Natural Convection Heat Transfer Filled With Nanofluids In Enclosure

This paper focuses on natural convection with nanofluids in squareenclosures. The thermal conductivity and viscosity of nanofluids were measured.Experimental work and numerical simulation had been performed to explore thefactors impact on nanofluids natural convection.A two-step was used to prepare nanofluids. The thermal conductivity andviscosity of nanofluids were respectively measured by transient hot-wire and rotaryviscometer. Particle volume fraction, base fluid, particle properties and particle sizewere studied for the effect on thermal conductivity, temperature and particle volumefraction were investigated for the effect on viscosity. The results show that thethermal conductivity and viscosity of nanofluids increase as the particle volumefraction increases, and the viscosity decreases with increasing temperature.Natural convection with nanofluids within rectangular cavities and horizontalannulus were researched by numerical simulation, and the thermal conductivity andviscosity were investigated to study the effect on natural convection. The resultsshow that the heat transfer decreases when the viscosity higher than the thermalconductivity and the heat transfer increases only when the thermal conductivity has acertain amount higher than the viscosity. Furthermore, the heat transfer decreaseswith increase the aspect ratio of rectangular cavities and horizontal annulus.Experimental work has been performed to study the natural convection heattransfer within square encloses filled with carbon nanotubes-water nanofluids.Nanofluids with particle volume fraction of0.48%,1.45%and2.95%were examinedat different Rayleigh numbers from2.7×104to3×107. The results show that the heattransfer of nanotubes-water nanofluids increases as the Rayleigh number increase,and the increment of average Nusselt number of nanofluids are larger than that ofwater. The average Nusselt number of nanofluids decreases with particle volumefraction increases. But the average Nusselt number of particle volume fraction of0.48%higher than water when the Rayleigh numbers reached at2×105.