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The present article focuses on a stepless capacity regulation system for reciprocating compressors in the capacity range between 0 and 100 per cent. This system is based on the socalled reverse flow regulation principle. The principle works by reversing part of the total gas that has been taken into the cylinder by conveying it back to the suction chamber by holding the suction valve open for a controlled and variable proportion of the compression stroke. Therefore the discharge capacity and power reduction are virtually proportional. In this study, the thermal cycle of reciprocating compressors in the case of stepless capacity regulation is analysed. The theoretical model of the thermodynamics cycle is first established. The relationship between the variation of the capacity and the opening time of the suction valve in a compression stroke can be obtained. Based on this approach, a new stepless capacity regulation system is designed, which consists of a hydraulic unit, a distributor, an unloader, and a control system. The resulting system is applied to a type 3L-10/8 reciprocating compressor to demonstrate its effectiveness. The experimental results show that the capacity of the compressor can be regulated steplessly, and the energy consumption is reduced proportionally with respect to the reduction in the capacity.

Liquid film flow over triangular corrugations is investigated by simulations and experiments. The volume of fluid (VOF) method is used to track the free surface between the liquid and gas in computational fluid dynamics (CFD) simulations.In the experiments, a sCMOS camera is applied to capture the film flow in a channel. The comparison of the results from threedimensional (3-D) simulations and experiments shows good agreement. To validate the simulations quantitatively, twodimensional (2-D) simulations are carried out and the velocity profiles in the liquid film flow field are compared with experimental results. With the validated model, a series of numerical investigations of liquid film flow over triangular corrugations are accomplished. Resonance between the free surface and the corrugations is found when the Reynolds number (Re) of the liquid flow reaches a certain value. When resonance occurs, the amplitude of the waves on the free surface gets the maximum but eddies in the troughs of the corrugations are suppressed. The steepness effect of the corrugations is also investigated. No relationship between the steepness and the resonance could be observed, but steeper corrugations can cause undulations with higher amplitude on the free surface in the low Re range. To investigate the surface tension effect, the inverse of Bond number is introduced. It is found that the inverse Bond number (Bo −1 ) has a direct relation to the resonance phenomenon. Film flow with a lower Bo −1 value encounters the resonance at a lower Re value. Since the velocity component normal to the corrugated plate plays a significant role during the convection of mass transfer in film flow, the normal flow intensity is investigated. A local maximum of the normal flow intensity is found at the resonance point.

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