CN109416224B

CN109416224B - Laminated microchannel heat exchanger

Info

Publication number: CN109416224B
Application number: CN201780037866.1A
Authority: CN
Inventors: 理查德·托德·米勒; 斯蒂文·G·舍恩
Original assignee: Oregon State University
Current assignee: Oregon State University
Priority date: 2016-04-18
Filing date: 2017-04-18
Publication date: 2022-05-06
Anticipated expiration: 2037-04-18
Also published as: KR102494649B1; WO2017184635A1; EP3446059A1; EP3446059A4; CN109416224A; IL263805A; EP3446059B1; KR20190016489A

Abstract

In one general aspect, a microchannel heat exchanger is disclosed. Comprising a lid, a base and thermally conductive sheets located between the lid and the base, each thermally conductive sheet defining a series of side-by-side channels aligned with the direction of flow. Each channel includes aligned slots defining microchannel sections and separated by cross ribs. The sheets are stacked between the base and cover such that at least some of the ribs are offset from one another and permit microchannel segments in the same channel of adjacent sheets to communicate with one another in the flow direction to define a plurality of microchannels in the heat exchanger.

Description

Laminated microchannel heat exchanger

Cross Reference to Related Applications

Priority is claimed for U.S. provisional application serial No. 62/324,327 filed on 18/4/2016 and U.S. application serial No. 15/402,511 filed on 10/1/2017, both of which are incorporated herein by reference.

Technical Field

The present invention relates to microchannel-based heat exchangers, including microchannel-based evaporators for cooling heat sources (e.g., electronic devices) having high heat fluxes.

Background

Fluid heat exchangers are used to transfer heat energy (typically in excess of 5 watts/cm) by receiving and dissipating heat energy from high heat flux heat sources²And generally substantially higher) to remove waste heat. Examples of such high heat flux heat sources include microelectronics, such as microprocessors and memory devices, solid state Light Emitting Diodes (LEDS) and lasers, Insulated Gate Bipolar Transistor (IGBT) devices, such as power supplies, photovoltaic cells, radioactive heat generators and fuel rods, and internal combustion engines.

Fluid heat exchangers dissipate heat by conducting the heat to the internal passages of the exchanger through which the coolant fluid flows, absorbing the heat conducted through the exchanger walls, and then transporting the fluid outside the exchanger, where the heat is rejected to an external heat sink. While the coolant fluid flowing through the exchanger may be a gas, it is generally preferred to use a liquid because a liquid has a higher heat capacity and thermal conductivity than a gas. The liquid may be maintained as a single phase, or the liquid may be partially or completely vaporized within the internal passages of the exchanger.

The flow of coolant liquid supplied to the fluid heat exchanger may be driven by a pump, or by natural convection due to density differences and/or elevations between the entering and exiting fluids (e.g. thermosiphons), or by capillary action in the internal channels, or by a combination of these mechanisms of the exchanger.

Evaporator type exchangers rely on boiling patterns and have the advantage of higher heat transfer coefficients per fluid flow rate of coolant (better heat transfer). They also require less coolant flow because most of the heat is absorbed by the latent heat of evaporation of the boiling fluid rather than the sensible heat (heat capacity) of a single phase liquid or gas.

It is well known that the thermal performance and efficiency of fluid heat exchangers can be greatly enhanced if the internal channels are constituted by microchannels (i.e. channels having a cross-sectional minimum dimension of less than 1000 microns, and more typically in the range 50-500 microns).

Disclosure of Invention

In one general aspect, the invention features a microchannel heat exchanger including a cover, a base, and a thermally conductive sheet positioned between the cover and the base, each thermally conductive sheet defining a series of side-by-side channels aligned with a flow direction. Each channel includes aligned slots defining microchannel sections and separated by cross ribs. The sheets are stacked between the base and cover such that at least some of the cross ribs are offset from one another and allow microchannel segments in the same channel in adjacent sheets to communicate with one another in the flow direction to define a plurality of microchannels in the heat exchanger.

