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Session: System design and optimization IV
Session starts: Tuesday 08 October, 11:20
Presentation starts: 11:20
Room: Ruys & Rijckenvorsel Zaal

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Hiroshi Kanno (Institute of Industrial Science, The University　of Tokyo)
Yusuke Hasegawa (Institute of Industrial Science, The University of Tokyo)
Isao Hayase (Institute of Industrial Science, The University of Tokyo)
Naoki Shikazono (Institute of Industrial Science, The University of Tokyo)

Abstract:
In the present study, thermodynamic performances of Rankine, trilateral and supercritical cycles with reciprocating expander are assessed. In the trilateral cycle, heat is transferred from the heat source to the single phase working fluid. Thus, the exergy loss of trilateral cycle can be drastically reduced because of favorable temperature profile matching between the heat source and the working fluid. Therefore, trilateral cycle can theoretically achieve highest exergy recovery from the heat source with finite heat capacity. In the expansion process, high pressure saturated liquid is flashed and expanded in the two-phase expander. The quality of working fluid in the expander becomes low, which results in very large expansion ratio of the expander. In this regard, reciprocating expander is suitable for the trilateral cycle. Physical properties of the working fluids are obtained using REFPROP 9.0. Heat sources assumed in this study are hot water and exhaust gas from Diesel engine． The temperature of hot water is 80 ℃ and the temperature of exhaust gas is ranged from 200 to 500 ℃. In the cycle simulation, operating pressure for each cycle with different working fluids is optimized so that to give highest available energy efficiency (availability efficiency, hereafter) for given heat source temperature, pinch point temperature difference and displacement of reciprocating expander (L). In addition, maximum operating pressure (MPa) and rotation velocity of expander (rpm) are evaluated as the criteria to check the feasibility of the cycles. We also investigated the effects of expander’s dead volume and volumetric expansion ratio. When R143a is used as the working fluid and volumetric expansion ratio exceeds 50, the availability efficiency of trilateral cycle becomes about 50 %, which is nearly 56 % larger than that of Rankine cycle for 80 ℃ case. For the 300 ℃ case, water is the optimal working fluid for the trilateral cycle. When volumetric expansion ratio is 400, the availability efficiency of trilateral cycle reaches about 70 %, which is nearly 54 % larger than that of Rankine cycle. However, availability efficiency of trilateral cycle is lower than that of Rankine cycle when volumetric expansion ratio is below 50. To realize the trilateral cycle system, an efficient two-phase expander is the key technology. We are now conducting the visualization experiment and adiabatic efficiency measurement of the two-phase expander. Output work of expander is obtained from p-v diagram. The feasibility of two-phase expander will be evaluated considering the effect of rotation velocity.