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Summary: Nitrate salt with low melting point as heat transfer and storage fluid simplifies the heat transfer, storage, and exchange processes, and organic Rankine cycle as heat and power conversion system can realize the distributed energy supply. This study experimentally investigated the solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid, and the main problems and phenomena during the operation process have been described and analyzed in detail. Experimental results showed that the temperature difference of collector tube changes with direct normal irradiation and lags behind the changes of direct normal irradiation. Molten salt heat storage system can effectively restrain the temperature fluctuation at the collector tube outlet. The abrupt temperature drop at the evaporator inlet was caused by the heat imbalance between R123 and nitrate salt and inappropriate design of the evaporator. The effects of expander inlet pressure and expansion ratio on the ORC electrical power output were obtained at different superheating degrees of the expander inlet. The researches on each component are instructive to the technology of the parabolic trough concentrated solar power generation system with molten salt as heat transfer and storage fluid and provide some guides for the subsequent research. Furthermore, the energy and exergy analyses on overall system were developed, and results indicated the system average efficiency can reach 1.5%. Novelty statement: Experimental study on parabolic trough concentrated solar ORC system with nitrate salt as heat transfer and storage medium were firstly analyzed.Single screw expander was firstly applied in a real solar thermal power generation system and showed a stable performance.Dynamic changes on the temperatures of PTC, molten salt tanks, and ORC were shown, and energy and exergy analyses on overall system were carried on. [ABSTRACT FROM AUTHOR]

The compressed air-powered system is widely studied as a promising, environment-friendly, and high-efficiency technology. The influences of centrifugal and filter oil-gas separator on the performance of single screw expanders for compressed air-powered systems are experimentally investigated. Results show that the intake volume flow rate using the centrifugal oil-gas separator is lower than that of the filter oil-gas separator. Meanwhile, the temperature difference between the inlet and outlet of a single screw expander, the average output power, and the average shaft efficiency by using the centrifugal oil-gas separator is 1.88, 1.67, and 1.42 times higher than that of the filter oil-gas separator under the same working condition in this study. The maximum expansion ratio in this work is 8.5 by using the centrifugal oil-gas separator. The actual total output power, effective working time, and exergy efficiency by using the centrifugal oil-gas separator are respectively 56.67%, 4.51%, and 92.52% substantially higher than that of the filter oil-gas separator. The performance of single screw expanders in compressed air-powered systems can be improved by using the centrifugal oil-gas separator. • Single screw expander is employed as an engine in air compressed powered system. • The maximum expansion ratio is 8.5 by using the centrifugal oil-gas separator. • Actual total output power, effective working time and exergy efficiency are studied. • Single screw expander with centrifugal oil-gas separator has better performance. [ABSTRACT FROM AUTHOR]

• A method was introduced to reduce under-expansion losses of single screw expander. • The energy conversion mechanisms of the new expander were investigated. • A model was developed and verified to predict the performances of the new expander. • The isentropic efficiency of the new expander was significantly improved. Using high-performance expanders is one of the keys to improve the efficiency of Organic Rankine Cycle (ORC). However, in large expansion ratio conditions, the performance deterioration caused by under-expansion seriously affects the performances of the ORC. For single-screw expanders, it is possible to utilize the kinetic energy of the screw groove exhaust to produce extra power. But there is still a lack of theoretical support for optimizing the exhaust kinetic energy utilization process of this new expander at present. Therefore, the energy conversion mechanism of Single Screw Expander with exhaust Kinetic energy Utilization (SSEKU) was investigated in this paper, and a mathematical model of SSEKU was developed to investigate the energy conversion mechanisms and predict the performances. The results show that introducing exhaust kinetic energy utilization process in single screw expander can reduce under-expansion losses effectively, and the effects in large size expanders were stronger than that in small scale machines. It was also found that the maximum increase in isentropic efficiency was 3.01, 5.47, and 9.38 percentage points for the expander with a screw diameter of 117 mm, 200 mm, and 350 mm, respectively. [ABSTRACT FROM AUTHOR]

• Single screw expanders (SSE) can achieve 92.7% volumetric efficiency. • The effect of oil with six viscosities on the performance of SSE was studied. • This research investigates the effect of lubrication oil on irreversible loss. • This research analyzes the optimum operating conditions of lubrication oil. • The maximum increment of shaft power reached 26% in the experiment. A single screw expander (SSE) is a small to medium-sized volumetric expander of high performance, which can be used for energy recovery in vapor compression refrigeration (VCR) systems and expansion refrigeration in air compression refrigeration (ACR) systems. As an energy recovery device, expander operation improvement is helpful to improve the efficiency of the system. The expander, however, suffers from gas leakage losses and friction losses due to the viscosity of lubrication oil, where greater viscosity results in lesser gas leakage and more viscous friction. This study undertook an experiment to investigate six different viscosity lubrication oils (oil viscosity type from small to large: 10#, 22#, 32#, 46#, 68#, and 80#) under different inlet pressures (0.5–1.1 MPa) for clarifying the influence of lubrication oil viscosity on the operation of SSE. The results showed that increasing the kinematic viscosity of the lubrication oil could reduce leakage loss, which results in a maximum increment of volumetric efficiency of 23.06%, and with the use of 68# and 80# lubrication oils, volumetric efficiency was the highest at 92.7%. In contrast, reducing the kinematic viscosity of the lubrication oil could improve the shaft power. The maximum difference in shaft power between 10# and 80# lubrication oil was greater than 26%. The SSE had a superior shaft efficiency and a lower gas consumption rate by using 10# lubrication oil at an inlet pressure <0.55 MPa, 46# lubrication oil at an inlet pressure of 0.55–0.9 MPa, and 80# lubrication oil at an inlet pressure of 0.9–1.1 MPa. [ABSTRACT FROM AUTHOR]

