【作者】 乔峰；

【导师】 朱海涛；

【作者基本信息】 青岛科技大学 ， 材料物理与化学， 2010， 硕士

【摘要】 纳米流体是指把金属或非金属纳米粉体分散到水、醇、油等传统换热介质中,制备成均匀、稳定、高导热的新型换热介质,这是纳米技术应用于热能工程这一传统领域的创新性的研究。纳米流体在能源、化工、汽车、建筑、微电子、信息等领域具有巨大的潜在应用前景,从而成为材料、物理、化学、传热学等众多领域的研究热点。本论文主要进行以下几个方面研究:以柠檬酸钠、硼氢化钠为还原剂,采用湿化学法制备了Ag-H2O纳米流体;采用分散法,将制备好的Ag纳米颗粒分散到乙二醇中,制备了Ag-EG纳米流体。以天然鳞片石墨为原料,制备了石墨烯-H2O纳米流体。利用粒度分析、zeta电位、透射电镜、扫描电镜、原子力显微镜、X-射线衍射、紫外-可见光谱等手段,研究了制备条件对产物结构、形貌的影响规律,并深入研究了纳米流体的流变及导热性能。研究结果表明:1)Ag纳米颗粒为类球形结构,平均粒径为60nm左右,随硝酸银浓度的增加,所制备的Ag纳米颗粒聚集成链状结构。2)石墨烯为片状结构,其单层厚度约为0.344nm,略高于理论值0.335nm,表面存在不同程度的褶皱。随着石墨烯-H2O纳米流体浓度的增加,石墨烯片之间产生堆垛现象。3)Ag-H2O、Ag-EG纳米流体为牛顿型纳米流体。石墨烯-H2O纳米流体,其浓度大于1mg·ml-1时,表现为非牛顿型纳米流体,反之,有向牛顿型纳米流体转变的趋势。4)20~60℃温度范围内,当Ag纳米颗粒的体积分数为0.121%时,与H2O相比,Ag-H2O纳米流体的导热系数提高了8.9%~78.5%; 25℃时,Ag-EG纳米流体的体积分数由0.03vol%提高到0.12vol%,其导热系数由1.6%增加到7.0%;55℃时,相同体积分数变化的条件下,其导热系数由5.0%增加到24.6%。石墨烯-H2O纳米流体的导热系数随固含量的增加而减小,随温度的升高而增大,25℃时,石墨烯-H2O(0.2mg·ml-1)纳米流体的导热系数提高17.7%。本论文的创新之处在于:1、采用湿化学法制备了高体积分数的Ag-H2O纳米流体;分散法将具有链状结构的Ag纳米颗粒分散到乙二醇中,制备了Ag-EG纳米流体。2、采用氧化-还原法首次制备了石墨烯-H2O纳米流体,石墨烯为单层片状结构,单层高度为0.344nm。更多还原

【Abstract】 Nanofluids are a new type of heat transfer fluids engineered by uniform and stable suspension of nanoparticles (metal or non-metallic nanopowder) into the traditional heat transfer medium (such as water, alcohol, oil at all). This is an innovative research of nanotechnology applied to energy projects in traditional areas. Nnaofluids have great potential application in many industrial sectors, including energy, chemical, automotive, construction, microelectronics, information and other fields, so, it is becoming the hot off the press of material, physical, chemical, heat transfer and many other fields.The main contents researched are as follows:1) Using Sodium citrate, sodium borohydride as reducing agent, Ag-H2O nanofluids were prepared by wet chemical method. Using dispersion method, the Ag- ethylene glycol (EG) nanofluids were successfully prepared by dispering chain-like Ag nanoparticles into EG. The Graphene-H2O nanofluids have been successfully prepared by useing natural flake graphite as raw materials. By Size distribution, Zeta potential, TEM, SEM, AFM, XRD and UV-Vis spectrometer, the influence of fabrication conditions on the structure and morphology of Ag nanopartickes and Graphene were characterized, the rheologic properties and thermal conductivity of the nanofluids were studied in depth.The results and conclusions are as followed:1) The Ag nanoparticles possessed sphere-like structure, the mean dimeter was 60nm, as the concentration of AgNO3 increasing, the Ag nanoparticles assembled into chain-like structure.2) Graphene was a single layer film with a thickness of about 0.344nm, slightly higher than the theoretical value of 0.335nm. The surfaces possessed varying degrees of fold. With the concentration of Graphene-H2O nanofluids increasing, the graphene films were overlapped and stacking phenomenon occursed.3) Ag-H2O and Ag-EG nanofluids showed Newtonian behavior. The Graphene-H2O nanofluids showed non-Newtonian behavior when the Concentrations greater than 1mg·ml-1, otherwise, it had a trend to change into Newtonian nanofluids.4) At the range of 20~60℃, when the volume fraction of Ag nanoparticles was 0.121%, the thermal conductivity of Ag-H2O nanofluid was increased by 8.9%~78.5% compared with the water. For the Ag-EG nanofluid, when the volume fraction increased from 0.03vol% to 0.12vol% at 25℃, its thermal conductivity arised from 1.6% to 7.0%, while, the same volume fraction of changing conditions at 55℃, its thermal conductivity was enhanced from 5.0% to 24.6%. Thermal conductivity of Graphene-H2O nanofluid decreased as the solid content increasesing, but boosted with the increasing of temperature. When the solid content of graphene reached to 0.2mg·ml-1, the thermal conductivity of Graphene-H2O nanofluid increased by 17.7%.Creative points:1) High volume fraction of the Ag-H2O nanofluids were successfully prepared by using a simple wet chemical method; Ag-EG nanofluids with different concentration were prepared by dispersed chain-like Ag nanoparticles into ethylene glycol.2) The Graphene-H2O nanofluids were synthesized by oxidation-reduction for the first time. The prepared Graphene was possessed of single-layer sheet structure, the height of single layer was 0.344nm.更多还原