涂层导热系数变化对换热器传热的影响

Influence of thermal conductivity of coatings on heat transfer performance of heat exchangers

采用换热器效能法,对不同种类换热器进行校核计算。研究换热工质为气气、气液、液液时,不同种类换热器的换热性能随涂层导热系数的变化趋势。结果表明,各种换热器的总传热系数皆随涂层导热系数的增加而增大,且在不同低温侧流体雷诺数下增加程度不同,雷诺数越大,增加程度越大。设定涂层厚度为200.000μm,涂层导热热阻所占比例随着涂层导热系数的增加在平板式空气预热器中的减小量最小,当冷流体雷诺数为8156时,从4.72%减小为0.25%,在可拆卸板式换热器中的减小量最大,当冷流体雷诺数为2843时,从53.40%减小为3.70%。当冷流体侧雷诺数取最大时,在平板式空气预热器、列管式省煤器和可拆卸板式换热器中,涂层导热系数分别达到0.175、0.922和31.500 W/(m·K)时,可以使换热器换热负荷达到设计值的99%。

The heat exchanger efficiency method is used for checking calculation of different types of heat exchanger.The heat transfer performance of different types of heat exchanger changes with the coating thermal conductivity are studied when the heat fluids are gas-gas,gas-liquid and liquid-liquid,respectively.The results show that the overall heat transfer coefficient of all kinds of heat exchangers increases with the increase of the thermal conductivity of the coatings,and the increase degree is different under the different Reynolds number of the fluid on the low temperature side.The greater the Reynolds number is,the greater the increase degree achieves.The thickness of coatings is set as 200.000μm,and the reduction of thermal resistance ratio of coating in flat air preheater is the smallest with the increase of thermal conductivity of coating,which reduces from 4.72%to 0.25%under cold fluid Reynolds number as 8156,while in removable plate heat exchanger it is the largest,which reduces from 53.40%to 3.70%under cold fluid Reynolds number as 2843.Under the maximum Reynolds number of the cold fluid side,when the thermal conductivity of the coatings in the flat air preheater,the tubular economizer and the removable plate heat exchanger reaches 0.175,0.922 and 31.500 W/(m·K),respectively,the heat transfer loads of the heat exchangers can reach 99%of the design values.