横流式冷却塔的热力分析

横流式冷却塔的设计和计算一般是基于Merkel在1925年提出的焓差法,它不但取路易思数等于1,而且忽略了水份蒸发引起水量减少以及进口相对湿度的影响.本文以空气的含湿量差为驱动力,考虑以上因素的影响,推导出它的微分方程组,编制程序进行计算,求得了横流塔的精确解.同时按焓差法编制程序求得横流塔的近似解,并和精确解进行了比较.计算表明焓差法的近似解求得的冷却塔填料容积偏低,偏差一般为10～20%,个别达30%,这在设计横流塔时应认真注意.本文还分析了一系列因素对横流式冷却塔热力性能的影响.其中有:进塔空气的干湿球温度,水温差,冷却幅高,大气压力以及容积散质系数对冷却数和填料体积的影响.还分析了不同地区气侯参数的影响.所得结论对横流塔的设计计算有参考价值.

Thermal Analysis of Crossflow Cooling Tower

The design and calculation of a crossflow cooling tower with mechanical draught is usually based on the enthalpy difference method developed by Markel in 1925. It not only assumes that the Le number is equal to 1.0, but neglects the influence of water evaporation on the decreasing of water flow rate and inlet air relative humidity as well. In this paper, a set of differential equations, taking moisture content difference of air as the driving force, has been deduced. A computer program has been compiled to derive an accurate solution to the crossflow cooling tower. Besides, the approximate solutions based on the enthalpy difference method are also derived by a computer program, whose results have been compared with the exact solutions. It can be seen from the calculations that the approximate solution of the enthalpy difference method underestimates the volume of cooling tower fill. The difference is generally about 10-20%; in some cases it may even reach 30%. This must be seriously considered in the design of a crossflow cooling tower. The influence of some parameters on a crossflow cooling tower is analysed in this paper, such as the influence of inlet air dry and wet bulb temperature, water temperature difference, approach, baromeoer, and volumetric mass transfer coefficient on unit transfer number and the volume of the fill. The influence of weather parameters of different areas are also analysed in this paper. The results obtained are useful in the design of a crossflow cooling tower.