CONDENSER BYPASS FOR TWO-PHASE ELECTRONICS COOLING SYSTEM

Abstract

An electronics cooling system utilizing a refrigerant fluid that evaporates to remove heat from electronics and is condensed back to liquid through heat exchange with a cold medium (air or water). The refrigerant fluid is circulated via a liquid pump between the condenser and heated evaporators. A bypass circuit is provided to divert flow around the condenser during conditions of cold ambient temperatures, which is controlled by a feedback loop using a mechanical or electronic control valve. This prevents the refrigerant fluid temperature from becoming very low and potentially inducing condensation on the outside of the refrigerant tubing from the warm and moist indoor air.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 61/309,909, filed Mar. 3, 2010, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an electronics cooling system utilizing an outdoor condenser and in particular to a valve controlled bypass circuit is provided to divert flow around the condenser during conditions of cold outdoor ambient temperatures.

BACKGROUND OF INVENTION

Power electronic devices, such as IGBTs, SCRs, etc., continue to achieve higher power switching capacity in a smaller envelope. The amount of heat created by these devices continues to climb as well. Conventional cooling methods include using blowing air, or circulating a water-based fluid through cold plates in thermal contact with the electronic device heat sink. A more recent cooling method utilizes a phase change fluid, or refrigerant, that will evaporate to remove heat from an electronic device heat sink, and condense back to liquid state through heat exchange process with a cold medium (air or water).

FIG. 1 shows a diagram of a typical prior art two-phase pumped loop cooling system 110. Liquid refrigerant enters the pump 1, where static pressure is raised and flow is induced. Sub-cooled liquid flows into an evaporator, shown herein as a plurality of cold plates 2, which can be connected in series, or parallel, or both. The cold plates 2 are each mounted in contact with the heat sink of the electronic device. Refrigerant fluid absorbs heat from the electronic device and partially evaporates as it flows through the cold plates 2. Partially evaporated refrigerant fluid is collected in a manifold, and then flows in the condenser heat exchanger 4. The condenser heat exchanger 4 may be air cooled or water cooled and it may be located indoors or outdoors. For the condenser 4 to reject heat to a cold medium, the refrigerant fluid temperature must be above that of the cold medium, or the ambient air. Since the refrigerant is undergoing a condensing process, the refrigerant pressure will follow the refrigerant temperature based on the fluid's saturation pressure—temperature relationship. The refrigerant fluid will leave the condenser 4 as a subcooled liquid, the temperature will be above ambient, and the pressure will correspond to an even higher saturation temperature. The sub-cooled liquid flows into a receiver tank 5, which acts a storage tank to compensate for varying volumes of the fluid in the system 110. The refrigerant fluid volume of liquid and vapor will vary throughout the system 110 based on operating temperatures and heat load, due to varying densities through the operating temperature range.

The system 210 shown in FIG. 2 is similar to that of FIG. 1, except that a liquid return line 6 is added from the cold plate exit manifold to the receiver tank 5. The liquid return line 6 provides a pathway for liquid refrigerant to return to the receiver tank 5, bypassing the condenser 4, while allowing the refrigerant vapor to proceed to the condenser 4. In this system 210 the liquid return line 6 is always open.

It is noted that in the prior art 2-phase cooling systems 110, 210, the system fluid pressure, and hence refrigerant fluid temperature will follow the ambient air temperature at the condenser 4. The system fluid temperature will be at some differential above the ambient air temperature at the condenser 4. When the ambient air temperature at the condenser is the same as the ambient air around the cold plates (such as where the power electronics devices and condenser are both located indoors), there will never be a danger of having moisture condensing out of the air and collecting on the fluid tubing, or pipes, or cold plates, and dripping onto the electronic devices, and damaging the electronics because the fluid temperature will always be above the ambient air dew point.

A problem exists in these prior art systems when the power electronics are located indoors (depicted in FIGS. 1 and 2 as area enclosed by a dashed line and designated A), exposed to warm humid air, and the condenser heat exchanger 4 is located outdoors (depicted in FIGS. 1 and 2 as an area enclosed by a dashed line and designated B) and exposed to extreme cold temperatures. Since the refrigerant fluid temperature will closely follow the condenser ambient air, there will be conditions where the refrigerant fluid entering back indoors will be cold enough to cool the refrigerant fluid conduit surface temperature to a level below the indoor air dew point thereby causing condensation on the fluid conduits and other system components from the moisture of the indoor air. This moisture can drip onto the electronic devices and cause damage from short circuiting.

