Study On Thermal Parameters Of Nanofluid In The Application Of Heat Pipe

With the rapid development of nanotechnology, nanomaterials have been applied into the heat transfer areas, breded as "nano-fluid". Nanofluid is a new type of heat working fluid, which is formed by adding nano-level metal, non-metallic or polymer solid particles into the liquid in a certain way and ratio. This kind of new heat transfer working substance may substitute traditional working substance in the heat exchange equipment. Heat pipe as one kind of highly effective heat transfer part in heat exchange equipment, nano-fluid may obviously improve the heat-transfer property, when it was applied in the heat pipe. Therefore, the research of nanometer class volumetric heat natural parameter used in heat pipe is innovative research of appling nanotechnology in the thermal engineering, it has the important project application value.In this paper, the Al₂O₃-water nanofluid was used to the heat pipe working medium, and through testing its various thermal parameters, the effects of the addition of Al₂O₃ nanoparticles on the thermal parameters of working fluid and heat transfer ability of heat pipe were studied. The main research contents are as follows:Fristly, the Al₂O₃ nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, two particle sizes (40nm,65nm) and five volume fractions (0.1% 0.5%) of Al₂O₃-water nanofluids were prepared by the two-step method. In order to prepare stable nanofluids suspended, the L9(34) orthogonal experiment was employed to analysis, the optimum process parameters are: pH value of 8, ultrasonic vibration time of 3h, not add the dispersing agent, magnetic stirring time of 30min. By using Zeta potential analyzer, laser particle size analyzer, the influences of the time of the ultrasonic vibration, dispersing agent, pH value on the suspension stability Al₂O₃-water nanofluids were studies, the obtained results are: the suspension stability of Al₂O₃-water nanofluid is best when the pH value was 8, ultrasonic vibration time was 3h, dispersion agent was 0.02%. The mechanism of the suspension stability was theoretically analyzed as well.Secondly, viscosity, surface tension, thermal conductivity, heat weight, latent heat of vaporization, density, boiling point and other thermal parameters for Al₂O₃-water nanofluids under different conditions were measured by rotating viscometer, automatic surface tension meter, KD 2 Pro thermal conductivity meter, thermogravimetric differential thermal spectrometer and other instruments. The results showed that: the viscosity of Al₂O₃-water nanofluid increases with increasing the volume fraction of nanoparticles, decreases with increasing temperature, increases with decreasing particle size; the surface tension coefficient of Al₂O₃-water nanofluid decreases with increasing volume fraction, decreasing particle size, and increasing temperature, respectively; the thermal conductivity of Al₂O₃-water nanofluid increases with increasing volume fraction, decreasing particle size, and increasing temperature, respectively; the phase transition rate of Al₂O₃-water nanofluid increases with increasing the particle volume fraction, the particle size did not affect its basic; the latent heat of evaporation of Al₂O₃-water nanofluid increases with decreasing the particle volume fraction; the nanofluids density of Al₂O₃-water increases with increasing the volume fraction of particles; the boiling point of Al₂O₃-water nanofluid decreases with increasing volume fraction of particles. The mechanism of the every thermal parameter was theoretically analyzed as well.Lastly, analyzed synthesis hot physical property of Al₂O₃-water nanofluid working substance which has applied in heat pipe. The result indicated that Al₂O₃-water nanofluid has the good synthesis hot physical property, suitable to make heat pipe's working substance; Its transmission factor enhanced 3.2%¹4.9% compared to water, has the good heat-transfer property.