Experimental investigation of performance of plate heat exchanger as organic Rankine cycle evaporator

Abstract

In this study, the experimental investigation of a plate heat exchanger was conducted, which was used as an organic Rankine cycle evaporator. The heat exchanger performance was investigated at the low mass flux and moderate evaporation temperature ranges, as it was designed for a cascade heat utilization in a fourth-generation district heating and cooling system. The experiments were conducted under various operating conditions by changing the R-245fa mass flux, evaporation pressure, R-245fa inlet temperature, heat source inlet temperature, and heat source mass flux. Moreover, the heat transfer and pressure drop mechanisms were thoroughly investigated with an internal process analysis. The two-phase heat transfer coefficient exhibited a strong dependency on the heat flux, indicating that flow boiling heat transfer was mainly dominated by the nucleate boiling mechanism. When both the evaporation pressure and R-245fa mass flux were increased, the single-phase heat transfer accounted for a significantly large portion of the total heat transfer, leading to the rapid decrease in the heat transfer rate. The port and elevation pressure drops together accounted for 27–47% of the total pressure drop due to the low R-245fa mass flux range. With the heat source side variation, the two-phase heat transfer coefficient was more affected by the heat source inlet temperature than the heat source mass flux owing to the increase in the excess temperature. Additionally, the overall heat transfer coefficient strongly depended on the R-245fa side heat transfer coefficient, because the R-245fa had lower heat transfer coefficients than the heat source, even in the two-phase region.