 402 having a non-uniform thickness is shown. Liner blank 402 includes a first thickness 416, corresponding to the areas for forming the substantially flat liner body, and a second thickness 418, corresponding to a thicker area 420 for forming each liner recess 424. In this embodiment, liner blank 402 can include an extruded thermoplastic material formed having the desired first and second thicknesses 416, 418. Generally, using a liner blank 402 providing a second thickness 418 larger than first thickness 416, where the thicker region is aligned with each liner recess channel 406, it is possible to achieve a thermoformed liner 422 having a first thickness 416 substantially equal to minimum recess thickness 426. In one embodiment first thickness 416 is between about 0.4 mm and about 0.8 mm and second thickness 418 is between about 1.0 mm and about 1.5 mm, producing a thermoformed liner 422 wherein first thickness 416 is substantially equal to minimum recess thickness 426, both values being between about 0.4 mm and about 0.8 mm. In yet another embodiment, a liner blank 402 is provided having a ratio of first thickness 416 divided by second thickness 418 between about 0.4 and about 0.6. This configuration can reduce liner material costs and waste while providing adequate stiffness for supporting both a heat spreader and a thermal element. It is understood that this method of forming a thermoplastic liner using a liner blank with varying initial thickness applies both to configurations having a liner 22 that fully backs heat spreader 18, as seen in FIG. 3A and to configurations having a liner 22 that only partially backs heat spreader 18, as seen in FIG. 12.

[00112] In an optimal embodiment of liner 422 may include one or more clips disposed to retain the thermal element in recess 424. The clip(s) may be integral to liner 422, attached to liner 422, adjacent an internal surface of liner 422, or any combination thereof. Alternatively, the clip may be practiced along with tab 30 or instead of tab 30. A further additional embodiment may include a piece of a graphite heat spreader, preferably comprising a compressed mass of exfoliated graphite particles disposed adjacent the clip, more preferably attached to the clip.

Method of Bonding Heat Exchanger

[00113] Another embodiment of the present disclosure provides a method of forming a heat exchanger 10, as generally seen in FIG. 3A. More specifically, a process for bonding a pre-formed heat spreader 334, as seen in FIG. 26, to a thermoformed liner 422, as seen in FIG. 29 is provided. Referring again to FIG. 26, a pre-formed heat spreader 334 is shown releasably secured to male vacuum die 314 by a reduced pressure therebetween. Prior to the removal of thermoformed liner 422 from female thermoforming die 404, male vacuum mold 314 along with pre-formed heat spreader 334 still secured thereto can be aligned opposite female thermoforming die 404, as seen in FIG. 31. From this configuration, heat spreader can be bonded to liner in at least two ways. First, pre-formed heat spreader 334 can be heated to a temperature at or near the softening point of the thermoplastic liner material comprising thermoformed liner 422. In some embodiments, male vacuum die 314 can also be heated, for example the assembly of pre-formed heat spreader 334 and male vacuum die 314 can be placed together in an oven prior to alignment with female vacuum die 404.

[00114] A thermal bonding process can be further used to bond heat spreader 334 to liner 422 by pressing male vacuum die 314 against female thermoforming die 404 while both pre-formed heat spreader 334 and thermoformed liner 422 are at or near the softening point of the thermoplastic liner material. By allowing the compressed assembly to cool, heat spreader 334 is thermally bonded to thermoformed liner 422, forming one embodiment of a heat exchanger suitable for heat transfer applications such as hydronic radiant above-subfloor or below-subfloor heating and cooling.

[00115] Additionally, an adhesive bonding process can be employed beginning with the configuration seen in FIG. 31 to bond heat spreader to liner. In one embodiment of an adhesive bonding process, the exposed surface of pre-formed heat spreader 334 is coated with adhesive while releasably retained against male vacuum die 314. Subsequently, male vacuum die 314 is pressed against female thermoforming die 404, adhesively bonding heat spreader to liner.

[00116] It is understood, that although the above described methods and corresponding figures generally illustrate a thermoplastic liner that fully backs heat spreader 18, such methods are equally applicable to other embodiments wherein the thermoplastic liner only partially backs heat spreader, as seen for example in FIG. 12.

