Parameter study on the performance of dropwise condensation

New amorpheous hydrogenated carbon films have been applied successfully to promote dropwise condensation (DWC) of steam on metallic surfaces at atmospheric pressure. The highest heat transfer coefficients have been measured for completely coated surfaces, maximum contact angle, largest thermal conductivity of the base material, vertically oriented wall and minimum wall height. The effect of these parameters on the DWC performance is evaluated quantitatively. The investigation of partly coated surfaces shows, that even for a small portion of coated surface (approx. 20 % DWC and 80 % filmwise condensation (FWC)) still nearly maximum heat transfer is achieved. This phenomenon is explained qualitatively by the application of numerical simulation of the local condensation process using the finite element method (FEM). Furthermore, this analysis technique also explains the dependence of DWC heat transfer on the thermal conductivity of the base material being coated.