Abstract:

A refrigerant R141b-based nanofluid was made by hydroxylated carbon nano-tube particles in 0.01%, 0.03%, 0.05%, 0.07% and 0.10% mass fractions. An experimental study was carried out to investigate the nucleate boiling heat transfer characteristics of nanofluid on a smooth copper surface at pressure of 90.3 kPa. The surface roughness was made by sandpaper of grade 5000^#. The result illustrates that the boiling heat transfer is enhanced by increasing nanoparticles. The improvement is related to the coefficient of thermal conductivity, deposition of nanoparticles and their disturbances to flow. The heat transfer coefficient increases with nanoparticle mass added except in later boiling period. The coefficient of thermal conductivity of 0.10% nanofluid is 1.18 times that of pure fluid R141b. The heat transfer coefficient is increased by 168% for 0.05% mass fraction at the heat flux of 87.4 kW·m^-2. The boiling process of 0.03% mass fraction was recorded by the high-speed CCD.

Key words: hydroxylated, carbon nano-tubes, nanofluids, heat transfer, visualization with CCD, thermodynamic process

摘要：

向多壁碳纳米管引入羟基基团,改善了其在制冷剂R141b中的分散性和稳定性。同时研究了不同质量分数纳米流体热导率、表面颗粒沉积、接触角变化对核沸腾传热性能的影响。结果表明:羟基化碳纳米流体强化沸腾传热,强化率随质量分数的增加而增加,沸腾后期有所下降。在测试浓度范围内,质量分数为0.05%,热通量为87.4 kW·m^-2时,强化率达到最大168%。流体的热导率随着质量分数的增加而增大,质量分数为0.10%时其热导率是纯R141b的1.18倍。分析认为:纳米流体热导率的增加、表面沉积颗粒及纳米颗粒扰动是强化传热的主要影响因素,接触角变化的影响可忽略不计。结论由质量分数为0.03%纳米流体沸腾过程高速成像得到验证。

关键词: 羟基化, 碳纳米管, 纳米流体, 传热, CCD高速成像, 热力学过程