Refrigerant flow and heat transfer prediction for propane in heat pump applications

As global warming intensifies, the heating and cooling sector is turning to heat pumps as sustainable alternatives. The phase-out of high global warming potential (GWP) refrigerants is driving the transition towards natural refrigerants, such as propane, which have significantly lower GWP. However, the high flammability of propane introduces new safety challenges, requiring system modifications to comply with stricter safety regulations. One approach to address these concerns is reducing the refrigerant charge while developing more energy and material efficient components. In this context, multiport tube heat exchangers are replacing conventional round tube designs as evaporators. These heat exchangers work with lower refrigerant charge, but they are prone to flow maldistribution, negatively impacting the system performance. To mitigate this, standard distributors alone are insufficient, but are installed in combination with headers. The design of the header is critical in improving the system efficiency, making it essential to investigate the flow behavior within the header. Furthermore, relevant experimental data are scarce in the current literature. This research aims to bridge this gap by developing experimental correlations for heat transfer and pressure drop during flow boiling of propane in multiport tube heat exchangers. Additionally, the distribution of the two-phase refrigerant within both the header and the heat exchanger will be investigated to better understand maldistribution effects. The findings will be used to calibrate and improve models for designing headers and heat exchangers, enhancing the reliability of simulations tool and reducing need for trial and error in design optimization. Specifically, this study focuses on operating conditions with mass fluxes between 5 and 50 kgm2/s, heat fluxes ranging from 0.3 and 1.3 kW/m2 and saturation temperatures between -20 and 5 °C – conditions currently unexplored in the literature.