WO2002056660A2

WO2002056660A2 - Helical screw heat exchange device, assemblies thereof, and methods of making the same

Info

Publication number: WO2002056660A2
Application number: PCT/US2002/000662
Authority: WO
Inventors: Dennis E. Hartzell; Edward J. Ognibene
Original assignee: Satcon Technology Corporation
Priority date: 2001-01-11
Filing date: 2002-01-11
Publication date: 2002-07-18
Also published as: WO2002056660A3

Abstract

Heat exchange devices (1) and methods of using and making them are disclosed. The heat exchange devices (1) have an elongate core (2) with a helical member (3) coiling along the outer surface of the core and extending along the longitudinal axis of the core. The heat exchange devices can be used alone or in groups, wherein a plurality of heat exchange devices can be connected independently to a substrate (10) and be disconnected from adjacent heat exchange devices. Fluids can be forced between the heat exchange devices to facilitate heat transfer.

Description

HELICAL SCREW HEAT EXCHANGE DEVICE, ASSEMBLIES THEREOF, AND METHODS OF MAKING THE SAME

FIELD OF THE INVENTION

The present invention relates to heat exchange devices and assemblies, and methods for using and making the heat exchange assemblies. More particularly, the heat exchange assemblies of the invention comprise at least one heat exchange device in the form of an elongate core with an integral helical member extending radially along the length of the core. The heat exchange devices can be used individually or in a group to form an array, and they find particular usefulness in small areas requiring temperature control, such as in electronic components.

BACKGROUND OF THE INVENTION

As the demand for faster and more powerful electronic components continues, so does the trend towards making these components smaller and more portable. With the manufacture of such power dense components, thermal control becomes increasingly critical.

Various heat exchangers and methods have been developed to maintain operable temperature ranges within electronic components. For example, high thermal flux heat sinks have been used to remove heat and in attempt to keep component temperatures at acceptable limits. However, heat sinks are capable of limited heat transfer.

To increase heat transfer capabilities, heat sinks were modified to include extensions from the generally flat surface of the heat sinks. For example, heat sinks comprising a flat surface with vertically extending cylindrical pins were designed. These pin structures provide additional surface area through which heat transfer may occur. Further, in attempts to provide more surface area and, thus, higher heat transfer capabilities, increasingly dense pin arrays were formed wherein the pin structures were packed together more tightly.

The manufacture of such pin arrays is accomplished typically by extrusion or die- casting combined with post-machining. The extrusion technique produces pins that are all in line, with dimensions, i.e., spacing, between pins down to 40 mm, depending on the pin length. Die-casting can produce staggered pins, which are coarser, typically more than 60 mm between pins, again depending on pin length. Generally, the pin density is dependent upon pin length and fabrication technique, with the machined extrusions providing the highest densities. However, both fabrication techniques require post machining and, thus, are relatively expensive processes. Additionaly, although these pin arrays are useful in enhancing heat transfer capabilities, such structures still are not capable of meeting the demand of the increasingly power dense electronic components. In these cylindrical pin geometries, the boundary layers between pins never merge. Thus, although an increase in pressure loss results, much of the flow simply bypasses the pins and does not absorb much thermal energy.

Metal forms have also been designed, whereby thin ligaments are placed so as to weave throughout a fluid flow path. Although the fluid contacts these ligaments, littie heat transfer occurs. The ligaments that are perpendicular to the flow field and attached to the base-plate carry most of the thermal energy. All other ligaments do little more than introduce additional pressure losses. Bi-axial compression increases the number of ligaments in contact with the base-plate, but results in choking up the flow area with useless ligaments, which increases pressure drop.

In response to this demand for higher heat transfer capabilities, fans are commonly used in combination with the heat sinks and pin arrays. However, fans are prone to failure, have short life-spans, and must be replaced often.

