The trilateral flash cycle shows a greater potentiality in moderate to low grade heat utilization systems due to its potentiality of obtaining high exergy efficiency, compared to the conventional thermodynamic cycles such as the organic Rankine cycles and the Kalina cycle. The main difference between the trilateral flash cycle and the conventional thermodynamic cycles is that the superheated vapor expansion process is replaced by the two-phase expansion process. The two-phase expansion process actually consists of a flashing of the inlet stream into a vapor and a liquid phase. Most simulations assume an equilibrium model with an instantaneous flashing. Yet, the experiments of pool flashing indicate that there is a flash evaporating rate. The mechanism of this process still remains unclear. In this paper, the flash evaporating rate is introduced into the model of the two-phase expansion process in the reciprocating expander with a cyclone separator. As such, the obtained results reveal the influence of evaporating rate on the efficiency of the two-phase expander.
Single screw compressor (SSC), a strong competitor of the twin screw compressor, is regarded as an excellent gas compressor because of symmetrical structure and balanced gas forces on the screw rotor. However, the market for the SSC is tiny compared with that for the twin screw compressor because of the serious abrasion of star-wheel teeth. In recent years, this problem has been solved due to the development of the new profiles of meshing pairs, and the SSC has attracted more attention due to its high application potential for low-temperature heat pump, mechanical vapor recompression, and two-phase expansion. Nevertheless, there are still many technical problems remained to be solved for applying SSC to these fields urgently. In this paper, a comprehensive review on the progress and development of SSC technologies is presented. The review first combs the current situation of SSC products. Besides, the design and processing of meshing pairs are clarified and analyzed. Moreover, the working process of SSC and its performance in new applications are discussed in detail. Finally, the further research direction of the SSC is also discussed, which will be beneficial for designing high-efficiency SSC.
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