EXPERIMENTAL VERIFICATION OF A NEW APPROACH FOR FILM CONDENSATION HEAT TRANSFER ENHANCEMENT OF ETHYLENE GLYCOL VAPOUR

In order to investigate the effect of surface-free-energy difference of condensate and solid surface, defining as Δσ=σ_l-σ_s, on the condensation pattern states and the heat transfer performance, two critical values of the surface-free-energy difference are proposed to classify the vapor condensation pattern states into film, mixing and perfect dropwise modes. Consequently, new condensation heat transfer enhancement mechanism in term of the surface-free-energy difference can be concluded.
The influence of free energy difference of solid surface and liquid on filmwise condensation heat transfer is studied by means of the ethylene glycol vapor condensation on surfaces of ion-implanted nitrogen surface, mechanical polishing surface and DLC surface on the substrates of copper and brass plates, respectively. The results obtained from the experiences are higher than the calculated results of classic Nusselt model, indicating that the specially treated surfaces with lower free energy takes an important role not only for promoting dropwise condensation mode, but also for enhancing the film condensation heat transfer.