Experimental Study Of Flow Condensation Heat Transfer Of Annuli Outside Horizontal Enhanced Tubes

Nowadays,in order to realize the development of ecological civilization construction,people are attempting to making efforts in energy reducing,which is considered to be an efficient way to promote the overall reform of the mode of energy consumption.Heat exchange system is widely utilized in industrial engineering,e.g.petroleum preheater,nuclear reactor,solar heater,energy storage,etc.It can be seen that heat exchangers paly a vital role in heating and cooling process of fluid.The irreplaceability of the heat exchange system makes itself a very valuable research hotspot.This paper experimentally studied the thermal-hydraulic performance of enhanced tubes during condensation on annular side using R410A as working fluid.The tested tubes were as follow:SS-DIM(an enhanced tube with dimples),SS-HB(an enhanced tube with herringbone fins),SS-HB+DIM(an enhanced tube with both dimples and herringbone fins).The effects of three kinds of surface structures on condensation heat transfer and friction pressure drop were discussed under different mass flow rates and vapor qualities.Tests were carried out at for a range of mass flow flux(75-200kg/(m~2s),the inlet and the outlet vapor quality are 0.8 and 0.2 respectively.The results showed that:the condensation heat transfer coefficients of three kinds of enhanced tubes increased with the increase of mass flow rate.The retention of condensing liquid in the dimple led to the case that the condensation heat transfer coefficient of the dimpled tube was lower than that of the smooth tube when the mass flux was under 125kg/(m~2s).Additionally,an intersection occured when G=100kg/(m~2s)during the experiments of dimpled tube and herringbone-fin tube.However,due to the existence of herringbone grooves,the condensation liquid trapped in the dimple can be discharged in time under the effect of surface tension,resulting in the increase of condensation heat transfer coefficient.The condensation heat transfer coefficients of the three kinds of enhanced tubes tended to increase with the increase of vapor quality.At high vapor quality,the vapor phase was relatively high in the annular region,and the condensation heat transfer coefficient was determined by the condensation rate of liquid film on the wall,so the increase of mass flow rate did not lead to the increase of condensation heat transfer coefficient.When the vapor quality was low,the dimples were mostly flooded,so that the condensation heat transfer coefficient of the dimpled tube was lower than that of the smooth tube.The condensation friction pressure drop in the annular area also increased with the increase of dryness,and the gap between the friction pressure drop of three kinds of enhanced tubes were gradually widening with an increasing mass flux.The performance factors of SS-DIM,SS-HB and SS-HB+DIM were 1.25-1.63、1.09-1.42 and 0.99-1.16respectively.The combination of dimples and herringbone fins brought better condensation heat transfer performance.To calculate the condensation heat transfer coefficient in annular area outside the tube,the author used Matlab to carry out the fitting calculation based on dimensionless special certificate number and mathematical statistics.In the preliminary fitting results,some parameters were adjusted combined with the classical convection theory to propose a new correlation.The mean absolute error(MAE)and the mean relative error(MRE)were 9.97%and 6.05%,which indicated that the fitting method had high accuracy and stability.