In a preferred embodiment, the thermally conductive sheet may also define an access channel opening at each end of the channel, which access channel opening forms an access channel for the microchannel when stacked. The lamellae may define a more dense packing of cross ribs at least one inlet end of the heat exchanger to reduce the open cross-section at the channel inlet end. The aspect ratio of the microchannel may be greater than 4: 1. the aspect ratio of the microchannel may be greater than 8: 1. the apparatus may further comprise a sheet of thermally conductive separator material positioned between the sets of thermally conductive sheets to form a multi-layer heat exchanger. The sheet may be made of at least one conductive metal. The sheet may be made of a sinterable, thermally conductive ceramic. The sheets may be bonded or fused. The microchannel may have a hydraulic diameter of less than 500 microns. The microchannel may have a hydraulic diameter of less than 200 microns. The base may be a thicker substrate than each sheet and the lid may include an access channel in communication with the microchannel. The base may be thermally conductive but electrically insulating. The heat exchanger may be configured for boiling or evaporating fluid service, the heat exchanger further comprising a flow restriction at the inlet end of the microchannel. The flow restriction may be formed by alternately closing the ends of first slots in the slotted channels in alternating layers of slotted sheets, the first slots having a cross-rib wider than the cross-rib body between the slots, the alternating closed-end slot channels being staggered with respect to the upper or lower slot channels such that when the sheets are stacked and bonded together, the cross-section of the parallel channels formed has a checkerboard pattern across the inlets of the plurality of channels which acts as an integral flow restriction covering approximately 50% of the cross-sectional area of the main channel.

The system according to the invention can help to suppress the Leding effect, allowing the heat exchanger to work with a two-phase system. By providing an inlet restriction, the microchannel evaporator according to the present invention can avoid flow instabilities due to the Leding effect, whereby boiling in a plurality of (parallel) microchannels may be non-uniform and lead to periodic backflow into the header or manifold due to the interaction of pressure drops in the various channels that vary as boiling progresses. This helps to achieve a steady and substantially uniform boiling flow, resulting in improved and more stable thermal performance when cooling high flux heat sources.

Drawings

FIG. 1 is a plan view of a first type of grooved sheet contained in a grooved laminate structure that may be used to implement a microchannel heat exchanger;

FIG. 2 is a plan view of a portion of the first type of fluted sheet of FIG. 1, as indicated by rectangle 2 in FIG. 1;

FIG. 3 is a plan view of a portion of a second type of fluted sheet included in a fluted laminate structure;

FIG. 4 is a plan view of a separator sheet contained in a fluted laminate structure;

fig. 5 is a perspective cross-sectional view of a laminated structure alternately formed by a first sheet type and a second sheet type as shown in fig. 1 to 4 in a direction indicated by an arrow 5 in fig. 2 and 3;

FIG. 6 is a more detailed cross-sectional view of the fluted laminate structure of FIG. 5;

FIG. 7 is a second perspective cross-sectional view of the laminated structure of FIG. 5, illustrating a flow path through the structure of FIG. 5, in the direction indicated by arrow 7 in FIGS. 2 and 3;

FIG. 8 is an exploded view of a laminate sheet for assembly to a fluted laminate core using the fluted laminate construction shown in FIGS. 1-7;

FIG. 9 is an exploded perspective view of a portion of a microchannel heat exchanger using the laminated core of FIG. 8; and

fig. 10 is a cross-sectional view of the fluted laminate of fig. 5, taken through the plane defining the flow restriction in the fluted laminate.

Detailed Description

Microchannel heat exchangers can be assembled using a grooved laminate structure composed of a plurality of thermally conductive sheets. One such first type of sheet 40 is shown in fig. 1. It includes common cut regions 42 that are parting lines 44 of grooves 46 that define microchannels.

More specifically, the first type of tab 40 includes a plurality of lines 44 of a plurality of slots 46, the slots in a given line being separated by thin walls that serve as cross ribs 48. The lines run between common cut-out regions at the slot connections at either end of each line of the slot. When the sheets are stacked, the common cutout regions are aligned with each other to form input and output manifolds.

Referring also to fig. 2 and 3, the alternating use of two or more types of flakes allows the definition of microchannels in three-dimensional space. In particular, the laminated core structure is assembled from alternating slotted and ribbed platelets, the transverse ribs being interdigitated with one another when the platelets are stacked, such that each line of slots forms a continuous serpentine flow path (see also fig. 5-7).

Referring to fig. 4, thermally conductive, non-slotted spacer sheets 60 with sheet cutout regions 62 may also be used on the top and bottom of the core and/or for separating microchannel layers, the cutout regions 62 being aligned with the common cutout regions of the slotted and ribbed sheets.

