喷雾直接蒸发冷却过程数值模拟与实验研究

发布时间：2018-04-06 23:22

本文选题：喷雾　切入点：直接蒸发冷却　出处：《重庆大学》2014年硕士论文

【摘要】：机械制冷的普遍使用导致空调能耗居高不下，夏季高温天气亦使城区热环境逐渐恶化。推广蒸发冷却技术能够一定程度上改善机械制冷耗能、影响环境的现状。近年来，作为直接蒸发冷却技术应用的新形式，喷雾降温日益受到重视，具有节能、高效、环保的优点，与常规直接蒸发冷却空调机组相比，，无需循环水、设备结构简化、蒸发效率高，应用前景广阔。本文对喷雾直接蒸发冷却系统进行了数值模拟和实验研究，针对喷雾降温过程中的关键问题，进行了以下探索。首先对喷雾降温传热传质过程进行分析，建立液滴群与空气热质交换的平衡方程，以及单个液滴与空气传热传质的数学模型。通过数学模型分析影响传热传质过程的主要因素，并建立数学模型作为数值模拟的基础，通过理论对数值模拟中模型的选择提供了指导。对于直接蒸发冷却过程的计算，无论是理论分析的方法还是实验研究的方法都有较大的限制，对于复杂的数学模型，计算流体力学（CFD）提供了一种可行的计算方法，具有成本较低且能模拟较复杂的过程等优点。基于计算流体力学软件FLUENT，对空气中喷雾蒸发过程的模型原理和方法进行了阐述，分别从连续相和离散相理论、相间计算的耦合方式、各相重要参数设置等问题上进行了探索，并总结出喷雾直接蒸发冷却过程的模拟方法。合理的数学模型和数值模拟方法对实验研究和理论分析具有指导作用，可以弥补实验工作的不足。提出了评价喷雾降温效果的参数和方法。搭建喷雾降温系统实验平台，对高温环境下的喷雾降温效果进行了实验测试。通过实验结果分析了室外空气参数和喷雾水气比的变化对蒸发效率和饱和效率的影响，并建立了与实验对应的物理模型，采用离散相计算模型进行数值模拟，得到喷雾降温后的温度场、湿度场，并将实验与模拟结果进行了比较，证明了数值模拟方法的可行性。采用数值模拟方法，对喷雾降温系统进行了变工况模拟，以优化的喷雾降温系统。数值模拟进行的工况有： 1)建立管道内喷雾蒸发冷却系统，研究雾滴粒径、喷头间距、风速和喷雾比等参数的改变对管内喷雾降温蒸发效率的影响。 2)对实验模拟模型增添模拟工况，对室外参数和水气比变化对喷雾降温效果的影响进行了深入分析。 3)对室外开敞空间进行了数值模拟，主要对风速和喷雾流量参数对固定人行高度处的喷雾降温效果的影响进行了分析。对于管道内喷雾降温，通过数值模拟方法进行优化设计后，在最优工况下蒸发效率可以接近100%，饱和效率可达到90%以上。不同于有限空间的喷雾降温过程，室外喷雾降温的效果与外场风速、风向密切相关，降温范围随风场的扩大或缩小直接导致降温效果的不同。对于管道内喷雾降温系统，数值模拟方法在研究喷雾降温机理、设备开发和优化方面体现了重要价值。对于室外开敞空间的喷雾降温，数值模拟能够通过模拟进行效果预测，对指导喷雾降温系统的布置方案具有指导意义。
[Abstract]:In recent years , as a new form of direct evaporative cooling technology application , spray cooling is becoming more and more important , which has the advantages of energy saving , high efficiency and environmental protection . In recent years , as a new form of direct evaporative cooling technology application , it has the advantages of energy saving , high efficiency and environmental protection , and has the advantages of energy saving , high efficiency and environmental protection .

First , the heat and mass transfer process of spray cooling is analyzed , the equilibrium equation of droplet group and air heat mass exchange is established , and the mathematical model of the heat and mass transfer of single liquid droplet and air is established . The mathematical model is used as the basis for numerical simulation , and the mathematical model is established as the basis of numerical simulation .

Based on the computational fluid mechanics software FLUENT , the model principle and method of spray evaporation in air are described , and the simulation method of direct evaporative cooling process is summarized . The mathematical model and numerical simulation method are used to guide the experimental research and theoretical analysis , which can make up for the shortage of experimental work .

The parameters and methods for evaluating the cooling effect of spray are put forward . The experimental platform of spray cooling system is set up to test the effect of spray cooling in high temperature environment . Through the experimental results , the effects of outdoor air parameters and spray water - gas ratio on evaporation efficiency and saturation efficiency are analyzed . The physical model corresponding to the experiment is established , and the temperature field and humidity field after spray cooling are obtained by using the discrete - phase calculation model , and the experiment and simulation results are compared . The feasibility of the numerical simulation method is proved .

A numerical simulation method was used to simulate the spray cooling system to optimize the spray cooling system . The numerical simulation was carried out with the following conditions :

1 ) The effect of changing parameters such as droplet size , nozzle spacing , wind speed and spray ratio on the efficiency of spray cooling and evaporation in the pipe was studied by establishing a spray evaporative cooling system in the pipeline .

2 ) The simulation working condition is added to the experimental simulation model , and the influence of outdoor parameters and water - gas ratio changes on the cooling effect of the spray is analyzed in depth .

3 ) Numerical simulation of outdoor open space is carried out , and the influence of wind speed and spray flow parameters on the spray cooling effect at fixed pedestrian height is analyzed .

For the spray cooling in the pipeline , the evaporation efficiency can be close to 100 % and the saturation efficiency can reach more than 90 % under the optimum working conditions . The effect of the outdoor spray cooling is closely related to the wind speed and the wind direction of the external field . The temperature reduction range is directly related to the expansion or contraction of the wind field , which directly leads to the difference of the cooling effect .

For the spray cooling system in the pipeline , the numerical simulation method reflects the important value in the research of the spray cooling mechanism , the equipment development and the optimization . For the spray cooling of the outdoor open space , the numerical simulation can predict the effect through simulation , which can guide the layout of the spray cooling system .

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU831.6

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