绕管式换热器壳侧降膜流动和相变传热的数值模拟

为了定量描述绕管式换热器壳侧降膜蒸发特性并进而优化换热器结构,建立了绕管式换热器壳侧降膜蒸发过程流动与传热的数值模型。首先对降膜流动过程中流型变化和传热传质机理进行分析;通过对降膜流动过程液膜所受表面张力、重力和剪切力的计算,实现层状流、柱状流和滴状流等不同流型的模拟;通过管壁面和气液交界面的组分守恒建立降膜蒸发过程的传质子模型,并基于传质速率计算得出潜热传热速率。将数值模拟结果与已有文献中实验数据进行了对比,结果显示89%的模拟数据与实验数据偏差不超过25%;模拟结果与实验数据吻合较好。基于提出的模型,对不同工况下的绕管式换热器壳侧降膜蒸发传热传质规律进行了分析。

Simulation of falling film flow and heat transfer at shell-side of coil-wound heat exchanger

The objective of this paper is to develop a numerical model to predict the two-phase flow,heat transfer and mass transfer at shell-side of coil-wound heat exchangers(CWHEs),which can predict the performance of heat exchangers and optimize the structure of CWHE.To achieve this goal,the mechanism of the status of shell-side two-phase flow should be analyzed.Then,a model for simulating flow pattern,including the droplet flow,the column flow and the sheet flow,is developed by employing the volume of fluid-continuous surface force method;the mass transfer model is developed and mass transfer rate can be predicted on tube surface and liquid-gas interface;then the latent heat during evaporation and condensation can be calculated based on the mass transfer rates;the forces and the heat and mass transfer rates are introduced into the control equations as the source terms.The proposed model is validated by the experimental data from the existing references.There is good agreement between experimental data and predictions.The validation results show that 89% of the predicted data can agree with the experimental data within a deviation of ±25%. The heat and mass transfer coefficients obtained by the model are also analyzed.