Heat transfer and pressure drop during condensation of low-GWP refrigerants inside bar-and-plate heat exchangers

摘要

This paper presents new experimental results of heat transfer coefficient and pressure drop measured during condensation of R1234ze(E) and R32 in a brazed aluminum multichannels test section with 1.6 mm hydraulic diameter at 40 °C saturation temperature, mass velocity from 55 to 275 kg m~(−2) s~(−1), heat flux up to 35 kW m~(−2) and a complete range of vapor quality. The test section displays parallel channels obtained through the bar-and-plate technology using perforated turbulators brazed to the aluminum plates. These are the first data of condensation in a similar geometry presented in the open literature. The measured heat transfer coefficients suggest that the condensation process is strongly affected by the surface tension effects in the whole range of operating conditions, while the effect of mass flux is very limited. This is related to the non-circular shape of the parallel minichannels. Condensation heat transfer has also been studied during flow of superheated vapor. The experimental data have been compared against prediction methods available in the literature. Fourteen models have been applied for the heat transfer coefficient, ten models have been applied for the pressure drop. Relevant suggestions are given for the design of condensers using such a technology.