Accordingly, there still exists a need for a heat exchange device and assembly capable of use in the increasingly power dense electronic components and the like, wherein only a small area is available for the location of the heat exchange assembly. Further, there still exists a need for a heat exchange device and assembly that can be altered to fit various sizes and locations with varying heat transfer requirements. Still further, there still exists a need for a simple and cost efficient method of forming the heat exchange devices and assemblies.

SUMMARY OF THE INVENTION

The present invention provides a heat exchange device that comprises a core and an integral helical member that extends radially from and along the longitudinal axis of the core. The helical member provides increased surface area for heat transfer, thereby ultimately enhancing the heat transfer capability of the heat exchanger. Preferably, the core is cylindrical in shape, having a proximal end and a distal end. The core is preferably solid with a smooth outer surface. The core diameter mψ vary along the length of the core, but preferably the core has a uniform diameter throughout.

The helical member is preferably a substantially flat member that extends radially from the outer surface of the core, beginning near the proximal end of the core and extending toward the distal end of the core in a helical fashion. Preferably, the helical member is a single structure that coils continuously along substantially the entire length of the core from the proximal end to the distal end.

In one embodiment, the helical member has a substantially uniform width, wherein the width is the radial dimension from the core surface to the outer extremity of the helical member. In other embodiments, the helical member may vary in width such that the helical member's outer extremity, for example, tapers from one end of the core to the other, or tapers from the center of the core toward each end.

The thickness of the helical member is preferably substantially uniform, but can may taper from the core surface, vd ere the helical member is attached to the core, toward the outer extremity of the helical member.

In one embodiment, the heat exchanger further comprises a thickened end-cap at one end of the core as a base. The end-cap has a bottom surface and a top surface, whereby the core extends from the top surface of the cap. Preferably, the core extends from the center portion of the end-cap, substantially normal to the end-cap. The endcap is preferably solid and can be of any geometric shape, for example, circular or rectangular. The bottom of the end-cap is preferably flat, thereby providing a solid foundation upon which to rest and/ or attach the heat exchange device onto a surface when in use. Further, to provide a stable support, preferably, the end-cap is at least as wide as the maximum width of the core and helical member structure.

In another embodiment, the heat exchanger comprises a thickened end-cap at each end of the core. The two end-caps are preferably similar in size and shape. In one preferred embodiment, one end-cap is thicker than the other end-cap such that, upon placing a plurality of heat exchangers in a the shaker or tumbling device, the heat exchangers all come to rest on the thicker end-cap with the thinner end-cap extending upward. The heat exchange device of the present invention is particularly useful in electronic components wherein a small amount of space is allotted for a heat transfer device. Based on the ultimate use of the heat exchange device of the present invention, the overall dimensions can vary.

Depending on the heat transfer requirements, the heat exchangers can be used singularly, as a stand-alone entity, or in groups.

Individual heat exchange devices can be used, for example, by attaching one end of the core or, where an end-cap is included, attaching one end-cap directly to a substrate, such as a surface of an electronic component or a heat sink.

In another embodiment, a plurality of heat exchange devices are used in a group by packing them into various arrays. In such arrays, to enable close packing of the heat exchange devices in a given area, the end-caps are preferably no wider than the maximum width of the core and helical member. The heat exchange devices can be removably or permanently attached to form an array of heat exchange devices directly on a substrate upon which electronic components are mounted. The heat exchangers are attached to the surface by known methods such as, for example, soldering, adhesion or sintering, using conductive materials.

It is believed that heat exchange arrays of the present invention, wherein each heat exchange device is disconnected from other heat exchange devices, are useful in reducing the propensity for stress build up due to differences in the coefficier± of thermal expansion between the heat exchange devices and the surface upon which the heat exchange devices are attached. Without being bound by theory, it is believed that the interface (e.g., joined by solder, adhesive, sintering) is able to yield locally relative to internal stress that develops, thereby reducing stress build up and potential fracture, which is a common problem encountered with large contiguous heat exchanger assemblies. As a result, the heat exchange devices of the present invention can be fabricated out of materials such as copper and aluminum and can be attached effectively directly to materials with different coefficients of thermal expansion.

