JP2000294706A - Method for cooling electronic system and electronic module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cooling device which can prevent cooling substance in a liquid state from returning to a compressor. SOLUTION: An auxiliary heat mechanism 20 functions to return a refrigerant in an evaporation type cooling plate 10 for an electronic module 40 to a compressor in a vapor state. Based on measured values of pressure and temperature of the refrigerant exiting from the cooling plate 10, a control unit controls ON and OFF operation of an electric-resistive auxiliary heating element 21 in order to compensate for a variation in heat dissipation caused in the module 40. Additional heat can be supplied by a single planar element or inline heating element. The auxiliary heating mechanism 20 prevents the refrigerant substance from returning to the compressor which adversely affects the life or operating efficiency of the compressor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system and method for solving the problem of variable heat load conditions in electronic modules that are generally cooled by refrigerant. More particularly, the present invention relates to an electronic system and method of cooling with variable heat load levels by providing additional heat to the refrigerant.

[0002]

BACKGROUND OF THE INVENTION Recent models of high-end computer processing systems incorporate cooling units to solve the problems associated with dissipating thermal energy within the chips and modules that make up the computer system. Such a cooling system, for example,
It is described in U.S. Pat. No. 5,954,127.

[0003] Conventional cooling systems are designed to handle relatively fixed heat loads. However, variations in cooling requirements can be addressed to some extent in a variety of ways.
Specifically, the speed of the motor that drives the compressor can be changed. In addition, an automatic temperature expansion valve or a hot gas bypass valve can be used to cope with fluctuations in heat load. However, the problem with all of these methods is that the time constant associated with their control function is such that, for the purposes of the present invention, relatively fast power fluctuations can occur in the module being cooled. Too long for proper cooling. in addition,
The control systems used for mechanisms that handle these various thermal loads are very complex. As a result of these conditions, a mismatch in the time constant between the thermal load adjustment mechanism and the thermal energy generated within the circuit module can cause the circuit temperature to rise above the desired temperature or fall below the minimum temperature level. In addition, significant problems arise when the power dissipation level in the processor module drops to a certain low level. In that case, beyond the capacity of the cooling system, the compressor may draw in liquid medium instead of steam. This greatly reduces the life of the compressor.

For example, a computer designed for 1 kilowatt heat output and dissipating 1 kilowatt heat output
When using a processor module, and when power fluctuations reduce the dissipated power level to 800 watts, there is 200 watts of excess capacity in a cooling system designed to cool this module. Thus, the refrigerant in the cooling loop may not completely evaporate in the evaporator / cooling plate. As a result, the liquid refrigerant returns to the compressor, and the life of the compressor may be shortened.
This is because such compressors are designed to work best with gases.

[0005] Since the cooling unit is designed to handle a fixed heat load, it is a problem in the system considered here. Further, the cooling system of the present invention is particularly unique in that it is designed to operate continuously. This is different from the mode of operation normally found in cooling systems. Further, the preferred evaporative cooling plates in various embodiments of the present invention are further complicated in that they include separate and separate refrigerant passages. These multiple passages have redundant passages and redundant cooling loops and as a result are part of separate cooling loops provided to ensure continuous operation.

[0006]

SUMMARY OF THE INVENTION It is, therefore, one object of the present invention to provide a cooling system for cooling electronic modules with varying dissipated power.

Another object of the present invention is to prevent liquid refrigerant from returning to the compressor in the cooling loop.

Another object of the present invention is to avoid complex control systems for addressing the problem of thermal load fluctuations in cooled electronic systems.

It is another object of the present invention to provide additional heat to the system to compensate for fluctuations in power dissipated from the refrigerant cooled electronic system.

It is another object of the present invention to provide faster compensation for thermal load variations with a more effective time constant than with other thermal compensation methods.

It is another object of the present invention to balance thermal fluctuations in an evaporative cold plate system using redundant cooling loops for redundant configurations.

Another object of the present invention is to prevent the circuit chip junction temperature from becoming higher than the maximum reliability temperature condition or lower than a desired minimum temperature.

Another object of the present invention is to extend the life of a compressor in a specified cooling system.

Finally, but not exclusively, it is an object of the present invention to control thermal fluctuations that occur in electronic systems that are cooled by refrigerant.

