【作者】 何叶从；

【导师】 付祥钊；

【作者基本信息】 重庆大学 ， 供热、供燃气、通风与空调工程， 2009， 博士

【摘要】 由于地铁沿线通常是城市最繁华的地区,地铁站附近更是寸土寸金,在地铁站地面上设置冷却塔,不仅成本高昂,而且影响城市景观和环境,带来极大的噪声污染和卫生隐患,迫切需要一种高效换热器替代目前常用的冷却塔,将冷却塔移入地铁站排风通道内,解决地铁站等地下建筑设置冷却塔的问题,本文通过调研地铁站排风通道内空气参数、比较现有换热器的传热机理、优选冷却方式,开发了一种新型间接蒸发冷却器,对其传热传质机理和性能进行理论和实验研究。本文研究的换热器是地铁站内排风通道内运行,排风通道内空气温湿度直接决定其性能,通过对广州地铁几个曲型站台的排风通道空气参数实测分析,发现在全新风工况下,地铁站排风通道内空气温、湿度没有明显升高,个别站台排风通道内空气参数甚至朝有利于传热传质的方向发展,表明排风通道内热湿源对排风温湿度影响很小,将冷却塔移入站台内部可行。通过对现有间接蒸发冷却器传热机理的比选研究,研发了一种新型螺旋管换热器(专利申请号:200910300390.3),利用fluent软件模拟分析了换热器的强化传热机理,研究了螺旋管换热器和蛇形管换热器在不同R/r比值下的二次环流,确定了螺旋管换热器R/r临界值,研究发现:蛇形管换热器在半圆形折返管出口形成稳定的二次环流,进入直管段100～200mm时,二次环流消失;螺旋管换热器中始终存在稳定的二次环流,对管内流体边界层的扰动始终存在,实验研究发现,与蛇形管换热器相比,螺旋管换热器换热性能提高40%左右。通过对固定喷雾冷却、喷淋水冷却(光管)、旋转喷雾冷却、换热器表面包覆吸水材料时的喷淋水冷却四种冷却方式的比选研究,确立旋转喷雾冷却为最佳冷却方式,研究发现:旋转喷雾冷却比固定喷雾冷却提高32%;与喷淋水冷却相比,旋转喷雾冷却换热能力提高将近80%;换热器表面包覆吸水材料初期能提高换热器性能,长期运行后换热器表面结垢、起泡现象严重,热阻迅速增加,布水均匀性恶化,削弱换热器换热。由于换热器表面水膜的均匀性和完整性对换热器性能有重要影响,本文提出了在每个换热器两侧旋转布水,利用喷雾液滴高速冲击换热器表面,形成厚度极薄的完整、均匀的水膜强化传热的理念,开发出相应的旋转布水装置(专利申请号:200910300391.8,200910300388.6)和新型气水雾化喷嘴(专利申请号:200820303833.5),发明了一种适合于地铁等地下建筑使用的新型间接蒸发冷却器(专利申请号:200910300389.0),确定了任意喷嘴布局方式时旋转装置所需的喷嘴数量,布水速度(转速)与喷嘴喷射方向与换热器表面法向夹角α、喷雾介质流量、喷嘴出口孔径等因素的关系,液滴在空气中的运动状态,奠定换热器传热性能分析的基础,实验研究了喷雾系统流量、喷嘴出口孔径,喷嘴喷射方向与换热器表面法向夹角α等参数对布水速度和雾化角的影响,获得了旋转装置的阻力、喷嘴雾化角的拟合公式及泄漏系数,确定了换热器关键运行参数――喷雾系统参数,为深入研究换热器性能提供基础数据。旋转喷雾布水冷却时,液滴粒径的大小决定换热器表面水膜状态和飘逸损失量和换热器外侧空气温湿度,喷嘴雾化角及液滴分布决定喷嘴数量和压缩空气量,本文在理论计算基础上初步确定喷嘴结构尺寸,利用fluent软件详细分析了喷嘴出口孔径、气水比对喷嘴性能的影响,研究发现:喷嘴出口孔径为0.6mm,最佳气水比对应的压缩空气量为8m3/h,液滴粒径60μm,雾化角为100°。建立了地铁专用间接蒸发冷却器――旋转喷雾间接蒸发冷却器传热模型,研究了换热器的传热传质机理,着重分析了喷雾水液滴、换热器表面水膜与空气的传热传质过程,获得了预冷后的水膜温度和喷雾水飘逸损失量和换热器最佳管长,分析了喷雾水流量,冷却水流量,空气温、湿度和换热器螺旋间距对换热器性能的影响,利用Matlab软件编写求解程序,获得了换热器熵产变化,最佳管长、阻力性能,研究发现,换热器最佳管长仅与螺旋间距和换热器直径有关,空气速度和喷雾水量存在最佳值。采用正交实验验证了模型中各参数对换热器性能的影响,研究不同换热器管径,喷雾水流量,空气流速,空气温、湿度时换热器的性能,分析了两个换热器并联运行时的换热情况,研究发现:空气流速为3m/s,喷雾水量为20L/h、压缩空气量为8m3/h时,换热器换热量最大;两个换热器叉排、并联运行时,其中一个换热器的换热量与单个换热器独立运行时的换热量相差很小,运行费下降将近一半;换热器表面有油污时,换热器表面水膜状态恶化,换热能力降低20%。经济性分析发现:在不考虑地铁站台土地成本基础上,换热器管长满足最佳管长,两个换热器叉排、并联运行时,其成本和运行费与冷却塔基本持平,该换热器可安装于地铁等地下建筑的排风通道内,实现了将冷却塔移入地下的构想,具有重大的经济意义。更多还原

【Abstract】 Along the MTR lines are the city’s most prosperous regions, the land prices nearby the subway station are more expensive. if the cooling tower is installed on the ground of the MTR station, not only the cost is very high, but also lead to the noise pollution, health problems, and impact the urban landscape. it is urgent need an efficient heat exchanger to alternative the currently used cooling tower, move the cooling tower into the MTR station and solve the problem that there is no place fo installing the cooling tower of the underground building, such as the subway station. This paper developed a new heat exchanger by researching the air parameters of the subway station’s exhaust channel, Comparing the heat and mass transfer mechanism of the existing heat exchangers, and optimizing the cooling methods, and making use of the computational fluid dynamics, Engineering Thermodynamics and the heat transfer theory to study heat and mass transfer mechanism and the performance of the heat exchanger.The air parameters of the exhaust channel where the new heat exchanger that we developed is installed in the station, directly determine whether the heat