Numerical Investigation On The Heat Transfer And Fluid Flow Characteristic Of Finned-tube Heat Exchanger And Direct Air Cooled Condenser Unit

In this paper, different forms of finned-tube heat exchangers used in direct air-cooling system in power plant were simulated, obtained the wind flow and temperature fields with different frontal wind velocity, the flow and heat transfer characteristics in the air-side were studied and make a horizontal comparison. At the same time, have a numerical simulation study on condenser unit, analysis the influence of different temperature, wind speed and other environmental parameters to its heat transfer and flow.For various forms of finned-tube heat exchanger, the heat transfer coefficient and the pressure drop in the air side increase with the frontal wind velocity. The fin pitch influenced the performance of single row flat wave-finned tube was optimized. The j to f factor ratio reaches maximum when fin pitch is 2.1 mm when other geometry structure parameter are given. The numerical analysis were performed for the air-side flow and heat transfer characteristics of double-rows rectangular-fin elliptic-tube, which on the surface of fins with interrupted holes, and simulated results revealed that relative to the first-row fin, the edge temperature of the surface dropped even more evident on the second-row fin, and it means that the efficiency of fins has been improved greater. The existence of interrupted holes have obvious impact on the destruction of boundary layer and the disturbance on the flow, played a role in enhancing heat transfer, but have little impact to the back flow zones at the tail of elliptic-tub. Study the change of heat transfer and resistance performance, with different surface front velocity to the three rows finned-tube heat exchanger. Had a horizontal comparison of the flow and resistance characteristic of tube bundles which with different structures, and make a conclusion that the heat transfer coefficient and the flow resistance of three rows fin-and-tube are relatively small, and it is fits well to the references [3]. As it's difficult to apply the 3D physics-mathematics models that complete agreement to the actual existence for the single row and double rows finned-tube heat exchangers, so the results can not be completely accurate reflection of their flow resistance and heat transfer performance, and need for further research. But the flow and heat transfer performance of single-row fin-and-tube are better than the double rows ,from the analysis to existing results and trends. Based on existing research, have a reasonable simplified to the air-cooled condenser unit, introduce the concept of porous media to replace the actual finned-tube, take the heat exchange model to simulate the internal heat exchanger of air-cooled unit, and analyzed the impact from different environmental parameters to the flow and heat exchanger of air-cooled unit. The results showed that with the increase of environment wind speed, heat flow of air-cooled unit and mass flow through the fan are all significantly reduced, the Phenomenon of the return of hot air is aggravated; with the increase of environment temperature, shaft power of the fan is decreases, air transport capacity of the fan is decline, and heat emission of air-cooled unit reduced.The current results not only have great significance to the design and optimization of the finned-tubes and the overall simulation of Air-cooled Island and power plant, but also serve as a theoretical basis for the fin-and-tube heat exchangers applied in engineering and as the reference for designing and operation of direct air-cooled condenser.