The heat exchangers of the present invention are generally fabricated by using a screw machine to produce the core with the helical member. To form heat exchangers without the end-caps, a substantial length of core with a helical member can be fabricated using the screw machine, followed by cutting suitable lengths of the core to form a plurality of individual heat exchangers of desired length. The heat exchangers with end- caps also are fabricated by machining, preferably a computer controlled machine, or by other means well known to those skilled in the art. The individual heat exchange devices can then be attached to a substrate by soldering, sintering, adhesion, or other fixation methods. Alternatively, an array of heat exchange devices can be formed by packing a plurality of heat exchangers into the desired array shape, followed by attachment of each heat exchange device to the substrate.

In a preferred embodiment of the invention, an array of heat exchange devices is formed by the following method. A plurality of heat exchangers are formed, each with one core end-cap being thicker than the other core end-cap. The heat exchange devices are then fed into a shaker or tumbler type-device which causes the heat exchange devices to align resting on their thicker (i.e., heavier) core end-cap. The heat exchange devices are then packed into a desired pre-form array, positioned over a substrate or other surface, and simultaneously fixed to the surface. Such fabrication technique can produce an array of heat exchange devices having densities much higher than those currently available, and at a lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a front elevational view of a heat exchange device in accordance with one embodiment of the present invention.

FIG. 2 shows a perspective view of the heat exchange device shown in FIG. 1.

FIG. 3 shows a perspective view of a heat exchange device in accordance with a second embodiment of the present invention.

FIG. 4 shows a side view of the heat exchange device shown in FIG. 3.

FIG. 5 shows a cross sectional view of the heat exchange device shown in FIG. 4 along the longitudinal axis thereof.

FIG. 6 shows a perspective view of a plurality heat exchange devices packed directly onto a substrate in accord with a preferred embodiment of the present invention.

FIG. 7 shows a perspective view of the substrate shown in FIG. 6, further illustrating electrical components arranged on the opposite side of the substrate from the plurality of heat exchange devices. FIG. 8 shows an exploded view of a heat exchanger containing an array of heat exchange devices of the present invention for insertion into a chamber that is adapted for fluid flow through the chamber.

FIG. 9 illustrates the use of two heat exchange devices deployed in an actively cooled switch assembly.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the various figures of the drawings wherein like reference characters refer to like parts, there is shown in FIGS. 1-5 various views of heat exchange devices 1 in accordance with the present invention.

The heat exchange device 1 comprises an elongate core 2, having a proximal end 4 and a distal and 5, and an integral helical member 3 extending along the length of the core 2 and coiling around the core's outer surface. As shown in FIGS. IS, the core 2 is preferably cylindrical with a circular cross-section uniform in diameter throughout. However, if desirable in some applications, the core may have other geometric cross sections, for example, an oval or square cross-section, and the cross-section of the core 2 may vary in diameter "2r" along the length of the core 2. Also, in some applications, the core can be hollow to permit fluids to flow therethrough.

The helical member 3 extends along a substantial length of the core 2. The helical member 3 is a generally flat, thin member and extends radially a distance "R" from the core's longitudinal axis 9. In some embodiments, as shown in FIGS. 1 and 2, R can be constant along the entire length of the core 2. Alternatively, R can be substantially constant along a center portion of the core and taper towards both ends of the core. R also can taper toward only one end of the core, or from both ends of the core toward the center of the core.

The heat exchange device 1 further can comprise an end-cap 6 at the proximal end 4 of the core 2 as shown in FIGS. 3 and 4. The end-cap 6 has a top surface 7 and a bottom surface 8. The bottom surface 8 of the end-cap 6 preferably is designed for attaching the heat exchange device 1 tightly to a surface and for adhering the heat exchange device 1 securely to the surface. For this reason, the bottom surface 8 of the end-cap 6 is preferably substantially flat. The core 2 preferably extends upwards from and normal to the end-cap 6 top surface 7 as shown in FIGS. 3 and 4. Preferably, the core 2 extends from the center of the end-cap 4 to provide maximum stability when the heat exchanger 1 is placed on a substrate in contact with the bottom surface 7 of the end-cap 6. The end-cap 6 can be of any geometric shape, for example, circular, square or hexagonal, and preferably is shaped and sized to provide sufficient stability when placed on a given surface.

