水平横槽管外R245fa降膜蒸发的流动与换热特性OA
Flow and heat transfer characteristics of R245fa falling film evaporation outside horizontal grooved tube
基于汽液两相流与蒸发模型,针对水平管外的降膜蒸发过程,对比制冷剂R245fa在降膜雷诺数Re=1 690,低、中、高热流密度(q=500,5 000,20 000 W/m2)工况下,水平光管与横槽管外的液膜流动(液膜铺展、液膜厚度与分布)与换热特性.结果发现:工质在横槽管外的液膜铺展较快,液膜完全覆盖横槽管需0.192 s,覆盖光管需0.222 s;与光管相比,横槽管外的液膜厚度有所减薄,减薄程度主要与周向角有关,以波峰处为例,[0°,60°)时减薄幅度较大,平均达20％,[60°,160°)时减薄幅度较小,约为10％,[160°,180°]时减薄约为13％;横槽管外的局部换热系数与液膜减薄幅度有关,周向角为[0°,60°)、[60°,160°)和[160°,180°]时分别为光管的1.5～3.0、1.1～1.2和1.1～1.5倍,3种工况下,横槽管外的平均换热系数高于光管;中、高热流密度工况下,横槽管可以有效避免局部干涸,而光管外的液膜内因伴有汽泡而出现局部隆起,特别是在液柱截面周向角为110°～180°时,因液膜内较大的汽泡产生"颈缩效应"致液膜厚度急剧减薄,诱发局部干涸.
Based on the gas-liquid two-phase flow and evaporation model,to investigate the process of the falling film evaporation outside horizontal tube,the liquid film flows of liquid film spreading,liquid film thickness and distribution and the heat transfer characteristics of refrigerant R245fa were compared outside smooth tube and grooved tube under the conditions of low,medium and high heat flux with q values of 500,5 000 and 20 000 W/m2 at falling film Reynolds number Re of 1 690.The results show that the liquid film spreads faster outside the grooved tube than that outside the smooth tube.It takes 0.192 s for the liquid film to completely cover the external wall of the grooved tube and 0.222 s for the smooth tube,respectively.Compared with the smooth tube,the thickness of the liquid film outside horizontal grooved tube is thinner,and the thickness decrease is mainly related to the circumferential angle.At the cross section of the two liquid films meeting,the thickness decrease values are about respective 20％,10％and 13％when the circumferential angles are[0°,60°),[60°,160°)and[160°,180°].The local heat transfer coefficients outside the horizontal grooved tube are related to the magnitude of liquid film thinning and are respective 1.5-3.0,1.1-1.2 and 1.1-1.5 times those outside the smooth tube when the circumferential angles are respective[0°,60°),[60°,160°)and[160°,180°].The average heat transfer coefficient of horizontal grooved tube is higher than that of smooth tube.Under the conditions of medium and high heat flux,the sudden local deformations of the liquid film outside the smooth tube can be found.Especially at the cross section of the liquid spraying from the nozzle at the circumferential angle of 110°-180°,the bubble in the liquid film outside the smooth tube is large enough to cause the sharp decrease of liquid film thickness due to the necking effect,which leads to the local dryout outside the smooth tube.However,the local dryout can be effectively avoided for the horizontal grooved tube.
王迎慧;王耀;卜昶瑞;杭范辰
江苏大学能源与动力工程学院,江苏镇江 212013江苏大学能源与动力工程学院,江苏镇江 212013江苏大学能源与动力工程学院,江苏镇江 212013江苏大学能源与动力工程学院,江苏镇江 212013
能源科技
水平横槽管降膜蒸发液膜流动汽液两相流传热
horizontal grooved tubefalling film evaporationliquid film flowgas-liquid two-phase flowheat transfer
《江苏大学学报（自然科学版）》 2026 (2)
175-181,7
国家自然科学基金资助项目(52276067)
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