Heat Transfer and Pressure Drop during Circulation of Non-Azeotropic Mixture in Heated Channel with Spiral Intensifiers

Abstract

Mixtures are widely used as refrigerants and coolants in various energy systems. The thermophysical properties of a mixture differ from the properties of its individual components. This paper presents the results of a study of the intensity of heat transfer to a non-azeotropic alcohol-water mixture with a highly volatile component with mass concentration of 30% during forced circulation in a circular channel with spiral intensifiers with a hydrophobic coating. The experiments were carried out in a closed circulation circuit at a pressure of 0.03–0.04 MPa in the storage vessel. The test section was a stainless steel tube 2 m long with internal diameter of 7.6 mm and wall thickness of 0.2 mm. The heating was result of electric current flow in the tube wall. The spiral intensifiers had a winding pitch of 4 mm, and the thickness of the fluoroplastic coating was 0.9 mm. The experiments were carried out at mass flow rates of 36–450 kg/m². The heat flux density range was \(8000 < q < 32000\) W/m². The pressure drop in this test section was measured in single-phase and two-phase flow regimes, and the dynamics of the pressure drop during the formation of a two-phase flow under various operating parameters was shown. The use of the spiral intensifiers with a hydrophobic coating during circulation of the non-azeotropic alcohol-water mixture (30%) in the circular channel at channel wall temperatures below the saturation temperature of this mixture has led to the formation of a significant amount of the vapor-gas phase in the flow. The appearance of the vapor phase in the flow reduced the pressure drop in the heat-release section with the spiral intensifiers. At almost complete transition of the flow into the vapor phase at the outlet from the section, the pressure drop increased tenfold compared to the pressure drop in the liquid phase flow at the same mass velocity of the flow.