[0015]

In accordance with one embodiment of the present invention, an electronic system having a variable thermal load level cooling capability includes an electronic circuit module and a cooling plate in thermal contact with the module. The cooling plate has at least one passage therein for carrying the refrigerant. Means are provided for sensing the level of power supplied to the module. In addition, and most important to the invention,
Means for heating the refrigerant and means for controlling the heating are provided such that the cooling load experienced by the refrigerant and the cooling system is maintained relatively constant. In one embodiment of the invention, the heating means comprises a flat electric resistance heater mounted on top of the cooling plate. According to another embodiment of the present invention, the additional refrigerant heating provided herein exposes refrigerant around one or both lines for returning refrigerant from the evaporator / cold plate to the respective compressor. This is done by a heater. Additional heating of the refrigerant can also occur upstream of the evaporator / cooling plate. However, a downstream position is preferred.

In another embodiment of the present invention, a method is provided for preventing liquid refrigerant from returning to a compressor. This is accomplished by determining the state of the refrigerant as it exits the cold plate, and then applying heat to the refrigerant under conditions that are liquid or near liquid. According to a preferred embodiment of the present invention, the state of the refrigerant is determined by measuring its pressure and temperature. In yet another embodiment of the present invention, the state of the refrigerant is monitored over a period of time and additional heat is applied depending on the conditions of anticipated temperature drop that occurs in the electronic module the system is cooling.

[0017]

FIG. 1 shows an embodiment of the present invention. In this embodiment, the electric heater 20 is arranged on the upper surface of the cooling plate 10. The bottom of the cooling plate 10 is in thermal contact with the module to be cooled (see FIG. 4). Specifically, the evaporative cooling plate 10 is connected to the inlet port 13 of the refrigerant loop 1.
And an outlet port 11 of the refrigerant loop 1. The refrigerant in loop 2 preferably flows in the opposite direction from inlet port 12 through plate 10 to outlet port 14. The hidden parts of such a loop embodiment are shown in more detail in FIG. Although the examples provided herein are particularly directed to the case where the cooling plate includes two independent cooling fluid passages, the invention is not limited to two passages. The cold plate can include single or multiple passages.

In the embodiment of the present invention shown in FIG. 1, the auxiliary heater 20 includes a resistance heating element 21 disposed on an electrically insulating substrate material 24. Power for additional heating is provided by contact pads 22 and 23. FIG. 2 shows the relative height between the heater 20 and the cooling plate 10. The heating element 21
They can be arranged in any convenient pattern. The pattern shown has the advantage, in particular, that the ends 22 and 23 of the contact pads are in adjacent positions and are easy to connect.

FIG. 3 shows an alternative embodiment of the invention, in which return lines 15 and 1 to compressors 91 and 92, respectively.
6 comprises in-line heaters 30 and 31, respectively. These heaters start when the power dissipation in the module to be cooled (see No. 40 in FIG. 4) is reduced. FIG. 3 also shows multiple passage sets 18 and 19 in cooling plate 10.
Is indicated by a broken line. The duplex set includes a passage 19 extending from the inlet port 13 to the outlet port 11 and a passage 18 extending from the inlet port 12 to the outlet port 14.

FIG. 4 illustrates the control variables used to monitor the condition of the refrigerant in the return path back to each compressor. FIG. 4 also shows a side view of an environment using the present invention. In particular, the cooling plate 10 is used to maintain the temperature of the junction of the transistors and other devices located on the electronic (circuit chip) module 40, and the module 40 is used to operate the circuits therein. Note that it is arranged on the lower substrate 50 including the connection wiring (not visible).

Further, a pressure sensor 6 for measuring the pressure of the refrigerant in the return path returning to each compressor.
3 and 64 are provided. Similarly, a temperature sensor 61 for measuring the temperature of the refrigerant passing through the two loops in FIG.
And 62 are also provided. These measurements are supplied to a control unit 60 that controls the power to the auxiliary heater 20. When using an inline heater as shown in FIG.
The control unit 60 controls the power supplied to these heating units, for example, to provide additional heat input to compensate for the reduced power level in the module 40 sensed by the temperature sensor 65. The temperature sensor 6
5 provides power to the elements of the module without measuring the power level within the module 40. It is also possible to measure power electrically.

In an alternative embodiment of the present invention, rather than using two separate in-line heaters as shown in FIG. 3, a single in-line heater 32 as shown in FIG.
It is also possible to use Note, however, that while the return lines 15 and 16 returning to the respective compressors pass through a single in-line heater unit 32, there is no liquid exchange between the refrigerant in the two lines. For reliability, the two refrigerant loops are always maintained independently and there is no liquid exchange between the two. Also note that although the illustrated embodiment includes only two independent refrigerant loops, any number of such loops can be used. The number of loops is limited only by substantial limitations on the size of the lines in the cold plate.

