Dropwise Condensation in Refrigerants: Experimental Setup Design

Abstract

Fluorinated refrigerants, widely used in refrigeration cycle applications, cause significant greenhouse gas emissions. In view of reducing environmental impact, natural refrigerants are applicable as an alternative. However, their imposed risks (flammability, toxicity & high pressure systems) raise safety concerns. These refrigeration cycle applications utilize a condensation process. By increasing the heat transfer coefficient, the damage potential can be reduced by decreasing the size of the condenser in its applications. Dropwise condensation has proven to significantly enhance the heat transfer coefficient relative to traditional filmwise condensation in steam applications. However, little research is conducted into the experimental heat transfer coefficient of dropwise condensation in refrigerants. Therefore, a setup is designed to estimate the heat transfer coefficient experimentally on different promoter layers. For derivative estimation, the total heat transfer rate, condensation wall temperature, and saturation temperature are needed. The optimal solution available to estimate these parameters is based on Fourier’s law of conduction in a designed test-section. Here, condensation takes place on one side and cooling on the other, causing heat transfer and a temperature gradient. By measuring the temperature at different points, the total heat transfer rate and wall temperature can be estimated. To supply saturated vapour, a pressurised loop is designed, including an evaporator, post-condenser, pump and coolant supply. While verifying the function of the test-section in a computational model, the resulting performance align with expectations. However, the one-dimensional model for estimation the heat transfer coefficient based on Fourier’s law of conduction, is not sufficient in accurately estimating the wall temperature. A temperature gradient occurs on the condensation surface, whereas the estimation model assumes a homogenous temperature. Therefore, the heat transfer coefficient of condensation will be severely underestimated at increased saturation and coolant temperatures.