exchanger is high efficiency. Several significant station’s air parameter of the Guangzhou Metro has been measured, it is find that moving the cooling tower into the MTR station from the ground is theoretically possible, because the air temperature and the humidity are not significantly higher on new wind operating conditions, some one even develop to the direction that benefit heat exchange, the heat and wet sourse in the exhaust channel has little effect on the air temperature and humidity.A new type of spiral heat exchanger (patent application number: 200910300390.3) was put forward through comparison of the existing indirect evaporative cooler, the secondary flow phenomenon in the spiral heat exchanger and the coiled tube heat exchanger is simulated using CFD, and identified the R/r critical value by comparing the secondary flow at different R/r value and mass flow rate. And found that the secondary flow phenomenon only exists at the entrance of the semi-annulus reentry pipe of the coiled tube heat exchanger, and disappeared rapidly 100～200mm away from the exit of straight tube, but always exists in the spiral heat exchanger, thus leads to the disturbance of the boundary layer always exists, compared to the coiled heat exchanger, the performance of the spiral heat exchanger improved about 40% .Experimental studied the performance of the heat exchangers by fixed spray cooling, spray cooling (fluorescent tubes and coated water-absorbent material), rotary spray cooling, and established the rotary spray cooling is the best cooling method. Compared to the fixed spray cooling and the spray cooling, the rotary spray cooling has improved the heat flux, respectively, 32% and 80%。Initially, coated water-absorbent material on the surface of the heat exchanger can enhance the performance of the heat exchanger, after running a week, the water-absorbent material fouled foamed seriously which lead to the thermal resistance increased and deteriorated the uniformity of the water film,so,coated water-absorbent material weak the performance of the heat exchanger.Because of the uniformity and integrity of the water film has an important impact on the performance of the heat exchanger, in this paper, a novel conception is put forward that rotating spray cooling on both sides of the special heat exchanger to form uniform, complete water film, and developed a new rotating water distribution installation(patent application number: 200910300391.8,200910300388.6) and a new type gas-water atomization(patent application number:200820303833.5),thus constituted a new indirect evaporative cooler(patent application number: 200910300389.0) with the former installations, obtained the required quantity of the nozzle, identified fitting function of the rotate speed that influenced by the frictional resistance, the angle between the spray direction and the direction vertical to the heat exchanger surface, the mass flow rate of the water and the compressed air,analysised the droplets distribution in the air, experimental studied its frictional resistance and the spray angle that influenced by the parameters that the mass flow rate of the spray medium ,the angle between the spray direction and