Numerical Study Of Flow And Heat Transfer Characteristics In The Fin Side Of The Intermittent Wave Finned Flat Tube Heat Exchanger

With the rapid development of science and technology, economic and social progress increasingly, expand of industrial layout, now the usage of water resources are more in industry and people’s life. Thermal power unit is given priority to with coal in our country,these units need a lot of water. The water resources are insufficient in our country, and the development of electric power industry is fast. The construction scale of electric power industry has increased year by year, so we must found the way of save water in electric power industry. Since the late 1930 s, electric power industry has using air as cooling medium,although air cooling capacity is much smaller than water, but it is cheaper and obtain at any time, this is the direct air cooling technology. Because direct air cooling technology is a kind of economy, water saving, environmental protection and good performance of heat exchange cooling technology, in recent years, direct air-cooling technology has been widely used in air-cooled condensers of a power plant.The heat transfer performance of fin play a decisive role in air-cooled condensers of air cooling system. The wave-finned flat tube heat exchangers are widely used in direct air cooling system of power plant. Compared with the rectangular finned elliptical tube heat exchanger, the heat transfer capacity is greatly improved of the wave-finned flat tube. The study of flow and heat transfer characteristics in the fin-side of the intermittent wave-finned flat tube heat exchanger in direct air-cooled condensers(ACC) requires accurate simulations.In this paper, the mathematical model are established of the wave-finned flat tube in power plants. The flow and heat transfer characteristics in the fin side of the wave-finned flat tube heat exchanger are numerically studied and compared with experimental results. Numerical simulation for various geometrical parameters of flow and heat transfer performances in the fin-side of intermittent wave finned flat tube, including the fin spacing, the wave spacing, the wave amplitude are systematically designed. The influence of the fin spacing, the wave spacing, the wave amplitude and Reynolds number on the flow and heat transfer performances is investigated also. It is shown that when fluid flows through the wavy channels, secondary flow can be generated. The characteristics of the Nusselt number and friction factor of the wavy channels are analyzed, respectively. Correlations of the Nusselt number and friction factor are obtained by fitting the numerical results using the multiple regression analysis methods. The modified formula for the fin-side calculation is more reliable.The results show that the intermittent wave finned than straight fin can significantly increase the heat transfer. The wavy channel of the intermittent wave finned can produce the longitudinal vortices and the span direction vortices. The longitudinal vortices and the spandirection vortices can enhance heat transfer. When the fluid flows through the wavy channel,the direction of fluid flow changes, the disturbance of the fluid increased, so the capability of heat transfer enhanced. Num, Seml and Sems increase with the increasing of fin spacing. Num and Sems increase with the increasing of the wave spacing, Seml decrease with the increasing of wave spacing. Num and Seml increase with the increasing of wave amplitude, Sems decrease with the increasing of wave amplitude. The suggestions of the best fin spacing, wave spacing,wave amplitude for improving the heat transfer performance in the fin-side of intermittent wave finned flat tube are obtained. Under the condition of the paper, JF gets the maximum value when the fin spacing is 3.0 mm, wave spacing is 9.5 mm and wave amplitude is 2.3 mm.The linear fitting equation includes all the parameters that relate to the performance of heat exchanger and can be used for the design process of snake intermittent wave-finned flat tube heat exchanger. It can be applied directly to the design of a flat tube bank fin heat exchanger and also useful in engineering applications.