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Session: Parallel Session: Prototypes and Experiments
Session starts: Friday 23 September, 09:00
Presentation starts: 10:40
Room: Auditorium

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Noboru Yamada (Nagaoka University of Technology)
Masataka Watanabe (Nagaoka University of Technology)
Akira Hoshi (Ichinoseki National College of Technology)

Abstract:
Among the components of the conventional organic Rankine cycle (ORC) for the low-temperature waste heat recovery, the working fluid pump tends to cause a critical decline in the net cycle efficiency. A pump’s efficiency drops sharply under off-design conditions, such as high or low pressures at the inlet/outlet and mass flow rates that are greater or lesser than the designed value. This trend is pronounced in systems whose power output is less than 10 kW and whose hot-source temperature level is less than 200C (473 K). Furthermore, the working fluid pump limits the compactness of the system arrangement because the pump must be placed at a level lower than that of the condenser (i.e., a net positive suction head of the pump) in order to maintain sufficient inlet pressure to prevent the occurrence of cavitation, which results in considerable power consumption by the pump. These adverse effects of the working fluid pump appear in any ORC system with a small power output and a low-temperature hot source whose temperature level and heat quantity vary during operation. It should be noted that heat obtained from renewable energy sources, such as solar thermal energy, waste heat from factory processes, and heat obtained from the automobile engine have similar characteristics; To overcome the abovementioned problems, one of the authors have attempted to develop “pumpless” ORC system [1]. The pumpless ORC mainly consists of an expander, two heat exchangers, and switching valves for the expander and heat exchangers. Instead of using a working fluid pump, the switching valves method (SVM) is employed to control the cycle. The SVM makes each heat exchanger switch between functioning as an evaporator and functioning as a condenser. In this arrangement, the working fluid flows back and forth between the two heat exchangers without a working fluid pump. Therefore, this cycle does not involve problems caused by a pump. The first experimental result with an displacement-type expander was carried out to clarify the feasibility of pumpless ORC. The experimental results shows that the proposed cycle works and produces power. Time-varying characteristics of the proposed cycle will be also shown and discussed. REFERENCES [1] N.Yamada, T.Minami, M.N.A Mohamad, Fundamental experiment of pumpless Rankine-type cycle for low-temperature heat recovery, Energy, Vol.36, pp.1010-1017, (2011).