The Research On Thermophysical Characteristic Of Nanofluids

Nanofluids refers to a new type of heat transfer carriers which is uniform, stable and high thermal conductive. It can be got through appending metallic or non-metallic nanoparticles in traditional transfer fluids such as water, oil or alcohol. The current research indicates that nanofluids has special properties, and it can be used in heat transfer enhancement largely.However some challenges exist in the research field: 1. The experiment results obtained by different researchers are lack of consistency. It means that there are potential factors affecting the characteristics of nanofluids. 2. How to prepare highly dispersive and steady nanofluids more efficiently.This paper studies the thermophysical characteristics of nanofluids. Exploratory works are done for preparing highly steady nano-suspensions and a new method is found. Experimental and theoretical research on themial conductivity and viscosity of nanofluids is done. A scheme is set up to investigate convective heat transfer characteristic of nanofluids in a tube. The main work is as follows.1. Nanofluids are prepared by chemical method (one step) and microfluidizer method (two step). The size and size distribution are analyzed by TEM and Laser Particle Size Analyzer. Zeta electric potential is measured for studying the stability of nanofluids. Both of two samples are highly dispersed and steady very well.2. Experiments are done for studying the viscosity of nanofluid in low concentration. The results show that the size of nanoparticles is one of most important factors in viscosity alternation. A modified empirical formula is obtained. The results calculated through the formula match the experimental data very well.3. The methods for measuring thermal conductivity of nanofluids are summarized in general. The thermal conductivity of nanofluids is measured and the mechanics is analyzed. A new model for predicting the thermal conductivity is established. The predictions obtained from the model are satisfactory coincidence with the experimental results. The factors affecting the thermal conductivity of nanofluids are studied through this model, which include volumetric concentration of nanoparticles, the average size of particles, thermal conductivity of basic fluid, thermal conductivity of particles, the thickness of film between particles and fluid etc.4. The system for measuring convective heat transfer coefficient of nanofluids is set up. The convective heat transfer coefficients of SiO2 and Al2O3 nanoparticles suspended are measured. The results indicate that the convective coefficient increases with diminution of particle size, and increase of volumetric concentration comparing with de-ionized water in the same Reynolds Number.