Numerical Simulation Of Novel Polypropylene Hollow Fiber Heat Exchangerand Its Heat Transfer Enhancement

Hollow fiber heat exchanger as one of compact plastic heat exchangers has attracted more and more attention because of its resistances to scaling and corrosion, substantial space, cost and energy savings, light weight and easy manufacture and installation. Nevertheless, inferior thermal performance is the constraint of its wide application. It is important to study flow and heat transfer characteristics, find ways to enhance heat transfer and develop new types of hollow fiber heat exchangers.In this study, we mainly focus on the polypropylene tube-and-shell hollow fiber heat exchanger. The Fluent is used to analyze the characteristics of hollow fiber heat exchanger and find ways of heat transfer enhancement.A three dimensional tube-and-shell hollow fiber heat exchanger model has been proposed, fluid-solid coupled method has been used to simulate and calculate. The impacts of velocities in tube-side and shell-side and flow mode of hot water and cold water on total heat transfer coefficient were simulated. The good consistency between the calculating results and laboratory measuring data of overall heat transfer coefficient is obtained. The simulation results and theoretical calculations of tube-side, shell-side and fiber wall heat transfer coefficients are in good agreement. These indicate the accuracy and reliability of the model. It also indicates that the heat transfer efficiency increases fairly with the increase of the fluid flow rate, especially with the flow rate of shell-side.The characteristics of tube-side, shell-side and fiber wall have been discussed separately. The calculated contributions of tube, shell and fiber wall heat resistances to the total resistance are20%,50%and30%, respectively. The influences of packing fraction of hollow fibers, length of hollow fibers, wall thickness and wall thermal conductivity of hollow fiber to overall heat transfer coefficient were simulated. The packing fraction of hollow fibers has impact on the fluid distribution of shell-side. The optimal packing fraction of hollow fibers is13%-19%。Under the same heat transfer area, the packing fraction and the length of hollow fibers commonly effect the structure of heat exchanger. Higher heat transfer conductivity and thinner wall thickness of hollow fiber can achieve better heat transfer performance. In order to provide the setting basis of wall boundary condition for simulation of only shell-side, statistical analysis of hollow fiber wall heat transfer has been given according to the simulation results. It is found that the wall boundary condition of tube-and-shell hollow fiber heat exchanger is approximated by constant heat flux.