Experimental and numerical investigation of pillow-plate condensers for heat pump applications

This thesis is based on the experimental and numerical analysis of two types of condensers with an innovative and scarcely studied geometry. These condensers consist of walls made of "embossed" plates through which the gas R515B flows, while the secondary fluid used is water. The first part of the thesis focuses on experimental data measurements of the two condensers in the laboratory, paying attention to the variation in vapor quality at the inlet and outlet and aiming to maintain a constant heat flux exchanged. Subsequently, additional measurements were carried out by varying the volumetric flow rate of the incoming water and keeping several parameters constant "in turn", such as the inlet water temperature, the refrigerant mass flow rate, and the superheating of the gas at the inlet. Following this, a data analysis was performed to understand the behaviour of the two prototypes as different variables were varied. It was found that different values of superheating at the inlet do not affect the heat flux value with the same water flow rate. Moreover, it was observed that counter current flow results in a higher heat flux for the same water flow rate compared to co-current flow and that the heat flux itself increases with the refrigerant mass flow rate. However, at relatively low water temperatures (30 °C rather than 35°C), the refrigerant at the outlet becomes subcooled, leading to a constant heat flux even as the water volumetric flow rate increases. A subsequent step was also carried out: using Ansys Fluent, a simple 3D model of a condenser was created, aiming to calculate the water-side heat transfer coefficient and, from that, to derive the gas-side heat transfer coefficient. Finally, we will evaluate, after all the final considerations, if the use of these condensers is suitable for heat pumps and whether their excellent efficiency can justify their high costs, resulting from the material used (stainless steel) and the geometry of the embosses created via laser technology.