蒸汽加热竖直窄矩形通道内流动沸腾换热实验与预测模型

Experimental and Prediction Model of Flow Boiling Heat Exchange in a Vertical Narrow Rectangular Channel Heated by Steam

为了研究窄通道的流动沸腾换热特性,利用单面蒸汽加热的方式在竖直窄矩形通道中进行实验,分析了质量流量、入口过冷度等因素对换热特性的影响,并建立了适用于竖直窄矩形通道的流动沸腾换热预测关系式。基于目前大部分经验公式均忽略了入口过冷度对气泡生长过程的影响,导致流动沸腾换热预测精确度偏低,故考虑窄矩形通道的尺寸限制和流体表面张力影响,引入相关系数后建立了新的预测模型。结果表明:当质量流量增加或入口过冷度减小时,壁面温度先上升后下降,然后逐渐趋于稳定;同时入口过冷度的减小将大幅增大传热系数,而质量流量的变化对传热系数影响较小,并且在入口过冷度较高时,质量流量的影响进一步减弱;新的预测模型可在本实验工况范围内较好地预测窄矩形通道流动沸腾传热系数。

In order to study the heat transfer characteristics of flow boiling in narrow channels,the single-sided steam heating experiments were carried out in a vertical narrow rectangular channel.The influences of mass flow rate,inlet subcooling rate were analyzed,and the prediction equation of flow boiling heat transfer suitable for vertical narrow rectangular channels was established.Currently,most empirical formulas ignore the influence of inlet subcooling on bubble growth process,which results in low accuracy in predicting flow boiling heat transfer.Considering the size limitations of narrow rectangular channels and the influence of fluid surface tension,a new prediction model was established by introducing correlation coefficients.Results show that with the increase of mass flow rate or the decrease of inlet subcooling,the wall temperature increases first,then decreases and tends to be consistent finally.The decrease of the inlet subcooling will greatly improve the heat transfer coefficient,while the mass flow rate has little influence on the heat transfer coefficient.When the inlet subcooling is high,the influence of the mass flow rate is further weakened.The new predicted model could better predict the flow boiling heat transfer coefficient of narrow rectangular channel within the experimental conditions.