RU2796457C1 - Method for lowering temperature of a cooled object using helium refrigerator with an excess reverse flow - Google Patents

Abstract

FIELD: cryogenic technology.

SUBSTANCE: invention is related in particular to helium refrigerators with excess reverse flow. Helium refrigerator with excess reverse flow contains a compressor, a heat exchanger with forward and reverse flow channels, a direct flow throttle valve, a cryogenic product collector, a liquid helium supply valve and temperature sensors at the inlet and outlet of the cooled object. The helium flow from the cooled object is directed through the atmospheric heat exchanger directly to the compressor inlet, and the degree of opening/closing of the liquid helium supply valve is determined by the temperature value of the temperature sensor at the cooled object inlet: when this temperature is below the set value, the liquid helium supply valve is closed and when this temperature is higher set value, the liquid helium supply valve opens slightly.

EFFECT: possibility of lowering the temperature of the cooled object directly by a helium refrigerator with an excess reverse flow is provided, critical mechanical stresses in the object are prevented.

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Description

The present invention relates to cryogenic engineering, and more specifically to helium refrigerators with excess reverse flow, and can be mainly used for testing/investigating electrophysical devices at helium temperatures (~4.5 K).

Known helium refrigerators with excess reverse flow for the production of cold at a temperature level of ~4.4 K, the principle of operation of which and the scope of the most fully reflected in the monograph: V.P. Belyakov. Cryogenic equipment and technologies. M., Energoizdat, 1982.

The known method is carried out as follows: in a stationary cooling mode, a direct stream of compressed helium with a relative flow rate equal to 1 is cooled in a heat exchanger, then throttled in a valve and enters in the form of a cold helium stream at T≈4.4 K into the channels of the cooled object. Liquid helium also enters the refrigerator collector through the valve with a relative flow rate y<1.

Vapors from the vapor-liquid flow and liquid helium evaporating from the heat load q with a total relative flow rate 1 + y enter the return flow channel of the heat exchanger. Thus, the return flow rate exceeds the forward flow rate by the value y, as a result of which a positive Joule-Thomson effect is achieved on the throttle valve, which ensures the production of cooling capacity q. The temperature of the cold produced is equal to the boiling point of liquid helium in the refrigerator tank and is usually about 4.4 K, since the helium pressure at the compressor inlet is equal to atmospheric pressure, about 1 bar abs.

Helium refrigerators with excess reverse flow, unlike classic helium refrigerators, do not contain expanders in the pre-cooling stage and therefore are simple both in design and operation and have a high degree of reliability. Thanks to these qualities, helium refrigerators with excess reverse flow have found wide application both in various research and testing facilities using cold at helium temperatures, and in large cryogenic systems, for example, in the cryogenic complex of the Tevatron superconducting accelerator (USA, National Laboratory named after A.I. Fermi). The use of helium refrigerators with excess reverse flow is also considered in the new megaproject of the NIKA superconducting accelerator complex (N.N. Agapov et al. Development and reconstruction of the VBLHEP cryogenic system of the NIKA accelerator complex (2012-2015). Preprint P8 2012-14, JINR, Dubna, 2012).

Before the stationary mode of cooling at Т≈4.4 K, the temperature of the object must be lowered from the ambient temperature to 4.4 K. object input.

If for some reason there are no damping devices in the cooled object, then its temperature is lowered by a helium flow, the temperature of which changes according to a law that excludes the occurrence of critical mechanical stresses in the object structure. (A. Ageev et. Bauman, Moscow: N.E. Bauman Moscow State Technical University Publishing House, 2020, pp. 26-33).

A disadvantage of the known method for obtaining a helium flow with a given law of temperature change is the use of additional expensive cryogenic equipment in which flows of gaseous and liquid helium are mixed. As a rule, such equipment is not mass-produced.

The task to be solved by the claimed invention is to find such a method of operation of a helium refrigerator with an excess reverse flow, in which this helium refrigerator would provide a decrease in the temperature of the cooled object according to a given law of temperature change, which excludes the appearance of critical mechanical stresses in the object without involving additional cryogenic equipment .

The technical result of the present invention is the possibility of lowering the temperature of the cooled object from the ambient temperature to 4.4 K directly by a helium refrigerator with an excess reverse flow.

