Abstract
The flow of air in the fan cooling tower sprinkler channels in certain initial conditions may be characterized by the presence of a section of saturated humid air. In this case, the calculation of mass transfer according to the criterion equation of mass transfer, obtained from the analogy of the processes of heat and mass transfer, gives an overestimated result of the mass flow value. For the section of saturated air, the intensity of the mass transfer process is calculated using the function of changing the density of saturated steam from the air temperature. The works studying water cooling processes in the fan cooling tower sprinkler channels contain no assessment of the influence the saturated air presence has on the intensity of water cooling. The paper proposes a method for calculating the processes of heat and mass transfer in the cooling tower channels in the presence of a section of saturated air flow, taking into account the peculiarities of calculating mass transfer between water and saturated air. The values of the discrepancy between the final water temperature in calculations according to the proposed method and the method for unsaturated air are given. It is shown that the presence of a saturated air zone leads to an increase in the final temperature of the water compared to the calculations using formulas for unsaturated air. It is revealed that the discrepancy of water temperature calculated by different methods increases with the length of the channel, the value of the initial relative humidity of the air decreases with the growth in the initial air temperature. The offered methodology and obtained results can be used in the deve¬lopment of regime maps and at the design stage of fan cooling towers.
Highlights
Ключевые слова: канал оросителя градирни, влажный воздух, коэффициент теплоотдачи, коэффициент массоотдачи, участок течения насыщенного влажного воздуха, методика расчета процессов тепломассообмена
The flow of air in the fan cooling tower sprinkler channels in certain initial conditions may be characterized by the presence of a section of saturated humid air
The calculation of mass transfer according to the criterion equation of mass transfer, obtained from the analogy of the processes of heat and mass transfer, gives an overestimated result of the mass flow value
Summary
Где Sc – критерий Шмидта; ξ – коэффициент межфазного трения на границе «вода – воздух». Зависимости (1) и (2) можно применять для расчета процессов тепломассообмена в каналах различной геометрической формы. В качестве характерного размера используется эквивалентный диаметр. Для расчета коэффициента межфазного трения в каналах оросителей применялась формула [20]. Где uср – средняя по толщине пленки скорость воды, м/с; σ – коэффициент поверхностного натяжения на границе «вода – воздух», Н/м; μвод – коэффициент динамической вязкости воды, Па∙с. Расчет процессов теплообмена и массообмена в канале оросителя будет проводиться снизу вверх. При таком подходе рост вертикальной координаты сопровождается увеличением температур воздуха и воды и повышением плотности водяных паров в воздухе. Температура воздуха изменяется за счет конвективного теплообмена между водяной пленкой и воздухом
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