[00117] Referring now to one embodiment shown in FIG. 32, a heat exchanger panel 200 in accordance with the present disclosure includes a base panel 122 having a base panel heat spreader 132 positioned thereon. Base panel heat spreader 132 in some embodiments comprises a sheet of flexible graphite. In some embodiments, base panel heat spreader 132 includes one or more sheets of compressed particles of exfoliated graphite having a density greater than about 0.6 g/cc and a thickness less than about 10 millimeters. In some embodiments, base panel heat spreader 132 can be secured to base panel 122 by gluing, stapling, nailing, screwing or using various other mechanical or adhesive fastening means. First and second channel panels 124, 126 are disposed on the base panel heat spreader 132 such that a channel panel gap 138 is defined between the first and second channel panels 124, 126. In some embodiments, each channel panel 124, 126 can be attached to base panel heat spreader 132 by nailing, screwing, or stapling directly through channel panel 124, 126 into base panel 122 through base panel heat spreader 132. In some embodiments, base panel 122, first channel panel 124 or second channel panel 126 include a wood or wood composite material, including plywood. In other embodiments, base panel 122, first channel panel 124 or second channel panel 126 can include other structural or building materials, including but not limited to concrete, stone, plastic or other composite materials. It is understood that in some embodiments, first and second channel panels 124, 126 can extend from one continuous panel having a panel groove 138 defined therein. As seen in FIG. 32, a thermal element 14 can be positioned in panel groove 138 to contact the base panel heat spreader 132.

[00118] Referring now to one embodiment of a heat exchanger panel 200 seen in FIG. 33, a base panel 122 includes a base panel heat spreader 132 disposed thereon. In one embodiment, base panel heat spreader 132 is a flexible graphite sheet. A first channel panel 124 is positioned on base panel 122. A first channel panel heat spreader 134 is positioned on first channel panel 124 between first channel panel 124 and base panel heat spreader 132 such that first channel panel heat spreader 134 is in thermal contact with base panel heat spreader 132. Similarly, in one embodiment a second channel panel 126 includes a second channel panel heat spreader 136 disposed thereon between second channel panel 126 and base panel heat spreader 132 such that second channel panel heat spreader 136 is in thermal contact with base panel heat spreader 132. As seen in one embodiment in FIG. 33, the first channel panel heat spreader 134 extends around first gap edge 162 of first channel panel 124 such that first channel panel heat spreader 134 substantially faces channel panel gap 138. In another embodiment, second channel panel heat spreader 136 extends around second gap edge 164 of second channel panel 126 such that second channel panel heat spreader 136 substantially faces channel panel gap 138. As also seen in FIG. 33, a thermal element 14 can be disposed in channel panel gap 138 such that thermal element 14 is in thermal contact with base panel heat spreader 132, first channel panel heat spreader 134 and/or second channel panel heat spreader 136. It is understood that in some embodiments, thermal element 14 can be positioned such that is compressed as seen in FIGS. 19B and 19C. In some embodiments, base panel heat spreader 132, first channel panel heat spreader 134 and/or second channel panel heat spreader 136 include at least one layer of a polymer material, such as polyethylene or polyethylene terephthalate, at least about ten microns thick disposed on at least one surface.

[00119] Thus, although there have been described particular embodiments of the present disclosure of a new and useful Heat Exchanger and Methods, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.

Claims

CLAIMS What is claimed is:

1. A heat exchanger for transferring heat between a thermal element and a wall assembly, the heat exchanger comprising:

a heat spreader comprising at least one sheet of compressed particles of exfoliated graphite having a density of at least about 0.6 g/cc and a thickness of less than about 10 mm, the heat spreader defining a spreader recess;

a liner attached to the heat spreader; and

an extended tab protruding from the liner toward the heat spreader,

wherein the extended tab is positioned for retaining the thermal element in the spreader recess.

2. The heat exchanger of claim 1, wherein:

the heat spreader defines a tab clearance void therein; and the extended tab protrudes through the tab clearance void into the spreader recess.