Referring to fig. 8, alternating slotted and ribbed platelets, with an unslotted separator platelet on both sides of the stacked assembly, allows for the formation of a core structure comprising one or more layers, each layer having a plurality of microchannels with interspersed cross ribs that intermittently partially interrupt the flow path while providing lateral strengthening of the channel walls. The number of alternating grooved and ribbed lamellae in each layer, as well as the lamella thickness and slot width, determines the channel depth of the channel layer: width aspect ratio. The laminae of the layered stack are preferably bonded to ensure that all of the laminae are in thermally conductive communication with each other.

Referring to fig. 9, the resulting subassembly may then be bonded to a substrate 74 to ensure that the substrate is in conductive thermal communication with the microchannel layer, and a cover 78 may be placed and sealed on top of the resulting assembly of microchannel layer 76 bonded to the substrate to form the completed microchannel heat exchanger assembly 70.

Referring to fig. 10, where the exchanger is used for boiling or evaporation services, the input side of the microchannel preferably includes a flow restriction. These restrictions can be built into the laminate structure by providing additional cross ribs 82 on the input side of the microchannels.

The above-described laminated structure provides a microchannel heat exchanger having one or more layers of microchannels with hydraulic diameters of less than 500 microns, the microchannels having any high depth: width aspect ratio and thin walls. The channels have internal cross-ribs that connect the channel walls and provide mechanical strength to the channel walls and a means of interrupting fluid flow lines to improve heat transfer. The heat-conducting sheet and the substrate material are preferably, but not limited to, metals and alloys thereof; a non-metallic element, a thermally conductive carbon allotrope or a thermally conductive ceramic. The bonding of the sheets may be performed in any convenient way that ensures a high thermal conductivity between the sheets and the substrate.

The multilayer microchannels are formed by inserting additional sheets of thermally conductive, non-grooved separator having cut-out regions aligned with the common cut-out regions of the grooved and ribbed sheets between stacks of grooved and ribbed sheets. The microchannels of any layer may have the same or different depths as compared to the microchannels in other layers: width aspect ratio and hydraulic diameter.

Depth of the formed microchannel: the width aspect ratio may be at least 2: 1, and preferably between 4:1 and 15: 1. The walls between the resulting microchannels may be less than 200 microns and preferably have a thickness of 40-100 microns. The substrate and microchannel walls may be made of materials having thermal conductivities in excess of 100W/m-K. The resulting microchannel may have a hydraulic diameter of less than 500 microns, preferably 50 to 200 microns.

The fluid inlet passage may be provided with a flow restriction to prevent flow instability of either the reverse flow or the two-phase flow. These inlet restrictions are achieved by closing the inlet side ends of the slots of alternate lamellae in a stack of grooved and ribbed lamellae (e.g., by adding additional cross ribs), thereby reducing the cross-sectional area of the opening of the inlet to the channel relative to the cross-sectional area of the main channel beyond the closed portion. Preferably, the length of the closed (restricted) portion of the microchannel is at least 1 mm.

The various components of the microchannel heat exchanger (e.g., microchannel stack, base plate, and upper plate) may be bonded or fused such that the exchanger is hermetically sealed (except for fluid inlets and outlets in communication with the manifold) such that the exchanger can maintain elevated internal pressures. The bonding or fusing may be accomplished by any convenient means.

The various components of the microchannel heat exchanger (e.g., microchannel stack, base plate, and upper plate) may also be mechanically coupled together with appropriate seals between the components so that the exchanger can maintain elevated internal pressures.

In another embodiment, the bottom substrate of the microchannel exchanger layer is made of or coated with an electrically conductive but electrically insulating ceramic or dielectric solid, such as aluminum nitride, silicon carbide, beryllium oxide, diamond film, and the like. The microchannel exchanger is then used as a substrate for (heat-generating) electronic components, mounted on and in thermal contact with the electrically insulating but thermally conductive bottom surface of the exchanger.

Manufacturing method

The various components of the microchannel heat exchanger (e.g., thermally conductive base, microchannel layers, manifolds, covers, fluid inlets and outlets, slotted and ribbed sheets, etc.) may be fabricated by any convenient means consistent with the final assembly of the heat exchanger. These means may include, but are not limited to, the following methods and combinations thereof:

subtractive manufacturing techniques such as machining, milling, etching, punching, photochemical machining, laser ablation or micromachining, Electrical Discharge Machining (EDM), ultrasonic machining, water jet cutting, and the like.

Mechanical deformation of the material, for example by scraping, "plowing", stamping, embossing, pressing, etc.

Lamination and bonding of patterned sheets to form three-dimensional structures with internal features and channels. The sheet may have repeating areas of the pattern so that after bonding, the bonded assembly can be cut or diced into individual microchannel exchangers or exchanger subassemblies.

