VARIABLE GEOMETRY HEAT SINK ASSEMBLY

A heat sink assembly and method wherein a base plate is mountable to a heat source and spaced fins on the base plate define flow channels therebetween. Self actuating louvers are configured to increase flow through select channels in response to increased temperatures.

DETAILED DESCRIPTION OF THE INVENTION

Heat sink assembly10,FIG. 1, in one preferred example includes substrate or base portion12mountable to a heat source such as electronic device14. Spaced fins16a-16fare on or otherwise extend upwards or outwards from base plate12. Base plate12and fins16may be made of aluminum. The fins define flow channels such as flow channels18a-18efor a fluid such as air, some other gas, or even a liquid. The predominant flow may be as shown at20. In this example, self actuating alloy louvers22a-22eare configured to increase flow through select channels18a-18ein response to increased temperatures. As shown in this particular embodiment, the louvers extend from the channel inlet ends of fins16a-16f.As shown inFIG. 1A, the louvers are preferably closed or mostly closed when the temperatures across the extent of base plate12are below the transition temperature of the shaped memory alloy material as shown at24.

InFIG. 1B, however, the temperature at flow channels18aand18bhas increased as shown at24bto a temperature above a transition temperature of the material chosen for the louvers and now louvers22aand22bmore fully open increasing the air flow through or across their respective flow channels18aand18b.This increase in temperature could be due, for example, to chips or components of electronic device14below channels18aand18bheating up. Louvers22c,22d,and22eremain more closed as shown.

Preferably, each louver22is made of a two way shape memory alloy material such as Nitinol. See WO 99/04429 incorporated herein by this reference and U.S. Pat. No. 6,689,486 also incorporated herein by this reference. The chosen material typically has a transition temperature below which the louver bends to a more closed position (seeFIG. 1A) and above which the louver bends to a more open position (seeFIG. 1B). Also, the transition temperature is typically less than the critical operating temperature of the device or devices coupled to the base plate of the heat sink assembly so the louvers open as shown inFIG. 1Band allow more air to flow in the heat sink flow channels before the critical operating temperature of the device is reached.

The hysteresis range for shape memory alloys is defined by the temperatures where the phase transition starts and the phase transition ends. Typically, the difference between these two temperatures is undesirable for shape memory alloy applications (such as actuator applications) since it is normally better for actuation to occur quickly. For this particular application, however, a wide hysteresis range may be preferable since a wide hysteresis range allows the shape memory alloy louvers to gradually deploy and more finely regulate the heat sink fin temperature over a wider range of temperatures.

Additionally, different phase transition regimes can also be used with a single heat sink to tune the performance over a wide temperature range. Components with more stringent heat sink requirements would be positioned under channels controlled by louvers with a lower transition temperature while components that have higher maximum operating temperatures would have channels controlled by louvers with higher transition temperatures.

InFIG. 2, fins16′ are angled across base plate12′. In this configuration, inclined or angled fins allow for more effective targeting by the self actuating louvers since each heat sink channel is shorter. Additionally, such a fin design has been shown to be more effective in certain geometries than vertically-oriented fins.

Here, a louver22′ is bonded or welded to the flow inlet ends of select angled or inclined fins and deflects between more open and more closed positions are shown by arrow30. In this way, flow through select channels is increased or decreased (regulated) in response to temperature changes experienced by the flow channels. In general, a louver opens fully as shown inFIG. 2as the temperature of its corresponding flow channel reaches or increases above the transition temperature of the material of the louver and the louver closes partially or fully when its corresponding flow channel temperature reaches or goes below the transition temperature of the material of the louver. These shape memory alloy flaps or louvers located at the inlet of the heat sink channels direct air flow resulting in a variable geometry heat sink assembly. The louvers are typically memorized to be more fully open and direct air flow to specific areas of the heat sink allowing for increased air flow when higher temperatures are present.

In the simulation shown inFIGS. 3-5, the upper most heat source has been targeted. In the activated state shown inFIG. 2, all of the louvers are identically positioned and are more fully open. The louvers serve as an extension of the heat sink fins allowing for increased air flow and channel air over the selected heat sources. A simulation was conducted using natural convection, although the concepts disclosed herein can be used in systems with forced convection. In the simulation, heat was generated by four identical heat sources on the bottom of the base plate12′. Heat sink materials were modeled as 3003-0 aluminum alloy.FIG. 3Ashows the heat sink temperature when three louvers22e′,22d′ and22eare activated (more fully opened) and the remaining louvers are not activated and are in a more closed position.FIG. 3Bshows the same heat sink temperature plot but now all the louvers are in a more closed position. The activated configuration shown inFIG. 3Ashows a reduction in air temperature of around 7° C. through the activated channels corresponding to louvers22c,22d,and22e.FIG. 4illustrates the flow velocity increase due to deployment of the louvers, at approximately a 30% increase over the non activated state shown inFIG. 4B. Perhaps the most important benefit can be seen in the surface temperature plot of the bottom based plate shown inFIGS. 5A and 5B. The target heat source sees an approximate 5% temperature reduction between the activated (FIG. 5A) and non activated (FIG. 5B) configurations.

Again, inFIGS. 3A,4A, and5A, louvers22c′,22d′, and22e′ are more fully open and inFIGS. 3B,4B and5B these louvers are in a more fully closed position or not activated. It is understood that the geometry of the fins, the selection of all the materials, the configuration of the self actuating louvers, and the like can be optimized for a specific application to achieve even better performance.

The activation temperature can be tailored to specific temperature requirements of electrical components and need not be uniform for all louvers on a given heat sink. Components with more sensitive temperature requirements could be placed underneath channels with SMA louvers that have a lower activation temperature, while electrical components with higher temperature capabilities could have SMA louvers with higher activation temperature. So, InFIG. 1Afor example, at temperature24a,louvers22aand22bmight open for sensitive components mounted proximate channels18aand18bwhile at the same temperature the louvers22c-22eremain closed for less sensitive components mounted proximate channels18c-18e.At a higher temperature, all the louvers may open.

FIG. 6shows an example for a situation in which louvered flow inlets are not feasible or desirable. In this example, there are still spaced fins16″ extending upward from based plate12″ but now cover40has been added to the top of fins16″ and self actuating louvers22′ are actuatable with respect to cover40as shown in order to increase flow through select channels in response to increased temperatures. The remaining louvers integral with cover40shown inFIG. 6are fully closed in the figure.

FIG. 7shows an example where based plate12′ includes spaced fins16′ and now the self actuating louvers22″ are attached to the top portion of the respective fins and actuatable between a closed or almost closed position as shown inFIG. 7and a more fully opened configuration where louvers22″ are fully vertical and lie in the same plane as their respective fins.