Performance Design of Low Temperature Condenser for Waste Heat Recovery System 2013-01-0046

The optimum design process of the low-temperature condenser of a dual-loop waste heat recovery system with Rankine steam cycles for improving the fuel efficiency of gasoline automobiles has been investigated. The waste heat recovery system consists of a high-temperature (HT) loop in which water as the HT working fluid recovers waste heat only from the exhaust gas of about 700°C and a low-temperature (LT) loop in which a refrigerant as the LT working fluid recovers heat dissipation from the HT loop, and waste heat from the engine coolant of relatively low temperature. The low temperature condenser plays a role to dissipate heat from the system by condensing the low temperature loop working fluid sufficiently. However, the refrigerant has low evaporation temperature enough to recover the waste from engine coolant but has small saturation enthalpy so that excessive mass flow rate of the LT working fluid, e.g., over 150 g/s, causes the enormously large pressure drop of the working fluid to maintain the heat dissipation performance of more than 20 kW.

This paper has dealt with the scheme to design the low temperature condenser that has reduced pressure drop while ensuring the required thermal performance from the waste heat recovery system. For the purpose of the performance predictions and the parametric study for the LT condenser, we have developed a 1-dimensional user-friendly performance prediction program that calculates feasibly the phase change of the working fluid in the tubes. Sustaining the scale of the existing vehicle refrigerant condenser, the number of pass, arrangement of the tubes of each pass and the structural design to enhance the flow uniformity through all the tubes of the multi-flow type low temperature condenser were analytically investigated.