SUMMARY

At least one embodiment of the invention provides a cooling system comprising: an evaporator, a pump, and a liquid receiver located in a first environment having a first ambient temperature; a condenser located in a second environment having a second ambient temperature; a refrigerant fluid circulated through the system by the pump by a primary fluid conduit to the evaporator, to the condensor, to the liquid receiver, and back to the pump; and a valve adapted to selectively redirect fluid flow to bypass the condenser through a bypass fluid conduit located in the first environment.

At least one embodiment of the invention provides a cooling system comprising: an evaporator, a pump, and a liquid receiver located in a first environment having a first ambient temperature; a condenser located in a second environment having a second ambient temperature; a refrigerant fluid circulated through the system by the pump by a primary fluid conduit to the evaporator, to the condensor, to the liquid receiver, and back to the pump; and a valve operable to redirect fluid flow from the evaporator to the liquid receiver through a bypass fluid conduit located in the first environment as needed in order to keep the fluid temperature within the first environment above a dew point of the first ambient temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this invention will now be described in further detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic of a prior art cooling system;

FIG. 2 is a schematic of another prior art cooling system;

FIG. 3 is a schematic of an embodiment of the cooling system of the present invention utilizing a pressure control valve;

FIG. 4 is a schematic of another embodiment of the cooling system of the present invention utilizing a pressure control valve;

FIG. 5 is a schematic of still another embodiment of the cooling system of the present invention utilizing a pressure control valve;

FIG. 6 is a schematic of another embodiment of the cooling system of the present invention utilizing an electronic control valve; and

FIG. 7 is a schematic of another embodiment of the cooling system of the present invention utilizing solenoid valves.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 3 shows a first embodiment of the cooling system of the present invention. The system 10 comprises an evaporator 2, a pump 1, and a liquid receiver 5 located in a first environment A having a first ambient temperature. The system 10 includes a condenser 4 located in a second environment B having a second ambient temperature. A refrigerant fluid is circulated through the system 10 by the pump 1 by a primary fluid conduit 21 to the evaporator 2, to the condensor 4, to the liquid receiver 5, and back to the pump 1. The evaporator 2 is shown as a plurality of cold plates which can be mounted in the system 10 in series, in parallel, or both. The cold plates of the evaporator 2 are each mounted in thermal contact with the heat sink of an electronic device. Refrigerant fluid absorbs heat from the electronic device and partially evaporates as it flows through the cold plates of the evaporator 2.

