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The organic Rankine cycle (ORC) is a popular and promising technology that has been widely studied and adopted in renewable and sustainable energy utilization and low-grade waste heat recovery. The use of zeotropic mixtures in ORC has been attracting more and more attention because of the possibility to match the temperature profile of the heat source by non-isothermal phase change, which reduces the irreversibility in the evaporator and the condenser. The selection of working fluid and expander is strongly interconnected. As a novel expander, a single screw expander was selected and used in this paper for efficient utilization of the wet zeotropic mixtures listed in REFPROP 9.1 in a low-temperature subcritical ORC system. Five indicators, namely net work, thermal efficiency, heat exchange load of condenser, temperature glide in evaporator, and temperature glide in condenser, were used to analyze the performance of an ORC system with wet and isentropic zeotropic mixtures as working fluids. The calculation and analysis results indicate that R441A with an expander outlet temperature of 320 K may be the suitable zeotropic mixture used for both open and close type heat source. R436B may be selected with an expander outlet temperature of 315 K. R432A may be selected with an expander outlet temperature from 295 K to 310 K. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to investigate the heat transfer characteristics of mixed molten salt, an experimental setup for the submerged jet impingement has been established in this paper. Firstly, an experimental investigation on heat transfer of submerged jet impingement with water as working fluid was carried out to verify reliability of experimental method. A good consistence was found between experimental results and those classical correlations from references for stagnation heat transfer, which indicate the reliability and accuracy of experimental method. On the basic of ensuring the reliability of experiment, a series of studies on jet impingement experiments were carried out with new mixed molten salt. The results indicated that effect of submerged jet impingement heat transfer enhanced gradually with the increase Reynolds number and the heat transfer characteristics at the stagnation are analogous with the water in the scope of experimental investigations. Further, a correlation about quaternary mixed molten salt was proposed based on experimental data. At same Reynolds number, the Nusselt number of mixed molten salt is obviously higher than that of water at stagnation zone because of its higher Prandtl number and becomes lower than water at larger radial distance due to its higher viscosity. The results indicated that thermophysical properties of working fluid have an enormous influence on the Heat transfer performance. The experimental results in this paper provide a necessary technical guarantee for the study of heat transfer of the high temperature fluid. [ABSTRACT FROM AUTHOR]

A single-screw expander (SSE) is a type of volumetric expander that can be applied to power generation, which is beneficial for energy conservation and environment protection. Investigating the SSE leakage characteristics is necessary because leakage has a significant influence on the SSE performance. This study provides theoretical and experimental analyses of the SSE internal leakage with compressed air as the working fluid. Both mathematical model of different leakage paths and leakage model have been established. The simulation model was verified by experimental data at internal volume ratios of 2.95 and shows a maximum deviation of 3.63%. Results show that fitting clearance height and rotational speed could clearly influence the volumetric efficiency and power output. The diameters of both the screw and the gate rotor could also significantly influence the volumetric efficiency. The volumetric efficiency decreased with the increase in internal volume ratio. [ABSTRACT FROM AUTHOR]

This paper reports a fundamental experimental investigation of the start-up characteristics of heat pipes using a dedicated molten-salt mixture as the working fluid. Based on four single salt, i.e. NaNO 3 (AR), KNO 3 (AR), LiNO 3 (AR) and Ca(NO 3 ) 2 (AR), a quaternary molten-salt working fluid was developed and charged at different masses into four heat pipes with the same dimensions of 980 mm in length and 22 mm in diameter. A parallel comparison on the start-up performance of these heat pipes was then conducted to observe the influence of the charging mass and the inclination angle under the consistent lab-controlled conditions. The experimental results showed the heat pipe with molten-salt charge of 40 g responded much quicker than those with molten salt charge of 60 g, 70 g and 80 g respectively; meanwhile, the molten-salt heat pipe achieved the maximum condensation temperature at inclination angle of 50°. Comparing to the conventional naphthalene heat pipe, the dedicated molten-salt heat pipe had a much shorter start-up time when they were charged with the same amount of 40 g. The overall research result is expected to provide certain guidance for further design and operation of molten-salt heat pipe in high-and-medium-temperature heat transfer and storage scenarios. [ABSTRACT FROM AUTHOR]