Modelling and experimental analysis of finned-tube heat exchangers using the low-GWP refrigerants R290 and R454C

This thesis focuses on the modelling and experimental analysis of finned-tube heat exchangers operating with low-GWP refrigerants, with particular reference to R290 and R454C. The work is motivated by the ongoing transition of heating, ventilation, air-conditioning and refrigeration systems towards refrigerants with reduced global warming potential, while retaining adequate thermal performance and acceptable pressure drop. Numerical models are developed for both condenser and evaporator operation in HVAC&R applications. One-dimensional and two-dimensional formulations are considered: the former enables computationally efficient parametric studies, while the latter accounts for non-uniform air and refrigerant distribution across the heat exchanger, providing a more detailed description of local heat transfer and pressure drop. The models represent the distinct thermodynamic regions occurring during operation, namely desuperheating, condensation, subcooling, evaporation and superheating, and implement dedicated correlations for single-phase, two-phase heat transfer and pressure drop on the refrigerant side. The air-side is modelled by accounting for the finned-tube geometry and the interaction with humid air, including condensation of water vapour (dehumidification) during evaporator operation. A numerical predictions are compared with available experimental data to assess the reliability of the proposed models and to identify their main limitations. A sensitivity analysis is then carried out to assess the influence of geometric parameters, refrigerant selection and operating conditions on heat exchanger performance, enabling comparison between configurations and informing design choices, particularly for compact heat exchangers with small-diameter tubes.