Executive Summary : | Condensation of vapour is of importance in wide range of applications such as power plants, desalination plants, and fog-water harvesters. Enhancement of condensation heat transfer has the capability to substantially improve thermal efficiency and, hence, cost of energy consumption in these applications. Depending on the wettability of the condensing surface, condensation is categorized as either filmwise condensation (FWC) or dropwise condensation (DWC). In FWC, the condensate forms a liquid film on the surface. This liquid film act as an additional thermal resistance to heat transfer between the surface and the vapor. Whereas, in DWC, the vapor condenses in the form of distinct liquid drops. The DWC provides an order of magnitude higher heat transfer rate compared to FWC because of recurrent cycles of droplet nucleation, growth, coalescence, and departure from the surface. Previous studies have shown that it is difficult to sustain DWC for a long period. Sustenance of DWC depends on the efficient removal of condensed droplets from the surface for which it is essential to understand how these drops grow on different wettability surfaces. Investigation for understanding the dropwise condensation on flat surfaces have been carried out in the past. The population growth and population balance models were used to understand the growth of the droplets and overall heat transfer during the dropwise condensation respectively. However, the dropwise condensation studies on pipes has not been performed yet, despite the fact that the pipes are predominantly used during the condensation process in power plants and desalination plants. One of the complexities in studying the dropwise condensation on pipes is due to nonuniform droplet distribution on the surface of the pipe and there movement over the curved surfaces. These phenomenon make it difficult to predict the droplet number distribution on the surface of the pipes. In the present study, lattice Boltzmann simulations will be performed to understand the growth of the droplets on pipe surfaces. The study will also be used to understand the overall distribution of droplets along the circumference of the pipe and their shedding rates due to the incoming vapour flux. The data obtained from the lattice Boltzmann simulations will then be used in population balance model for studying the overall heat transfer on pipes for varying pipe radius, surface contact angle and the sub-cooling. |