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Session: Session 13: Waste heat recovery from engines II
Session starts: Tuesday 13 October, 15:00
Presentation starts: 16:00
Room: 1B Europe

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Taehong Sung (Pusan National University)
Sang Youl Yoon (Pusan National University)
Kyung Chun Kim (Pusan National University)

Abstract:
Organic Rankine cycle (ORC) system is a low-temperature waste heat recovery system. The system configuration is simple and the operating characteristics are also stable. Usually ORC systems emit heat to ambient air or accessible water. In this study, an ORC system which utilizes both low-temperature heat source and cold energy heat sink is thermodynamically analysed. Unlike the typical ORC application, amount of heat source is sufficient for cycle operation (temperature gradient is gradual for heat source), temperature of heat sink is very low, amount of heat sink is also limited (temperature gradient is steep for heat sink). The effect of condensing temperature and exit temperature of heat sink to system power output, mass flow rate, thermal efficiency and exergy efficiency are delineated here. R134a and R1234yf refrigerant working fluids are also compared. Two different heat source temperatures of 45 oC and 80 oC are compared. Heat sink temperature is fixed at -160 oC. In case of sufficient amount of heat source, decrease in condensing temperature results in increase in power output and decrease in refrigerant mass flow rate. At the same time, thermal efficiency and exergy efficiency also are increased due to increase in net work. Thus, the cycle be designed with low condensation temperature considering whether condensing pressure goes bellow ambient pressure (which causes incompressible component penetration into system), whether evaporating pressure is in the range of pressure tolerance of the system, and whether the pressure ratio is realiziable with turbo-machienry devices.