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Efficient heat recovery from low-grade heat sources is an achievable scientific frontier in the coming decade. One of the promising technologies in waste heat recovery is the organic Rankine cycle (ORC) system. Major obstacles to low-grade heat recovery include economic viability, scale, system efficiency, and exergy efficiency. In low temperature ORC systems, the cost of condenser becomes significant and hence air-cooled condenser is a feasible option. However, the performance of the air-cooled condenser is sensitive to the variation in ambient air conditions. India, being a tropical country, have villages and cities whose average temperature varies from -2°C in winter to 50°C in summer. The present work involves the study of heat transfer effects on the condenser using common organic working fluids and quantifying the consequences of environmental temperature variations. The constant thermal evaporator load is supplied with a medium-enthalpy heat source at 100 and 150°C. The atmospheric temperature associated with heat rejection from the condenser is varied from 273K to 313K for 5 working fluids. A MATLAB model of the ORC system is developed to study the effect of condenser performance on the first and second law efficiency of the ORC system. The MATLAB model is used to investigate the effect of varying inlet temperatures of the working fluid on the performance of ORC system to choose an organic working fluid suitable for Indian climatic conditions. R365 mfc, and R1233zd exhibit higher expander work and show higher heat rejection. At higher heat source temperatures of 150°C, the simulation shows a higher second law efficiency for the working fluid R1224yd(Z), which has critical temperature closed to the heat source temperature. [ABSTRACT FROM AUTHOR]

Organic Rankine Cycle (ORC) is a proven technology in the field of waste heat recovery and present days ORC is extensively being used in exploiting biomass, geothermal and solar energy. The overall performance of ORC depends on the expander, making it a core component of the system. Generally, these expanders are classified into velocity type and displacement type. The velocity type expanders find their applications in large scale power generation and are not preferred in small scale power applications as their rotational speeds exponentially increase with a decrease in expander power output. As a result, the displacement type expanders are best suited for small scale power generation in ORC. Yet, till date expanders capable of producing power at small scale are not commercially available in the market for ORC application. As an effect commercially available scroll compressors are modified to work as expanders in ORC systems. The present study aims to examine the feasibility of using one such scroll compressor as an expander in ORC with and without modification. A test rig was developed to test the compressor running in reverse as expander using compressed air, before and after modifications. The scroll machine was tested for operating conditions consisting of pressure varying from 0.5 bar to 4.5 bar and the load varying from 0.2 kg to 2.2 kg for a constant airflow rate. The configurations tested were, scroll compressor with the suction port as inlet, modified scroll compressor with the suction port as inlet and modified scroll compressor with discharge port as an inlet. Based on the experimental test data obtained it is observed that, in all three configurations, for various loading conditions at given inlet air pressure there exists a maximum power generation point and a further increase in the load at given pressure has a negative effect on power output. Also, a significant increase in speed is observed from 300 to 4250 rpm at no load condition with increasing inlet air pressures. Maximum power of 210 W was achieved at a load of 1.1 kg with the inlet pressure of 4.5 bar for modified scroll machine when the discharge port was used as an inlet. Finally, it is recommended to use a modified scroll machine with discharge port as inlet as it gives more power when compared with other configurations for the same operating conditions. [ABSTRACT FROM AUTHOR]