This study characterizes and optimizes natural convection heat transfer of two Newtonian Al2O3 and Ti O2/water nano fluids in a cylindrical enclosure. Nusselt number(Nu) of nano fluids in relation to Rayleigh number(R...This study characterizes and optimizes natural convection heat transfer of two Newtonian Al2O3 and Ti O2/water nano fluids in a cylindrical enclosure. Nusselt number(Nu) of nano fluids in relation to Rayleigh number(Ra) for different concentrations of nano fluids is investigated at different con figurations and orientations of the enclosure.Results show that adding nanoparticles to water has a negligible or even adverse in fluence upon natural convection heat transfer of water: only a slight increase in natural convection heat transfer of Al2O3/water is observed,while natural convection heat transfer for TiO2/water nano fluid is inferior to that for the base fluid. Results also reveal that at low Ra, the likelihood of enhancement in natural convection heat transfer is more than at high Ra: at low Ra, inclination angle, aspect ratio of the enclosure and nanoparticle concentration in fluence natural convection heat transfer more pronouncedly than that in high Ra.展开更多
Water-based nanofluids were prepared with multi walled carbon nanotubes （MWCNTs） of different lengths in concentrations of 0,1,0,25 and 0,5 vol%, To improve their dispersibility, pristine MWCNTs were functionalized ...Water-based nanofluids were prepared with multi walled carbon nanotubes （MWCNTs） of different lengths in concentrations of 0,1,0,25 and 0,5 vol%, To improve their dispersibility, pristine MWCNTs were functionalized and cut into small lengths by reflux in an oxidizing mixture of 3：1 sulfuric and nitric acids, The initial length of the carbon nanotubes （CNTs; 10-15 μm） was reduced to 203, 171 and 134nm after 1, 2 and 4 h of reflux, respectively, Surface modification and the reduced length of the CNTs, improved the stability of the nanofluids with no significant sedimentation observed after 80 days. Furthermore, the thermal conductivities of nanofluids prepared using refluxed CNTs, were higher than that of the pristine CNTs. The thermal conductivity also increased with the nanofluid temperature, The nanofluid prepared with 1 h refluxed CNTs had the highest thermal conductivity, The enhanced thermal conductivity and stabilitv of the nanofluids was attributed to the decreased length of CNTs.展开更多
文摘This study characterizes and optimizes natural convection heat transfer of two Newtonian Al2O3 and Ti O2/water nano fluids in a cylindrical enclosure. Nusselt number(Nu) of nano fluids in relation to Rayleigh number(Ra) for different concentrations of nano fluids is investigated at different con figurations and orientations of the enclosure.Results show that adding nanoparticles to water has a negligible or even adverse in fluence upon natural convection heat transfer of water: only a slight increase in natural convection heat transfer of Al2O3/water is observed,while natural convection heat transfer for TiO2/water nano fluid is inferior to that for the base fluid. Results also reveal that at low Ra, the likelihood of enhancement in natural convection heat transfer is more than at high Ra: at low Ra, inclination angle, aspect ratio of the enclosure and nanoparticle concentration in fluence natural convection heat transfer more pronouncedly than that in high Ra.
基金Shahid-Chamran University of Ahvaz for the financial support of this workNational Iranian South Oil Company(NISOC) for their help and assistance
文摘Water-based nanofluids were prepared with multi walled carbon nanotubes （MWCNTs） of different lengths in concentrations of 0,1,0,25 and 0,5 vol%, To improve their dispersibility, pristine MWCNTs were functionalized and cut into small lengths by reflux in an oxidizing mixture of 3：1 sulfuric and nitric acids, The initial length of the carbon nanotubes （CNTs; 10-15 μm） was reduced to 203, 171 and 134nm after 1, 2 and 4 h of reflux, respectively, Surface modification and the reduced length of the CNTs, improved the stability of the nanofluids with no significant sedimentation observed after 80 days. Furthermore, the thermal conductivities of nanofluids prepared using refluxed CNTs, were higher than that of the pristine CNTs. The thermal conductivity also increased with the nanofluid temperature, The nanofluid prepared with 1 h refluxed CNTs had the highest thermal conductivity, The enhanced thermal conductivity and stabilitv of the nanofluids was attributed to the decreased length of CNTs.
