Experimental Investigation On Falling Film Flow And Heat Transfer Outside Horizontal Tube

Water film evaporative air cooler is a kind of device which can save energy and water. It is a kind of device combined water cooling and air cooling, heat and mass transfer. The main advantage is the evaporation of falling film to enhance heat and mass transfer. It is one important research direction for enhancement of heat and mass transfer.This paper based on the water film evaporative air cooler. Establish the experiment device with the single-tube and the single-sheet. Measured the distribution rules of the film thickness on the different angles(40°,90°and 140°) of the heat exchange tube and the film thickness on the different heights(10mm, 37.5mm and 65mm) of the sheet under the conditions of convection and heat transfer . Researched the impact of the falling film flow out of the horizontal tube and the sheet under the different conditions, for example different spray quantities, different diameters, different tube internal heat water temperature, forced ventilation and the natural convection. The datas indicated that, as the spray quantity increases, the film thickness increase. And the film thickness is different on the different angles of the tube and the different heights of the sheet. The impact of the film thickness is smaller under different diameters and different tube internal heat water temperature. In addition, the ruler of the film thickness is consistent under forced ventilation and natural convection. But the film thickness is thicker under forced ventilation.Researched the average heat transfer coefficient out of the horizontal tube and the sheet under the above factors. The datas indicated that, as the spray quantity increase, the average heat transfer coefficient out of the tube increases first and then decreases, and when the spray quantity is 0.200kg·m^-1·s^-1, the average heat transfer coefficient is largest. As the spray quantity increase, the average heat transfer coefficient out of the sheet is increase. As the diameter decrease, the average heat transfer coefficient out of the tube is increase. As the tube internal heat water temperature increase, the average heat transfer coefficient out of the tube and the sheet is increase. In addition, the average heat transfer coefficient out of the tube and the sheet is increase under forced ventilation compared with natural convection.Researched the relationship with the flow pattern of film and the heat transfer. Fixed the turning Re of laminar flow and turbulence. Used the same turing Re for different diameter to judge laminar flow or turbulence. The aim is make the judgement and calculation of film flow pattern easy. Fitting the relational of the Nu, Re and the Pr under the condition of convection and heat transfer out of the tube. Provide the basis for the heat transfer design of the water film flow out of the tube.