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Thermal and Mechanical Design
Published in Shen-En Qian, Hyperspectral Satellites and System Design, 2020
The regenerative cryocoolers use at least one heat exchanger (i.e., regenerator) and operate with oscillating flow and pressure. In a regenerator, incoming hot gas transfers heat to the matrix of the regenerator, where the heat is stored for a half cycle in the heat capacity of the matrix. In the second half of the cycle, the returning cold gas, flowing in the opposite direction through the same channel, picks up heat from the matrix and returns the matrix to its original temperature before the cycle is repeated. At equilibrium, one end of the regenerator is at room temperature while the other end is at the cold temperature. Enhanced heat transfer is obtained in regenerators through the use of stacked fine-mesh screens or packed spheres because of their large effective surface areas. Stirling cryocoolers and pulse tube cryocoolers (PTCs) are the most common regenerative cryocoolers.
Performance investigation of a pulse-tube refrigerator with different regenerative materials
Published in Alka Mahajan, B.A. Modi, Parul Patel, Technology Drivers: Engine for Growth, 2018
A. Shah Balkrushna, R. Parikh Krunal
A cryocooler is a refrigeration system used for cooling temperature below 123 K. Cryocoolers have special applications, such as liquefaction of gases, cryogenic catheters and cryosurgery, storage of biological cells and specimens, cooling of infrared sensors, and satellites. Therefore, cryocooler requires less weight and vibration reliable, long life. To fulfill such requirements, a pulse-tube refrigerator is used. A compressor, wave generation device, regenerator, pulse tube and two heat exchangers are the main components of the pulse-tube refrigerator [1]. The compressor compresses the working gas that flows through a pulse (wave) generation device to the regenerator, which absorbs heat from the cold gas leaving the pulse tube and returns it to the warm gas entering the pulse tube in the next cycle. The pulse tube is a hollow tube which has some residual gases that are compressed by the high pressure gas. Residual gas temperature increases due to compression which is produced by a water jacket at the closed end of the pulse tube. Because of the switching of flow in and out of the pulse tube, the gas is compressed and then expanded to a low pressure and temperature, ultimately being used to produce a cooling effect at the cold end. The cooling effect is further absorbed in the regenerator and the gas leaves at about atmospheric pressure. This cycle repeats and achieves the cold end-temperature (Gifford & Longsworth, 1964). The cool-down effect mainly depends upon the regenerator. An efficient regenerator must have a low thermal conductivity and high specific heat (Mikulin et al., 1984).
Infrared systems fundamentals
Published in Antoni Rogalski, Infrared and Terahertz Detectors, 2019
In a regenerative system, the gas flow oscillates back and forth between hot and cold regions driven by a piston, diaphragm, or compressor, with the gas being compressed at the hot end and expanded at the cold end. Stirling, Gifford-McMahon, and pulse tube cryocoolers are the most common types of regenerative cryocooler systems.
40 K single-stage split-type Stirling cryocooler
Published in International Journal of Ambient Energy, 2022
Fayaz H. Kharadi, A. Karthikeyan, Bhojwani Virendra
Stirling cycle cryocooler due to high coefficient of performance (COP) are most preferred Cryocooler technology. The Stirling cryocooler works on Stirling cycle, which is a closed thermodynamic cycle. It consists of four processes, namely isothermal compression, isothermal expansion and constant volume heat addition and constant volume heat rejection. The Stirling cycle cryocooler utilise valve-less linear compressor. In valve-less linear compressor, moving coil linear motor (top pole piece, bottom pole piece and magnet arrangement) is used to give linear motion to the piston in the cylinder. This arrangement eliminates mechanical linkages essential for converting rotary motion into linear motion as it directly produces linear motion. Stirling cooler is preferable over other system due to its high operating speed and pressure which directly enhance the cooling capacity. The high operating speed and pressure reduces the specific mass (mass of cooler per unit cooling capacity). The linear motors used in Stirling cryocooler are either moving magnet or moving coil type. The moving coil linear motor has the advantage over the moving magnet type of lesser inertia forces involved in moving the coil (Dang 2015). Therefore, in this set up, moving coil motors were used. The Neodymium-Iron-Boron (Nd-Fe-B) material was used for the magnet. Those materials have high energy density which directly affects the power of linear motor. As the working fluid helium gas was used (Walker 1983). To maintain the piston to its mean position during the operation, a stack of flexure bearing was used. The flexure bearing is a circular flat metallic disc on which spiral arms are cut for flexing. The radial clearance between the piston and the cylinder bore is maintained by these bearings which increase the service life of the cryocooler. To seal and suspend the piston in the cylinder, Caughley et al. (2016) used a pair of metal diaphragms in Stirling cryocooler. Wang et al. (2016) developed a two-stage high capacity Stirling cryocooler for cooling high-temperature superconductor devices in which the concept of free piston supported by flexure bearing was used. The leakage increases with increase in clearance between the piston and the cylinder bore over a period of time. As leakage increases, it lowers pressure ratio developed by the compressor and thus drastically bring down the cooling capacity of the cryocooler. For that purpose, the piston of compressor and displacer is coated with Rulon. To estimate the operating and geometric parameters of the present cryocooler, thermal analysis proposed by Atrey (1990) was used.