FIG. 6 shows the principle of a control method applicable to the present invention. In particular, the control unit 60 determines the phase of the refrigerant returning to each compressor according to the pressure, temperature, and measurement. If it is determined that the liquid-phase refrigerant is returning, or if the phase of the refrigerant returning to the compressor is within the range of the guard band phase as shown in FIG. 20, 30
Or supply power to 30 'to add additional heat. FIG.
The guard zone shown at +/- about 1.7 ° C
(3 degrees Fahrenheit).

To determine the capacity of each auxiliary heater to be used, there are two options. In one embodiment, the auxiliary heater is sized to provide the full power generated within the electronic module to be cooled. In this case, even if the power supply of the module is cut off, the cooling unit can be operated as it is, and the auxiliary heater essentially constitutes the total heat load. For example, if the electronic module is designed to generate one kilowatt of power, the auxiliary heater will also be sized to generate one kilowatt of power. However, another more desirable option is to size the auxiliary heater to accommodate normal power fluctuations that occur within the module. This option makes the heater smaller and more manageable. For example, if in this case the module is also designed to generate 1 kilowatt of power and the variation in normal system use is 200 watts, then the auxiliary heater will be sized for 200 watt variation instead of a full 1 kilowatt. Only needs to be done. However, it should be noted that this inline heater option is not desirable if the auxiliary heater is designed to compensate for the total heat load generated within the electronic module. This is because such in-line heaters typically cannot be used at such power levels. However, it should also be noted that for inline auxiliary heaters, they can be located upstream of the evaporator plate.

However, in a preferred embodiment of the present invention,
The design of the auxiliary heater is as shown in FIGS.
In this form of auxiliary heater, the device is a foil, film, or mat heater mounted on the top of the evaporative cooling plate. This configuration is shown in FIGS. The heater is connected to a power supply and is controlled by a sensor as shown in FIG. One advantage of such an auxiliary heater design is that only one heater is required, even if there are multiple loop refrigerant passages in the cold plate. In this regard, it should also be noted that the use of the present invention is not limited to cold plates with dual refrigerant loops.

The control of the auxiliary heater is best understood by considering the state diagram shown in FIG. Control of the auxiliary heater is easiest and most accurate by monitoring the temperature and pressure immediately downstream of the evaporative cooling plate. However, other sensors and other sensing locations can be used. Knowing the temperature and pressure characteristics allows a near-immediate, real-time determination as to whether liquid may be present in the refrigerant flow in the return path back to the compressor.
Further, the actual control scheme preferably includes monitoring the rate of change of these characteristics to determine whether additional power needs to be increased or decreased. This results in a system that can anticipate and control the upcoming heat load and refrigerant phase state.

An embodiment using an in-line heater is shown in FIG. In this figure, the single auxiliary heater 20 of FIGS. 1 and 2 has been replaced by in-line heaters 30, 31 for each refrigerant return line. Therefore, two in-line heaters are required for a dual passage evaporative cooling plate. The actual heater can have any suitable design, such as a cartridge heater or a foil heater that includes one or more return lines. This second means typically does not have sufficient surface area and is unlikely to be able to provide an additional thermal load comparable to that of the modular design. However, this method can be used to mitigate normal fluctuations within the module, so that the overall heat load of the cooling system is relatively constant and the compressor does not draw in liquid refrigerant. The embodiment of FIG. 3 is also used for supplementary purposes to ensure that the refrigerant leaving the evaporative cooling plate and entering the compressor is completely vapor. However, because the power level of the electronic module fluctuates, there is no effect of adjusting the actual circuit temperature at this downstream location. However, as noted above, there is another option of using an in-line auxiliary heater located upstream of the evaporative cold plate. In this position, the heaters can be used to preheat the refrigerant when the module power is reduced, thereby increasing the temperature stability of the circuit.

From the foregoing, it should be understood that all of the objects set forth herein have been met by the methods and systems described above. In particular, it can be seen that a method and system for providing additional heat to a cooling electronic module and evaporative cooling plate to compensate for power fluctuations in the electronic module is provided.

In summary, the following is disclosed regarding the configuration of the present invention.

