A new approach to predict void fraction flow, regime and heat transfer accounting for non equilibrium in condensers with superheated inlets.

A new approach to predict the void fraction, flow regime and heat transfer in a condenser with superheated inlet by accounting for the effects of non-equilibrium is introduced. The paper presents evidence (by visualization and temperature and heat transfer measurements) of condensation while the specific enthalpy of the bulk flow indicates superheated vapor because of the temperature gradient causing the wall temperature to drop below saturation temperature. The presence of liquid film induces discrepancies between the void fractions, flow regimes and heat transfer coefficients in a real condenser and the predictions from a model assuming thermal equilibrium. The new approach attempts to address this issue by bringing new predictions of void fractions, flow regimes and heat transfer coefficients from thermodynamic quality one and zero to the real onset and end of the condensation. From extensive measurements and flow characterizations based on visualization in diabatic conditions, the new approach of predicting void fraction, flow regime and heat transfer coefficient is specifically explained and validated.

本文提出一种考虑非平衡（non-equilibrium）效应的新方法，可用于预测带过热入口（superheated inlet）的冷凝器内的空泡份额（void fraction）、流型（flow regime）与传热特性。本文通过可视化实验、温度与传热测量，证实了即使主流流体（bulk flow）的比焓（specific enthalpy）显示为过热蒸汽，仍存在冷凝现象——这是由于温度梯度（temperature gradient）使得壁面温度降至饱和温度（saturation temperature）以下所致。实际冷凝器中液膜（liquid film）的存在，会导致其空泡份额、流型与传热系数（heat transfer coefficient）的实测值与基于热平衡（thermal equilibrium）假设的模型预测结果之间产生偏差。该新方法旨在解决这一问题，将空泡份额、流型与传热系数的预测范围从热力学干度（thermodynamic quality）为1和0的工况，拓展至冷凝过程的实际起始与终止阶段。本文基于非绝热工况（diabatic conditions）下的大量实测数据与可视化流场表征，对该空泡份额、流型与传热系数预测新方法进行了详细阐释与验证。