水平肋片管外自然凝结换热特性研究

Research on natural condensation heat transfer characteristics on horizontal finned tube

中文关键词: 凝结  数值分析  换热系数  肋片管优化  理论模型

英文关键词: condensation  numerical analysis  heat transfer coefficient  finned tube optimizing  theoretical model

中文摘要:

      基于Nusselt凝结换热理论,沿肋片管圆周方向划分有限个微元角,建立了每个微元角内肋侧壁、肋间基管及肋顶三个区域的凝结换热模型,通过求解非淹没区和淹没区总换热量,推导管外平均换系数计算式。计算不同肋片高度、肋密度时,R134a饱和蒸汽的管外平均凝结换热系数,结果表明：随肋密度的增加,平均换热系数先增大后减小,肋密度为25fpi时换热最佳；高肋片管的平均凝结换热系数大于低肋片管的,肋片高度达到一定值时,平均换热系数几乎不随肋高增加而增加。当R134a饱和蒸汽为20℃时,两种不同翅片密度的管外平均凝结换热系数随温差的增大而减小,并通过所建模型得到的计算值与Beatty-Kate模型进行了比较,平均误差分别为约16.1%和8.3%,故所建模型基本反映肋片管外蒸汽凝结换热机理。

英文摘要:

      The paper presented an analytical model to calculate the condensation heat transfer coefficient on horizontal finned tube based on the Nusselt condensation heat transfer theory. The model depended on elemental calculation by dividing the tube wall into finite elements, established the condensate heat transfer model of the fin flank, the channel between fins and the fin tip in the small annular element. The model is able to predict the mean condensation heat transfer coefficient outside finned tubes by calculate the total heat transfer. Then calculated the average condensation heat transfer coefficient of the saturated steam R134a outside the pipe versus fin heights , fin densities. The result show that: the average heat transfer coefficient first increase then decreases with the increase of fin density, the optimum fin density is 25fpi; the average condensation heat transfer coefficient of the higher finned tube is greater than that of lower finned tube, the average heat transfer coefficient hardly increased with the increase of fin height until it reaches a certain value. Compared with the Beatty-Kate model, at the saturation temperature of 20℃, the mean condensation heat transfer coefficient of the tubes with two different fin densities show a mean deviation 16.1% and 8.3%, respectively; and it decrease versus the temperature difference. The model reflects the mechanism of condensation heat transfer on horizontal finned tube.