the direction vertical to the heat exchanger surface and the nozzle exit diameter, acquired fitting function of the rotate speed , the spray angle and the leakage coefficient, determined the key parameters of the spray system, to provide the basic data for the research of the heat exchanger.The droplet size has important impact on the air temperature, humidity and the state of the water film, the quantity of the nozzle and the compressed air are determined by the spray angle and the droplet distribution, acquired the initial structures parameters of the nozzle through theoretical calculation, and make use of the CFD to analysis the influence of the ratio between the mass flow rate of the compressed air and the spray water , the nozzle exit diameter on the performance of the nozzle, when the nozzle exit diameter d= 0.6mm, the compressed air mass flow rate of the optimum ratio is 8 m3/h,and its atomization is best, the spray angle is 100°.Set up the heat transfer model of the rotary spray indirect evaporative cooler for the MTR, studied the heat and mass transfer mechanism of the heat exchanger, analysised the heat and mass transfer process between the spray water and the droplet, and the process between the water film and air, obtained the cooled water film temperature by first cooling ,the float rate of the spray water and the best tube length of the Spiral heat exchangers,rasearched the performance with different parameters that the mass flow rate of the spray water and the cooling water, air temperature, humidity and the structural parameters of the heat exchanger. and solved it using Matlab software, acquired the temperature of the cooling water and the water film along the tube, and the air enthalpy, entropy, resistance and the optimum tube length of the heat exchanger which is short for Lopt, and found that the Lopt is only concerned with the spiral pitch and the diameter of the heat exchanger, the air speed and spray water exist the best values.The influence on the performance of the tube diameter, mass flow rate of the spray water, air velocity, air temperature and humidity is studied by orthogonal test. Experimentally researched the performance and found that the heat flux is maximum when the air velocity is 3m/s, the volume flow rate of the compressed air and the spray water are, respectively, 8 m3/h and 20L/h; when two heat exchangers operating in parallel, the difference between the heat flux of one exchanger and a single one running independent is very small, and the compressed air volume will be halved; if the surface has oil ,the heat flux will reduce by 20%.Through simple economic analysis of the rotary spray indirect evaporative cooler and the closed cooling tower that current commonly used, found that without considering the land costs of the cooling tower that installed on the ground of MTR station, the costs of the heat exchanger nearly the same when the tube length reach to the Lopt value, and operating in parallel, and come true the dream that moving the cooling tower into the station from the ground floor, and solved the problem that there is no place for installing the cooling tower in the MTR station, is of great economic significance.更多还原