The system 10 also comprises a valve 3 operable to redirect fluid flow from the evaporator 2 to the liquid receiver 5 through a bypass fluid conduit 8 located in the first environment A as needed in order to keep the fluid temperature within the first environment A above a dew point of the first ambient temperature. The valve 3 as shown is a pressure control valve 3. The partially evaporated refrigerant fluid leaving the evaporator 2 will enter the pressure control valve 3. The pressure control valve 3 will divert refrigerant fluid to flow either to the outdoor condenser 4 or to the bypass circuit 8, based on a pressure feedback line 7 in comparison to a predetermined control valve internal set point. The pressure feedback line 7 is fluidly connected to the evaporator outlet line. The control valve 3 will divert flow to the condenser 4 when the fluid pressure leaving the evaporator 2 is higher than the internal set point. Otherwise, the control valve 3 will divert flow to the bypass circuit 8 and around the condenser 4 when the fluid pressure leaving the evaporator 2 is lower than the internal set point. The control valve internal set point will be set to a pressure corresponding to a fluid saturation temperature that is above the highest expected dew point for the indoor conditions. During operation, the refrigerant fluid will build up pressure based on the amount of heat entering the cold plate evaporators 2. If the system pressure is below the control valve set point, the refrigerant fluid will circulate into the bypass circuit 8, and into the receiver tank 5, and back to the pump 1. Thus, the refrigerant fluid will bypass the condenser 4 and not be exposed to extreme cold air temperatures. The refrigerant fluid temperature will always be above the indoor air dew point, because it is not exposed to any cold medium. With continued heat load on the cold plate evaporators 2, the refrigerant fluid temperature and pressure will exceed the control valve set point. With cold plate fluid pressure exceeding control valve set point, the control valve shuts off flow to the bypass circuit 8 and allows flow to the condenser 4. Depending on the heat load and outdoor ambient conditions, the system pressure may continue to rise (as in a warm outdoor temperature), or it may begin to fall again (as for a cold outdoor temperature). If the outdoor temperature is warm, the system pressure will settle at a steady-state point based on a temperature differential between the fluid saturation temperature and ambient air temperature. This is a similar operation to the prior art systems. If the outdoor temperature is extremely cold, the control valve 3 will selectively allow flow to the condenser 4. As the refrigerant fluid is exposed to the very cold outdoor air temperature, the fluid temperature and system pressure will eventually drop. The system pressure could drop below the control valve set point, and refrigerant flow will again be diverted around the condenser 4 and into the bypass circuit 8. Thus, the system self regulates, keeping the fluid pressure at or above the control valve internal set point. Therefore, refrigerant fluid temperature will always be above the indoor air dew point, due to the control valve regulating flow either to the outdoor condenser 4 or around it. There will be no danger of having moisture collect on the refrigerant tubing due to condensation, even with an outdoor condenser 4.

FIG. 4 shows another embodiment of the system similar to that of FIG. 3 except on where the bypass circuit is routed. In this embodiment the bypass circuit 8′ is routed directly into the top of the receiver tank 5. Likewise the refrigerant fluid tube 9 leaving the condenser 4 is also routed directly into the top of the receiver tank 5. This embodiment of the invention allows liquid refrigerant that has accumulated in the condenser to drain back into the receiver tank, thus providing more sub-cooling at the pump inlet.

FIG. 5 shows another embodiment of the invention. For this embodiment, the control valve 3 is placed between the condenser 4 and the receiver tank 5. It accomplishes the same purpose in that it allows flow either from the condenser 4, or around it, based on fluid pressure leaving the cold plates 2. Fluid pressure leaving the cold plates 2 that is above the control valve internal set point will cause the control valve 3 to allow flow from the condenser 4 and shut-off the bypass circuit 8. Fluid pressure leaving the cold plates 2 below the control valve internal set point will cause the control valve 3 to block flow from the condenser 4 and allow flow from the bypass circuit 8.

FIG. 6 shows another embodiment of a cooling system 10′″ of the invention. The control valve 18 is in the same position as the system described in FIG. 3. However, for this system 10′″, the control valve 18 is an electronic control valve. The cooling system 10′″ will have a micro-processor controller 12 that reads inputs from various sensors 11 that monitor the refrigerant fluid temperatures and pressures and possibly ambient air temperature. The micro-processor controller 12 will use various fluid temperatures and pressures in an algorithm and will determine whether the control valve 18 should divert flow to the condenser 4 or to the bypass circuit 8 around it. The micro-processor controller 12 will send an electronic signal to the control valve 18 to properly position it.

FIG. 7 shows another embodiment of a cooling system 10″″ of the invention. The control valve 10 could actually be split into two, 2-way valves 13, such as a solenoid valve; one valve 13A at the condenser inlet circuit, and one valve 13B on the bypass circuit as shown in FIG. 7. The solenoid valves 13 are controlled by a micro-processor controller 12, or could be simply wired in series to a pressure switch 11 located at the cold plate exit line. One solenoid valve 13 would be normally-closed, and the other solenoid valve 13 would be normally-open. High pressure at the cold plate exit line would activate the pressure switch, which would close bypass circuit solenoid valve 13B, and open the condenser entering line solenoid valve 13A.

Although the principles, embodiments and operation of the present invention have been described in detail herein, this is not to be construed as being limited to the particular illustrative forms disclosed. They will thus become apparent to those skilled in the art that various modifications of the embodiments herein can be made without departing from the spirit or scope of the invention.

