Experimental study on film condensation of superheated vapour on a horizontal tube

Starting from a proposed theoretical two-phase boundary model for the film condensation of ambient air on a cryogenic horizontal tube (Zhao et al., 2014), we conducted an experimental study on the film condensation of superheated vapours for further study. Condensation experiments were performed for the R134a vapour with various superheating outside a horizontal tube cooled by inside flowing cryogenic nitrogen gas. The reduction of experimental data to obtain condensation-side heat transfer coefficient was accomplished by using two different approaches, individually, which were tube wall measurement technique and modified Wilson plot technique. The results obtained under different conditions were compared with each other, in which a certain divergence existed acceptably. The result shows that the condensation heat transfer coefficient increases by 9.79% when the superheating changes from 39.5 K to 131.9 K. Meanwhile, the condensation heat transfer performance becomes worse due to the combination of condensation and natural convection as the cooling capacity inside the tube is smaller than the critical heat flux. This phenomenon is only available for the condensation of superheated vapour especially for the higher superheating. The condensation heat transfer coefficients from experimental measurement in this paper are compared with the simulated results from the two-phase boundary model previously presented, and a good agreement is reached.