Heat transfer in a round channel with circulation of a non-azeotropic mixture

Abstract

Mixtures are widely used as refrigerants and heat carriers in various energy systems. When a non-azeotropic mixture boils, a light-boiling component releases intensively, which leads to a change in its concentration both in the liquid and vapor phases. The studies were carried out using a non-azeotropic alcohol-water mixture with a mass concentration of ethanol of 20% in a round stainless steel channel. The inner diameter of the channel was 7.6 mm; the wall thickness was 0.2 mm. In this series of experiments, the absolute pressure in the vessel was maintained within 0.050.001 MPa. The range of liquid mass flow rates through the channel was 44–46 kg/m2s; the heat flux density was 1260–11981 W/m2. The wall temperature was measured at 10 points on the lower generatrix of the channel and at 3 points on the upper generatrix. It is shown that with a phase transition, the heat transfer coefficient on the upper generatrix of the channel is significantly higher than that on the lower generatrix of the channel. The heat transfer coefficient on the lower generatrix in the single-phase flow is approximately twice as high as in the two-phase flow.