Refrigeration Technology

For the HED@FAIR project, NRC “Kurchatov Institute” — IHEP creates four quadrupole magnets with a unique combination of a large internal diameter of the superconducting winding and a high magnetic field gradient in the magnet aperture. To evaluate these superconducting magnets in different operation modes (cooling, maintaining operating parameters, heating, and transitioning magnet to the normal state), a cryogenic facility equipped with a diagnostic system was created. The main measured parameters of the unit were temperature, pressure, and vacuum in the equipment and pipelines, levels of liquid helium and liquid nitrogen, level of the gas holder, and helium flow rate. The control devices were represented by valves with electric and valves. For processing incoming signals from sensors and generation of control actions, the equipment of the domestic company OVEN was used, particularly analog input modules MV110, discrete output modules MU110, and interface converters alternating current four and direct current power supplies. The critical part of the diagnostics system, namely, the control of cryogenic valves, was provided through analog output modules NI 9219 and input modules NI 9212 (feedback) of the CompactRIO chassis. The program part of the installation for the study of superconducting quadruples is a mnemonic diagram with interactive graphic elements, physically located on the computer (operator console), and available in the read mode via the remote desktop protocol to users outside the installation. The mnemonic scheme allows the manual control of the plant’s valves and the automatic regulation of some indicators, depending on the settings assigned by the operator. The dynamics of the processes can be monitored with graphs on the right side of the interface. These graphs are displayed on a separate display at the operator’s console, whereas they are displayed on a unified screen for remote users.

BACKGROUND: Existing refrigeration machines contain four main units, i.e., compressor, condenser, expander, and evaporator that perform the refrigeration cycle. Currently, the liquefaction of the refrigerant occurs in the condenser. The creation of the conditions under which condensation of the working fluid would occur in the compressor unit would make the development of a compact refrigeration machine possible by eliminating the condenser from it.

AIMS: This work aims to investigate the possibility of creating a compact refrigeration machine with the implementation of the condensation process of the working fluid in the compression chamber of the compressor.

MATERIALS AND METHODS: The object of the study is a low–speed compressor, in which the pressure ratio significantly exceeds known analogs and simultaneously the temperature is significantly lower than that of high–speed machines because of the creation of conditions under which compression occurs with polytropic indicators below 1.08. The research method involves determining the gas temperature at critical pressure and comparing the obtained result with the critical temperature. The system of equations and assumptions used relates to the model with lumped parameters of the working fluid.

RESULTS: The results obtained on the compression of such refrigerants as ammonia, carbon dioxide, R12, R22, and Freon–134a showed the possibility of obtaining the required pressures in a low–speed machine at temperatures significantly below the critical temperature.

CONCLUSIONS: This work examines and proposes to study further those working fluids of refrigeration machines that can go into the liquid phase in a low–speed compressor unit because of their characteristics and operating parameters in the refrigeration machine. Further experimental confirmation of this will enable partial or complete elimination of the condenser unit in the refrigeration machine.

BACKGROUND: A promising method for treating musculoskeletal disorders to alleviate symptoms and promote recovery is local cryotherapy (LC). Proper control and regulation of the procedure enable safe interventions with predictable therapeutic effects for various locations.

AIMS: This study aims to identify measurable physical criteria for the effectiveness of the LC procedure and the dosing characteristics and to compare and analyze the capabilities of various methods.

MATERIALS AND METHODS: The experiment involved 16 volunteers who were randomized into 4 groups. The first and second groups underwent LC using ice bags for 20 min with a cooling agent consisting of an ice and water mixture and a 23.1% sodium chloride solution. The third and fourth groups underwent nitrogen (for 3 min) and air (for 20 min) LC, respectively. During the experiment, the skin temperature was measured using a temperature sensor and thermal imaging camera.

RESULTS: The lowest value of the minimum final temperature after cooling was recorded with liquid nitrogen vapor as equal to 0.88 ± 1.75 ℃. The minimum area of the work zone was 33.7 ± 7.1 cm². When cooled with an ice bag with water and ice, the most uniform distribution of the temperature field among the investigated cases was observed, with the highest values of the minimum final temperature (i.e., 6.43 ± 0.90 ℃) and minimum area of the work zone (i.e., 135.2 ± 34.6 cm²) among the investigated methods.

CONCLUSIONS: The main physical criteria for the effectiveness of LC are identified as temperature and the dynamics of its changes on the surface of the object of exposure. A dosing characteristic, i.e., the area of the work zone, was proposed and evaluated. In the area of the work zone, the target temperature is achieved. Based on the main physical criteria, the three main cooling methods are compared. These methods achieve the target result in different ways. The easiest to use and prepare are contact methods using ice bags. Air cooling in the investigated mode is more easily tolerated by the subjects, and in terms of the physical criteria, it is equivalent to contact methods. Cooling with nitrogen vapor leads to the fastest achievement of the target temperature on the surface and the least cooling of internal tissues; therefore, cooling deep into the biological tissue is limited.

Based on an analysis of the technical level of equipment utilized in cryotherapy, the issue of increasing the dosing accuracy and, accordingly, ensuring accurate and uniform cooling of a biological object was identified, which required research into the issues of controlled cooling. A software for predicting the result of cryotherapy has been developed, and a range of rational parameters for supplying gas to the cabin of the installation has been determined when performing controlled cryotherapy (i.e., from 40 to 70 g/s and from −140℃ to −160℃). An experimental model of a new type of installation, which enables cryotherapy to be conducted with changes in the main parameters of the equipment in operation in a wide range of cooling gas flow temperatures from −50℃ to −160℃, free-flow velocity from 0.1 to 2 m/s, and cryotherapy time up to 420 s, has been developed and implemented. The experimental model, together with the prediction software, forms a complex system for research and controlled implementation of cryotherapy in a wide range of operating parameters. Algorithms for implementing regulated modes for various biological objects and purposes of exposure have been developed and recommendations have been provided, enabling the practical application of the proposed concept.

Vyacheslav Vladimirovich Sychev (December 11, 1933, Odessa — February 14, 2023, Moscow) — Soviet and Russian scientist, doctor of technical sciences, professor at the Moscow Power Engineering Institute (MPEI); specialist in thermodynamics; Honored Scientist of the Russian Federation (1996). His main areas of scientific interest were thermodynamics, thermophysics, and information technologies. He was an author of more than 200 printed works, including monographs and books that have been published many times: "Technical Thermodynamics", "Complex Thermodynamic Systems", "Differential Equations of Thermodynamics" and others.
Full member of the International Academy of Sciences, Academy of Technological Sciences of the Russian Federation, Academy of Electrotechnical Sciences, International Academy of Cold, International Academy of Creativity. Member of the Expert Council of the Higher Attestation Commission (HAC) under the Ministry of Education and Science of the Russian Federation and the Dissertation Council of MPEI.

Laureate of the State Prizes of the USSR (1976, 1988) and the State Prize of the Russian Federation (1996), the Polzunov Prize of the USSR Academy of Sciences (1984), J. Gibbs Prize and Medal of the International Academy of Creativity (1993), Moscow Power Engineering Institute Prize "Honor and Recognition of Generations" (2013). Laureate of the State Prizes of the USSR (1976, 1988) and the State Prize of the Russian Federation (1996). Awarded the Order of Friendship of Peoples, Order of Friendship of the Socialist Republic of Vietnam.