No abstract

Organic Rankine cycles (ORC) are used to produce power from low-temperature heat sources. In the low power output range (<10 kW e ), scroll expanders are preferred. However, the performance of the ORC system is dependent on the expander efficiency. The present work focuses on the parametric investigation of the open-drive scroll expander used for micro-organic Rankine cycle. A 5 kW e expander was used and its built-in volume ratio was 3.5. R245fa was used as the working fluid. The analysis was carried out using a well-known semi-empirical model available in the literature. Effect of key parameters such as expansion ratio, shaft speed, and expander inlet temperature on power output and expander efficiency wasevaluated for four different cases. Results showed that, at an inlet pressure of 10 bar, peak efficiency of 58% and 60% was achieved at shaft speeds of 1500 RPM and 2000 RPM respectively. It was also evident that,at higher shaft speeds, the increase in mass flow rate is not sufficient to counter frictional and mechanical losses within the expander. The analysis also indicated that increasing the expander inlet temperature could have a negative impact on the expander efficiency as well as the overall performance of the ORC system, as the thermal energy dissipation is higher at higher inlet temperatures for all cases.

The present work deals with the development of thermodynamic model of low temperature basic Organic Rankine Cycle (ORC) system and a chevron plate heat exchanger evaporator sub-model using Engineering Equation Solver (EES). Work output is evaluated using the ORC thermodynamic model, while the evaporator sub-model calculates the total surface area of the heat exchanger. Using these mathematical models, the effect of evaporation pressure, expander inlet temperature and pinch point temperature difference (PPTD) on the network output and evaporator cost are studied. In addition to this, the effect of plate spacing and plate width of chevron plate heat exchanger on pressure drop and evaporator cost are analyzed in detail. Finally, thermodynamic and geometric optimization is carried out using genetic algorithm to identify the optimum parameters at which the network output is maximized and pressure drop in the evaporator is minimized. Sensitivity analysis showed that optimum evaporator pressure existed at which network output is maximum. Thermodynamic optimization showed that work output was maximum (5.03 kW) at evaporator pressure of 5.77 bar. No improvement in the work output was seen with increase in PPTD and expander inlet temperature. Increase in plate width and plate spacing led to increase in evaporator cost and decrease in pressure drop.

One of the most promising technologies in the field of distributed energy is the use of installations operating on the so-called organic Rankine cycle (ORC). The ORC technology is applicable for the utilization of low-potential thermal energy of natural or man-made origin. At the same time, in each specific case of using ORC systems, it is important to carry out technical and economic optimization of the project. In this paper, it is proposed to estimate the cost of electricity production by an ORC power unit using an exergoeconomical model. To optimize the system parameters in order to minimize the electricity cost rate, the method of a genetic algorithm is used. The paper presents the results of optimization of the parameters of the ORC system, which includes a solar collector in combination with an ORC power unit. R245fa is used as the working fluid in this analysis. With the help of a mathematical model, the electricity cost is calculated by comparing the costs for each of the components of the ORC system. For a given operating range of parameters of an ORC power unit with an electric capacity of 1.03 kW, a minimum cost rate of $0.056/(kW h) is determined. The optimal parameters of the working fluid in the ORC power unit, at which the minimum electricity cost can be obtained, are also determined.