The heat exchange device further can comprise, in addition to an end-cap 6 at the proximal end 4, a second end-cap 6' at the distal end 5 of the core 2, as shown in FIGS. 1 and 2. As with the proximal end 4 end-cap 6, the distal end 5 end-cap 6' has a top surface 7' and a bottom surface 8'. The core 2 extends from the bottom surface 8' of endcap 6' preferably normal to and in the center of end-cap 6\ The second end-cap 6' also can be of any geometric shape. Preferably, both end-caps have the same geometric shape.

The two-end-caps 6, 6' can be identical, such that the heat exchanger is symmetrical about a transverse axis through its center and whereby the heat exchanger can rest on a given surface on either end-cap 6 or 6\ As such, both endcaps 6, 6' are shown (FIGs. 2 and 3) having a substantially flat and solid bottom surfaces 8, 8' and top surfaces 7, 7' respectively.

Alternatively, the two end-caps 6, 6' can be dissimilar in shape and/or size. Most preferably, the proximal end 4 end-cap 6 is heavier (i.e., thicker) than the distal end 5 end- cap 6', such that in the manufacture of a plurality of heat exchange devices 1, the heat exchange devices can be fed into a shaker or tumbler type device wherein they are tossed around and automatically come to rest on the thicker proximal endcap 6 bottom surface 8.

Preferably, as shown in FIGs. 1-4, each end-caps 6, 6' is as wide as the maximum width of the core 2 and helical member 3 combined for maximum stability of the heat exchanger 1 when resting on or attached to a surface. Preferably, the end-caps 6, 6' are no larger than the maximum width of the core 2 and helical member 3 combined to enable close packing of a plurality of heat exchangers 1 in a given area where the heat exchanger is resting on its end-cap 6 or 6' and the core is extending away from the surface.

Alternatively, in certain embodiments, the end-cap 6, 6' can be smaller or larger than the maximum width of the core 2 and helical member 3 combined. If the endcaps 6, 6' are smaller, at least one end-cap 6, 6' is preferably sized sufficiently to provide a stable support for resting and adhering the heat exchange device 1 on asurface. The end-caps 6, 6' can also be larger than the maximum width of the core 2 and helical member 3 combined if the heat exchange devices 1 are either used singularly or if a plurality of heat exchange devices are placed side by side with spaces intentionally left between the the helical members. It is preferred in such cases that the end-caps 6, 6' are sized small enough so that each end-cap 6, 6' is disconnected from adjacent end-caps 6, 6', thereby decreasing the propensity for stress build up due to any difference in the coefficients of thermal expansion in the array.

The overall dimensions of the heat exchange devices can vary based on their ultimate use. For example, for a cylindrical core with a circular cross-section, it has been found that in order to provide effective cooling capacities, the ratio of the maximum radius "R" of the helical member 3 (wherein "R" is measured from the from the core's longitudinal axis 9) to the maximum radius V of the core 2 (wherein "r" is measured from the core's longitudinal axis 9) is preferably greater than or equal to about 1.6/1. The maximum ratio is limited by the thickness of the helical member, the strength of the material used, and heat conduction properties of the material used and the fluid for vhich it is designed, if any. Preferably, the ratio of "R" to V ranges from about 1.6/1 to about 3/1, more preferably, from about 1.6/1 to about 2.2/1. These dimensions would apply equally for cores of different cross- sectional geometries wherein the ratio involves the ratio of the maximum dimension of the helical member cross section to the corresponding dimension of the core cross section (equivalent diameters can be used for the ratio). For example, for other geometries, V can be the maximum distance of the core 2 radially from the core's longitudinal axis 9, and "R" can be the maximum distance of the helical member 3 radially from the core's longitudinal axis 9.

