【作者】 陈萍；

【导师】 晋欣桥；

【作者基本信息】 上海交通大学 ， 制冷及低温工程， 2011， 硕士

【摘要】 翅片管换热器在动力、化工、石油化工、制冷工程中应用非常广泛,是当前使用最多的换热器之一。因此,分析和研究翅片管换热器的特性,不仅有很重要的现实意义,而且对当前的节能减排有重要的推动作用。影响翅片管换热器性能的参数主要包括翅片间距、管排数、翅片厚度、管径、翅片材料、管内介质温度、流量、干湿球温度、流速和换热器倾斜角度等方面。目前,由国内外大量的研究资料可以看出,对换热器的倾斜角度以及进风条件对其换热及压降的影响的研究比较少,多集中在翅片管换热器本身的结构参数上。本文利用焓差法实验台对换热器进行实验,除了保证传感器的精度外,还必须保证实验工况的稳定性。实验工况的稳定性已经在搭建实验台阶段经过调试得到保证,也得到了稳定的测试方法。本文即对所选被测换热器通过此种测试方法进行实验。本文的研究对象是换热器的空气侧换热及压降特性。本文以实验作为主要研究手段,同时辅助于CFD数值模拟的方法,对不同倾斜角度的换热器、分别在自由进风及受限进风条件下的性能进行了研究和分析。主要研究工作内容有:1.实验研究了自由进风下换热器的传热及压降特性被测换热器在6种倾斜角度(-60°,-45°,-30°,30°,45°,60°)下空气侧的换热及压降特性有何不同;2.实验研究了当换热器在以上六种倾斜角度下,自由进风和受限进风对空气侧换热和压降特性的影响;3.实验研究了在受限进风条件下,当换热器倾斜角度相同时,换热器空气侧换热和压降特性受进风角度的影响。4.空气侧换热特性的数值模拟计算利用Fluent软件对换热器进行数值模拟,对实际被测换热器进行了模型简化,计算了自由进风条件和受限进风条件下换热器空气侧换热系数,选取了几种角度下的计算结果与对应的实验结果相比较,由实验和模拟的结果可以看出该实验和模型结果可靠性。通过以上的研究工作,得出了以下结论:1.在自由进风条件下,换热器倾角θ=±45°时的换热系数较高,正倾斜角度的换热效果优于负倾斜角度,数值模拟结果发现在θ=±45°时出口空气平均温度低于其他角度的出口空气平均温度,故换热系数较高;2.压降随着倾斜角度θ的绝对值的增大而增大;3.在正倾斜角度下,自由进风的换热效果优于受限进风的换热效果,负倾斜角度得到的结果相反。数值模拟选取负倾斜角度研究,发现负倾斜角度下自由进风的换热器出口空气平均温度高于受限进风条件下的温度,故换热系数前者高于后者。4.压降不受有无进风管存在的影响;5.相同倾斜角度下,换热和压降都不受进风角度的影响。并且数值模拟的结果可以发现由于空气回流的影响使得进风角度对换热不起作用;6.不同的进风角度对压降的影响很小。更多还原

【Abstract】 The fin-tube heat exchanger is widely used in power, chemical, petrochemical, refrigeration engineering. Currently, it is one of the most used heat exchanger. To analyse and study the characteristics of fin-tube heat exchanger not only has important practical significance, but also is an important role in promoting the current energy conservation.The parameters, which can influence the performance of fin-tube heat exchanger, include fin pitch, row number, fin thickness, tube diameter, fin material, media temperature and flow rate inside the tube, dry bulb and wet bulb temperature, air velocity and installation inclination. However, it has hardly reported in the field study that the impact of installation inclination and inlet condition on the performance of heat transfer and pressure drop, most of the studies are focused on the structural parameters of fin-tube heat exchanger.In this study, the heat exchanger is tested on the test rig with using of enthalpy difference method. To ensure precision of test results, the accuracy of the sensors and the stability of the experimental conditions should be validated. And they are done when the test rig is setting.The object of this study is to evaluate the performance of heat transfer and pressure drop of heat exchanger under the different inlet conditions. Based on experiment, the effects of the different inclination angles and the effects of free and restricted air intaking conditions are included. To validate the test result, a CFD simulation model is setup to analyse the performance of the heat exchanger. The following contents are included in this study:1. Experimental studies are carried out to analyse the performance of heat transfer and pressure drop under free air inlet condition with six inclination angles(-60°,-45°,-30°,30°,45°,60°);2. Experimental studies are carried out to analyse the influence on heat transfer and pressure drop under free and restricted air inlet conditions with six inclination angles listed above;3. Experimental studies are carried out to analyse airside performance of heat transfer and pressure drop with the same inclination angle under restricted air inlet condition. 4. Numerical simulation of airside heat transfer performance.The simulation model based on Fluent software is setup by simplified the actual model, and the heat transfer coefficient under free and restricted air inlet conditions are simulated. Several inclination angles are selected to compare the results with the experimental results to investigate the reliability.Some conclusions are obtained after the studies listed above:1. Under free air inlet condition, the heat transfer coefficient of inclination angleθ=±45°is larger than that of others. The heat transfer coefficient of positive inclination angle is better than that of negative inclination angle. The results of simulation show that the outlet air average temperature whenθ=±45°is lower than other inclination angles;2. Pressure drop increases with the increasing of the absolute value of the inclination angleθ;3. When the inclination angle is positive, the heat transfer under free air inlet condition is better than that under restricted air inlet condition. The result is opposite when the inclination angle is negative. The results of simulation show that the outlet air average temperature under restricted air inlet condition is lower than that under free air inlet condition;4. The existence of duct has no effect on pressure drop; 5. When the inclination angle is the same, inlet air angle has no effect on heat transfer and pressure drop. The simulation shows the same result;6. Inlet air angle has less effect on the pressure drop of the heat exchanger.更多还原