Selecting and Optimizing a Heat Exchanger for Automotive Vehicle Rankine Cycle Waste Heat Recovery Systems

This paper contributes for the selection and optimization of an adequate compact heat exchanger (HEX) for an automotive vehicle Rankine cycle Waste Heat Recovery Systems (RC-WHRS). Both tube type and plate type HEX were considered. Among the different HEX designs available, a robust cross-flow tube heat exchanger (CFT-HEX), with the working fluid circulating inside the tubes was selected. The selected HEX accomplishes with the specific pressure drops limits on both exhaust gas and working fluid side. The compactness of the CFT-HEX strongly depends on the optimization of the HEX pre-heater section, which mainly depends on the augmentation of the working fluid heat transfer coefficient. The present study data reveals that a transitional flow regime with a working fluid Reynolds number, Re > 3200, allows a significant increase of the Nusselt number (Nu > 20) as compared to laminar flow regime.