Effects of EHD on heat transfer enhancement and pressure drop during two-phase condensation of pure R-134a at high mass flux in a horizontal micro-fin tube

Effects of electrohydrodynamic (EHD) on the two-phase heat transfer enhancement and pressure drop of pure R-134a condensing inside a horizontal micro-fin tube are experimentally investigated. The test section is a 2.5 m long counter flow tube-in-tube heat exchanger with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The inner tube is made from micro-fin horizontal copper tubing of 9.52 mm outer diameter. The electrode is made from cylindrical stainless steel of 1.47 mm diameter. Positive high voltage is supplied to the electrode wire, with the micro-fin tube grounded. In the presence of the electrode, a maximum heat transfer enhancement of 1.15 is obtained at a heat flux of 10 kW/m2, mass flux of 200 kg/m2 s and saturation temperature of 40 °C, while the application of an EHD voltage of 2.5 kV only slightly increases the pressure drop. New correlations of the experimental data based on the data gathered during this work for predicting the condensation heat transfer coefficients are proposed for practical application.