The study of the electrical properties of materials at cryogenic temperature is significant for the design of insulation structures of superconducting equipment. Here, epoxy resin was combined with a small amount of KH650 modified SiC nanoparticles. When the dosage of SiC nanoparticles increased from 0.1% to 0.3%, the DC breakdown strength of the composite increase from 83.93 kV/mm to 97.51 kV/mm at room temperature and from 90 kV/mm to 120 kV/mm at 77 K. Furthermore, we used differential scanning calorimeter (DSC) and dynamic thermomechanical analysis (DMA) to analyze the effect of low-content SiC nanoparticles on the thermal behavior of epoxy resin.

For abundant cryogenic experiments, systems, and so on, visualization is necessary to observe the cryogenic fluid. Therefore, the visualization methods of cryogenic fluid have been widely studied, such as shadowgraph technique, schlieren technique, and laser holographic interferometry technique. A cryostat for visualization study must have optical windows to meet the requirement of various image acquisition equipment. Due to the difference of shrinkage between transparent glass and device materials at low temperatures, especially at large diameter flow channels, it is difficult to meet the requirement of visualization. This paper studies a kind of cryogenic visualization device with an inner diameter of 200 mm, which can meet the visualization requirements of cryogenic fluid with the maximum working pressure at 0.7 MPa and the lowest temperature at 77 K. Liquid nitrogen was used to test the visualization of the device at low temperatures. The device was also subjected to vibration conditions to test the ability of the device to withstand harsh environments. The results show that the device has good sealing performance and can meet the visualization requirements well.

The cryogenic mechanical properties of materials are particularly important in cryogenic engineering fields. The digital image correlation technique is a method to measure strain and displacement with high precision without contact. The optical window is necessary for DIC technology to obtain the cryogenic mechanical properties of materials. However, the thermal radiation energy between the light source, the glass and the sample greatly affects the limit temperature of the cryogenic mechanical measurement. In this paper, the spectral radiation properties of the glass and sample surfaces for the wavelength of 0.38-25 μm were measured. The thermal radiation energy between the power density emitted by the light source, the radiation energy emitted by the glass surface and the radiation energy emitted by the sample were analyzed. Finally, the effects of illumination distances on the radiation energy density and the sample temperature were studied. The results indicate that the power density emitted by the light source accounts for the main part of the radiant energy density received by the sample, and the radiant energy on the glass and the sample surface are negligible. Moreover, increasing the illumination distance is effective to reduce the radiation energy and temperature rise of the sample.

The thermocompressor is the driving source and the core heat-work conversion part of Vuilleumier (VM) refrigerator, which cause pressure fluctuation of the gas by converting the thermal energy at a constant volume. The thermocompressor is consists of cylinder, heater, generator, cooler, displacer, driving mechanism, load, hot cavity and cold cavity. Therefore, the ideal thermocompressor was introduced for thermal analysis to simplify the thermodynamic process and components. In order to better understand the principle of heat-work conversion in the ideal thermocompressor, firstly, the thermodynamic concept of the variable mass system that can be used in the ideal thermocompressor was introduced. Secondly, the thermodynamic process of the ideal thermocompressor under the Euler view was analyzed. Thirdly, the internal operation characteristics of the thermocompressor without load and driving displacer type refrigerator were discussed. At last, the distributions of enthalpy flow, entropy flow and exergy flow in all parts of the ideal thermocompressor were carried out. The results show that the thermocompressor does not output the net entropy flow to the load in one cycle and the flow exergy output by thermocompressor is equal in quantity to the acoustic power output by thermocompressor.

The epoxy resin is one of the critical components of large-scale superconducting magnets which find wide applications in magnetic confinement fusion, high energy accelerator and magnetic resonance imaging. In general, magnetic confinement fusion, high energy accelerator and magnetic resonance will be used at cryogenic temperatures. An approach with respect to real-time monitor of epoxy curing and cryogenic process is practically significant for magnetic reliability, maintainability as well as future mass production. Fiber Bragg Grating (FBG) sensors are excellent candidates of this measurement for their anti-electromagnetic interference characteristics and high sensitivity. The aim of this work is to use the embedded Fiber Bragg Gratings (FBG) to obtain real-time strain response of curing epoxy, and the strain change of the epoxy at cryogenic temperature from 4.2K to 300K. An FBG pre-tensioning device was designed to keep the FBG embedded in the epoxy in a stretched state during the epoxy curing process. Moreover, strain gauge sensors were also embedded to monitor the curing process at the same time. There are subtle differences in strain values obtained by the two sensors, which illustrate higher sensitivity of FBGs. This work verifies the reliability of FBG monitoring the strain response of epoxy during curing process as well as the cryogenic service.

The calculation of radiant heat leakage is a part of the design of cryogenic insulation system. The numerical radiation simulation considering geometric structure of cryogenic insulation system is established through Monte Carlo method and view factor. The difference of the multi-layer insulation outer surface temperature is about 0.5% between the simulation and experimental results. Additionally, the structure and shape of the insulation system would make radiation to redistribute between surfaces. The surface would have less heat leakage with large aspect ratio and small radius.