Parametric Investigation of Organic Rankine Cycle Evaporator for Low Temperature Applications

Abstract

The present work deals with the development of thermodynamic model of low temperature basic Organic Rankine Cycle (ORC) system and a chevron plate heat exchanger evaporator sub-model using Engineering Equation Solver (EES). Work output is evaluated using the ORC thermodynamic model, while the evaporator sub-model calculates the total surface area of the heat exchanger. Using these mathematical models, the effect of evaporation pressure, expander inlet temperature and pinch point temperature difference (PPTD) on the network output and evaporator cost are studied. In addition to this, the effect of plate spacing and plate width of chevron plate heat exchanger on pressure drop and evaporator cost are analyzed in detail. Finally, thermodynamic and geometric optimization is carried out using genetic algorithm to identify the optimum parameters at which the network output is maximized and pressure drop in the evaporator is minimized. Sensitivity analysis showed that optimum evaporator pressure existed at which network output is maximum. Thermodynamic optimization showed that work output was maximum (5.03 kW) at evaporator pressure of 5.77 bar. No improvement in the work output was seen with increase in PPTD and expander inlet temperature. Increase in plate width and plate spacing led to increase in evaporator cost and decrease in pressure drop.