圆锥槽结构强化低压水蒸气的膜状凝结实验研究

Experimental research on conical groove structure strengthening film-wise condensation of low-pressure steam

通过在冷凝面上构造圆锥槽结构,使冷凝液膜内部形成结构梯度,利用圆锥槽内冷凝液膜产生的轴向拉普拉斯压差使冷凝液自发向圆锥槽半径减小的方向运动,实现冷凝液快速排出,从而强化低压蒸气膜状凝结。实验结果表明,冷凝流量较小时,圆锥槽内凝结液膜能快速排出,膜状凝结换热得到增强,而光滑表面由于接触角滞后造成冷凝液块钉扎在冷凝面,造成传热热阻增大,凝结换热恶化;而在较大冷凝流量下,圆锥槽表面冷凝液膜变厚,液膜内部轴向压力梯度减小,轴向输运能力减弱,光滑表面冷凝液块脱离频率增加,同时合并路径上的其他液块与液珠,加快表面更新频率,造成蒸气在光滑表面的冷凝速率略大于圆锥槽表面。

In this paper,the conical groove structure on the condensation surface is proposed to form a structural gradient in the condensate film.The axial Laplace pressure difference genera-ted by the condensate film in the conical groove makes the condensate move spontaneously in the direction of the tip the conical groove,so as to realize the rapid discharge of the condensate and strengthen the film condensation of low-pressure steam.The experimental results show that when the condensation flow is small,the condensed liquid film in the conical groove can be discharged quickly so that the film condensation heat transfer is enhanced.While the condensate block is pinned on the smooth surface due to the hysteresis of contact angle on the smooth surface,resul-ting in the increase of heat transfer resistance and the deterioration of condensation heat transfer.Under big condensation flow,the condensed liquid film on the surface of the conical groove be-comes thicker so the axial pressure gradient inside the liquid film and the axial transport capacity decreases.On the other hand,the separation frequency of condensate blocks on the smooth sur-face increases and the block film combines other films and beads on the path to speed up the sur-face renewal frequency,resulting in a slightly higher condensation rate of steam on the smooth surface than that on the surface of the conical groove.