Study On Enhanced Condensation Heat Transfer Of Gas Flue Gas Based On Heat Exchange Surface Modification

By 2030,natural gas will account for 15%of China's primary energy consumption.Natural gas flue gas condensation heat transfer is an important technical means to achieve energy efficiency improvement.Strengthening the condensation heat transfer process under the condition of high non-condensing gas partial pressure,can reduce the heat exchanger volume,reduce the flue gas side resistance,and break through the technical bottleneck of the partition wall type low temperature heat exchanger.In this paper,the surface of the heat exchanger is modified to study the condensation process of water vapor in the gas flue gas.The important influence parameters of low temperature condensation heat transfer are analyzed.The change law of heat transfer coefficient is obtained,and the condensation mechanism is explained by the phenomenon.This paper consists of two parts:the comparative surface heat transfer capacity comparison experiment and the modified surface visualization mechanism:First,build a condensing seal test bench,and apply high-purity N₂ to steam ratios to simulate the combustion of natural gas at the tail.The temperature integrated device is used to measure the temperature gradient of the material heat exchanger,and the heat transfer capacity is calculated in combination with the thermal conductivity.The modified surface was obtained by sanding spray coating?PTFE?and heat treatment.The effects of different flue gas temperature,circulating water temperature,heat transfer material and non-condensing gas on the heat transfer performance before and after modification were studied.By analyzing and comparing the heat exchange instability time and heat transfer coefficient,combined with the thermal imaging dynamic change image,the infiltration ability,hydrophobicity and bead condensation characteristics were qualitatively evaluated.The results show that the modified coating has good hydrophobicity,and the heat exchange capacity after modification is obviously improved.The non-condensing gas reduces the partial pressure of water vapor,and the heat transfer coefficient decreases by 41%.Secondly,in order to explain the reason why the modified surface improves the heat exchange capacity,the infrared thermal imaging camera,CCD,contact angle measuring instrument,XRD and scanning electron microscope are used for visualization experiments.On the modified surface and copper surface,the droplet temperature field,microscopic size morphology,surface static infiltration mode,surface thermal resistance distribution,surface composition before and after pickling,and condensation droplet distribution.After modification,the condensed droplet base circle radius on the heat exchange surface is reduced,the static contact angle is increased,the single droplet thermal resistance is reduced,and the degree of subcooling is reduced.The surface modification mode changes from Wenzel to Cassie,which facilitates the formation of bead condensation and droplet shedding.Finally,combined with the heat transfer contrast experiment and the surface visualization experiment,the strengthening mechanism is characterized by the condensation phenomenon.The coating process of this paper adopts physical fit,which is different from other scholars'chemical modification and is not limited by the combined metal materials.Although the modified surface has a non-moisturizing ability?static contact angle of 143.58°?which is inferior to the superhydrophobic surface,it has good acid resistance and surface self-cleaning property,and can avoid low temperature corrosion of heat exchange equipment and heat in the low temperature heat exchange temperature range.Dust and fouling under the action.Its own hydrophobic properties can improve the heat exchange capacity of the low temperature section heat exchange equipment.