There is a growing demand from the industrial sector and the population to cover the need for water temperature increases that can be covered with systems such as heat pumps. The present research aims to increase the heat transfer to the working fluid in a collector/evaporator, part of a solar-assisted direct expansion heat pump. This research was developed using a numerical analysis and by applying computational fluid dynamics; different simulations were performed to compare the performances of collector/evaporators with models exhibiting variations in the cross-section profile under similar conditions. An average incident solar radiation of 464.1 W·m−2 was considered during the analysis. For the comparison, profiles with hexagon-, four-leaf clover-, and circular-shaped sections with floral shapes, among others, were analysed, resulting in a temperature increase at the outlet of the working fluid of 1.3 °C. In comparison, the collector/evaporator surface temperature varied between 4 and 13.8 °C, while the internal temperature of the fluid reached 11.21 °C. Finally, it is indicated that the best results were presented by analysing the profile corresponding to the circular section with the flower shape.