水平翅片管外凝结液膜分布及换热特性影响研究

Study of the condensate heat transfer and the condensate film distribution outside horizontal finned tube

肋片管换热技术被广泛应用于工程实践,当有凝结现象发生时,液膜对换热产生热阻,因此,为强化换热有必要对液膜分布进行研究.建立了水平翅片管的物理模型,基于Nusseh理论及修正的膜理论,推导出了肋片侧壁以及肋间基管的凝结液膜厚度和换热系数计算式,并对模型进行了验证.通过对水平梯形肋片管的计算,结果表明：在非淹没区,肋片侧壁的凝结液厚度沿圆周方向不断增厚,沿肋高方向变薄,局部凝结换热系数沿圆周向减小,沿肋高方向增加;基管上圆周角0 ＆#176;～妒f范围内液膜不断增厚,并在靠近淹没区急剧增厚,局部凝结换热系数减小;肋片间距的大小对换热性能有较大的影响,因此,通过优化最佳肋片间距可以提高肋片管的换热性能,为设计出高效换热器提供一定的参考.

Fin-tube as a heat transfer enhancement technology has been widely used in engineering practice, when condensation occurs the condensation film is heat transfer resistance, so it is necessary to research film distribution for heat transfer enhancement. Based on the Nusselt theories and modified film theory the paper establishes the physical model on horizontal finned tube, and calculates the thickness of film and heat transfer coefficient on the fin flank and the channel between fins. Then the paper verifies the model. Results show that in the unflooded region the thickness of film on fin flank constantly thickening follows the angle of circumference and constantly thinning follows the direction of rib height, and the local heat transfer coefficient on fin flank decreases in the circumferential direction and increases in the direction of the rib height. On the channel between fins the thickness of film increases and the heat transfer coeffi- cient decreases from the angle 0~ tocp/of circumference , when it arrives at the flooded region the thickness sharply in- creases and the heat transfer coefficient sharply decreases. The size of fin pitch influences the heat transfer perform- ance. Therefore, the paper provides a reference for designing the high efficient heat exchanger by optimizing the fin pitch to improve the heat transfer characteristics.