It has been found that when the core 2 of the heat exchange device has a maximum

V of about 0.125 inch, the helical member 4 preferably has a pitch "p" that is greater than or equal to about 0.02 inch. However, the preferred pitch depends on the core maximum "r" and, thus, varies as the core size varies. Generally, as the core diameter increases, the pitch decreases, and as the core thickness or radius decreases, the pitch increases. As used herein, pitch is defined as the distance between two corresponding points on adjacent helix threads. Preferably, the pitch is constant along the entire length of the core 2, and, as such, the pitch can be calculated generally by the following formula: p = length of core "L"/number of helical threads.

In certain preferred embodiments, the helical member 4 preferably forms an angle α, as shown in Figs. 4 and 5, that ranges from about 15 to about 45°. Preferably, the angle α ranges from about 20° to about 45°. Most preferably, the angle α is about 20°. This yields a helical member 4 that is steep in its angle αand thin at its connection with the core 2.

In some embodiments, the ratio of "R" to the overall length of the core "L" ranges from about 1:2 to about 1:8. In one preferred mbodiment, the ratio of "R" to "L" is approximately 1:4. However, the dimensions are sized by the physical parimeters of the application and the materials used.

The heat exchange device is particularly useful in packaging of electronic components wherein a small amount of space is allotted for a heat transfer device 1. Used as such, for example, a typically sized beat exchange device 1 can have a core length "L" of about 0.5 inch and a core maximum radius V of about 0.125. Using the above-described dimensional relationships, the helical member radius "R" is at least about 0.2 inch. The core diameter "d" is about 0.25 inch, and the pitch is at least 0.02 inch. Accordingly, in this device there are 25 helical threads along the length of the core 2. In applications for removing heat from electronic components, the core length of the heat exchange devices is typically less than about one inch. However, lengths of up to several inches can be useful for particular applications for heat removal from electronic components.

The heat exchange devices 1 can be used individually, as desired in some applications, or in groups as shown in FIGs. 6-9.

In one embodiment, shown in FIG. 6 a plurality of heat exchange devices 1 are packed tightly together directly onto a double DBGclad layer 10. As shown in FIG. 7, a plurality of heat exchange devices 1 are packed together on the opposite side of the DBC layer 10.

A preferred fabrication process is as follows. A screw machine is used to produce a core 2 with a helical member 3 with the desired geometry and helix-to-core aspect ratio, as shown on FIG. 1. Preferably, one end-cap of the heat exchange device is intentionally thicker and heavier than the other. Once the screwtype devices are made, they are fed into a shaker, or tumbler, which causes them to flip over with their heavy side down. Next, the screws, which are now standing on end, are collected and packed into a preform array having the desired shape and packing arrangement, and the array is attached to or positioned, at least temporarily, over the substrate upon which electronic components are mounted. Next the assembly is fed into a reflow oven, in which the screw-type devices are soldered to the substrate. FIG. 6 shows the resulting array, with form removed, on one side of a double DBC-clad substrate. FIG. 7 shows the electrical components mounted to the DBC layer on the flip side of the substrate. Depending on the thermal convection environment, substrate materials and thickness, components area and load pattern, cross dimensional thermal spreading may or may not be significant. If spreading is significant, then the heat exchange devices can be attached to the lower DBC layer of the substrate. If the spreading is insignificant, then the heat exchange devices can be attached directly to the back side of the die through small holes drilled into/through the substrate. This can eliminate several stack and interfacial resistances.

This fabrication technique can produce an extremely high density heat exchange device array. The heat exchange devices can be packed against one another, such that a fluid can flow essentially between the helical members of the heat exchange devices, thereby providing superior heat transfer by forcing the fluid into close contact with larger surface areas. Both the helical member spacing and the core spacing can be easily altered to achieve pressure loss goals.

