Investigation On Heat Transfer Enhancement Of Nanofluids

An investigation has been performed to clarify the heat transfer characteristics of nanofluids by means of experimental study and numerical simulation. The thermal conductivity and viscosity of graphite/water, Fe₃O₄/water and ZrO₂/water nanofluids are measured respectively. The preparation and stability of ZrO₂/water nanofluid are analyzed. Experimental equipment is improved and used to measure the convective heat transfer coefficient of ZrO₂/water nanofluid. Measured value and simulated results are compared to analyze the heat transfer and flow mechanism of nanofluids in the pipe.The thermal conductivity of graphite/water and Fe₃O₄/water nanofluids with various volume fractions are measured by the transient hot-wire instrument. The measured results show that the thermal conductivity of nanofluids has clearly increased with an increase of the volume fraction of nanoparticles, and the thermal conductivity of Fe₃O₄/water nanofluid is larger than that of graphite nanoparticles suspension. Thus the property of nanoparticles effects on the thermal conductivity of nanofluids. Measured results of thermal conductivity of nanofluids are remarkably larger than calculated results according to sutra formula.The viscosity of ZrO₂/water nanofluid with various mass concentrations is measured. Compared with calculated value according to sutra formula, measured value is a little larger.In the range of Reynolds with 3000¹8000, the convective heat transfer coefficient of ZrO2/water nanofluid with various mass concentration are measured. The results show that convective heat transfer coefficient increases with adding nanoparticles in fluid and with an increase of nanoparticles concentration.A numerical simulation on the convective heat transfer and flow of the samples in the axial of tube are presented. A mixture model is applied for the simulation. The particle thermal diffusion, granule gravity and Reynolds in the suspension are thought the important factors for improving the capacity of the heat transfer in the nanofluids.Experimental equipment is improved to measure the convective heat transfer coefficient of ZrO2/water nanofluid. Fireclay is used tO decrease thermal resistance between the testing tube and heated thread. That improved the veracity of the measured value.