Study On Condensation Heat Transfer Characteristics And Enhancement Method Of High Humidity Flue Gas Inside Horizontal Tube

Natural gas is a low-carbon clean energy source,the flue gas of which has high water vapor content.Which will cause energy waste when flue gas is discharged directly into the environment.Therefore,the deep recovery and utilization of waste heat of flue gas is of great significance for the efficient utilization of natural gas.The exhaust heat in flue gas includes two parts:sensible heat and latent heat.In order to recover the latent heat of flue gas better,it is necessary to understand and master the characteristics and strengthening mechanism of condensation heat transfer process of wet flue gas.The condensation and heat transfer process of wet flue gas is essentially a vapor-condensation heat transfer process with non-condensing gas.At present,the experimental research on the condensation heat transfer of wet flue gas in the horizontal tube is still limited,and the research on the means of condensation heat transfer enhancement is not enough,so it is necessary to conduct in-depth research.This paper experimentally studied the condensation and heat transfer characteristics of wet flue gas with a moisture content in the range of 0.05 to 0.2kg/kga inside horizontal smooth tubes and enhanced tubes.The details are as follows:Firstly,the flow and heat transfer characteristics of humid air inside horizontal smooth tube was studied.The effects of Reynolds number Rem,wall subcooling ΔT and inlet moisture content Xin on the heat transfer of condensation were investigated respectively.The results showed that the increasement of Rem and Xin showed the effect of promoting condensation heat transfer,and the increasement of ΔT inhibited the heat transfer process.Furthermore,an experimental correlation formula which is suitable for the condensation and heat transfer process of wet flue gas inside horizontal tube was proposed.The experimental correlation can well predict the experimental results and provide a basis for the subsequent engineering application.The flow and heat transfer characteristics of humid air inside corrugated tube and spiral tube were studied.Since there is no suitable empirical formula to calculate the surface heat transfer coefficient on the cooling water side of corrugated tubes and spiral tubes,the Wilson diagram method was used to solve the problem.Comparing and analyzing the heat transfer performance of the three heat exchange tubes,the Num of the corrugated tube and the spiral tube were 1.63 times and 1.26 times than that of the smooth tube,respectively.This was mainly because the wall structure of the two enhanced tubes helped to destroy the non-condensable gas layer and the liquid film layer that hindered heat transfer.The resistance performance of the three heat exchange tubes was compared and analyzed.The resistance coefficients of the corrugated tube and the spiral tube were 2 times and 1.28 times than that of the smooth tube,respectively.Finally,the overall heat transfer performance of the two enhanced tubes was analyzed.The PEC value of the corrugated tube was generally greater than that of the spiral tube.That meant that when the external pump power was constant,the corrugated tube should be selected as heat exchange tube.