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This article presents the investigation on the oil—gas two-phase leakage flow through the micro gaps in oil-injected compressors and provides a new way of investigating the internal leakage process in the compressors. The oil—gas leakage rates were measured through the micro gaps of various gap sizes, the volume ratios of oil to gas, and pressure differences/ratios; and the flow patterns reflecting the flow characteristics were observed by using a high-speed video. The experimental results showed that the leakage flowrate was significantly related to the flow patterns in the gap, which were similar to those found in the existing literature and agreed well with the predicted ones by the Weber number. The gas leakage flowrate through the gap increased rapidly with the increased pressure ratio until the pressure ratio reached the critical pressure ratio, which ranged from 1.8 to 2.7. At the critical pressure ratio, the flow pattern transition from churn flow to annular flow occurred, resulting in gas leakage driven by a different sealing mechanism. As the volume ratio of oil to gas increased by 0.5 per cent, the gas leakage flowrate decreased by 77 per cent.

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The switching mechanism and the thermal process of Gallium Arsenide (GaAs) photoconductive semiconductor switch (PCSS) with opposed-contact is investigated by numerical simulation of the two-dimensional (2D) structure using temperature-dependent physical parameters of the carriers in GaAs. Triggered by a low-energy laser pulse, the PCSS switches on due to the formation and evolution of multiple powerful avalanche domains. The 2D evolving characteristics of avalanche domains on the two sides of photogenerated plasma during the switching transient are comparatively analyzed. It is found that the ionizing center of each domain moves with the drift of accumulated electrons inside the domain. Meanwhile, the evolution of avalanche domains causes obvious thermal effect along the drift path of ionizing centers during the switch-on stage of PCSS. Then the temperature still keeps increasing at the edge of anode and cathode although the switching current starts dropping after the conduction of PCSS, and finally peaks at ~491 K and ~541 K, respectively. The simulation results indicate that the 2D filamentary current flows along the drift path of ionizing centres inside avalanche domains, which finally leads to the filamentary erosion after continuous operation of PCSS. On the basis of numerical simulation, the experiment of opposed-contact GaAs PCSS with 2.5-mm gap at the bias field of ~90 kV/cm is performed. The thermal erosion is found to initially accumulate at the edge of electrodes and then spreads along the current channel into GaAs substrate, which is in accordance with the simulation results and analysis.

Piston ring is one of the most important sealing components that can be easily damaged in reciprocating compressors. The severe non-uniformity of the pressure distribution was suggested to be the essential reason for the premature failure of the piston rings. Therefore, a test rig was set up to measure the pressure distributions as well as the build-up of the dynamic pressure difference, which could reveal the root cause for the non-uniformity of the pressure distributions. The results showed that the build-ups of the pressure differences between different rings were not simultaneous; there existed a threshold pressure, and the latter ring could work only when the pressure before the former ring reached to the threshold value. The pressure distributions were also investigated at the start-up and shut-down of the compressor, which further validated the cause of the premature failure of the first ring.

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