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Micro-tube/multi-port counter flow radiator design for electronic cooling applications

Micro-tube/multi-port counter flow radiator design for electronic cooling applications description/claims

This Patent Application claims priority under 35 U.S.C. 119 (e) of the co-pending U.S. Provisional Patent Application Ser. No. 60/927,424, filed May 2, 2007, and entitled “MICRO-TUBE/MULTI-PORT COUNTER FLOW RADIATOR DESIGN FOR ELECTRONIC COOLING APPLICATIONS”. The Provisional Patent Application Ser. No. 60/927,424, filed May 2, 2007, and entitled “MICRO-TUBE/MULTI-PORT COUNTER FLOW RADIATOR DESIGN FOR ELECTRONIC COOLING APPLICATIONS” is also hereby incorporated by reference.

The invention relates to an apparatus for cooling a heat producing device in general, and specifically, to a fluid-air heat exchanger used in fluid cooling applications.

Cooling of high performance integrated circuits with high heat dissipation is presenting significant challenge in the electronics cooling arena. Conventional cooling with heat pipes and fan mounted heat sinks are not adequate for cooling chips with ever increasing wattage requirements.

A particular problem with cooling integrated circuits within electronic devices is that more numerous and powerful integrated circuits are configured within the same size or smaller chassis. As more powerful integrated circuits are developed, each with an increasing density of heat generating transistors, the heat generated by each individual integrated circuit continues to increase. Further, more and more integrated circuits, such as graphics processing units, microprocessors, and multiple-chip sets, are being added to electronic devices, such as electronics servers and personal computers. Still further, the more powerful and more plentiful integrated circuits are being added to the same, or smaller size chassis, thereby increasing the per unit heat generated for these devices. In such configurations, conventional chassis' provide limited dimensions within which to provide an adequate cooling solution. Conventionally, the integrated circuits are cooled using a heat sink and a large fan that blows air over the heat sink, or simply by blowing air directly over the circuit boards containing the integrated circuits. However, considering the limited free space within the device chassis, the amount of air available for cooling the integrated circuits and the space available for conventional cooling equipment, such as heat sinks and fans, is limited.

Closed loop liquid cooling presents alternative methodologies for conventional cooling solutions. Closed loop liquid cooling solutions more efficiently reject heat to the ambient than air cooling solutions. A closed loop cooling system includes a cold plate to receive heat from a heat source, a radiator with fan cooling for heat rejection, and a pump to drive liquid through the closed loop. The design of each component is often complex and requires detailed analysis and optimization for specific applications.

FIG. 1 illustrates a first conventional radiator 2 configured with one-direction fluid flow. The radiator 2 is configured with a fluid input header 10, a fluid output header 12, a set of parallel fluid channels 14 through which heated fluid flows, and a set of cooling fins 16 thermally coupled to the set of fluid channels 14. Heated fluid enters the fluid input header 10 and flows into the fluid channels 14. The fluid channels 14 and the cooling fins 16 are made of a thermally conductive material to enhance heat transfer from the fluid flowing through the fluid channels 14 to the cooling fins 16. The cooling fins 16 are exposed to airflow for cooling. The airflow is provided in a direction that is perpendicular to a fluid flow direction of the fluid flowing through the fluid channels 14. In this configuration, each of the fluid channels 14 is exposed to the same temperature airflow. As the fluid temperature in each of the fluid channels 14 is the same, and the air temperature intersecting each of the fluid channels 14 is the same, the temperature difference between the fluid temperature and the air temperature is the same for each fluid channel 14. Cooled fluid flows from the fluid channels 14 to the fluid output header 12 and exits the radiator 2.

FIG. 2 illustrates a second conventional radiator 4 configured with two-direction fluid flow. The radiator 4 is configured with a first fluid header 20, a second fluid header 22, a first set of parallel fluid channels 24, a second set of parallel fluid channels 25, and a set of cooling fins 26 thermally coupled to the first set of fluid channels 24 and the second set of fluid channels 25. The first set of fluid channels 24 are parallel to the second set of fluid channels 25. Heated fluid enters the first fluid header 20 and flows into the first set of fluid channels 24. The first fluid header 20 includes a fluid divider 28 configured to prevent fluid input to the first fluid header 20 from entering the second set of fluid channels 25 via the first fluid header 20. The fluid channels 24 and the cooling fins 26 are made of a thermally conductive material to enhance heat transfer from the fluid flowing through the fluid channels 24 to the cooling fins 26. The cooling fins 26 are exposed to airflow for cooling. Cooled fluid flows from the fluid channels 24 to the second fluid header 22 and is directed into the fluid channels 25. The fluid channels 25 are made of a thermally conductive material to enhance heat transfer from the fluid flowing through the fluid channels 25 to the cooling fins 26. Further cooled fluid flows from the fluid channels 25 to the first fluid header 20 and exits the radiator 4. The fluid divider 28 prevents fluid exiting the fluid channels 25 from recirculating into the fluid channels 24.

As in the first conventional radiator 2, the airflow is provided to the second conventional radiator 4 in a direction that is perpendicular to a fluid flow direction of the fluid flowing through the fluid channels 24, 25. In this configuration, each of the fluid channels 24, 25 is exposed to the same temperature airflow. However, the fluid flowing through the second set of fluid channels 25 is cooler relative to the fluid flowing through the first set of fluid channels 24. Since the air temperature of the airflow intersecting each of the fluid channels 24, 25 is the same, there is a greater temperature difference between the airflow and the fluid flowing through the first set of channels 24 then the temperature difference between the airflow and the fluid flowing through the second set of fluid channels 25. Therefore, the cooling efficiency of the radiator 4 is non-uniform.

