Abstract
The organic Rankine cycle (ORC) is a popular technology used in waste heat recovery and medium-low-temperature heat utilization. Working fluid plays a very important role in ORC. The selection of working fluid can greatly affect the efficiency, the operation condition, the impact on the environment, and the economic feasibility of ORC. The expander is a key device in ORC. As a novel expander, single-screw expanders have been becoming a research focus in the above two areas because of their many good characteristics. One of the advantages of single-screw configurations is that they can conduct a vapor–liquid two-phase expansion. Therefore, in order to give full play to this advantage, a working fluid selection for ORC using a single-screw expander was conducted in this paper. Three indicators, namely, net work output, thermal efficiency, and heat exchange load of condenser, were used to analyze the performance of an ORC system. Through calculation and analysis, it can be seen that an ORC system that uses a single-screw expander and undergoes a vapor–liquid two-phase expansion is able to obtain a higher thermal efficiency, higher net work output, and a smaller heat exchange load of the condenser. Regardless of whether isentropic efficiency of the expander is considered or not, cis-butene may be the best candidate for working in subcritical cycles. HFO working fluids are more suitable for working in transcritical cycles, and HFO-1234ze(E) may be the best.
Highlights
Renewable and sustainable energy utilization and recovery of low-grade waste heat are two measures for alleviating the global energy crisis and for solving the environmental problems caused by the consumption of traditional energy sources
Tolerance of vapor–liquid two-phase expansion, which is an important characteristic of single-screw expanders, has not been considered or utilized in previous analysis and research
Here, that single-screw expanders are able to carry out vapor–liquid two-phase expansion, wet working fluids have still not been adopted in organic Rankine cycle (ORC) systems with single-screw expanders as a result of three considerations
Summary
Renewable and sustainable energy utilization and recovery of low-grade waste heat are two measures for alleviating the global energy crisis and for solving the environmental problems caused by the consumption of traditional energy sources. He et al conducted an experiment to study the influence of intake pressure on the performance of a 175-mm-diameter single-screw expander working with compressed air [22] They found that the highest overall efficiency could reach 55% or so, that the greatest torque reached nearly 100 N·m, that the highest power output amounted to about 22 kW, and that the lowest gas consumption was about 60 kg/kWh. Subsequently, some work was done on single-screw expanders employed in ORC systems for the purposes of waste heat recovery. The selection of working fluids that match the characteristics of vapor–liquid two-phase expansion in single-screw expanders has not been carried out, in a review paper, White et al compared the power output predicted by two different models of n-pentane, n-hexane, and isopentane within partially evaporated and a superheated cycles [29]. Working fluid selection is conducted for ORC using a single-screw expander on the basis of three indicators, namely, net work output, thermal efficiency, and heat exchange load of condenser
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