| Impinging fluid jet can achieve high local heat transfer coefficient, so it is considered as one of the most powerful cooling solutions for industrial heat transfer problems. However, with the increasing demand for industrial heat exchange, the traditional working fluids may not be suitable for some specific heat transfer situations. Nanofluid refers to a new type of heat transfer medium by suspending nanoparticles into the base working fluid. As compared with the traditional working fluids, heat transfer coefficient of nanofluids is higher. The purpose of the paper is to introduce the nanofluids as working fluids into the impinging fluid jet technology to explore the effect of nanofluids on the heat transfer performance of the single nozzle free jet impingement. The main contents of experimental research are as follows:Firstly, the different volume fractions of SiO2-water and Al2O3-water nanofluids are prepared by two step method. Then suspension stability and electron microscope scanning experiments for the prepared nanofluids are carried out. Experimental results show that the suspension situation of the nanofluids we prepared is very stability. Then the research on the thermal physical properties of nanofluids is carried out. The viscosity and thermal conductivity of nanofluids are measured through experimental instruments and experimental results show that the viscosity and thermal conductivity of nanofluids will be influenced by the volume fraction of nanoparticles and temperature.Then, an experimental platform for investigating the heat transfer performance of the single nozzle jet impingement has been established. Pure water, different volume fraction of SiO2-water and Al2O3-water nanofluids are respectively used as working fluids of the experiment platform to explore the influence of the distance between the nozzle outlet and the heated surface, the impact angle, the jet Reynolds number, the volume fraction and size of nanoparticles on the heat transfer performance of the single nozzle jet impingement. At the same time, the temperature distribution of the heated surface along the radial direction has been researched. Experimental results show that the adding of nanoparticles into the base fluids can significantly enhance the heat transfer performance of the single nozzle free jet impingement and the adding of metal oxide particles seems to be more effective than the adding of nonmetal oxide particles. The heat transfer performance of nanofliuds in a single nozzle free impinging jet will be influenced by the volume fractions and the size of nanoparticles. At the same time, the influence of the distance between the nozzle outlet and the heated surface and the jet impact angle on the heat transfer performance of pure water, SiO2-water and Al2O3-water nanofluids are very similar and the temperature distributions of the heated surface along the radial direction for pure water, SiO2-water and Al2O3-water nanofluids are very similar, this is to say, the adding of nanoparticles may not bring too much effect on the flow characteristics of the base fluids.Finally, a heat transfer correlation of nanofluids in a single nozzle free impinging jet has been proposed taking the effects of the suspended nanoparticles as well as the condition of impinging jet into consideration. There exists a satisfactory coincidence between the calculated values gained through the heat transfer correlation and the measured values gained through our experiment. Therefore, the correlation can be used to predict the heat transfer coefficient of nanofluids in a single nozzle free impinging jet. |