The performance of the radiator depends on an air flow rate over the cooling fins, a fluid flow rate through the fluid channels, a surface area of the cooling fins, and the difference in temperature between the air and the fluid.

What is needed is a more efficient cooling methodology for cooling integrated circuits within electronic devices. What is also needed is a cooling methodology that increases cooling performance within a given space constraint.

A counter flow radiator is air cooled and is applicable for fluid cooling in electronic systems. Heated fluid, such as heated liquid or two-phase fluid, enters the counter flow radiator and travels through a fluid path including multiple micro-conduits, such as micro-tubes, micro-channels, or micro-ports, while rejecting the heat from the fluid into fin assemblies coupled to the micro-conduits. Airflow is directed over the surface of the fin assemblies to remove heat from the fin assemblies to the air. The counter flow radiator is configured with multiple cooling cores. Each cooling core includes at least one layer of micro-conduits and at least one layer of cooling fin assemblies alternatively stacked on top of each other. The cooling cores are coupled together in series along a first direction. The airflow is also directed along the first direction. The fins are aligned in the direction of air flow. The heated fluid enters the counter flow radiator through one or more inlet points in a first header. The one or more inlet points are positioned on an air exhaust side of the counter flow radiator. The heated fluid follows a serpentine-like path that passes though the multiple cooling cores, crossing the air flow path multiple times, and leaves the counter flow radiator through one or more outlet points in a second header. The one or more outlet points are positioned on an air intake side of the counter flow radiator. One or both of the headers, depending on the number of cooling cores, include a divider or dividers that selectively separates the multiple cooling cores and facilitate the serpentine-like fluid path. The counter flow radiator configuration improves the thermal efficiency of the radiator by flowing fluid in an opposite direction of airflow, thereby exposing the hottest temperature fluid to the hottest temperature air and the coldest temperature fluid to the coldest temperature air. In some embodiments of the counter flow radiator, a constant temperature differential exists in the direction of air flow, across the width of the heat sink

In one aspect, a fluid-air heat exchanger includes a plurality of fluid-air cooling cores, a first fluid header, and a second fluid header. Each cooling core includes at least one layer of one or more thermally conductive fluid conduits and at least one layer of thermally conductive cooling fins coupled to at least one fluid conduit layer, wherein each fluid conduit is configured along a first direction from a first end of the cooling core to a second end of the cooling core, further wherein the plurality of cooling cores are stacked side by side along a second direction perpendicular to the first direction such that the fluid conduits of the plurality of cooling cores are configured in parallel. The first fluid header is coupled to the first end of each cooling core, wherein the first header includes an inlet port configured to receive an input fluid. The second header is coupled to the second end of each cooling core, wherein the first header and the second header are configured to direct fluid flow in series from a first cooling core closest to the inlet port of the first header to each successively stacked cooling core along the second direction.

A second cooling core is positioned furthest from the first cooling core within the plurality of stacked cooling cores. In some embodiments, the second cooling core is configured to receive an intake airflow into the fluid-air heat exchanger along the second direction and the first cooling core is configured to exhaust the airflow from the fluid-air heat exchanger. If a number of cooling cores is even, then the first fluid header includes an outlet port configured to output fluid received from the second cooling core. In this configuration, the first header includes at least one divider to separate the inlet port from the outlet port. If a number of cooling cores is odd, then the second fluid header includes an outlet port configured to output fluid received from the second cooling core. In this configuration, the first header and the second header cumulatively include at least one fluid divider configured to direct fluid flow from the inlet port to the outlet port via the plurality of cooling cores. The fluid flows between the first header, the second header, and from cooling core to cooling core in a serpentine-like manner. In some embodiments, a temperature of the input fluid is greater than a temperature of the fluid output from the outlet port. In this case, a hot-to-cold fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core. In some embodiments, a temperature of the intake airflow is colder than a temperature of the exhaust airflow. In this case, a hot-to-cold air temperature gradient is formed along the second direction from the first cooling core to the second cooling core.

In some embodiments, a temperature of the input fluid is less than a temperature of the fluid output from the outlet port, and a temperature of the intake airflow is greater than a temperature of the exhaust airflow. In this case, a cold-to-hot fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core, and a cold-to-hot air temperature gradient is formed along the second direction from the first cooling core to the second cooling core. Each cooling core is exposed to a different temperature airflow.

In some embodiments, the inlet port is positioned proximate a first end of the first fluid header, and the first cooling core is positioned proximate the first end of the first fluid header and a first end of the second fluid header. The second cooling core is positioned proximate a second end of the first fluid header and a second end of the second fluid header. Each layer of fluid conduits can include a plurality of individual thermally conductive micro-tubes, wherein each micro-tube is configured such that fluid flow therethrough is isolated from each other micro-tube. Alternatively, each layer of fluid conduits can include a plurality of individual thermally conductive micro-tubes, wherein each micro-tube includes one or more common openings with an adjacent micro-tube such that fluid flow therethrough is intermixed between adjacent micro-tubes. Each cooling fin is configured along the second direction. In some embodiments, each cooling core includes a plurality of core layers, each layer including at least one layer of cooling fins and a layer of at least one fluid conduit, further wherein each core layer within a given cooling core is stacked along a third direction that is perpendicular to the first direction and perpendicular to the second direction.

In another aspect, the fluid-air heat exchanger is included within a fluid-based cooling system. The fluid based cooling system includes the fluid-air heat exchanger, one or more air movers configured to provide the intake airflow to the fluid-air heat exchanger, and a fluid-based cooling loop coupled to the fluid-air heat exchanger, wherein the cooling loop is configured to provide heated fluid to inlet port of the first fluid header.

In yet another aspect, the fluid-air heat exchanger has a concurrent flow configuration in which the fluid inlet is on the same side of the heat exchanger as the air flow intake side.

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