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Session: New applications: Automotive
Session starts: Monday 07 October, 10:00
Presentation starts: 10:00
Room: Willem Burger Zaal

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Jan Wiedemann (Ruhr-Universität Bochum)
Roland Span (Ruhr-Universität Bochum)

Abstract:
A basic ORC plant for waste heat recovery consists of four main components: a pump, a heat exchanger, an expansion device and a condenser. Most studies on this subject assume expansion devices, which require dry expansion to avoid liquid droplets at their later stages and thus working fluid in superheated state during the entire expansion process. Since the superheating process accounts for a major portion of exergy destruction in the heat exchanger, the use of dry organic fluids or expansion devices, which allow wet expansion, is suggested. Other studies even propose to heat up the working fluid just to its boiling point and to flash evaporate it in a two-phase expander, due to the fact, that the evaporation process in the heat exchanger also contributes a large portion of exergy destruction. Partial heating may reduce exergy destruction but also enlarge volume flows and the size of system components. The expander considered in the present study is an oil-lubricated screw expander. The working fluid is a mixture of water and/or wet organic fluids and lubricating oil. To guarantee sufficient lubrication and to avoid oil deposition, a minimum liquid content of the working fluid in every system component is required to entrain the oil in the fluid circulation. To prevent superheating of the working fluid in the heat exchanger and to control its liquid content during the expansion process in transient system operation, some components have to be added to the system. Downstream of the heat exchanger the working fluid is separated into its saturated vapor component, which is injected into the expander and its oil-rich liquid component, which is stored in a tank. The oil-rich liquid from the tank is partly injected into the expander in the required quantity by an additional pump. Via a bypass it may also be fed back into the circulation upstream the heat exchanger. The fuel savings, i.e. the ratio of recovered power to motor power, achieved by this process should at least amount to 5\%. Simulation results yield preliminary estimates regarding ideal process parameters and suitable working fluid compositions. They show that fuel savings of 5% can easily be achieved in marine applications. Due to more restricting recooling capacities the fuel savings are lower in rail application.