碳纳米管-水纳米流体的光热转化特性

摘要

Stable aqueous suspensions of multi-walled carbon nanotubes (MWCNTs)with mass fractions ranging from 0.0015% to 0.1% were prepared via two-step method.The impacts of mass fraction,setting time,and heating times on the optical absorption property of MWCNT-H 2 O nanofluid were investigated according to the transmittance measured by UV-VIS-NIR spectrophotometer over the wavelength from 200 to 2000 nm.Furthermore,an insolation experiment was performed to investigate the effects of mass fraction and light irradiation times on the photo-thermal property of MWCNT-H 2 O nanofluids.Results show that the transmittance of MWCNT-H 2 O nanofluid was decreased evidently after the addition of MWCNTs in deionized (DI)water,and long setting time leads to smaller transmittance.Heating is beneficial to improve light-absorption property of nanofluids.An optimal mass fraction of 0.01% with respect to the best photo-thermal conversion was found.Compared to DI water,the temperature of MWCNT-H 2 O nanofluid at the optimal mass fraction was increased by about 15.1℃ (or 22.7%)after a lighting time of 45 min.Additionally,photo-thermal conversion performance is enhanced with increasing the lighting time at a low concentration of nanofluid,while it is just opposite at higher concentrations.The nanoparticle agglomeration may account for the above results.%通过两步法配制了浓度范围0.0015%~0.1%(质量，下同)的多壁碳纳米管(MWCNT)-水纳米流体，并利用分光光度计对不同浓度、静置时间和加热次数下纳米流体在波长200~2000 nm 范围内的透射率进行了测试。同时，还对上述纳米流体开展了闷晒实验，研究了浓度和光照次数对纳米流体光热转换性能的影响。结果表明，水中添加 MWCNT 后透射率明显下降，纳米流体的透射率随着静置时间的增加而减小，加热有利于提高纳米流体的吸光性能；同时，闷晒实验发现存在利于光热转化的 MWCNT-水纳米流体最佳浓度(0.01%)，光照45 min 后与水相比最佳浓度下的纳米流体温升提高了约15.1℃(或22.7%)。另外，纳米流体浓度较低时其光热转换性能随着光照次数的增加而提高，但浓度较高时则刚好相反，纳米颗粒团聚作用可能是造成上述结果的主要原因。