The Optimization And Evaluation Of Convective Heat Transfer For Single Phase In Tube

Along with the worldwide energy shortage increasingly more serious, heat transfer enhancement technologies with energy saving-orientation seize people’s extensive attentions and gain rapid development. Especially for our country, industrial energy saving is priority for all at current. In our country’s industry, the proportion of heat transfer crafts and devices in the energy utilization process is more than90%. Therefore, active optimization design for the basic convective heat transfer problem is discussed in this thesis, and the flow field structure with excellent comprehensive heat transfer and flow resistance characteristics is expected to obtain.On the basis of existing entropy generation minimum principle and entransy dissipation minimum principle, the power consumption minimum principle and heat consumption minimum principle are proposed in this thesis. Optimal field equation for convective heat transfer can be derived by functional variation and seeking for extreme value. It can be found that from the numerical solution, longitudinal swirl flow structure with multi-vortexes appears in the flow field of pipeline flow. Compared with the heat transfer and resistance characteristics in bare tube without optimization, it can be found that the multi-vortexes flow structure has outstanding comprehensive heat transfer effect. Specifically, when the Re number is200for the laminar flow, the the Nusselt number can be increased to170%, while the resistance coefficient is only increased less than10%compared with the bare tube; when the Re number is20000for the turbulent flow, the the Nusselt number can be increased to15%, while the resistance coefficient is only increased to25%compared with the bare tube.Through adding component which can disturb the fluid in the core flow inside tubes in this thesis, the manner and principle of heat transfer enhancement based on fluid is proposed in this thesis. Dividing flow area inside a tube, disparate optimization objects and constraint conditions are applied in different flow area, and then, optimization method is obtained which can support above-mentioned principle. Also, a superduper numerical solution is achieved, whose increasing range of Nusselt number is three times more than increasing range of resistance coefficient comparing with fluid flow in smooth tube without optimization. Under the guidance of the principle of heat transfer enhancement based on fluid, heat exchanger with a kind of vane-type spoiler insets for the sake of heat transfer enhancement among pipes inside the tube-and-shell heat exchanger is presented in this thesis. The turbulent simulation results of the vane-type spoiler heat exchanger show that, when Re number is in the scope of3000-21000, the heat transfer coefficient increases by10%-60%while the resistance coefficient decreases by0%-50%compared with rod baffle heat exchanger. Also, the comprehensive performance evaluation criterion of vane-type spoiler heat exchanger relative to rod baffle heat exchanger reaches up to1.5superlatively.In addition, based on the heat consumption characterization of irreversibility dissipation loss in heat transfer process, efficiency of heat transfer process is proposed in the view of the second law of thermodynamics in this thesis. It can be inferred from the numerical calculation, the efficiency of heat transfer process suggested in this thesis can guide the optimization design of convective heat transfer well.