Boiling Heat Transfer of Binary Mixture in a Tube

1.对氟利昂R11-R113混合工质在不同组成、压力、质量流速、热流密度和入口条件下沿垂直管内流动的沸腾换热进行了实验研究。通过使直流电通过管来加热试管，这导致焊接在管的外表面上的热电偶结两端的过度电压降。提出了电压降的修正方法，并发现可以提供准确的壁温.在沸腾开始前，管壁温度和流体温度沿管长沿着线性增加。在此非沸腾强制对流区的传热系数与Dittus和Boelter的公式有很好的关联。在沸腾起始点，壁面温度突然福尔斯下降，因此传热系数从无相变的强制对流水平突然上升.低干度沸腾区的传热系数与质量流速无关。与通过加权摩尔分数对其单组分值线性插值的系数相比，发现该区域中混合物的传热系数变得较低。实验结果表明，现有的池沸腾关联方法不能关联流动沸腾数据，高干度下两相强制对流换热系数与局部干度的关系很弱.为了更深入地研究二元混合物的传热特性，不仅需要二元混合物的热力学性质，而且需要二元混合物的输运性质。

1. Boiling heat transfer of Freon R11-R113 mixture flowing a uniformly heated vertical tube was experimented under various combinations of composition of mixture, pressure, mass velocity, heat flux and inlet condition. The test tube was heated by passing direct current through the tube which resulted in an excessive voltage drop across thermocouple junctions welded on the outer surface of the tube. Correcting method for this voltage drop was proposed and found to provide accurate wall temperature.2. Both the tube wall temperature and the bulk fluid temperature increase linearly in parallel along the tube length before the incipience of boiling. Heat Transfer coefficients in this non-boiling forced convection region are correlated well with Dittus and Boelter's Formula.3. At the point where boiling is initialed, wall temperature abruptly falls and hence heat transfer coefficient abruptly rises from the level of forced convection without phase change.4. Heat transfer coefficients in nucleate boiling regime at relatively low quality are independent to mass velocity. Heat transfer coefficients of mixture in this regime are found to become lower compared to the coefficients linearly interpolated by weighing the mole fraction on their single-component values. Proposed correlating methods for pool boiling of binary mixture are found to fail to correlate the data for flow boiling.Heat transfer coefficients in two-phase forced convection regime at relatively high quality are rather a weak function of local quality.6. For further detailed consideration to be performed on heat transfer characteristics of binary mixture, there are urgently required not only thermodynamic properties but transport properties for binary mixture.