三维微肋管内凝结换热流型及环状流关联式

Flow Patterns and the Annular Flow Experimental Correlation of R134a Condensation Heat Transfer in Three-Dimensional Microfin Tube

为了得到不同流型下的换热性能 ,以R134a为工质对两种不同微肋几何结构的三维水平内微肋管进行了实验研究 ,通过可视化措施对流型及其转换进行了观测 .结果表明 :在Soliman流型图上 ,三维内微肋管环状流的分界线较之于光管向左平移了一段距离 ,即环状流与波状流的转换判据由Fr等于 7减小到Fr等于 2 .在较低的蒸汽流速和较低的干度下 ,三维内微肋管仍能维持环状流的状态 .环状流区的实验数据回归的换热关联式与实验值的最大偏差在± 2

Studies of the two phase flow patterns and their transitions during condensation have gained increasing interest and importance from the well accepted view that the heat transfer characteristics are strongly dependent on the flow patterns. Therefore, it is very important to know which flow pattern is expected to exist at certain flow conditions in a condenser and to develop heat transfer correlations consistent with the prevailing heat transfer mechanism in each flow pattern. The condensation heat transfer for R134a in two kinds of in tube three dimensional (3 D) microfin tubes with different geometries is investigated experimentally. In the range of experimental conditions, six distinguishable flow patterns (annular flow, semi annular flow, stratified flow, wavy flow, slug and plug flow) are recorded by a video camera. The obtained results are as follow. In the Soliman flow regime map, the annular flow region of 3 D microfin tube is larger than that of smooth tube. The flow regime transition criterion Fr decreases from 7 to 2 between annular flow and wavy flow. The annular flow region extends toward lower vapor mass flux and lower vapor quality. In this region, the heat transfer coefficients h of the two kinds of in tube 3 D microfin tubes decrease as the vapor qualities x decrease. The regressed condensation heat transfer correlation is obtained from the experimental data of annular flow region. The dispersities of the experimental data are in the limits of plus or minus 25 percent.