水平管束降膜蒸发中CO_(2)解吸的微观特性

Microscopic characteristics of CO_(2) desorption in falling film evaporation in horizontal tube bundles

水平管降膜蒸发中释放的不凝气严重降低了管内冷凝传热速率,会使海水淡化的能耗成本显著增加,因此研究水平管束降膜蒸发中CO_(2)解吸的微观过程具有重要意义。文章建立了耦合水平管束降膜蒸发传热和CO_(2)解吸的理论模型,计算得到CO_(2)解吸单元体、碳酸盐组分浓度,分析了CO_(2)解吸量的微观特性。结果表明:传热系数的模拟值与实验值吻合良好;化学反应时间沿竖直管排方向减小且其速率逐渐降低,而沿水平管长方向随竖直管排节点数的增加而变长;主导CO_(2)解吸速率的HCO^(-)_(3)和CO^(2-)_(3)在微元内的浓度显著高于CO_(2)和H+浓度;单位面积的蒸发速率和每吨海水CO_(2)解吸量沿竖直管排、水平管长方向均减少。

The energy consumption in seawater desalination is greatly increased as the non-condensable gas released in falling film evaporation in horizontal tube bundles decreases the rate of condensing heat transfer in the tubes.Therefore,it is of great importance to study the CO_(2) desorption process.This paper establishes a theoretical model of heat transfer of falling film evaporation in horizontal tube coupled with CO_(2) desorption,calculates the concentrations of CO_(2) desorption units,carbonate concentration and CO_(2) desorption rate.The results show that the simulated heat transfer coefficients are in good agreement with the experimental data.The chemical reaction time decreases and its decreasing rate reduces along the vertical tube row,while along the length direction of horizontal tubes it increases with the increase of the number of nodes in the vertical tube row.The concentrations of ions of bicarbonate and carbonate dominating CO_(2) desorption rates in infinitesimal elements are obviously higher than those of carbon dioxide and hydrogen ions.The evaporation rate per unit area and CO_(2) desorption per ton of seawater decrease along in the vertical tube rows and the horizontal tube length.