Numerical Simulation And Experimental Study On Convective Heat Transfer Of Shell Side In Special-shaped Tube Heat Exchangers

Shell and tube heat exchangers are widely used nowadays. The efficient heatexchange tube has been a hot research, and the researches were mainly focused on theheat transfer enhancement of tube pass. However, the overall heat transfer coefficientis subject to a lower convective heat transfer coefficient of shell side. Thusstrengthening the convective heat transfer of shell side plays an important role inimproving the overall heat transfer coefficient.The impacts of structural parameters on the heat transfer characteristics,resistance characteristics and comprehensive performances have been analyzedthrough numerical simulation, and the own characteristic of each tube has been gotthrough the comparison of the flow field distribution. The relationships betweenboiling heat transfer coefficient and the influences factors (for example, the flux andtemperature of heat source flux and working fluid flux) has been studied. The twophase flow patterns were recorded by high speed camera in the visualizationexperiments. The conclusions can be summarized as follows:(1) The magnitude and direction of velocity of corrugated and nodal tube changeperiodically, the speed change rate of horizontal grain tube is not obvious for its smallgroove depth. Corrugated tube performs best in heat transfer enhancement. However,higher heat transfer enhancements are at the expense of higher pressure losses. Thepressure loss of horizontal grain tube is much smaller than that of corrugated andnodal tube.(2) For corrugated tube, when the heat transfer performance is selected as theobjective function, the factors sorting should be D2>R1>R2; when the pressure loss isselected as the objective function, the factors sorting should be D2>R1>R2; when thecomprehensive performance is selected as the objective function, the factors sortingshould be D2>R2>R1.(3) The experiment results have shown us that the boiling heat transfer coefficientpresents a growth trend with the increasing of heat source temperature, and the trendis more obvious when the flux increases. The effect of the flux of heat source onboiling heat transfer coefficient can be neglected. The boiling heat transfer coefficientincreases with the increasing the flux of working fluid. (4) Visualization experiments were conducted on the flow patterns along the tube.The gasification core is mainly concentrated in the valley. In the process of floatingup, the collision between the bubbles promotes the bubble coalescence, and thisphenomenon results in generating large bubbles. The number of gasification coreincreases with increasing the temperature of heat source, the bubble generation rate isaccelerated, resulting in the increase of bubble density. Increasing the flux of workingfluid leads to the increase of the relative speed between gas and liquid, and it ishelpful to bubble coalescence, so the percentage of large bubbles is improved.