Simulation And Optimization Of Radical Heat Pipe Heat Exchanger With Different Fins

Abstract:Radial heat pipe heat exchanger,which is used in many fields, such as metallurgy and chemical industry,especially in low temperature waste heat recovery,not only has the advantages such as high heat transfer efficiency, low pressure loss and high reliability,but also can solve the problem of low-temperature corrosion which often happens in traditional heat exchangers. Researches on structure optimization of radial heat pipe heat exchanger are significant in heat exchange efficiency improvement, energy conservation and environment protection.Radial heat pipe heat exchanger was studied in this dissertation, and the flow field, pressure field and temperature distribution in shell side were analysised based on FLUENT software. The heat transfer characters influenced by fin parameters and pipe pitches under different fins, namely rectangle, triangle and parabolic, was researched with PEC as the heat exchanger evaluation criteria. Structure parameters were optimized by orthogonal experiments under different fins and the optimal type of fins and corresponding structure parameters were obtained. Main research work and findings are as follows:(1) The flow field, pressure field and temperature distribution in shell side of radial heat pipe heat exchanger were studied by using numerical simulation method. The results show that:there is a couple of vortexes rotating in opposite directions at the recirculation zones of upstream heat pipes and periodic shedding which can lead to bias current at the recirculation zones of downstream. The pressure on both sides of heat pipes perpendicular to the flow direction changs constantly, causing vibrations in heat exchanger. The maximum pressure points are at the stagnation points in front of the first row pipes, the minimum pressure points at the smallest flowing section area between the last row pipes. The gas flows fast on the windward side of heat pipes, which leads to dense isotherm and heat transfer enhancement, and the contrary happens on the leeward side. Low-temperature corrosion tends to occur at the recirculation zones in the last row pipes, so some effective measures should be adopted to prevent it. (2) The heat transfer characters influenced by fin parameters and pipe pitches was researched under different fins. The results show that: the fin parameters and pipe pitches impose remarkable influence on the heat transfer characters. The changing rules of integrated performance PEC with some parameter are consistent under different fins in a specific range. The PEC increases first and then decreases with the increasement of fin spacing, fin thickness, horizontal and longitudinal spacing of heat pipes, and it decreases with the increasement of fin height. The optimal range of the heat exchanger structure parameters are as follows:the fin spacing is from125mm to130mm, fin thickness1.0mm-2.0mm, horizontal spacing125mm-135mm, longitudinal spacing105mm-125mm, and the fin height should be half of the outside diameter of the heat pipe.(3) Five structure parameters of radical heat pipe heat exchanger with three different fins were optimized by orthogonal experiments and the optimal shape of fins and the corresponding optimal structure parameters were obtained with PEC as the optimization goal. The parabolic fin is optimal and the corresponding structure parameters are as follows:the fin spacing is7mm, horizontal spacing135mm, longitudinal spacing125mm, fin height22mm and fin thickness1.0mm-2.0mm. The value of PEC is25.0percent higher than standard operating condition.42figures,13tables,66references...