Experimental Study And Simulation On Turbulent Heat Transfer And Resistance Characteristics Of Three Dimensional Internally Finned Tubes

As a main equipment of recovering waste heat and improving the heat utilization rate,the heat transfer performance and power consumption of heat exchanger is related to the production efficiency and energy saving,the pipe,which is the core components in heat exchanger,its structure has great influence on heat transfer coefficient of heat exchanger.This paper studied flow resistance and heat transfer of three-dimensional internally finned tube,one of the highly efficient enhanced tubes with experiment and numerical simulation method.Using air as working medium,the orthogonal experiment was used to study heat and flow characteristics of turbulent flow in 89 mm and 102 mm,two kinds of big diameter three-dimensional internally finned tube while the Reynolds number within the range of 25000 ~ 110000.Using the thermal performance coefficient defined by Webb as reinforcement index,to analyze the width,height,spacing and density of rib which may influence the thermal performance coefficient of three-dimensional internally finned tube according to the range method and variance method of the orthogonal design.Thus to get the direction to optimize and to select the best type tube.Least square method will be used to obtain the experimental correlations of Nusselt number and the fanning friction factor with Reynolds number and parameters of three-dimensional internally finned tube.Results show that characteristics of three-dimensional internally finned tube is better than that tube of the same diameter,Heat transfer coefficient up to three point one five times that of the light tube and thermal performance coefficient up to one point four five times,which indicates the feasibility of application in tubular heat exchanger;In addition,the biggest impact on thermal heat transfer characteristics is the density of rib,rib height comes second,spacing comes third,while width is the smallest,which shows the direction of parameter optimization.Provided by ANSYS CFX and FLUENT software,numerical simulation select a 102 mm diameter light pipe and the three-dimensional internally finned tube to simulate flow and heat transfer,pressure field,velocity field and temperature field in the same condition were analyzed.The comparison shows that air flow past the rib and accelerate near the wall between the ribs,besides the axial velocity air has circumferential velocity and radial velocity,which increased the degree of turbulence in the fluid flow,and attenuate the thickness of thermal boundary layer,in addition,the fluid flow across three-dimensional rib which increase the heat transfer,these are conducive to strengthen the convective heat transfer.