RU2576768C2 - Helium refrigerator with excess back flow for cold generation at two temperature levels - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: satellite refrigerator comprises helium compressor, heat exchange unit, two throttle gates, cryostat of the first cooled device at the temperature of approx. 4.4 K. Claimed refrigerator operates as follows. Backflow helium is compressed in the compressor and force into heat exchange unit straight flow channel to be cooled to the temperature of the second cooled device and, then, divided into two flows. One flow cools the second device and, then, forced back to the extra flow of heat exchange unit communicated via throttle with the first device cryostat. Another flow is also communicated with the first cooled device cryostat via the second throttle.

EFFECT: cooling of the second structure at temperatures above approx 4,4 k with no extra expander, simple and reliable design, enhanced performances.

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Description

The invention relates to cryogenic technology, and more particularly to helium refrigerators with excessive backflow.

Known helium refrigerators with excess return flow for the production of cold at a temperature level of ~ 4.4 K, the principle of operation of which and the scope are most fully reflected in the monograph: V.P. Belyakov. Cryogenic engineering and technology. M., Energy Publishing House, 1982. N.N. Agapov et al. Development and reconstruction of the cryogenic system of VBLHEP of the NIKA accelerator complex (2012-2015) Preprint P8 2012-14, JINR, Dubna, 2012. A functional diagram of this device is shown in FIG. 1. The helium backflow n is compressed in the compressor 1 to the forward flow pressure m. The direct flow m is cooled in the heat exchange unit 2, then throttled in the valve 3 and enters the cryostat 4 in the form of a vapor-liquid mixture. Vapors enter the reverse flow channel n of the heat exchange unit, where they are heated by the direct flow m. Liquid helium evaporates in the cryostat 4 due to heat influx from the environment and the heat load from the cooled device Q and in the form of vapors also enters the return channel n of the heat exchange unit. In addition, liquid helium LHe is supplied to the cryostat, the vapors of which create a reverse flow n, which is excessive in comparison with the direct flow m, necessary to achieve the positive Joule-Thomson effect on the butterfly valve 3.

As can be seen from FIG. 1, helium refrigerators with excess backflow, unlike classical helium refrigerators, do not contain expanders in the pre-cooling stage and therefore are simple both in the device and in control and have a high degree of reliability. Due to these qualities, helium refrigerators with excess return flow are widely used both in various experimental facilities that use cold at helium temperatures, and in large cryogenic systems, for example, in the cryogenic complex of the Tevatron superconducting accelerator (USA, Fermi National Laboratory). The use of helium refrigerators with excess return flow is also considered in the new megaproject of the NIKA superconducting accelerator complex (JINR, Dubna).

The disadvantage of a helium refrigerator with excess backflow is that it produces cold only at one temperature level of ~ 4.4 K. However, almost all objects operating at this temperature have low-temperature screens operating at higher temperatures to reduce heat influx from the environment. . As a rule, these screens are cooled by a stream of liquid nitrogen (T≈80 K). But when, according to safety conditions, the use of liquid nitrogen is prohibited, then you have to abandon the helium refrigerator with excessive backflow and use more expensive and less reliable classic refrigerators with expanders in the pre-cooling stage and an additional expander for the helium stream cooling the low-temperature screens.

The problem to which the claimed invention is directed is to create such a helium refrigerator with excess return flow that would produce cold at two temperature levels: the first at T = 4.4 K to cool the device and the second at 4.4 K <T <80 K to cool the screens of this device.

The technical result of the present invention is the presence in a helium refrigerator with an excess return flow of two sources of cold at different temperature levels, which will allow it to be used in cases where, according to safety conditions, the use of liquid nitrogen to cool the screens of a device operating at 4.4 K is prohibited <T <80 K.

The technical result of the invention is ensured by the fact that part of the direct flow of the helium refrigerator with excess backflow is allocated to cool low-temperature screens at 4.4 K <T <80 K. Then, the heat removed from the screens is transferred using an additional direct flow to the return flow in the heat exchange unit and then this part of the direct flow is used to obtain cold even at T≈4.4 K.

The invention is illustrated by the drawing shown in FIG. 2. The helium refrigerator with excess return flow for the production of cold at two temperature levels contains a compressor 1, a heat exchange unit 2 with channels for return flow m, forward flow n and additional forward flow s, throttle valves 3 and 5 and cryostat 4.

The helium backflow n is compressed in the compressor 1 to the forward flow pressure m. The direct flow m is cooled in the heat exchange unit 2 to a temperature of T. At this temperature, a portion (additional direct flow s) is taken from the direct flow, which is used to cool low-temperature screens. The rest of the flow m passes through the heat exchange unit 2 and the throttle valve 3, producing cold at a temperature of T≈4.4 K.

The flow s, passing through the channels of the low-temperature screens, cools them, while heating from a temperature Tn> 4.4 K to a temperature Tv <80 K, and at this temperature it is directed to a separate channel of the heat exchange unit 2, passing through which it is cooled by a reverse flow from the temperature Tv to the temperature Tn, thus giving off heat taken from the low-temperature screens to the reverse flow n. Then, the flow s enters the additional throttle valve 5, producing cold at a temperature of T≈4.4 K.

Thus, the proposed helium refrigerator with excess return flow provides cooling of the second object (low-temperature screens) at temperatures above 4.4 K without introducing an additional expander into its circuit, which preserves the simplicity and reliability of the helium refrigerator with excess return flow while expanding its capabilities.

Claims (1)

An excess return helium refrigerator for producing cold at two temperature levels, comprising a compressor, a heat exchange unit with direct and return flows, a direct flow throttle valve and a cryostat of the device to be cooled at a helium temperature of ~ 4.4 K, characterized in that for cooling the second devices at temperatures above 4.4 K, part of the direct flow is removed from the heat exchange unit to the second cooled device and after the second cooled device is returned to the heat exchange unit in Accessory downstream channel connected to the first cryostat cooling device an additional throttle valve.

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