Experimental study of horizontal flattened tubes performance on condensation of R600a vapor

An empirical setup has been established to study heat transfer and pressure drop characteristics during condensation of R600a, a hydrocarbon refrigerant, in a horizontal plain tube and different flattened channels. Round copper tubes of 8.7 mm I.D. were deformed into flattened channels with different interior heights of 6.7 mm, 5.2 mm and 3.1 mm as test sections. The test conditions include heat flux of 17 kw/m2, mass velocity in the range of 154.8–265.4 kg/m2s and vapor quality variation from approximately 10% to 80%. Results indicate that flattening the tubes causes significant enhancement of heat transfer coefficient which is also accompanied by simultaneous augmentation in flow pressure drop. Therefore, the overall performance of the flattened tubes with respect to heat transfer enhancement considering the pressure drop penalty is analyzed. It is concluded that the flattened tube with 5.2 mm inner height tube has the best overall performance. Due to the failure of pre-existing correlations for round tube condensation heat transfer, a new correlation is proposed which predicts 90% of the entire data within ± 17% error.