Propane, condensation, pressure drop, minichannel
The use of propane as a refrigerant is a good opportunity to develop environmentally friendly heat pump and air-conditioning equipment, since the direct effect on the anthropogenic global warming due to atmospheric emissions is almost completely avoided, while the indirect effect can be reduced by exploring the favourable thermodynamic properties of these fluids. Because of flammability, charge minimization is a major design objective for such equipment using hydrocarbons. From previous experience, it appears that the estimated charge of unitary air conditioners is expected to be mainly trapped in the heat exchangers. In this regard, microchannel technology appears to be a very good opportunity to minimize the charge without energy performance loss. This was demonstrated at the University of Padova in a heat pump with 100 k-W heating capacity, using minichannel shell-and-tube heat exchangers within the European project Sherhpa. Nevertheless, a very limited number of data of condensation of propane in minichannels is available to validate predicting correlations. In this paper, the local heat transfer coefficient measured during condensation of propane 0.96 mm diameter circular minichannel is reported and compared versus available correlations. Tests are carried out on the experimental apparatus available at the Heat Transfer Lab of the University of Padova. During condensation tests, the heat is subtracted from the fluid by using cold water. The heat transfer coefficient is obtained through the measurement of the local heat flux and the saturation-to-wall temperature difference. Tests are carried out at mass fluxes ranging between 100 and 800 kg m-2s-1. Since the saturation temperature drop directly affects the heat transfer rate, also pressure drop during adiabatic two phase flow of propane is measured and compared to predicting models.