Numerical investigations on two-phase flow modes in evaporative condensers
Numerical investigations on two-phase flow modes in evaporative condensers
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DOI：
10.1016/j.applthermaleng.2015.10.099
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发表时间：
2016-02
影响因子：
6.4
通讯作者：
M. Fiorentino;G. Starace
中科院分区：
文献类型：
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作者：
M. Fiorentino;G. Starace
水平管上的降膜蒸发包括同时的传热和传质过程：在蒸发式冷凝器中，它提高了从冷凝制冷剂到空气的排热。液体流动受粘性、重力、张力效应、液体质量流量、管径、管间距以及与进料系统的距离等因素的影响，本文建立了水平管降膜蒸发的二维数值模型。研究了液膜流动过程的时间变化特性，通过改变水-气质量流量比，研究了稳定膜流和液滴流两种模式，并分析了管的布置方式对流动模式的影响。纵向节距增加73%对应于防止膜破裂的最小水质量流速增加66.7%。获得了给定几何形状的权衡曲线：在特定的空气质量流量下，稳定膜与液滴模式条件之间的过渡区是个性化的，其中10%的不确定性是指10%的水质量流量变化。
Falling film evaporation over horizontal tubes consists of simultaneous heat and mass transfer processes: in an evaporative condenser it improves the heat rejection from the condensing refrigerant to the air. The liquid flow is generally influenced by viscous, gravity, tension effects, liquid mass flow rate, tube diameter and spacing and distance from the feeding system.In this work, a two-dimensional numerical model of the falling film evaporation on horizontal tubes is presented. The temporal change characteristics of the film flow process were studied and different types of flow (stable film and drops mode) were investigated, by varying the ratio between the water-to-air mass flow ratio.The effect of the tubes arrangement on the flow mode was analyzed too: an increase of 73% of the longitudinal pitch corresponds to an increase of 66.7% of the minimum water mass flow rate that prevents the film break-up. The trade-off curve for a given geometry was obtained: at a specific air mass flow rate, a transition zone between the stable film to the drops mode conditions was individuated, with an uncertainty of 10% referring to a water mass flow rate variation of 10%.