湿式冷却塔填料通道几何特性对于热力性能的影响研究

发布时间：2018-04-28 02:37

本文选题：冷却塔填料 + 数值模拟　；参考：《山东大学》2017年硕士论文

【摘要】：在电厂中,冷却塔的作用就是冷却温度较高的冷却水,通过塔内冷却水与空气的热量交换将热量扩散到空气中。在冷却塔内部,其冷却性能主要受填料的热力性能、运行的外界温度、给水量、外界风速、除水器等的影响。填料是冷却塔内非常重要的换热元件,分析其内部的气液换热性能对分析冷却塔的性能有重要意义。液膜的流动形态受到很多因素的影响,包括液体性质、壁面材质、壁面结构、风速、水速等,而液膜的形态是影响换热效果的重要因素,因此,本文从液膜形态的角度分析填料通道内气液两相流的流动与换热。本文首先通过壁面等效法建立了填料内气液两相逆向流动换热的数值计算模型,并通过对比与其他学者的计算结果验证了模型的准确性。通过此模型计算了弯曲的填料通道内的气液两相逆流换热的情况,分析了液相的流动状态随时间的变化。给出了填料通道内的温度场、压力场、液膜形态等参数随风速、水速、通道倾斜角度变化的规律。通过对模拟计算结果分析可知,在电厂的工况范围内提高风速能够有效的提高填料通道内的持液量,冷却效率,降低阻力系数。在电厂工况范围内提高进水速度使得填料通道内的液膜流动状态变差,冷却效率下降且阻力系数增加。文中分析了两种倾斜角的填料通道内液膜流动形态的差异,热力特性的差异,由结果表明,30°倾斜角的模型在冷却效果方面比45°和60°倾斜角的模型差,但在阻力方面比45°与60°倾斜角模型好,因此填料的倾斜角度的设置与实际工程的需求是相关的。通过计算三维通道内气液两相逆流过程的流动状态与换热,分析了三维通道内气液流动过程与气水比的关系,给出了流态、冷却效率、阻力系数随气水比变化的关系。通过分析计算结果可知,随着气水比的增加,填料通道内的冷却效率明显提高,且阻力系数有小幅度的减小。本文对不同的填料结构进行研究,分析了填料通道结构与热力特性的关系。给出了三种孔径的填料模型在液膜流动状态,持液量,温度场、冷却效率,阻力系数等参数的不同,并对影响差异的因素进行深入分析。通过对比结果发现,由于比表面积的差别,随着填料孔径的减小冷却效率有明显的提高。缩小后的阻力系数比改进前的结构有明显的减小。给出了三种波形的填料模型在冷却效率和阻力系数,并对影响因素进行了分析。由于S波通道其结构最复杂、持液量最大、比表面积最大,所以冷却效率最高,而斜波的比表面积最小其冷却效率最低。斜折波由于其结构上的优势而阻力系数最小,S波由于其弯曲通道的复杂性,其阻力系数最大。
[Abstract]:In the power plant, the cooling tower is used to cool the cooling water with higher temperature, which diffuses the heat into the air through the heat exchange between the cooling water and the air in the tower. In the cooling tower, the cooling performance is mainly affected by the thermal performance of the filler, the external temperature of the operation, the water supply, the external wind speed, the water remover and so on. Packing is a very important heat transfer element in cooling tower. It is very important to analyze the gas-liquid heat transfer performance of cooling tower. The flow pattern of liquid film is affected by many factors, including liquid property, wall material, wall structure, wind speed, water velocity and so on. In this paper, the flow and heat transfer of gas-liquid two-phase flow in packing channel are analyzed from the point of view of liquid film morphology. In this paper, the numerical model of heat transfer of gas-liquid two-phase reverse flow in packing is established by wall equivalent method, and the accuracy of the model is verified by comparing the results with those of other scholars. Through this model, the heat transfer of gas-liquid two-phase countercurrent in the curved packing channel is calculated, and the change of liquid phase flow state with time is analyzed. The variation of temperature field, pressure field and liquid film shape with wind speed, water velocity and channel inclination angle are given. Through the analysis of the simulation results, it can be seen that increasing the wind speed in the power plant can effectively increase the liquid holdup, cooling efficiency, and reduce the resistance coefficient in the packing channel. Increasing the influent speed in the power plant makes the liquid film flow in the packing channel worse, the cooling efficiency decreases and the resistance coefficient increases. In this paper, the differences of liquid film flow patterns and thermodynamic characteristics in two kinds of tilted packing channels are analyzed. The results show that the model of 30 掳tilting angle is worse in cooling effect than that of 45 掳and 60 掳tilting angles. But the resistance is better than that of 45 掳and 60 掳angle model, so the setting of the tilting angle of packing is related to the requirement of practical engineering. By calculating the flow state and heat transfer of gas-liquid two-phase countercurrent in three-dimensional channel, the relationship between gas-liquid flow process and gas-water ratio in three-dimensional channel is analyzed, and the relationship among flow state, cooling efficiency and resistance coefficient with gas-water ratio is given. The results show that with the increase of air-water ratio, the cooling efficiency in the packing channel is obviously increased, and the resistance coefficient is reduced to a small extent. In this paper, different packing structures are studied, and the relationship between packing channel structure and thermal characteristics is analyzed. In this paper, three kinds of packing models with pore diameter are given, and the factors influencing the difference are analyzed, such as the flow state of liquid film, liquid holdup, temperature field, cooling efficiency, resistance coefficient and so on. The results show that the cooling efficiency increases with the decrease of packing aperture due to the difference of specific surface area. The reduced resistance coefficient is obviously smaller than that of the improved structure. The cooling efficiency and drag coefficient of the packing models with three waveforms are given, and the influencing factors are analyzed. Due to the most complex structure, the largest liquid holdup and the largest specific surface area of the S-wave channel, the cooling efficiency is the highest, while the minimum specific surface area of the oblique wave is the lowest. The resistance coefficient of oblique fold wave is the smallest because of its advantage in structure. Because of the complexity of the curved channel, the resistance coefficient is the largest.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM62

【相似文献】