At present, the most prominent technical problems of small and medium capacity expanders are low internal efficiency and small expansion ratio. In order to promote the practical application of small and medium capacity Organic Rankine Cycle (ORC) system, improving the thermodynamic performance of the expander was a remarkable issue, and the systematic research on the irreversibility of expander's working process is the fundamental work to achieve this goal. Summarizing the related research on various small capacity volumetric expanders, the research on flow problem is lacked. For an atypical volumetric expander, the flow mechanism of single screw expanders (SSEs) is more complex. In this paper, we discussed the effect of the pressure loss in the inlet and exhaust passages on the performance of SSEs. We selected two SSE prototypes developed by our laboratory to carry out the experiment under variable working conditions. The internal volume ratios are 2.95 and 3.98 respectively. The pressure differences of inlet and exhaust passages were measured. In order to evaluate the effect of the flow losses on the performance, we defined two indexes: pressure loss rate ( PLR ) and pressure energy loss influence rate of shaft efficiency ( PELR e). From the results, the pressure losses of inlet and exhaust passages for each SSE increase gradually, PLR in increases slightly and PLR out increases gradually. At the maximum point of shaft efficiency, the losses of the SSE with 2.95 are 28.06 kPa and 46.09 kPa, and the values of the SSE with 3.98 are 37.58 kPa and 33.79 kPa, respectively. It shows that the pressure losses are relatively high. The maximum values of internal and external expansion ratio for the SSE with 2.95 are 4.8 and 6 respectively, and the values of the SSE with 3.98 are 5.7 and 7 respectively. For ideal volume expansion, the internal expansion ratio of two prototypes should be 4.55 and 6.9, respectively. Summarizing the above results, how to enhance the pressure drop effect of leakage and reduce the flow resistance loss of inlet and exhaust passages simultaneously is an important technical premise to improve the expansion ratio by structural optimization. Meanwhile, PELR e of two prototypes are 16.01% and 13.59% respectively at the point. It shows that the flow losses of inlet and exhaust passages could significantly influence the performance of SSEs. [ABSTRACT FROM AUTHOR]

At present, the performance analysis of volumetric expanders by semi-empirical model is a very popular method. How to improve the universality without reducing the calculation accuracy is the key issue. For an atypical volumetric expander, the irreversibility analysis of the working process for single screw expanders is still lacking. In this paper, we explore the possibility of using a semi-empirical model considering geometric constraints to improve the universality. Firstly, a basic model of SSEs is proposed, in which the model parameters related to the structure are directly calculated by the geometry instead of being calculated by the optimization algorithm. So, the number of the model parameters is reduced to 5. And then, the model is solved by our previous experimental results. However, the deviation between the calculation results and the experimental data is significantly large. So, the sub-process assumptions and calculation formulas are adjusted, including mechanical loss, leakage loss and pressure resistance loss. Then, the modified model is solved and compared with the result of the basic model. From the calculation results, the deviation of the modified model is significantly lower than that of the basic model. Meanwhile, the calculation results are in good agreement with the experimental data. Moreover, due to considering the exhaust resistance loss, not only improves the calculation accuracy of the modified model, but also makes the physical meaning of the model clearer. The work of this paper indicates that adding geometric constraints and modifying sub-process assumptions at the same time is an effective method to improve the accuracy and universality of the semi-empirical model simultaneously. • A semi-empirical model of SSEs considering geometry was proposed. • The number of the model parameters was reduced to 5. • The sub-process of adiabatic exhaust pressure drop was added. • The formulas of mechanical loss, leakage loss and flow loss in the basic model are modified. • The modified model improve the accuracy and universality simultaneously. [ABSTRACT FROM AUTHOR]

The operating performance of the expander, as the core component of the ORC system, directly determines the comprehensive performance of the system. Single screw expander (SSE) has received widespread attention due to its advantages such as large single-stage expansion pressure ratio, insensitivity to liquid, wide working range, and balanced forces. This study fully considers the strong coupling, high nonlinearity, large time variability and uncertainty between SSE performance evaluation indexes and operating parameters. On this basis, a scatter–bilinear interpolation hybrid feature selection approach is proposed, and the feature selection and analysis of the correlation degree among SSE performance evaluation indexes are conducted. In the high-dimensional space, the influence of operating parameters on different performance evaluation indexes is analyzed. Then, this study proposes the ensemble learning-driven non-dominated sorting genetic algorithm-III (NSGA-III) approach. An ensemble learning-driven NSGA-III model for SSE performance limit optimization is constructed on the basis of the scatter–bilinear interpolation hybrid feature selection method and the ensemble learning-driven NSGA-III approach. In the hyperdimensional space, the performance limits of SSE are obtained. When the comprehensive performance of SSE reaches its limit, the shaft efficiency, expansion pressure ratio, and power output are 53.71%, 7.76, and 10.83 kW, respectively. This research provides a reliable reference for analyzing, designing, and optimizing the SSE performance limits, and it also provides a direct guidance for obtaining the SSE performance limits in the ORC system. • A hybrid feature selection approach for single screw expander is proposed. • The coupling and nonlinear characteristics of operating parameters are analyzed. • Ensemble learning-driven NSGA-III model is introduced for performance limit analysis. • A trade-off exists among the performance indexes of the single screw expander. [ABSTRACT FROM AUTHOR]