Experimental Study Of Nano-fluids Convective Heat Transfer

Nano-fluids, that a kind of homogeneous ,stable high thermal conductivity of new heat transfer media, is made through the way that the metal or nonmetal nanoparticles dispersed into the water, alcohol, oils and other traditional heat transfer medium, which is an innovation research that makes nanotechnology applied in the tradition field of thermal engineering. Nano-fluids as new type heat transfer working fluid is widely used in metallurgy, vehicle, aviation, shipping, electronics and other fields, which has not only important significance in improving heat exchange system economy, reliability, and in its miniaturization, but also has broad application prospects and potential enormous economic value. The purpose of this paper is primarily to do the experimental research on Nano-fluids convective heat transfer area.Preparing for 2wt% TiO2-DW Nano-fluids, 1.5wt% MgO-DW Nano-fluids and 0.5wt % ATO (Antimony Doped Tin Oxide)-DW Nano-fluids by two-step and other mass fractions of Nano-fluids completed by dilution, after analysis, every kind of Nano-fluids dispersed evenly, has good stability and meets experimental requirements. Using the empirical formula on calculating the thermal conductivity of every kind of Nano-fluids respectively, and it is found that adding nanoparticles in liquid can increase the thermal conductivity, and along with the increasing of nanoparticles mass fraction in the fluid, the thermal conductivity of Nano-fluids has continuously increasing trend.Designing and building the Nano-fluids convective heat transfer experimental test system, making the whole experimental device precision below 8% through commissioning to meet the test requirements. In this paper, copper smooth tube and internally ribbed copper tube were used in Nano-fluids convective heat transfer experimental system, to measure convective heat transfer coefficients h and Nu of different mass fractions of TiO2-DW Nano-fluids, MgO-DW Nano-fluids and ATO-DW Nano-fluids in the range of Reynolds number from 3000 to 8000, and then got different results, which shows that: the fluid velocity or Re is one of the factors that impact the convection effect, the nusselt number Nu and convection heat transfer coefficient h are all gradually improving with the increasing fluid velocity or increasing Re. At the same Re, the Nu and h of the Nano-fluids in smooth tube are higher than those of distilled water and the increase degree is constantly increasing along with the increasing fluid velocity , while the Nu and h of the Nano-fluids in internally ribbed copper tube are lower than those of distilled water and the decrease degree is constantly decreasing along with the increasing fluid velocity; Nanoparticles contents is a factor affecting the heat transfer process, the same pattern is gotten from the three kinds of Nano-fluids: On base of the same Re and the fluid keeps constant temperature, with the increasing content of nanoparticles, the heat transfer effect of Nano-fluids in smooth tube is better, while heat transfer effect of Nano-fluids in internally ribbed tube is worse; The increase of Nano-fluids thermal conductivity and Nano-fluids temperature lead the improvement of the Nano-fluids convective heat transfer coefficient h and nusselt number Nu; The Nu and h of Nano-fluids are changing along the tube axis direction, the values of Nu and h are firstly gradually decreasing, and then tending to be stable, which achieving the maximum at entrance area of the tube; Nano-fluids type is one of the factors that affecting the heat transfer, the degrees of heat transfer enhancement of different kinds of Nano-fluids with the same mass fraction are different.Through comparison, it is found that compared other three species of Nano-fluids, the distilled water convection heat transfer coefficient h and nusselt number Nu in internally ribbed tube compared smooth tube have the highest relative rate of increase, whose Nu relative average improve 37.68%, h average improve 38.72%, having obvious effect; The heat transfer effects of the three species of Nano-fluids with different of mass fraction in internally ribbed tube are enhanced compared smooth tube, but the strengthening degrees are all less than one of the distilled water. As the mass of nanoparticles constantly increase, the degree is gradually reduce; For internally ribbed tube, the heat transfer efficiency of the base fluid(the distilled water) is better than that of the three types of Nano-fluids used in this paper, which has a certain significance on the experimental research of Nano-fluids convection heat transfer.