The structure provided by the present invention provides a heat exchange device wherein all of the area in contact with the fluid is sufficiently thermally connected to the base-plate, thereby enhancing heat conduction transfer. Therefore, the incurred pressure loss is directly correlated with the overall heat transfer from the baseplate (or source) to the fluid. Furthermore, the design of the present invention is well suited for flow from any angle, and can be utilized in impingement schemes in which the effluent flows out radially over 360°.

The combination of high surface density with the unique core/helical geometry results in thermal performance that considerably exceeds that of conventional heat exchange devices. In addition, the fabrication technique, primarily a screw machine and reflow process, does not require post-machining and can be considerably less expensive than conventional extrusion/ machining and die-casting/ machining manufacturing techniques.

The heat exchange devises of the present invention will be further illustrated with reference to the following Examples which are intended to aid in the understanding of the present invention, but which are not to be construed as a limitation thereof. EXAMPLE 1

A tests were carried out using aluminum heat exchange devices. A 6 x 9 aligned array of 54 heat exchange devices 1 was soldered to the bottom surface of a DBC-AINDBC substrate 10 using gold-tin solder (see FIG. 8). An aluminum frame was used tofix the substrate and the array in an aluminum reservoir 27, through which was pumped a 50-50 (by volume) mixture of water and ethylene glycol (WEG). An O-ring and a silicon rubber pad provided the proper sealing. The heat exchange devices 1, which were constructed of 6061-T6 aluminum, were plated with nickel and gold. The nominal dimensions of the heat exchange devices 1 were 0.250" diameter x 0.500" long. Three 50-W resistors were mounted to the top side of the substrate with T-resistors. These resistors were used to supply about 50 to about 250 W of heat for testing. Pressure was measured in two ways: (1) a set of pressure transducers and (2) a set of analog pressure gauges measured the pressure drop at the inlet and exit of the array. Two thermocouples were also used to measure the inlet and exit WEG temperature.

The test results, along with the calculated per-unit-area thermal resistances, are shown in Table 1. The tested array produced a per-unit- thermal resistance of about 1.5 to about 2.0 cm²K/W over an about 0.5 to about 1.5 gpm range of WEG flow rates. This array also developed a pressure drop of about 0.05 to about 0.2 psi over this same range of flow rates. As shown in Table 2, the model showed that a staggered array of the same heat exchange devices produced a per-unit-thermal resistance of about 0.6 to about 1.0 cm²K/W over the same flow rate range, which is about 50-60% better than that produced by the aligned array. Although the pressure drop in the aligned array is about 60-75% lower than that developed in the stagger array, the staggered array outperformed the aligned array when the two are compared at the same levels of required pump power.

Table 1. Aligned Array Test Results

EXAMPLE 2

An actively cooled switch cell prototype 30, as illustrated in FIG. 9, was tested using Therminol D-12 as the coolant. During this testing, the temperature of the top surface of the copper collector contactor was measured with a thermocouple. This temperature measurement quickly reached steady state in approximately 20 seconds each time the electrical current was adjusted. As shown in Table 3, this temperature data matched the predictions quite accurately (typically within _+ 10% error).

Table 3 summarizes all of the thermal test data and calculated predictions. The system gauge pressure was also measured near the inlet fittings 35, 37. However, because the pressure measurements include most of the pressure drop through the whole test system, it is difficult to verify the predicted pressure drop through the heat exchange array. However, predictive pressure drop calculations for the inlet and exit fittings 35, 37 and 36, 38 predicted pressure drop in the heat exchange array is consistent with the test data.

Table 3. Thermal Test Results and Predictions

A variety of heatsink technologies were also evaluated, and their various properties are summarized below in Table 4.

Table 4. Tested Heat Sink Technology

Test samples measured 3.5" (wide) x 1.5" (long) x 0.05" (deep). Predictions for carbon foam are not currently available. * Less than 0.01 psi l¹) Effective per-unit-area resistance due to medium (e.g., foam, pin array, etc.) only

(²) Dimensions for the tested present heat exchange array: 1.5" (wide) x 2.25" (long) x 0.05" (deep)

(³) Staggered heat exchange array

(⁴) Aligned heat exchange array It can be appreciated that the heat exchange array of the present invention provides substantial benefits over many of the prior art devices.

