Refrigeration – Processes – Condensing and evaporating
Reexamination Certificate
2001-03-28
2003-02-18
Jiang, Chen-Wen (Department: 3744)
Refrigeration
Processes
Condensing and evaporating
C062S259200, C165S080400, C361S688000
Reexamination Certificate
active
06519955
ABSTRACT:
TECHNICAL FIELD
The present invention relates to cooling of electrical and electronic components, and more particularly, to a liquid refrigerant pump to circulate refrigerant to multiple cold plate/evaporators in thermal contact with the electrical or electronic component to be cooled.
BACKGROUND OF THE INVENTION
Electrical and electronic components (e.g. microprocessors, IGBT's, power semiconductors etc.) are most often cooled by air-cooled heat sinks with extended surfaces, directly attached to the surface to be cooled. A fan or blower moves air across the heat sink fins, removing the heat generated by the component. With increasing power densities, miniaturization of components, and shrinking of packaging, it is sometimes not possible to adequately cool electrical and electronic components with heat sinks and forced air flows. When this occurs, other methods must be employed to remove heat from the components.
One method for removing heat from components when direct air-cooling is not possible uses a single-phase fluid which is pumped to a cold plate. The cold plate typically has a serpentine tube attached to a flat metal plate. The component to be cooled is thermally attached to the flat plate and a pumped single-phase fluid flowing through the tube removes the heat generated by the component.
There are many types of cold plate designs, some of which involve machined grooves instead of tubing to carry the fluid. However all cold plate designs operate similarly by using the sensible heating of the fluid to remove heat. The heated fluid then flows to a remotely located air-cooled coil where ambient air cools the fluid before it returns to the pump and begins the cycle again. This method of using the sensible heating of a fluid to remove heat from electrical and electronic components is limited by the thermal capacity of the single phase flowing fluid. For a given fluid to remove more heat, either its temperature must increase or more fluid must be pumped. This creates high temperatures and/or large flow rates to cool high power microelectronic devices. High temperatures may damage the electrical or electronic devices, while large flow rates require pumps with large motors which consume parasitic electrical power and limit the application of the cooling system. Large flow rates may also cause erosion of the metal in the cold plate due to high fluid velocities.
Another method for removing heat from components when air-cooling is not feasible uses heat pipes to transfer heat from the source to a location where it can be more easily dissipated. Heat pipes are sealed devices which use a condensable fluid to move heat from one location to another. Fluid transfer is accomplished by capillary pumping of the liquid phase using a wick structure. One end of the heat pipe (the evaporator) is located where the heat is generated in the component, and the other end (the condenser) is located where the heat is to be dissipated; often the condenser end is in contact with extended surfaces such as fins to help remove heat to the ambient air. This method of removing heat is limited by the ability of the wick structure to transport fluid to the evaporator. At high thermal fluxes, a condition known as “dry out” occurs where the wick structure cannot transport enough fluid to the evaporator and the temperature of the device will increase, perhaps causing damage to the device. Heat pipes are also sensitive to orientation with respect to gravity. That is, an evaporator which is oriented in an upward direction has less capacity for removing heat than one which is oriented downward, where the fluid transport is aided by gravity in addition to the capillary action of the wick structure. Finally, heat pipes cannot transport heat over long distances to remote dissipaters due once again to capillary pumping limitations.
Yet another method which is employed when direct air-cooling is not practical uses the well-known vapor compression refrigeration cycle. In this case, the cold plate is the evaporator of the cycle. A compressor raises the temperature and pressure of the vapor, leaving the evaporator to a level such that an air-cooled condenser can be used to condense the vapor to its liquid state and be fed back to the cold plate for further evaporation and cooling. This method has the advantage of high isothermal heat transfer rates and the ability to move heat considerable distances. However, this method suffers from some major disadvantages which limit its practical application in cooling electrical and electronic devices. First, there is the power consumption of the compressor. In high thermal load applications the electric power required by the compressor can be significant and exceed the available power for the application. Another problem concerns operation of the evaporator (cold plate) below ambient temperature. In this case, poorly insulated surfaces may be below the dew point of the ambient air, causing condensation of liquid water and creating the opportunity for short circuits and hazards to people. Vapor compression refrigeration cycles are designed so as not to return any liquid refrigerant to the compressor which may cause physical damage to the compressor and shorten its life by diluting its lubricating oil. In cooling electrical and electronic components, the thermal load can be highly variable, causing unevaporated refrigerant to exit the cold plate and enter the compressor. This can cause damage and shorten the life of the compressor. This is yet another disadvantage of vapor compression cooling of components.
It is seen then that there exists a continuing need for an improved method of removing heat from components when air-cooling is not feasible.
SUMMARY OF THE INVENTION
This need is met by the pumped liquid cooling system of the present invention wherein cooling is provided to electrical and electronic components with very low parasitic power consumption and very high heat transfer rates away from the component surface. This invention also reduces the temperature drop required to move heat from the component to the ambient sink.
In accordance with one aspect of the present invention, a liquid refrigerant pump circulates refrigerant to cold plate/evaporators which are in thermal contact with the electrical or electronic component to be cooled. The liquid refrigerant is then partially or completely evaporated by the heat generated by the component. The vapor is condensed by a conventional condenser coil, and the condensed liquid, along with any unevaporated liquid, is returned to the pump. The system of the present invention operates nearly isothermally in both evaporation and condensation.
Accordingly, it is an object of the present invention to provide cooling to electrical and electronic components. It is a further object of the present invention to provide such cooling to components with very low parasitic power consumption and very high heat transfer rates away from the component surface. It is yet another object of the present invention to reduce the temperature drop required to move heat from the component to the ambient sink.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.
REFERENCES:
patent: 3774677 (1973-11-01), Antonetti et al.
patent: 3817321 (1974-06-01), von Cube et al.
patent: 4314601 (1982-02-01), Giuffre et al.
patent: 5333677 (1994-08-01), Molivadas
patent: 5406807 (1995-04-01), Ashiwake et al.
patent: 5713413 (1998-02-01), Osakabe et al.
Haushalter Barbara Joan
Jiang Chen-Wen
Thermal Form & Function
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