Falling Film Evaporation, Vertical Corrugated Plate Conduit, Numerical Simulation, Heat Transfer Enhancement, Thermal Spray Metal Coating
In falling film evaporation process the heat is transferred from the condensing fluid to the liquid flowing over it. Falling film types of evaporators are widely used in refrigeration, desalination, petroleum refining, chemical industries, etc. Compared to flooded type evaporators, falling film evaporators need less amount of refrigerant and will give higher heat transfer rates even at lower heat fluxes. Tube geometry and tube size have an important role on the performance of the falling film evaporators. Geometry of the tube can be varied by heat transfer enhancing techniques and also by changing the shape of the tube. Thermal spray metal coating is a heat transfer enhancement technique which is done by spraying molten metal on any heat transfer surface. Vertical plate with sinusoidal corrugation is a surface enhancement technique which can be cheaper, compact and lighter for falling film evaporation compared to shell and tube configuration. This paper presents a two dimensional CFD study of water falling film evaporation on a thermal spray metal coated vertical corrugated conduits. Two-phase flow simulation is done by using a finite volume method based commercial software, with turbulence modeling which is done by k-Â two equations with shear stress transport (SST). Sinusoidal corrugations with different porosity have been selected for the study. Evaporation and heat transfer during falling film evaporation are included through user defined functions (UDFs). Effect of Reynolds number (Re), wall superheat and surface roughness on heat transfer coefficient is presented. Surface roughness is varied from 0.33 to 4.73. Re is varied from 500 to 2000 for two Prandtl numbers 2.9 and 3.4. Wall super heat is varied from 2K to 10K. The numerical results are compared with the results of horizontal circular tube falling film evaporation from literature. An enhancement of film heat transfer coefficient is observed for the vertical corrugated plate conduits.