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Isochoric freezing is a pressure freezing technique that could be used to retain the beneficial effects of food storage at temperatures below their freezing point without ice damage. In this study, potato cylinders were frozen in an isochoric system and examined using full factorial combinations of three processing procedures (immersed in water, vacuum-packed and immersed in ascorbic acid solution), four freezing temperatures/pressures (-3 °C/37 MPa, -6 °C/71 MPa, -9 °C/101 MPa and -15 °C/156 MPa) and two average compression rates (less than 0.02 and more than 0.16 MPa/s). The effects of process variables on critical quality attributes of frozen potatoes after thawing were investigated, including mass change, volume change, water holding capacity, color and texture. Processing procedure and freezing temperature/pressure were found to be highly significant factors, whereas the significance of the compression rate was lower. For the processing procedures, immersion in an isotonic solution of 5% ascorbic acid best preserved quality attributes. At the highest pressure level of 156 MPa and low compression rate of 0.02 MPa/s, potato samples immersed in ascorbic acid retained their color, 98.5% mass and 84% elasticity modulus value. These samples also showed a 1% increase in volume and 13% increase in maximum stress due to pressure-induced hardening.

To address the research gap regarding the flow characteristics of cryogenic perforated plate flowmeters in vertical pipes and to enhance measurement reliability in challenging environments, this study investigates the flow characteristics of liquid hydrogen in a vertical pipe using a perforated plate flowmeter. Numerical simulations are performed based on an extended derivation of performance parameter formulas in the vertical direction. Various inlet Reynolds numbers, plate thicknesses, and equivalent diameter ratios are analyzed to assess their effects on key performance parameters, including the discharge coefficient, pressure loss coefficient, and stable region. The results indicate that the influence of flow direction on the performance parameters decreases with increasing Reynolds number. Downward flow is associated with smaller discharge coefficients, lower pressure loss coefficients, and reduced upper limits of Reynolds numbers in the stable region. Furthermore, the effects of gravity become more pronounced at larger thicknesses and greater equivalent diameter ratios. [ABSTRACT FROM AUTHOR]

As a crucial temperature range for space applications as well as the pre-cooling temperature of mK-level refrigeration, the acquisition of the liquid-helium temperature has become a key research topic in recent years. Benefiting from the merits of no moving parts at the cold end, compact structure, high reliability, and low weight, high-frequency pulse tube cryocoolers (HPTCs) have become a conspicuous alternative for directly obtaining temperatures below 4 K. However, due to insufficient specific heat capacity of the commonly used regenerator materials at low temperatures, the large heat transfer losses of HPTCs limit its access to the liquid-helium temperature. Considering that the working gas 4He itself has a higher specific heat capacity than the commonly used rare earth materials below 10 K, an adsorptive regenerator scheme was proposed using non-magnetic, low-cost porous activated carbon (AC) to adsorb a part of working gas 4He as the low-temperature regenerator material to cool the remaining helium. Firstly, an adsorption model was established to simulate the dynamic adsorption characteristics of 4He with AC, and it was pointed out that low temperature and high pressure were beneficial to the adsorption of helium, which improves the cold storage capacity of the regenerator. Then, a three-stage HPTC was built for experimental verification. By filling AC in the low-temperature regenerator to substitute a part of the conventional rare earth material HoCu2, the cryocooler obtained a record-breaking no-load temperature of 3.27 K using 4He as the working gas. The cooling power at 4.0 K increased by 41.71%, verifying the feasibility of this adsorption scheme. [ABSTRACT FROM AUTHOR]

The thermoelastic martensitic transformation and its reverse transformation of the Cu-Al-Mn cryogenic shape memory alloy, both with and without compressive stress, has been dynamically in situ observed. During the process of thermoelastic martensitic transformation, martensite nucleates and gradually grow up as they cool, and shrink to disappearance as they heat. The order of martensite disappearance is just opposite to that of their formation. Observations of the self-accommodation of martensite variants, which were carried out by using a low temperature metallographic in situ observation apparatus, showed that the variants could interact with each other. The results of in situ synchrotron radiation X-ray and metallographic observation also suggested there were some residual austenites, even if the temperature was below Mf, which means the martensitic transformation could not be 100% accomplished. The external compressive stress would promote the preferential formation of martensite with some orientation, and also hinder the formation of martensite with other nonequivalent directions. The possible mechanism of the martensitic reverse transformation is discussed. [ABSTRACT FROM AUTHOR]