溴化鋰溶液在微肋圓管外降膜吸收過(guò)程的傳熱傳質(zhì)性能研究
發(fā)布時(shí)間：2018-09-19 13:02
【摘要】：由于溴化鋰吸收式冷水機(jī)組可以使用低品位熱能作為驅(qū)動(dòng)力,對(duì)環(huán)境無(wú)危害作用,并且在可利用余熱、廢熱的場(chǎng)所具有不可替代的經(jīng)濟(jì)性,在減少環(huán)境污染、合理使用能源、緩解夏季電力緊張方面具有獨(dú)特的優(yōu)越性,所以得到越來(lái)越多的重視。但是和電制冷相比,較低的性能系數(shù)(COP)一直是制約其發(fā)展的重要因素。所以,提高溴化鋰吸收式制冷系統(tǒng)的性能系數(shù)顯得尤為重要。而在溴化鋰吸收式制冷系統(tǒng)中,吸收器是其最為重要的部件之一,所以強(qiáng)化吸收器中傳熱傳質(zhì)的研究對(duì)提高整個(gè)吸收式制冷機(jī)組效率具有重大意義。本文通過(guò)建立在表面包敷一層金屬絲網(wǎng)的強(qiáng)化換熱管的二維模型,對(duì)溴化鋰溶液在其表面降膜吸收過(guò)程的傳熱傳質(zhì)規(guī)律進(jìn)行了理論和數(shù)值模擬研究。本文首先分析了溴化鋰溶液在表面包敷金屬絲網(wǎng)的換熱管外降膜吸收的物理過(guò)程和強(qiáng)化傳熱傳質(zhì)機(jī)理。然后,將表面包敷金屬絲網(wǎng)的換熱管簡(jiǎn)化為表面帶有矩形微肋的換熱管,通過(guò)建立二維微肋圓管外溴化鋰溶液降膜吸收的物理和數(shù)學(xué)模型,利用FLUENT軟件進(jìn)行數(shù)值模擬,分析了降膜過(guò)程中微肋圓管外溴化鋰溶液的溫度、速度和濃度的分布規(guī)律,并針對(duì)不同目數(shù)和絲徑的金屬絲網(wǎng)包敷的換熱管進(jìn)行了管外降膜吸收過(guò)程模擬,通過(guò)分析其傳熱傳質(zhì)規(guī)律,得出了包敷金屬絲網(wǎng)的換熱管提高傳熱傳質(zhì)效率最有利條件。最后,建立光滑表面換熱管外降膜吸收模型并進(jìn)行數(shù)值模擬,通過(guò)對(duì)光滑表面換熱管和表面包敷金屬絲網(wǎng)的換熱管進(jìn)行管外降膜吸收過(guò)程的傳熱傳質(zhì)規(guī)律對(duì)比分析,研究換熱管包敷金屬絲網(wǎng)后對(duì)傳熱傳質(zhì)的強(qiáng)化效果;此外,在前面模型的基礎(chǔ)上研究了吸收器結(jié)構(gòu)(換熱管管徑和間距)和吸收過(guò)程中溴化鋰溶液變物性對(duì)降膜吸收過(guò)程傳熱傳質(zhì)效果的影響。研究結(jié)果表明:(1)通過(guò)和光滑換熱管模擬結(jié)果對(duì)比,微肋換熱管對(duì)溴化鋰溶液降膜吸收過(guò)程的傳熱傳質(zhì)效果具有明顯的強(qiáng)化作用;使用微肋換熱管(包敷的金屬絲網(wǎng)絲徑為0.3mm、目數(shù)為30)時(shí)降膜吸收過(guò)程換熱量要比使用光管時(shí)增加30%左右,水蒸氣吸收量增加35%左右。(2)當(dāng)換熱管包敷絲徑為0.3mm,目數(shù)為30的金屬絲網(wǎng)時(shí),降膜吸收過(guò)程的換熱效果和吸收效果最好。(3)降膜吸收過(guò)程的換熱量和吸收蒸氣量隨著微肋換熱管的管間距和管徑的比值S/D的增大而增大,隨換熱管直徑D的增大而增大。(4)溶液為變物性時(shí)降膜吸收過(guò)程的換熱量和吸收蒸氣量比溶液為常物性時(shí)略小,但是變化量不大。
[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.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TU831
本文編號(hào)：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.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TU831
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