Numerical Study On Flow And Heat Transfer Of Air Across Rectangular Plate Fin-and-tube Heat Exchangers

With the rapid development of science and industrial technology and the increasingly scarce energy resources, the heat transfer of heat exchange equipment is widely used in various fields and enhancement technique research has become more and more urgent. The method of expanding the heat transfer surface to enhance the convective heat transfer coefficient of the lower side in heat exchanger is the most simple and common one among all those numerous enhanced heat transfer technologies. The finned tube heat exchanger is a type of heat exchanger by extending heat transfer area which was widely used in the field of power, energy, metallurgy, chemical industry, air conditioning, refrigeration fields and so on. The finned tube is the most commonly used method to enhance heat transfer in all kinds of pipe heat exchanger surfaces. The shape of fin of finned tube heat exchanger is rectangular, circular, corrugated, seam and so on. The straight fin is widely used in heat-exchange equipment of the refrigeration, ventilation, air conditioning, automobile etc, because the straight fin is convenient in processing and manufacturing and easy in assembly and not easy to deform in the use process. The thesis conducts three dimensional numerical simulations for the characteristics of the steady state, the heat transfer and fluid flow resistance of incompressible air inside the tube of plate-fin and tube heat exchangers by using the commercial CFD software. The paper researches the effects on convective heat transfer and fin efficiency of fin surface by changing the position of the tube relative to the fin leading edge. Through the analysis of numerical simulation, the paper gets the conclusion that the effects of the inlet velocity and the different position of the tube center distance away from fin entrance (l/d) on flow and heat transfer; and also gets the relation between the flow resistance coefficient (f) and average Nusselt number (Nu) of the fin and tube surface and the Reynolds number (Re) and the tube relative position(l/d) change. The best structure type of the six different tube position(l/d) is obtained for different Re and spacing of fins by comparing the overall heat transfer performance index and fin efficiency. The reliability and validity of the results is examined by field synergy principle analysis at last. In addition, through analyzing and comparing the change of the fin aspect ratio under the same area of fins and analyzing its effect on the convective heat transfer, the fins efficiency and flow resistance of the fin surface, the paper gets the optimum heat transfer performance of the fin aspect ratio structures, which provides reference for the design of straight fin tube.The simulation results indicate that the change of the position of the fin tube has a quite significant impact on the flow and heat transfer in the fin channel and making the fin tube arranged away from the fin leading edge can improve number of Nu and the reduced flow resistance coefficient, but the fin efficiency doesn’t increase gradually with the tube away from the fin leading edge and there is an optimal position of fin tube that makes the effect of heat transfer to be best fin tube. There are vary characteristics of flow and heat transfer in the structure of the different fin aspect ratio, the best structure type of the fin aspect ratio is1to1.5by comparing the overall heat transfer performance index and fin efficiency. In this fin aspect ratio range, the fin efficiency and heat effect is the best.