Research On Twisty Flow Heat Transfer Enhancement Mechanism And New Type High Efficiency Heat Exchangers

As one of the widely used heat exchange equipment,shell-and-tube heat exchanger is very important for energy saving and utilization.The type of trapezoidlike tilted baffle heat exchanger as the research foundation,the theoretical and numerical simulation methods are used to analyze the shell side fluid flow and heat transfer characteristics,also compared with segmental baffle heat exchanger and shutter baffle heat exchanger.Proposing trapezoid-like tilted baffle heat exchanger with droplet shaped tube,the fluid flow and heat transfer characteristics are analyzed on shell side and tube side respectively,the main results as follows:Because of the vertical model baffle,the fluid present twisty flow in the shell side of trapezoid-like tilted baffle heat exchanger.In the same Reynolds number,compared with sideling flow and lateral flow in shell side of shutter baffle and segmental baffle heat exchanger,cross flow tube bundle more intensive,thickness of the thermal boundary layer is reduced,improve the fluid velocity and temperature gradient synergistic,so the shell side convection heat transfer is enhanced.The shell side convection heat transfer coefficient of trapezoid-like tilted baffle heat exchanger is 12.43%-24.33% higher than segmental baffle heat exchanger,6.71%-11.51% higher than shutter baffle,also shutter baffle heat exchanger is 2.53%-5.93% higher than segmental baffle heat exchanger.The twisty flow fluid in shell side improve the synergistic,it also the synergistic of velocity and pressure gradient,that is,the flow resistance and pressure in shell side are increased.The shell side comprehensive performance of shutter baffle heat exchanger is 5.7%-16.47% lower than segmental baffle heat exchanger,trapezoid-like tilted baffle heat exchanger is 5.85%-9.06% higher than segmental baffle heat exchanger and 6.71%-11.51% higher than shutter baffle heat exchanger.Replacing traditional circular tube with the same cross section perimeter of droplet shaped tube as heat exchange tube of trapezoid-like tilted baffle heat exchanger,the calculation results show that: droplet shaped tube have better streamline fit with main fluid flow direction in shell side,so the fluid flow is closer to ideal inclined scour tubebundle,and the synergistic between velocity and temperature gradient is improved,so that the shell side convection heat transfer coefficient is 27.16%-29.71% higher than trapezoid-like tilted baffle heat exchanger with circular tube,fluid flow in droplet shaped tube side also improve the synergistic of velocity and temperature gradient,so the heat transfer coefficient in tube side is 25.63%-28.69% higher than circular,but the synergistic of velocity and pressure gradient is reduced in shell side and tube side,cause the pressure drop increased.However,the shell side and tube side comprehensive performance are still 31.47%-35.23% and 8.64%-13.28% higher than heat exchanger with circular tube.