Additive manufacturing techniques (3D printing), such as selective laser sintering, direct metal laser sintering, selective laser melting, stereolithography, fused deposition modeling, and the like.

Bonding or fusing techniques such as diffusion bonding, brazing, soldering, welding, sintering, and the like.

Mechanical assembly techniques such as bolts, studs, clamps, adhesives, etc., using seals such as washers, O-rings, caulks, etc., as the case may be.

Embodiments in accordance with the present invention may be developed in a variety of different cooling configurations and applied to a variety of different cooling tasks. For example, they may be implemented in conjunction with the teachings of published PCT application WO2009/085307 filed on 26.12.2008 and published us application No. us-2009-0229794 filed on 10.11.2008, which are all incorporated herein by reference.

The invention has now been described in connection with a number of specific embodiments thereof. It is contemplated, however, that many modifications, which fall within the scope of the invention, should be apparent to those skilled in the art. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. Additionally, the order of presentation of the claims should not be construed as limiting the scope of any particular term in the claims.

Claims

1. A microchannel heat exchanger comprising:

a cover having an inlet access passage and an outlet access passage,

a heat-conducting base, wherein the base is provided with a plurality of heat-conducting holes,

a plurality of thermally conductive sheets between the lid and the base, each thermally conductive sheet defining a series of side-by-side channels aligned with a flow direction, wherein each of the channels includes a plurality of aligned slots defining a microchannel section and separated by cross-ribs,

wherein the lamellae further define a common cut-out region at either end of the channel in communication with the channel;

wherein the flakes are stacked between the base and cover such that at least some of the cross ribs are offset from one another and allow microchannel segments in the same channel of adjacent flakes to communicate with one another along a flow direction to define a plurality of microchannels in a heat exchanger; wherein the cross-ribs reinforce walls defined by stacked sheets separating the microchannels; and

wherein the sheets are stacked between the base and the lid such that the common cutout area forms the at least one input manifold and at least one output manifold that align with the inlet and outlet channels on the lid, respectively.

2. The microchannel heat exchanger of claim 1 wherein the thermally conductive sheet further defines an inlet channel opening at each end of the channel, the inlet channel openings forming inlet channels for the microchannels when stacked.

3. The microchannel heat exchanger of claim 1 wherein the platelets form a more dense packing of transverse ribs in at least one inlet end of the heat exchanger to reduce the open cross-section at the inlet end of the channel relative to the cross-section of the portion of the channel between the channel inlet and outlet ends.

4. The microchannel heat exchanger of claim 1 wherein the length to width ratio of the microchannels is greater than 4: 1.

5. The microchannel heat exchanger of claim 1 wherein the length to width ratio of the microchannels is greater than 8: 1.

6. The microchannel heat exchanger of claim 1 further comprising a sheet of thermally conductive spacer positioned between the sets of thermally conductive sheets to form a multilayer heat exchanger.

7. The microchannel heat exchanger of claim 1 wherein the sheet is made of at least one thermally conductive metal.

8. The microchannel heat exchanger of claim 1 wherein the sheet is made of a thermally conductive ceramic capable of sintering.

9. The microchannel heat exchanger of claim 1 wherein the sheet is bonded or fused.

10. The microchannel heat exchanger of claim 1 wherein the microchannels have a hydraulic diameter of less than 500 microns.

11. The microchannel heat exchanger of claim 1 wherein the microchannels have a hydraulic diameter of less than 200 microns.

12. The microchannel heat exchanger of claim 1 wherein the base is a thicker substrate than each sheet and the lid includes an access channel in communication with the microchannels.

13. The microchannel heat exchanger of claim 1 wherein the base is thermally conductive and electrically insulating.

14. The microchannel heat exchanger of claim 1 wherein the heat exchanger is configured for boiling or evaporating fluid service, and wherein the heat exchanger further comprises a flow restriction at an inlet end of the microchannel.

15. The microchannel heat exchanger of claim 14 wherein the flow restrictions are formed by closing the inlet ends of every other channel in each sheet having cross-ribs, the channels of the closed ends of the slots being staggered relative to one another in adjacent sheets when the sheets are stacked and bonded together to form a checkerboard pattern across the inlets of the plurality of channels, the checkerboard pattern isolating approximately 50% of the cross-sectional area of the channels.

16. The microchannel heat exchanger of claim 15 wherein the cross ribs forming the flow restrictions are wider than the cross ribs between the slots.