(1) An electronic system having a cooling function with a variable heat load level, comprising: an electronic circuit module; and a cooling plate having one or a plurality of passages for making thermal contact with the module and transferring refrigerant. An electronic system comprising: means for sensing power supplied to the module; means for heating the refrigerant; and means for controlling the heating means to maintain a substantially constant cooling load on the refrigerant. . (2) The system of (1) above, wherein the cooling plate comprises two passages for separate refrigerant loops. (3) The system according to (1), wherein the sensing means comprises a temperature sensor disposed in thermal contact with the module. (4) The system according to (1), wherein the sensing means comprises a pressure sensor and a temperature sensor for the refrigerant. (5) The system according to (4), wherein said pressure and temperature sensing means is located substantially immediately downstream of said cold plate. (6) The system according to (1), wherein the heating means comprises an electric resistance heating element on the cooling plate. (7) the heating means includes an in-line heater surrounding one or a plurality of conduits for conveying the refrigerant;
The system according to (1). (8) The system according to (1), wherein the cooling plate includes a plurality of refrigerant passages. (9) A method of preventing the refrigerant from returning to a compressor of a cooling system for cooling an electronic module that is in thermal contact with a cooling plate through which the refrigerant passes, wherein the state is determined before the refrigerant returns to the compressor. Applying heat to the refrigerant when the refrigerant is in or near a liquid state. (10) The method according to (9), wherein the state of the refrigerant is determined by measuring pressure and temperature. (11) The method according to (9), further comprising monitoring a state of the refrigerant over a period of time, wherein the heating is performed in accordance with an expected phase state. (12) The method according to (9), wherein the determination of the refrigerant state is performed when the refrigerant exits the cooling plate.

[Brief description of the drawings]

FIG. 1 is a top view illustrating an evaporative cooling plate and an electric resistance heating element according to an embodiment of the present invention.

FIG. 2 is a side view of the cooling plate of FIG. 1;

FIG. 3 is a top view illustrating an alternative embodiment of the present invention, wherein in-line heaters are each used in a separate return path back to the compressor.

FIG. 4 is a side view of a control mechanism used in the present invention.

FIG. 5 shows a single in-line heater placed around two lines connected to the compressor inlet;
It is a side view showing other embodiment of the present invention.

FIG. 6 is a graph showing pressure versus temperature illustrating the liquid and gas phase regions of a typical refrigerant, with the desired guard zones for controlling additional heat levels.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refrigerant loop 2 Loop 10 Cooling plate 10 Plate 11 Outlet port 12 Inlet port 13 Inlet port 14 Inlet port 15 Return line 16 Return line 18 Passage 19 Passage 20 Auxiliary heater 21 Resistance heating element 22 Contact pad 23 Contact pad 24 Electrical insulation Substrate material 30 Auxiliary heater 31 In-line heater 32 In-line heater 40 Electronic (circuit chip) module 60 Control unit 61 Temperature sensor 62 Temperature sensor 63 Pressure sensor 64 Pressure sensor 65 Temperature sensor 91 Compressor 92 Compressor

Continued on the front page (72) Inventor Gregory M. Chrysler 85226 United States Chandler, Arizona North Diane Court 411

Claims (12)

[Claims] 1. An electronic system having a cooling function with a variable heat load level, comprising: an electronic circuit module; and a cooling plate having one or more passages for thermally contacting the module and transferring a coolant. An electronic system comprising: means for sensing power supplied to the module; means for heating the refrigerant; and means for controlling the heating means to maintain a substantially constant cooling load on the refrigerant. 2. The system of claim 1, wherein said cold plate comprises two passages for separate refrigerant loops. 3. The system of claim 1 wherein said sensing means comprises a temperature sensor disposed in thermal contact with said module. 4. The system according to claim 1, wherein said sensing means comprises a pressure sensor and a temperature sensor for said refrigerant. 5. The system of claim 4, wherein said pressure and temperature sensing means is located substantially immediately downstream of said cold plate. 6. The system of claim 1, wherein said heating means comprises an electrical resistance heating element on said cooling plate. 7. The system of claim 1, wherein said heating means comprises an in-line heater surrounding one or more conduits for transporting said refrigerant. 8. The system according to claim 1, wherein said cooling plate comprises a plurality of refrigerant passages. 9. A method for preventing the refrigerant from returning to a compressor of a cooling system for cooling an electronic module that is in thermal contact with a cooling plate through which the refrigerant passes, wherein the state is changed before the refrigerant returns to the compressor. A method comprising: determining; and applying heat to the refrigerant when the refrigerant is in or near a liquid state. 10. The method of claim 9, wherein the state of the refrigerant is determined by measuring pressure and temperature. 11. The method of claim 9, further comprising monitoring the condition of the refrigerant over a period of time, wherein the heating is performed in response to an expected phase condition. 12. The method of claim 9, wherein the determination of the refrigerant state is made as the refrigerant exits the cold plate.