3. The heat exchanger of claim 1, further comprising:

a U-shaped incision formed in the heat spreader along the spreader recess, the U-shaped incision defining a flap in the heat spreader,

wherein the flap overlaps the extended tab between the liner and the thermal element when the thermal element is positioned in the spreader recess; and

wherein the flap is in thermal contact with the thermal element.

4. The heat exchanger of claim 1, further comprising:

a plurality of extended tabs protruding from the liner along the liner recess, each extended tab integrally formed in the liner; and

a plurality of tab clearance voids defined in the heat spreader, wherein each tab clearance void is aligned with one of the plurality of extended tabs such that each one of the plurality of extended tabs protrudes through one of the plurality of tab clearance voids for securing the thermal element in the spreader recess.

5. The heat exchanger of claim 1, further comprising:

a thermal element disposed in the spreader recess, the thermal element having an outer diameter D; and

the heat spreader defining a heat spreader recess having a height H,

wherein the ratio of D divided by H defines a recess interference ratio greater than about 1.0.

6. A heat exchanger for transferring heat between a thermal element and a wall assembly, the heat exchanger comprising:

a heat spreader comprising at least one sheet of compressed particles of exfoliated graphite having a density of at least about 0.6 g/cc and an in-plane thermal conductivity of at least about 140 W/m*K, the heat spreader having a first side and a second side;

a liner attached to the first side of the heat spreader; and a sheet layer attached to the second side of the heat spreader, wherein the sheet layer includes a thickness between about ten microns and about fifty microns.

7. The heat exchanger of claim 6, wherein:

the heat spreader includes a first outer perimeter edge;

the liner includes a second outer perimeter edge extending beyond the first outer perimeter edge by distance A; and

the sheet layer includes a third outer perimeter edge extending beyond the first outer perimeter edge by distance B, wherein distance

B is less than distance A.

8. A heat exchanger for distributing thermal energy from a thermal element to an environment, the heat exchanger comprising:

a panel having a thermal conductivity less than about 1.0 W/m*K, the panel including a panel groove shaped for receiving the thermal element; a heat spreader disposed on the panel, the heat spreader including at least one sheet of compressed particles of exfoliated graphite having an in-plane thermal conductivity of greater than about 140 W/m*K, the heat spreader defining a spreader groove shaped for mating with the panel groove; and

a thermoplastic liner positioned between the panel and the heat spreader, the liner including an extended tab protruding toward the spreader groove.

9. The heat exchanger of claim 8, further comprising a tab clearance void defined in the heat spreader, wherein the extended tab protrudes through the tab clearance void.

10. A foldable heat exchanger panel for transferring heat from a thermal element to an environment, the panel comprising:

a first base including a first surface groove defined therein;

a second base pivotally attached to the first base;

a first liner disposed on the first base;

a second liner disposed on the second base; and

a heat spreader disposed on the first and second liners and defining a flexible bridge between the first and second bases, the heat spreader including at least one sheet of flexible graphite.

11. The panel of claim 10, further comprising:

the heat spreader defining a first tab clearance void aligned with the at least one snap tab,

wherein the at least one snap tab extends through the tab clearance void into the spreader recess.

12. A heat exchanger apparatus for transferring heat from a thermal element to an environment, the apparatus comprising:

at least one flexible graphite sheet having an in-plane thermal conductivity greater than about 250 W/m*K and a thickness less than about 2 millimeters; a thermoplastic liner having a U-shaped groove defined therein, wherein the flexible graphite sheet extends into the U-shaped groove between the thermal element and the thermoplastic liner; and

at least one snap tab integrally molded on the thermoplastic liner protruding into the U-shaped groove.

13. A heat exchanger panel apparatus, comprising:

a base panel;

a base panel heat spreader disposed on the base panel, the heat spreader including at least one sheet of compressed particles of exfoliated graphite having a density greater than about 0.6 g/cc and a thickness less than about 10 millimeters; and

a channel panel disposed on the heat spreader, the channel panel defining a channel panel gap.

14. The apparatus of claim 13, further comprising:

a channel panel heat spreader disposed between the channel panel and the base panel heat spreader such that the channel panel heat spreader engages in thermal contact with the thermal element and the base panel heat spreader.