School of Mechanical Engineering, Iran University of Science and Technology, Tehran, 16846-13114, Iran
The effects of different hydrophobic and superhydrophobic coatings of PDMS, TGIC, SiO2 and a commercial coating called Danphobix on the condensation heat transfer characteristics of the plates were investigated and compared with the uncoated surface. The initial investigation showed that the values of heat flux and condensation heat transfer coefficient of the plate with Danphobix coating are higher than other coatings. Then, the plates with the commercial coating Danphobix were investigated at five different thicknesses to enhance the condensation heat transfer coefficient. Scanning Electron Microscopy analysis of surface with Danphobix coating showed that the hydrophilic-hydrophobic parts of the generated hybrid surface are formed irregularly in a new intertwined manner. According to the obtained results, decreasing the initial thickness of coating to a definite value, the condensation heat transfer coefficient was augmented. By further decrease, the condensation heat transfer coefficient was reduced due to the elimination of the physical structures of the coating against steam. The highest values of condensation heat transfer coefficient and heat flux of plates with Danphobix coating, that was obtained at the coating thickness of 17 µm comprised 65.2% of the surface coating by Danphobix. The results indicated that the heat flux and condensation heat transfer coefficient values of the plate with Danphobix coating thickness of 17µm was increased by 1.97-2.14 times and 1.96-2.46 times compared to the non-coated plate, respectively. In what follows, in addition to the critical thickness, the critical area of the coated surface is also obtained.