Study On The Flow And Heat Transfer Characteristics Of The Dimpled Tube With Ribs

In recent years,with the rapid development of the economy,the consumption of energy has increased.In the traditional petrochemical,refrigeration HVAC,aviation and other fields,fossil fuels are the main source of energy consumption,and the development process of most of these industries is accompanied by the heat transfer process.The heat exchanger,as the main equipment for heat transfer,has disadvantages such as low heat transfer efficiency and high heat loss.Therefore,it is particularly important to further improve the heat transfer efficiency of heat exchangers.In order to improve the efficiency of heat exchanger,it can be done by roughing the inner and outer surfaces of heat transfer tubes,such as grooved tubes,dimpled tubes,ribbed tubes,etc.This paper investigates the arrangement of spiral ribs on the dimpled tube to effectively improve the overall heat transfer performance of the dimple tube.The effects of different spiral ribs,interrupted spiral rib lengths,dimpled rotation angles and aspect ratios on the flow and heat transfer characteristics of the tube are analyzed from the consideration that both spiral ribs and dimples can increase the heat transfer surface area and change the fluid flow state.The numerical results are compared with the experimental results to verify the correctness and applicability of the numerical method.The distributions of temperature,velocity,vorticity and local Nu inside the tube are studied,and the variation curves of surface averaged Nu,drag coefficient f and integrated heat transfer performance PEC with Re are quantitatively analyzed.The results of the study show that:(1)The dimpled tube with spiral ribs can effectively improve the heat transfer in the channel,with larger longitudinal vortex,thinner boundary layer,and enhanced heat transfer between hot and cold fluids compared with the dimpled tube,resulting in a significant improvement in the overall heat transfer performance of the channel compared with the smooth circular tube and the dimpled tube.(2)The surface averaged Nu and PEC of the dimpled tube with interrupted spiral ribs are improved by 55% and 14.3%,respectively,compared with the smooth circular tube,and by33% and 9.03%,respectively,compared with the dimpled tube.(3)In the study of the flow and heat transfer characteristics of the tube with different interrupted spiral rib lengths,it was found that the 8 mm interrupted spiral rib channel has the best overall heat transfer performance,and PEC is improved by a maximum of 15.6%compared with the smooth circular tube.(4)When the dimpled rotation angle is α=45°,the integrated heat transfer performance of the channel is the best.When the dimpled rotation angle is α=60°,the surface Nu of the heat transfer channel becomes larger.However,the pressure drop loss is also large,so the increase of f of this channel is large,which leads to the decrease of PEC.(5)At Re=5000,the comprehensive heat transfer performance of the channel is the best at the dimpled ratio of a:b=6:3,and PEC increases by 19.6% at maximum compared with the smooth circular tube.At Re=10000～40000,the comprehensive heat transfer performance of the channel is the best at the ratio of a:b=5:3,and PEC of the channel can be increased by15.5% compared with that of the smooth circular tube.(6)It is found that the integrated heat transfer performance under different calculation models has different improvement compared with the circular tube.When Re=5000,the integrated heat transfer performance of the channel with interrupted spiral rib length L=8mm,dimpled rotation angle α=45° and a:b=6:3 is the best.PEC is improved by 19.6% compared with that of the smooth circular tube.