Claims

1. A cooling system comprising:

an evaporator, a pump, and a liquid receiver located in a first environment having a first ambient temperature;

a condenser located in a second environment having a second ambient temperature;

a refrigerant fluid circulated through the system by the pump by a primary fluid conduit to the evaporator, to the condensor, to the liquid receiver, and back to the pump; and

a valve adapted to selectively redirect fluid flow to bypass the condenser through a bypass fluid conduit located in the first environment.

2. The cooling system of claim 1, wherein the valve is a pressure control valve.

3. The cooling system of claim 2, wherein the pressure control valve has a predetermined pressure setpoint, the valve allowing fluid flow to the condenser when the pressure of the fluid entering the valve is greater than the pressure setpoint, the valve preventing fluid flow to the condenser and allowing fluid flow to bypass the condenser through a bypass fluid conduit located in the first environment when the pressure of the fluid entering the valve is less than the pressure setpoint.

4. The cooling system as in claim 1, wherein the valve is located in the first environment downstream of the evaporator and upstream of the condenser.

5. The cooling system as in claim 1, wherein the valve is located in the first environment downstream of the condenser and upstream of the liquid receiver.

6. The cooling system as in claim 1, wherein the valve is an electronic control valve that is operated by a micro-processor controller in response to at least one of a pressure sensor or a temperature sensor.

7. The cooling system as in claim 1, wherein the bypass fluid conduit is connected to the primary fluid conduit between the condenser and the liquid receiver.

8. The cooling system of claim as in claim 1, wherein the bypass fluid conduit is directly connected to the liquid receiver.

9. A cooling system comprising:

an evaporator, a pump, and a liquid receiver located in a first environment having a first ambient temperature;

a condenser located in a second environment having a second ambient temperature;

a refrigerant fluid circulated through the system by the pump by a primary fluid conduit to the evaporator, to the condensor, to the liquid receiver, and back to the pump; and

a valve operable to redirect fluid flow from the evaporator to the liquid receiver through a bypass fluid conduit located in the first environment as needed in order to keep the fluid temperature within the first environment above a dew point of the first ambient temperature.

10. The cooling system of claim 9, wherein the valve is a pressure control valve.

11. The cooling system of claim 10, wherein the pressure control valve has a predetermined pressure setpoint, the valve allowing fluid flow to the condenser when the pressure of the fluid entering the valve is greater than the pressure setpoint, the valve preventing fluid flow to the condenser and allowing fluid flow to bypass the condenser through the bypass fluid conduit when the pressure of the fluid entering the valve is less than the pressure setpoint.

12. The cooling system of claim 10, wherein the valve is located in the first environment downstream of the evaporator and upstream of the condenser.

13. The cooling system of claim 10, wherein the valve is located in the first environment downstream of the condenser and upstream of the liquid receiver.

14. The cooling system as in claim 10, wherein the valve is an electronic control valve that is operated by a micro-processor controller in response to at least one of a pressure sensor or a temperature sensor.

15. The cooling system as in claim 10, wherein the bypass fluid conduit is connected to the primary fluid conduit between the condenser and the liquid receiver.

16. The cooling system as in claim 10, wherein the bypass fluid conduit is directly connected to the liquid receiver.

17. A cooling system comprising:

an evaporator, a pump, and a liquid receiver located in a first environment having a first ambient temperature;

a condenser located in a second environment having a second ambient temperature;

a refrigerant fluid circulated through the system by the pump by a primary fluid conduit to the evaporator, to the condensor, to the liquid receiver, and back to the pump; and

a pressure control valve having a predetermined pressure setpoint, the valve allowing fluid flow to the condenser when the pressure of the fluid entering the valve is greater than the pressure setpoint, the valve preventing fluid flow to the condenser and allowing fluid flow to bypass the condenser through a bypass fluid conduit located in the first environment when the pressure of the fluid entering the valve is less than the pressure setpoint.

18. The cooling system of claim 17, further comprising a pressure feedback conduit.

19. The cooling system as in claim 17, wherein the valve is located in the first environment downstream of the evaporator and upstream of the condenser.

20. The cooling system as in claim 17, wherein the valve is located in the first environment downstream of the condenser and upstream of the liquid receiver.