Research On Thermophysical Property Of Nanofluids And Flow Behavior In A Wavy-walled Tube

With the development of science and technology, the problem of energy sources is getting more and more serious than ever. It is very important to reduce power consumption and enhance the heat transfer rate in heat tansfer capabilities. Nowadays, the traditional pure liquid heat-transfer medium can't meet the requirements in some special work condition. It is necessary to prepare a higher thermal conductivity and more efficient heat-transfer medium. To solve this problem, a new concept of heat transfer fluids called "nanofluids" has been proposed. It refers to a new kind of heat transfer medium created by suspending nanoscaled metallic or nonmetallic particles in the base fluids.This research focuses on the preparation and stability of nanofluids. Two steps method is used to prepare many kinds of nanofluids with better stability. On this basis, research on thermophysical characteristic of nanofluids and measure the conductivity, viscosity and specific heat of nanofluids through the experimental method; generalize the research achievement of thermophysical characteristic proposed by researchers in the recent years; confirm the effective thermal property models of nanofluids after comparison between the experimental data and the calculated results.Experiments are carried on flow behavior of different volume concentration SiO2-water nanofluids in a wavy-walled tube. Because of the structural characteristics of the wavy-walled tube, the SiO2-water nanofluids can be in a turbulent area in smaller Reynolds numbers and the flow structural characteristics can be easily measured in the laminar, transitional and turbulent flow regimes. The result of resistance tests shows that the friction factor of SiO2-water nanofluids increases with the concentration of nanoparticles in the laminar and transitional flow regimes, but it is almost unchanged in the turbulent flow regimes. The photos of flow visualization show that the SiO2-water nanofluids have better uniformity due to the micro-movements of the nanoparticles. The result of mass transfer tests show that the mass transfer of SiO2-water nanofluids is higher than pure water in the laminar, transitional and turbulent flow regimes.The flow behavior of pure water and SiO2-water nanofluids(2%) in a wavy-walled tube is simulated by using FLUENT software based on the standard k-εmodel. The flow line pictures of pure water and SiO2-water nanofluids(2%) are achieved, which is under the condition of the same Reynolds number and the same inlet velocity. It is found that the simulation results of SiO2-water nanofluids(2%) are not entirely consistent with the experimental results and the reasons for this phenomenon are analyzed. The software provides a new method for further research on the flow behavior as well as the heat and mass transfer mechanisms of the nanofluids.