新型纳米流体管内流动与换热过程的实验研究

发布时间：2018-05-31 18:05

本文选题：石墨烯 + 纳米流体　；参考：《华北水利水电大学》2017年硕士论文

【摘要】：纳米流体作为一种新型高效的传热工质,在太阳能发电、工业余热回收、相变材料、氢内燃机散热等领域具有广泛的应用前景。本文对石墨烯纳米流体的制备、稳定性、导热性能、黏度、传热特性进行了实验研究,并对实验所得的结论进行了初步分析,为纳米流体的理论研究和实际应用提供依据。选用“两步法”制备了石墨烯纳米流体。静置沉降实验证明实验室制备的石墨烯纳米流体具有良好的稳定性;通过不同基液石墨烯纳米流体沉降情况的对比发现,基液黏度越大,配置的纳米流体稳定性越好。采用基于瞬态热探针法的液体导热系数测试仪测量了石墨烯纳米流体的导热系数,并将实验值与纳米流体导热系数模型计算值进行比较。结果表明,石墨烯纳米粒子的添加强化了基液的导热性能;纳米粒子的质量份额、基液的性质、流体温度都是影响纳米流体导热系数的重要因素。依据实验结论从纳米颗粒的布朗运动与微对流、溶液属性等方面对纳米流体导热性能的强化机理进行了初步分析。采用乌式黏度计对水基石墨烯纳米流体的黏度进行了测量,并将实验值与纳米流体黏度模型计算值进行比较。结果表明,纳米粒子的添加增大了基液的黏度;纳米粒子的质量份额、粒子形状、粒子尺寸以及流体温度都是影响纳米流体黏度的因素,其中流体温度为主要影响因素。设计并搭建了管内流动与换热实验系统,测试了水基石墨烯纳米流体在Re=8000-12000范围内的对流换热性能。结果发现,纳米粒子的添加强化了基液的对流换热性能,且纳米流体对流换热性能的增幅大于导热性能的增幅;壁面热流率、粒子的浓度、湍流强度都是影响纳米流体强化对流换热性能的因素。纳米颗粒对圆管内壁的修饰改性有利于能量的传输。基于流动与换热实验系统,采用ANSYS Workbench对水基石墨烯纳米流体管内流动与换热进行数值模拟。将实验结果与模拟结果对比可得,石墨烯纳米流体内粒子的无规则布朗运动是强化纳米流体的传热性能的重要因素。从模拟结果中的温度场、速度场以及压力场对纳米流体管内流动与传热的规律进行了分析。
[Abstract]:As a new and efficient heat transfer medium, nano-fluid has a wide application prospect in the fields of solar power generation, industrial waste heat recovery, phase change material, heat dissipation of hydrogen combustion engine and so on. In this paper, the preparation, stability, thermal conductivity, viscosity and heat transfer characteristics of graphene nanofluids are studied experimentally, and the experimental results are analyzed preliminarily, which provides a basis for the theoretical research and practical application of nano-fluids. Graphene nanofluids were prepared by two-step method. The static settling experiment proved that the graphene nanofluids prepared in the laboratory had good stability, and the higher the viscosity of the base solution, the better the stability of the nano-fluids. The thermal conductivity of graphene nanofluids was measured by a liquid thermal conductivity tester based on transient thermal probe method, and the experimental values were compared with those calculated by the thermal conductivity model of nano-fluids. The results show that the addition of graphene nanoparticles enhances the thermal conductivity of the base solution, and the mass fraction of the nanoparticles, the properties of the base solution and the temperature of the fluid are the important factors affecting the thermal conductivity of the nano-fluids. Based on the experimental results, the strengthening mechanism of thermal conductivity of nanoscale fluids was preliminarily analyzed from the aspects of Brownian motion and micro-convection of nanoparticles and solution properties. The viscosity of water-based graphene nanofluids was measured by using a black viscometer, and the experimental values were compared with those calculated by the nano-fluid viscosity model. The results show that the viscosity of the base solution is increased with the addition of nanoparticles, and the mass fraction, particle shape, particle size and fluid temperature are the main factors affecting the viscosity of the nano-fluid, among which the temperature of the fluid is the main factor. An experimental system of flow and heat transfer in a tube is designed and built. The convection heat transfer properties of water-based graphene nanofluids in Re=8000-12000 range are tested. The results show that the convection heat transfer performance of the base solution is enhanced by the addition of nanoparticles, and the increase of convection heat transfer performance of nano-fluid is greater than that of thermal conductivity, the wall heat flux, particle concentration, The turbulence intensity is the factor that affects the convection heat transfer performance of nano-fluid. The modification of the inner wall of the tube by nanoparticles is beneficial to the energy transfer. Based on the experimental system of flow and heat transfer, ANSYS Workbench was used to simulate the flow and heat transfer in water based graphene nanofluid tube. By comparing the experimental results with the simulation results, it is found that the irregular Brownian motion of particles in graphene nanofluids is an important factor in enhancing the heat transfer performance of nano-fluids. From the temperature field, velocity field and pressure field in the simulation results, the flow and heat transfer in nanofluid tubes are analyzed.
【学位授予单位】：华北水利水电大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1;TQ127.11

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