Experimental Investigation On Heat Transfer Characteristics Of ZnO Nanofluids

Nanofluids have great values in practicability and business competitiveness as its good heat transfer characteristics. To analyze the heat transfer performance and find out a nanofluid with better heat transfer capability, a group of international and domestic academics both experimen tally and numerically researched the heat transfer properties of ethylene glycol and/or water based nanofluids, and there has been a great improvement in the mechanism of heat transfer enhancement of nanofluids. However, these kinds of nanofluids were serely limited by their unsatisfactory physical properties, especially, thermal conductivity, anti-freezing capability, viscosity, etc. In addition, metallic oxide nanoparticles such as Cu O, Al2O3 and Ti O2 are most commonly considerated as nanoparticles additives, and those kinds of nanofluids have been widely investigated. What attractes us most in Zn O is that the Zn O nanofluid ha s not well been investigated. For this purpose, this subject mainly focus es on the transport properties, natural convective characte ristics and boiling heat transfer characteristics of ethylene glycol and water based Zn O nanofluids.Stable ethylene glycol based nanofluids containing Zn O nanoparticles w as prepared and polyvinyl pyrrolidone was used as dispersing agent, following with the measurement of transport properties. Result shows that the optimal mass factions of PVP and nanoparticles are 2.12% and 5.25%, respectively. On the other hand, Zn O-EG/DW nanofluid has good heat transfer performance as the advantages of excellent conductivity, smaller flow resistance and not easy to be frozen, so it is reasonable to use Zn O-EG/DW as a working medium in the characteristics research of natural convective and boiling heat transfer.A series of ethylene glycol aqueous solution based Zn O nanofluids was prepared, and the temperature difference between heating wall and cooling wall was measured as a function of heating power. The effect of heating power on convective heat transfer was analyzed under calculation results. It shows that the natural convection heat transfer coefficient, