Experimental Investigation of Heat Transfer Coefficients in a Plate Heat Exchange for an Organic Rankine Cycle

Enhancing the evaporator configuration of plate heat exchangers is essential for improving the overall efficiency of organic Rankine cycle (ORC) systems. To investigate the evaporator’s heat transfer characteristics, an experimental ORC test rig was developed. The experiments were conducted at saturation temperatures of 62.8–86.2 °C, mass fluxes of 5.0–16.6 kg/(m²·s), and heat fluxes of 3.1–9.2 kW/m², spanning subcooled boiling, saturated two-phase, and superheating regions. The heat flux showed minimal variation with heat source temperature, whereas higher mass fluxes resulted in substantial increases in generator power and thermal efficiency due to enhanced convection and vaporization. The overall and refrigerant heat transfer coefficients rise with heat source temperature and mass flux, peaking under moderate conditions and declining as the superheating region becomes constrained. Comparison with existing correlations reveals pronounced deviations, indicating their limited applicability under the present operating conditions. A nondimensional correlation was established using dimensional analysis and multivariate regression to predict heat transfer across the subcooled boiling, saturated two-phase, and superheating regions. The proposed correlation yielded a mean absolute percentage error of 15.9%, demonstrating good predictive accuracy and providing a reliable theoretical basis for performance evaluation and design optimization of plate evaporators in ORC systems.