The Flow And Heat Transfer Coupled Calculation Model For Helical Baffled Heat Exchangers

Shell and tube heat exchanger is the most widely used heat exchanger in industrydepartments, with the development of heat transfer enhancement and the implementof saving energy and reducing emission strategy in China, many novel shell and tubeheat exchangers, including helical baffles heat exchangers, aimed at energy saving aredeveloped and applied，However, as the big differences in the structure, the researcheson the new type heat exchangers are always self-contained，In this paper, The flowand heat transfer coupled calculation model for shell and tube heat exchanger apply toall kinds of shell internal component was present, besides, with the application of newmodel, the paper also analyzed the heat transfer enhancement mechanism in thehelical baffled heat exchanger under the new evaluation system， NumericalSimulation and experiment were applied as the research method in this paper，themain contents are summarized as follows:The flow field based calculation model is established based on the streamanalyze method used in the segmental baffles heat exchangers，Firstly, the influencemechanism of the internal component in shell side to the flow field was summed up,included the divide of flow streams, the adjust of flow angle, and the change ofchannel Reynolds number; Secondly, proposed the mathematical description for theinternal component according to the stream dividing and flow field influence in thedivided channel; Lastly, take the qualitative analysis to the effect of local flow field onthe heat transfer and pressure drop of heat transfer surface.Established2D physical tube models for fluid flow and heat transfer withdifferent helical angles, according to the size of Reynolds number, the Laminar modeland (RNG) k-ε were adopted in the simulation，The conclusion included:1, the heattransfer performance increases with helical angle arises;2, in laminar flow, the tubeheat transfer performance is controlled by the thermal boundary layer thickness on thetube surface, in the turbulence flow, which is dominated by the ratio of high turbulentintensity fluid in the near outer space of the for heat tube;3, the resistanceperformance degrades as the increase of helical angles;4, under the same localReynolds number, the incident angle with45°has the best performance consumptionratio, and the performance consumption ratio increases under the same inlet velocity for spiral flow;5, finally the heat transfer correlations and local resistance correlationswith different incident angles were present, and the quantity correlations for the localflow field to the local heat transfer and pressure drop was summed up.Compared the stream dividing results in the shell side of helical baffles heatexchanger and segmental baffles heat exchanger, the factors causes the leakage streamflow F through the axis of heat exchanger to infer the reason of the was present，Thenumerical simulation for helical baffles heat exchanger with clearances between tubesand baffles and clearances between baffles and shells proceed，The simulationconclusion were as follows, first, as the increase of Reynolds number, the ratio ofmain flow stream B falls, and the ratio of the leakage stream flow F falls, besides, asthe helical angle raises, the ratio of effective flow steam decreases, and the ratio of theleakage stream F increases; second, the correlations for the ratios of all flow streamsunder different Reynolds numbers and helical angles were present, and the flow fieldbased calculation model for helical baffles heat exchanger was amended.Established the numerical model for helical baffles heat exchanger andsegmental baffles heat exchanger without the inlet influence, the reliability andaccuracy of the model was demonstrated by comparing with the relative experimentresults，Via the simulation, the following conclusions were drawn: firstly, the helicalbaffle forms channels for shell side fluid to moving spirally and constantly, reducesthe local resistance of the flow path dominantly, and enhances the heat transfer withthe maintain and even increase the Reynolds number of the main flow stream channel,results in the boost of performance consumption ratio, however, in the laminar flow,the spiral flow path vanishes as the big increase of leakage stream flow; secondly, asthe comprehensively consideration of the length (heat transfer area), pressure dropand ratio of heat exchanger, the appropriate helical angles for fluid with differentviscosity was present.