纳米颗粒强化溴化锂溶液的传热特性研究

发布时间：2018-06-02 12:51

本文选题：纳米流体 + 导热系数　；参考：《青岛科技大学》2015年硕士论文

【摘要】：随着全世界能源消耗量增加与资源短缺之间的矛盾日益加剧以及环境污染日益严重,寻求低耗能、低污染工业产业的呼声越来越高。纳米粒子作为一种具有特殊性能的物质成为研究者研究的热点,并逐渐被应用于各行业中。将纳米粒子均匀分散于基液中,制备出性能稳定的新型换热工质,是提高换热设备换热能力的重要举措。本文将两种纳米粒子添加到浓度为50%的溴化锂溶液中,采用“两步法”制备分散性能优异的纳米流体。采用自制的热探针式导热仪测试了纳米流体的导热系数。用乌氏粘度计测量了纳米流体的粘度。采用重力沉降法观察了纳米流体的稳定性。实验结果表明,纳米粒子浓度与分散剂的添加量是影响纳米流体导热性能及粘度的重要影响因素。随着纳米粒子质量分数的增加,纳米流体导热系数跟粘度均呈现先逐渐增加后趋于平缓并略有下降的趋势。阿拉伯胶添加量对液体粘度的影响明显大于纳米粒子。溴化锂溶液中添加CNT纳米粒子质量分数为1.0%,阿拉伯胶添加量为0.4%时,纳米流体导热系数增加了约22%。设计组建了单管喷淋换热系统实验台,研究分析了喷淋密度、温度、管间距以及碳纳米管浓度等因素对纳米流体喷淋换热性能的影响。实验结果表明,管间距、喷淋密度、热水温度、CNT浓度等因素对管外平均换热系数均有影响。随着喷淋密度跟管间距的增大,管外平均换热系数均先增大后降低；当管间距为换热管管径的1.2倍,喷淋密度为Γ=0.0833～0.104kg/(ms)时,效果最佳。随着CNT纳米粒子浓度的增加,管外平均换热系数先逐渐增大,后趋于平稳。当添加的质量分数为0.8%时,管外平均换热系数增加了31%。在溴化锂溶液中添加CNT纳米粒子能显著提高液体的导热、换热性能。建立了水平管外降膜流动的二维模型,模拟了溴化锂溶液在水平管外的降膜流动特性。研究分析了喷淋密度、管间距以及管径对降膜流动的影响。结果表明,管间距、喷淋密度和管径对液膜分布及液膜厚度均有不同程度的影响。采用合适的管间距和喷淋密度才能使换热系统性能达到最优。
[Abstract]:With the increasing contradiction between the increasing energy consumption and the shortage of resources and the increasingly serious environmental pollution, there is a growing demand for low energy consumption and low pollution industrial industries. As a kind of material with special properties, nanoparticles have become the research hotspot of researchers, and have been gradually applied in various industries. It is an important measure to improve the heat transfer capacity of heat transfer equipment by uniformly dispersing nanoparticles in the base solution to prepare new heat exchanger with stable performance. In this paper, two kinds of nanoparticles were added to 50% lithium bromide solution to prepare nano-fluid with excellent dispersion performance by "two-step method". The thermal conductivity of nanofluids was measured by a self-made thermal probe thermal conductivity instrument. The viscosity of nanoscale fluid was measured by using the Wurtzian viscometer. The stability of nanoscale fluid was observed by gravity sedimentation method. The experimental results show that the concentration of nanoparticles and the amount of dispersant are important factors affecting the thermal conductivity and viscosity of nano-fluids. With the increase of the mass fraction of nano-particles, the thermal conductivity and viscosity of nano-fluids increase gradually and then gradually decrease. The effect of Arabic gum addition on the viscosity of liquid is obviously greater than that of nanoparticles. When the mass fraction of CNT nanoparticles in lithium bromide solution is 1.0 and the amount of Arabic gum is 0.4, the thermal conductivity of nano-fluids increases by about 22g. A single tube spray heat transfer system was designed and constructed, and the effects of spray density, temperature, tube spacing and carbon nanotube concentration on the spray heat transfer performance of nano-fluid were studied and analyzed. The experimental results show that the average heat transfer coefficient outside the tube is affected by such factors as tube spacing, spray density and CNT concentration of hot water. With the increase of spray density and tube spacing, the average heat transfer coefficient first increases and then decreases, and the effect is the best when the tube spacing is 1.2 times of the diameter of the heat exchanger tube and the spray density is 螕 0.0833 ~ 0.104 kg 路s ~ (-1) 路m ~ (-1). With the increase of the concentration of CNT nanoparticles, the average heat transfer coefficient firstly increases gradually, and then tends to steady. When the mass fraction is 0.8, the average heat transfer coefficient increases by 31. The addition of CNT nanoparticles in lithium bromide solution can significantly improve the thermal conductivity and heat transfer properties of the liquid. A two-dimensional model of falling film flow outside a horizontal tube was established, and the falling film flow characteristics of lithium bromide solution outside the horizontal tube were simulated. The effects of spray density, tube spacing and pipe diameter on the falling film flow are studied and analyzed. The results show that the distance between tubes, spray density and diameter have different effects on the distribution and thickness of liquid film. The optimal performance of the heat transfer system can be achieved by adopting proper pipe spacing and spray density.
【学位授予单位】：青岛科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1

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