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基于Nusselt凝结传热理论,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传热模型,通过求解非淹没区和淹没区总传热量,推导管外平均传热系数计算式。计算不同肋片高度、肋密度时,R134a饱和蒸汽的管外平均凝结传热系数。结果表明:随肋密度的增加,平均传热系数先增大后减小,肋密度为25fpi时传热最佳;高肋片管的平均凝结传热系数大于低肋片管的,肋片高度达到一定值时,平均传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传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传热机理。
Based on the Nusselt condensation heat transfer theory, a finite number of microhorn angles are divided along the circumference of the finned tube. The condensation heat transfer model is established for the three ribbed sidewalls, Non-submerged areas and submerged areas of the total heat transfer, the deduction of the average outside the tube heat transfer coefficient formula. Calculation of different fin height, rib density, R134a saturated steam outside the tube condensation heat transfer coefficient. The results show that with the increase of the density, the average heat transfer coefficient firstly increases and then decreases, and the heat transfer is the best when the density is 25fpi. The average heat transfer coefficient of the high-finned tube is greater than that of the low-finned tube, When reaching a certain value, the average heat transfer coefficient hardly increases with the increase of rib height. When the saturated steam of R134a is 20 ℃, the average external condensation heat transfer coefficient of two different fin densities decreases with the increase of temperature difference, and the calculated values obtained by the model are compared with Beatty-Kate model. The average errors are about 16.1% and 8.3%, respectively. Therefore, the model basically reflects the condensation heat transfer mechanism outside the fin tube.