Numerical Study On The Flow And Heat Transfer Characteristic For Outward Convex Helical Corrugated Tubes

Energy is the economic lifeline of a country, and closely related to people’s lifelevel and living environment, plays an important role in the society as a whole. With therapid development of the national economy, energy shortage has become a key problemthe world is facing today. Heat exchanger is indispensable equipment in the field ofindustrial production. The development of compact type and high efficiency new type ofheat exchange equipment has become one of the important methods to solve theproblem of energy. This subject puts forward the new type of a heat exchangecomponent to improve the efficiency of heat exchanger. According to the outwardconvex helical corrugated tube, the main contents are as follows:(1)The CFD numerical simulation software is used to calculate the smooth tube ofa two-dimensional axisymmetric model and three-dimensional model, analyzing gridindependence, determining the optimum thickness of the first layer of the grid andmainstream area grid spacing. Compared the simulation result of2d and3d model withempirical formulas, the correctness of the numerical model was verified. In addition,comparing to the3d model,2d axisymmetric model can effectively reduce calculatedamount under the premise of almost no loss of accuracy.(2)The heat exchange performance of the outward convex helical corrugated tubeis researched, studying the influence law which the helical pitch P, depth H andchamfering r to its performance, and comparing the heat transfer characteristic withcorrugated tube and smooth tube. The result shows that heat transfer performance of theoutward convex helical corrugated tube increases by18.4%~27.3%. The heat transferperformance decreases while the helical pitch P increases; increasing the helical depthH is not only improve the heat transfer performance of helical corrugated tube, but alsoincrease the resistance performance; and increasing helical chamfering r can reduce theresistance performance with the condition of heat transfer performance is almost thesame.(3)The intensive study on the parameters of flow and heat transfer of the outwardconvex helical corrugated tube (velocity field, temperature field, pressure field,turbulent kinetic energy and turbulent kinetic energy dissipation rate) reveals itsstrengthen heat transfer mechanism, and with the flow and heat transfer mechanism ofcorrugated tube and smooth tube are analyzed in comparison. It investigates theinfluence of the helical pitch P, depth H and chamfering r of outward convex helicalcorrugated tube to flow and heat transfer performance. The research result shows thatthere is a detached vortex formed in the outward convex helical corrugated tube whichcauses by the change of internal pressure gradient, the vortex will destroy the velocity and thermal boundary layer of fluid and thermal boundary layer, leads to increase theeffect of strengthening heat transfer.(4)In this thesis, the outward convex helical corrugated is optimized design byusing the response surface method, determined the relationship between the impactfactors and the response values. Regression model is obtained by analysis of variance ofthe response value of linear, quadratic and interaction of significance, thus thecorresponding response value of binary regression equation can be got. Responsesurface analysis is carried out to study two interactions various influencing factors,determining the different response values of each influencing factor to the influence ofsignificant size. It gets the optimal synthesis in the thermal efficiency η curve ofoutward convex helical corrugated tube by pareto, and η trends to increases before itdecrease with Nu_h/Nu_s, when η is equal to1.5, Nu_h/Nu_sreached the maximum.