The present invention has been described in detail including the preferred embodiments thereof. However, it will be appreciated that modifications and improvements within the spirit and scope of this invention may be made by those skilled in the art.

Claims

What is claimed is:

1. A heat exchange device comprising: an elongate core having a proximal end, a distal end, and a longitudinal axis; and an integral helical member extending radially from the core and winding helically along the longitudinal axis of the core from the proximal end to the distal end; wherein the elongate core has a cross section with a maximum radial dimension "r", the helical member has a cross section with a maximum radial dimension "R", and the ratio of R to r is greater than or equal to about 1.6 to 1.

2. The heat exchange device of claim 1, wherein the elongate core is cylindrical.

3. The heat exchange device of claim 1, wherein r is less than or equal to about 0.125 inch.

4. The heat exchange device of claim 3, wherein the helical member has a pitch that is greater than or equal to about 0.02 inch.

5. The heat exchange device of claim 1, wherein r is greater than about 0.125 inch.

6. The heat exchange device of claim 5, wherein the helical member has a pitch that is less than or equal to about 0.02 inch.

7. The heat exchange device of claim 1, wherein the a helical member has two surfaces extending substantially radially from the core to intersect at an outermost edge and wherein, at the outermost edge, an angle α is formed between the two surfacesD

8. The heat exchange device of claim 7, wherein angle α ranges from about 15° to about 45°.

9. The heat exchange device of claim 7, wherein angle α ranges from about 20° to about 45°.

10. The heat exchange device of claim 7, wherein angle α is about 20°.

11. The heat exchange device of claim 1 , wherein the proximal end and the distal end each have an end-cap that is at least as large in cross-section as the maximum core cross-section.

12. The heat exchange device of claim 11, wherein the proximal end-cap is larger in cross-section than the maximum core cross-section.

13. The heat exchange device of claim 11, wherein both the proximal endcap and the distal end-cap both are larger in cross-section than the maximum core cross section.

14. The heat exchange device of claim 11, wherein the proximal endcap and the distal end-cap are no larger in cross-section than the maximum core plus helical member cross-section.

15. The heat exchange device of claim 1 further comprising a first endcap at the proximal end of the core, wherein the first end-cap has a top surface and a bottom surface, and wherein the core extends approximately normal to the top surface.

16. The heat exchange device of claim 15, wherein the first end-cap has a bottom surface that is substantially flat.

17. The heat exchange device of claim 16, wherein the outer surface of the first end-cap provides a stable support for the device.

18. The heat exchange device of claim 15 further comprising a second endcap at the distal end of the core, wherein the second end-cap has a top surface and a bottom surface, and wherein the core extends approximately normal to the bottom surface.

19. The heat exchange device of claim 18, wherein the top surface of the second end-cap is substantially flat.

20. The heat exchange device of claim 18, wherein the first end-cap is heavier than the second end-cap.

21. A heat exchange device comprising: an elongate core having a proximal end, a distal end and a longitudinal axis; an integral helical member extending radially from the core and winding helically along the longitudinal axis of the core from the proximal end to the distal end; and an end-cap at the proximal end of the core, the end-cap having a top surface and a bottom surface, the elongate core extending away from and substantially normal to the top surface, and the bottom surface being substantially flat, wherein the bottom surface is capable of supporting the heat exchange device in a perpendicular orientation on a substantially flat surface.

22. The heat exchange device of claim 21, wherein the elongate core has a maximum radial dimension "r", the helical member has a maximum radial dimension "R", and the ratio of R to r is greater than or equal to about 1.6 to 1.

23. A heat transfer apparatus comprising: a substrate; and a plurality of heat exchange devices mounted on and extending substantially perpendicular to the substrate, each heat exchanger comprising: an elongate core having a proximal end and a distal end, wherein the proximal end is mounted on the substrate surface; and a helical member extending radially from the core and winding helically along the longitudinal axis of the core from the proximal end to the distal end.