THERMODYNAMIC ANALYSIS OF SOLAR OPERATED COMBINED POWER AND EJECTOR REFRIGERATION CYCLE USING ECOFRIENDLY REFRIGERANTS

Abstract

Development of innovative thermodynamic cycles is important for the efficient utilization of low-temperature heat sources such as solar, geothermal, and waste heat sources. This work is an investigation of a novel concept to produce power and cooling with the energy contained in low-temperature, thermal resources. Exergy destructions within the system and exergy losses to environment are investigated to determine thermodynamic inefficiencies in the system and to assist in guiding future improvements in the system. In this study, thermodynamic analysis of a solar operated combined power and ejector refrigeration cycle has been carried out to evaluate the performance of the cycle using R141b refrigerants as working fluid and duratherm 600 oil as the heat transfer fluid, which produces cooling and power simultaneously. The effect of various parameters as the turbine inlet pressure (0.9MPa-1.3MPa), evaporator temperature (262K-270K), condenser temperature (297K-303K), and extraction ratio (0.2-0.8) on the performance of the cycle (the net power output, refrigeration output, first law efficiency and second law efficiency) along with the exergy destruction in its various components is evaluated. The results show that the exergy loss is biggest in central receiver and heliostat which is around 52.5% and 25% respectively. Exergy losses/destruction is observed in the HRVG, ejector, and turbine is 5.3%, 2.6% and 1.6% respectively, other components of the cycle is less than unity. A Parametric study has been carried out to analyses the effect of some influenced parameters such as turbine expansion ratio, driving pressure ratio, and compression pressure ratio on the performance (entrainment ratio, net power output, v | P a g e

refrigeration output, first law and second law efficiency) of the solar driven combined power and ejector cooling cycle with ecofriendly refrigerants (R290, R152a, R134a, and R717) as working substance. It is observed that the turbine expansion ratio, driving pressure ratio, and compression pressure ratio have significant effect on the net power output, refrigeration output, entrainment ratio, first law efficiency and second law efficiency. The results also show that at high turbine expansion ratio the performance of R290 and R152a is better than that of other refrigerants, at high compression ratio the performance of R717 and R134a shows better than that of R290 and R152a, and at high driving pressure ratio R290 and R134a gives better performance. Therefore the performance of the system depends upon the type of refrigerant used and operating conditions. Nowadays some of the refrigeration industries required double effect cooling along with power. In this context, an ejector organic Rankine cycle (EORC) integrated with a triple pressure level vapour absorption system (TPLAS) based on parabolic trough collector (PTC) solar field was thermodynamically analyzed. This cycle produces power and cooling effects at two evaporators at two different temperatures using single source of solar energy. This system meets out the demand of electricity, space air-conditioning and preservation of fruits & vegetables in cold storage. Results of exergy distribution show that 89.5% of the input exergy is destroyed/losses due to irreversibilities/losses from various components, 10.5% is available as exergy output. There are many applications where simultaneously power and cooling at different temperatures is required. In this context, recently a PTC (parabolic trough collector) field based double ejector organic cycle (DEORC) using refrigerant R141b as working fluid and Therminol VP1 as heat transfer fluid is presented and thermodynamically analyzed. This cycle produces power and cooling at two different temperatures by using single source of solar energy. Thermal storage tanks are also used to store the thermal energy from the Sun which provides the continuous power and cooling effect during insufficient solar radiation. Parametric analyses of DEORC and EORC show that inlet temperature and pressure of turbine at various extraction ratios has the significant effect on first law efficiency & second law efficiency and cooling to power ratio of this system. With the addition of ejector in EORC the first law efficiency increases from 11.43% to 11.85% while second law efficiency decreases from 10.44% to 9.785%.