Solid Cryogen Heat Transfer Apparatus

Abstract

An apparatus for transferring heat from a heat load to a solid cryogen having the solid cryogen in an insulated container. The solid cryogen has a plurality of gas passages therethrough. A gas circulator supplies sublimed gas from the passages in the solid cryogen to heat exchanger adjacent the heat load. A portion of the return gas is supplied to a heat exchanger for the gas circulator motor. The flow in the motor heat exchanger is controlled by the pressure of the gas in the return conduit from the load heat exchanger to the solid cryogen chamber and a pressure control valve connected in the output of the motor heat exchanger.

Description

BACKGROUND OF THE INVENTION

The present system for transferring heat from a device being cooled to a solid cryogen makes use of a highly conductive metal matrix. In such a system, the solid cryogen is formed around a highly heat conductive metal matrix which transports heat from the device being cooled to the solid cryogen. With such a system, the solid cryogen sublimes away from the metal matrix after a short time, thus leaving a low pressure vapor gap across which the heat must be transferred to the solid cryogen. Heat transfer across the gap is very inefficient which permits a temperature rise in the device being cooled. Also, with such a system, the cooling load must be placed close to the solid cryogen.

BRIEF SUMMARY OF THE INVENTION

According to this invention, cooling passages are provided in the solid cryogen and a gas circulator pump circulates sublimed gas from the solid cryogen to a heat exchanger near the heat load and the heated gas is returned to the solid cryogen. A portion of the return gas is used to cool the motor driving the gas circulator pump.

IN THE DRAWINGS

FIG. 1 is a schematic illustration showing one prior art solid cryogen cooler configuration.

FIG. 2 is a schematic illustration showing the vapor gap normally formed around the metal matrix of FIG. 1.

FIG. 3 is a schematic diagram partially in block form showing the solid cryogen heat transfer apparatus of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 of the drawing which shows a prior art solid cryogen cooler 10, an insulated cooling chamber 12 with a solid cryogen 14 and a metal heat conducting matrix 16 with a heat load 20, such as an infrared detector, positioned adjacent metal rod 22 of the metal matrix 16.

FIG. 2 shows a vapor gap 24 formed around the metal matrix 16 which is very inefficient for heat transfer.

In the device of FIG. 3, a solid cryogen 28, having a plurality of gas flow passages 30, is placed in an insulated cooling chamber 32. Sublimed gas in the flow passages in solid cryogen 28 is circulated through insulated conduit 34 by means of a gas circulator 36, driven by a motor 38, to a load heat exchanger 40, located adjacent the heat load 20. The gas leaving the heat exchanger 40 is returned to chamber 32 through insulated conduit 42. A portion of the return gas is supplied to the gas circulator motor heat exchanger 44 through conduit 46. A pressure control valve 48 is connected to the output of heat exchanger 44. In systems wherein other means are used to cool the circulator motor, the pressure control valve 48 may be connected directly to return line 42. A vacuum source 49 is connected to the output of pressure control valve 48. However, in space, no vacuum source is required and the output of valve 48 may be vented directly to space.

In the operation of the device, the gas circulator 36 draws sublimed gas from passages 30 in the solid cryogen 28 and circulates it through heat exchanger 40. After taking up heat in the heat exchanger 40, the gas is returned to the chamber 32 through conduit 42. As heat is transferred from the gas to the solid cryogen, more solid cryogen is sublimed. In this way, heat is uniformly transferred to the solid cryogen and the temperature of the device in the heat load being cooled is controlled since the mass of gas sublimed is proportional to the content of heat in the gas returning to chamber 32.

The gas leaving heat exchanger 40 is still cool enough to provide cooling for the circulator motor 38. A portion of the gas in return conduit 42 is passed through conduit 46 and is supplied to heat exchanger 44. The pressure control valve 48 controls the flow in conduit 46. The pressure level of the control valve 48 is selected to control the temperature within the passages 30, since the temperature in a solid cryogen is determined by pressure as is known in the art. For example, with solid Neon used as the cryogen, the pressure valve 48 would be set to hold the pressure in line 42 at approximately 250 mm of mercury to hold the temperature in the solid cryogen at approximately 24.degree. Kelvin. An increase in temperature of the gas in conduit 42 will cause a greater amount of gas to be sublimed in solid cryogen 28, thus increasing the pressure in the system. An increase in pressure in the system causes valve 48 to operate to maintain the pressure in conduit 42 substantially constant. This also provides an increase in flow through heat exchanger 44. Thus, the flow in heat exchanger 44 increases as the temperature increases in conduit 42 so as to automatically provide proper cooling for motor 38.

There is thus provided an apparatus to provide cooling for a heat load, such as an infrared detector, which provides more reliable cooling for the heat load.

Claims

We claim:

1. An apparatus for transferring heat from a heat load to a solid cryogen, comprising: an insulated container; a solid cryogen within said container; a heat exchanger adapted to be positioned in heat transfer relation to the heat load; means for providing a gas circulation path within the solid cryogen; means for transferring the gas sublimed within the solid cryogen to the heat exchanger and means for returning the gas in the output of said heat exchanger to the insulated container, whereby the rate of sublimation of the solid cryogen is determined by the heat transfer from the heat load to the gas in the heat exchanger; means for maintaining the pressure within the heat return means at a predetermined level to thereby control temperature in the solid cryogen; said means for transferring the gas sublimed within the solid cryogen to the heat exchanger includes a conduit connecting the insulated container to the heat exchanger and a gas circulator connected in said conduit; a motor driving said gas circulator; a heat exchanger for cooling said motor; means for passing a portion of the return gas from the heat load heat exchanger to the motor cooling heat exchanger; said means for maintaining the pressure within the heat return line being a pressure control valve for controlling the flow of gas through the motor heat exchanger.