溴化锂溶液在微肋圆管外降膜吸收过程的传热传质性能研究
发布时间：2018-09-19 13:02
【摘要】：由于溴化锂吸收式冷水机组可以使用低品位热能作为驱动力,对环境无危害作用,并且在可利用余热、废热的场所具有不可替代的经济性,在减少环境污染、合理使用能源、缓解夏季电力紧张方面具有独特的优越性,所以得到越来越多的重视。但是和电制冷相比,较低的性能系数(COP)一直是制约其发展的重要因素。所以,提高溴化锂吸收式制冷系统的性能系数显得尤为重要。而在溴化锂吸收式制冷系统中,吸收器是其最为重要的部件之一,所以强化吸收器中传热传质的研究对提高整个吸收式制冷机组效率具有重大意义。本文通过建立在表面包敷一层金属丝网的强化换热管的二维模型,对溴化锂溶液在其表面降膜吸收过程的传热传质规律进行了理论和数值模拟研究。本文首先分析了溴化锂溶液在表面包敷金属丝网的换热管外降膜吸收的物理过程和强化传热传质机理。然后,将表面包敷金属丝网的换热管简化为表面带有矩形微肋的换热管,通过建立二维微肋圆管外溴化锂溶液降膜吸收的物理和数学模型,利用FLUENT软件进行数值模拟,分析了降膜过程中微肋圆管外溴化锂溶液的温度、速度和浓度的分布规律,并针对不同目数和丝径的金属丝网包敷的换热管进行了管外降膜吸收过程模拟,通过分析其传热传质规律,得出了包敷金属丝网的换热管提高传热传质效率最有利条件。最后,建立光滑表面换热管外降膜吸收模型并进行数值模拟,通过对光滑表面换热管和表面包敷金属丝网的换热管进行管外降膜吸收过程的传热传质规律对比分析,研究换热管包敷金属丝网后对传热传质的强化效果;此外,在前面模型的基础上研究了吸收器结构(换热管管径和间距)和吸收过程中溴化锂溶液变物性对降膜吸收过程传热传质效果的影响。研究结果表明:(1)通过和光滑换热管模拟结果对比,微肋换热管对溴化锂溶液降膜吸收过程的传热传质效果具有明显的强化作用;使用微肋换热管(包敷的金属丝网丝径为0.3mm、目数为30)时降膜吸收过程换热量要比使用光管时增加30%左右,水蒸气吸收量增加35%左右。(2)当换热管包敷丝径为0.3mm,目数为30的金属丝网时,降膜吸收过程的换热效果和吸收效果最好。(3)降膜吸收过程的换热量和吸收蒸气量随着微肋换热管的管间距和管径的比值S/D的增大而增大,随换热管直径D的增大而增大。(4)溶液为变物性时降膜吸收过程的换热量和吸收蒸气量比溶液为常物性时略小,但是变化量不大。
[Abstract]:Because the libr absorption chillers can use low grade thermal energy as the driving force, have no harm to the environment, and have irreplaceable economy in the places where the waste heat and waste heat can be used, it can reduce the environmental pollution and make rational use of energy. Because of its unique advantages in reducing power stress in summer, more and more attention has been paid to it. However, compared with electric refrigeration, low performance coefficient (COP) has been an important factor restricting its development. Therefore, it is very important to improve the performance coefficient of libr absorption refrigeration system. In the lithium bromide absorption refrigeration system, the absorber is one of the most important parts, so the study of heat and mass transfer in the absorber is of great significance to improve the efficiency of the whole absorption refrigeration unit. In this paper, the heat and mass transfer law of lithium bromide solution in the process of falling film absorption on the surface is studied theoretically and numerically by establishing a two-dimensional model of the enhanced heat transfer tube coated with a metal mesh on the surface. In this paper, the physical process of falling film absorption and the mechanism of enhanced heat and mass transfer in the heat transfer tube with lithium bromide solution coated with metal wire are analyzed. Then, the heat transfer tube coated with wire mesh on the surface is simplified as a heat transfer tube with rectangular ribs on the surface. The physical and mathematical models of falling film absorption of lithium bromide solution outside the tube are established, and the numerical simulation is carried out by using FLUENT software. The distribution law of temperature, velocity and concentration of lithium bromide solution outside the micro-ribbed tube was analyzed in the process of falling film, and the absorption process of falling film was simulated for the heat transfer tube coated with metal wire mesh with different mesh numbers and wire diameters. By analyzing the law of heat and mass transfer, the best conditions for improving the efficiency of heat and mass transfer are obtained. Finally, a falling film absorption model of a smooth surface heat exchanger tube is established and numerically simulated. The heat and mass transfer law of the falling film absorption process of the smooth surface heat transfer tube and the heat exchange tube coated with metal wire are compared and analyzed. The enhancement effect of heat and mass transfer on heat and mass transfer was studied after the heat transfer tube was coated with metal wire. Based on the previous model, the effects of the structure of absorber (diameter and spacing of heat transfer tubes) and the physical properties of lithium bromide solution on the heat and mass transfer in falling film absorption process are studied. The results show that: (1) compared with the simulation results of smooth heat transfer tube, the heat and mass transfer effect of the micro-ribbed tube on the falling film absorption process of lithium bromide solution is obviously enhanced; The heat transfer in the falling film absorption process is about 30% more than that in the light tube when the diameter of the wire mesh is 0.3 mm and the number of mesh is 30 mm using the micro-ribbed heat exchanger tube, and the heat transfer rate of the falling film is about 30% higher than that of the light tube. The absorption of water vapor is increased by about 35%. (2) when the wire diameter of the heat transfer pipe is 0.3 mm and the mesh number is 30, The heat transfer and absorption efficiency of falling film absorption process are the best. (3) the heat transfer and absorption vapor amount of falling film absorption process increase with the increase of the distance between tubes and the ratio of tube diameter S / D. (4) when the solution is variable physical property, the heat transfer and absorption vapor amount of the falling film absorption process is slightly smaller than that of the solution with constant physical property, but the change is not significant.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU831