The technical result of the invention is ensured by the fact that in the mode of lowering the temperature, helium after the cooled object is fed directly through the atmospheric heat exchanger to the inlet of the refrigerator compressor, and the temperature at the inlet of the cooled object is controlled by the amount of liquid helium supplied to the refrigerator collector with an excess reverse flow.

During the process of lowering the temperature of the cooled object from the ambient temperature to ~5 K, helium from the cooled object with a relative flow rate equal to 1 is sent to the atmospheric heat exchanger, where it is heated to the ambient temperature due to atmospheric heat and, after the atmospheric heat exchanger, is sent directly to the compressor inlet . Liquid helium with a relative flow rate y enters the refrigerator collector through the valve, where it evaporates due to thermal contact with the collector heat exchanger and enters the refrigerator heat exchanger in a gaseous state.

After the compressor, the helium flow with a relative flow rate equal to 1 is cooled in the refrigerator heat exchangers to a predetermined helium temperature at the inlet to the cooled object Ti. The law of change in temperature Ti from the temperature at the outlet of the cooled object To is given by the equation Ti=f(To), obtained from the analysis of mechanical stresses in the object when it is cooled from the ambient temperature to ~5 K. The value of the temperature Ti equal to the specified one is achieved by supplying the required amount of liquid helium into the collector through the valve: when the temperature Ti is below the set value, the liquid helium supply valve is closed, and when this temperature is above the set value, the valve opens slightly. This regulation is quite easy to perform both in manual control mode and in the mode using an automated control system. After reaching the To value of ~5 K, the helium refrigerator operates in the stationary mode of object cooling at a temperature of 4.4 K.

The essence of the proposed method is illustrated by the drawings of Fig. 1 and FIG. 2.

In FIG. 1 shows a functional diagram of a helium refrigerator with an excess reverse flow operating in a stationary cooling mode, when the object under test/investigation 5 already has a temperature of ~4.4 K. Here 1 is a compressor, 2 is a heat exchanger with channels for direct m and reverse n flows, 3 - direct flow throttle valve, 4 - liquid helium collector, 5 - cooled object, 6 - liquid helium supply valve, 7 - collector heat exchanger, L - liquid helium level gauge, Ti and To - inlet and outlet temperatures of the cooled object, respectively. The relative flow rate of the forward flow is 1, the relative flow rate of liquid helium is y, the relative flow rate of the reverse flow is 1+y, the amount of heat removed from the cooled object is q.

In FIG. 2 shows a functional diagram of a helium refrigerator with excess reverse flow, which implements the proposed method for lowering the temperature of a cooled object from ambient temperature to helium temperature ~5 K. Here 1 is a compressor, 2 is a heat exchanger with channels for direct m and reverse n flows, 3 - direct flow throttle valve, 4 - liquid helium collector, 5 - cooled object, 6 - liquid helium supply valve, 7 - collector heat exchanger, 8 - atmospheric heat exchanger, L - liquid helium level gauge, Ti and To - inlet and outlet flow temperatures, respectively helium of the cooled object. The relative flow rate of the forward flow is 1, the relative flow rate of liquid helium is y, the relative flow rate of the reverse flow is y, the relative flow rate through the atmospheric heat exchanger is 1.

At the Institute of High Energy Physics named after A.A. Logunov National Research Center "Kurchatov Institute" created a cryogenic facility for testing / researching various electrophysical devices at helium temperatures. This setup allows for the "assembly" of various configurations of refrigerated backflow refrigeration vehicles, including the configuration shown in FIG. 2 descriptions of the invention. At this installation, during the commissioning starts on November 26, 2019, December 2, 2020 and December 07, 2021, the object was successfully cooled according to the law Ti=f(To) (Fig. 3), obtained for the FFS superconducting quadrupole magnet being created.

Claims (1)

A method for lowering the temperature of a cooled object by a helium flow from a helium refrigerator with an excess reverse flow, containing a compressor, a heat exchanger with forward and reverse flow channels, a forward flow throttle valve, a cryogenic product collector, a liquid helium supply valve and temperature sensors at the inlet and outlet of the cooled object, characterized in that that the helium flow from the cooled object is directed through the atmospheric heat exchanger directly to the compressor inlet, and the degree of opening/closing of the liquid helium supply valve is determined by the temperature value of the temperature sensor at the cooled object inlet: when this temperature is below the set value, the liquid helium supply valve is closed and when this temperature is higher than the set value, the liquid helium supply valve opens slightly.

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