Study On Preparation And Properties Of Al-nanofluids Used For Thermal Collection

With the development of nanotechnology, nanofluids is becoming one research focus of academic circles for the predominant thermal physical properties. Nanofluids refers to a new type of heat transfer carrier which is uniform, stable and of high thermal conductivity, and can be obtained through dispersing metallic or non-metallic nanoparticles in traditional transfer fluids. The current research indicates that nanofluids have special properties, and can be used in heat transfer enhancement. Collector is one kind of important component in collector system and the application of nanofluids in collector system may obviously improve its performance. Therefore, the research on the heat natural parameter and photothermal property of nanofluids used in the solar collector is an innovative research of applying nanotechnology in the field of solar energy heat utilization; it has the important project application value.In this thesis, Al nanoparticles characterized by X-ray diffraction and Al-nanofluids were prepared by the two-steep method. Suspension stability of Al-nanofluids was characterized and analyzed by using sedimentation method and absorbance analysis. The optimum dispersion condition was obtained, i.e. the content of sodium hexametahposphate is 0.5 g/L and ultrasonic vibration time is 50 min, the suspension stability of 0.5 g/L Al-nanofluids is the best.Viscosity and thermal conductivity of Al-nanofluids under different conditions were measured by NDJ-1 rotation viscometer and hot disk thermal constants analyzer respectively. The results showed that the viscosity of Al-nanofluids increased with the increase of the nanoparticles content, and decreased with the increase of temperature Furthermore, the corresponding mechanism was theoretically analyzed; the thermal conductivity of Al-nanofluids increased with the increase of the nanoparticles content and dispersant.Photothermal stabilities of Al-nanofluids were obtained by measuring the absorbance of 0.5g/L Al-nanofluids with different dispersant concentrations and ultrasonic vibration time before and after exposure to sunlight. The result showed that Al-nanofluids had good photothermal stability as proved.Infrared emissivity of Al-nanofluids and CNT-nanofluids with different massic volume concentration in 5～14μm vaveband were measured by 302 far-infrared emissivity tester. The results showed that the infrared emissivity of nanofluids decreased with the increase of nano-particles content in the case of certain test conditions; the infrared emissivity of Al-nanofluids was bigger than that of CNT-nanofluids with the same massic volume concentration.The photothermal conversion properties of two kinds nanofluids and their base fluids were studied by the insolation experiment. The results showed that Al-nanofluids had higher rise velocity and insolation temperature than the base fluids and Carbon Nanotube Nanofluids, and when the insolation temperature was stable, the insolation temperature of Al-nanofluids was nearly 25℃higher than that of the base fluids and 10℃higher than that of the Carbon Nanotube Nanofluids, showing better photo-thermal conversion properties.Because of the excellent photo-thermal property and flow performance, Al-nanofluids are used as recycle fluids for direct absorption type solar collector and may improve the thermal efficiency greatly. Therefore, the research results indicate that nanofluids have extensive application prospect and potential economic value.