本文编号：2250204
[Abstract]:Because the libr absorption chillers can use low grade thermal energy as the driving force, have no harm to the environment, and have irreplaceable economy in the places where the waste heat and waste heat can be used, it can reduce the environmental pollution and make rational use of energy. Because of its unique advantages in reducing power stress in summer, more and more attention has been paid to it. However, compared with electric refrigeration, low performance coefficient (COP) has been an important factor restricting its development. Therefore, it is very important to improve the performance coefficient of libr absorption refrigeration system. In the lithium bromide absorption refrigeration system, the absorber is one of the most important parts, so the study of heat and mass transfer in the absorber is of great significance to improve the efficiency of the whole absorption refrigeration unit. In this paper, the heat and mass transfer law of lithium bromide solution in the process of falling film absorption on the surface is studied theoretically and numerically by establishing a two-dimensional model of the enhanced heat transfer tube coated with a metal mesh on the surface. In this paper, the physical process of falling film absorption and the mechanism of enhanced heat and mass transfer in the heat transfer tube with lithium bromide solution coated with metal wire are analyzed. Then, the heat transfer tube coated with wire mesh on the surface is simplified as a heat transfer tube with rectangular ribs on the surface. The physical and mathematical models of falling film absorption of lithium bromide solution outside the tube are established, and the numerical simulation is carried out by using FLUENT software. The distribution law of temperature, velocity and concentration of lithium bromide solution outside the micro-ribbed tube was analyzed in the process of falling film, and the absorption process of falling film was simulated for the heat transfer tube coated with metal wire mesh with different mesh numbers and wire diameters. By analyzing the law of heat and mass transfer, the best conditions for improving the efficiency of heat and mass transfer are obtained. Finally, a falling film absorption model of a smooth surface heat exchanger tube is established and numerically simulated. The heat and mass transfer law of the falling film absorption process of the smooth surface heat transfer tube and the heat exchange tube coated with metal wire are compared and analyzed. The enhancement effect of heat and mass transfer on heat and mass transfer was studied after the heat transfer tube was coated with metal wire. Based on the previous model, the effects of the structure of absorber (diameter and spacing of heat transfer tubes) and the physical properties of lithium bromide solution on the heat and mass transfer in falling film absorption process are studied. The results show that: (1) compared with the simulation results of smooth heat transfer tube, the heat and mass transfer effect of the micro-ribbed tube on the falling film absorption process of lithium bromide solution is obviously enhanced; The heat transfer in the falling film absorption process is about 30% more than that in the light tube when the diameter of the wire mesh is 0.3 mm and the number of mesh is 30 mm using the micro-ribbed heat exchanger tube, and the heat transfer rate of the falling film is about 30% higher than that of the light tube. The absorption of water vapor is increased by about 35%. (2) when the wire diameter of the heat transfer pipe is 0.3 mm and the mesh number is 30, The heat transfer and absorption efficiency of falling film absorption process are the best. (3) the heat transfer and absorption vapor amount of falling film absorption process increase with the increase of the distance between tubes and the ratio of tube diameter S / D. (4) when the solution is variable physical property, the heat transfer and absorption vapor amount of the falling film absorption process is slightly smaller than that of the solution with constant physical property, but the change is not significant.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU831
【参考文献】
相关期刊论文 前8条
1 滕振亚;;吸收式制冷技术的应用与发展研究[J];山东工业技术;2014年21期
2 张峰榛;王海;刘兴勇;周小兵;;溴化锂溶液吸收制冷传热传质实验研究[J];四川理工学院学报(自然科学版);2014年05期
3 王长庆,陆震;吸收压力、溶液浓度、冷却水温度和流量对溴化锂吸收式制冷机吸收过程的影响[J];暖通空调;2001年04期
4 王长庆;吸收式制冷技术的应用与发展[J];能源技术;2000年01期
5 王长庆,陆震;吸收器结构对其性能影响[J];流体机械;1999年06期
6 胡德福;溴化锂吸收式制冷机高效传热管应用技术研究[J];船舶工程;1998年05期
7 崔晓钰,蔡祖恢,李美玲;膜内横向对流对溴化锂降膜吸收过程影响的数值计算[J];上海理工大学学报;1998年02期
8 李维,杨小琼,王启杰,罗来勤;水平圆管外溴化锂水溶液降膜吸收过程的数值分析[J];流体工程;1993年12期
相关会议论文 前1条
1 陈昀;解国珍;;溴化锂水溶液物性参数模拟计算和可视化编程[A];2004空调器、电冰箱（柜）及压缩机学术交流会论文集[C];2004年
相关博士学位论文 前1条
1 薄守石;溴化锂溶液降膜流动及传热传质的数值研究[D];大连理工大学;2011年
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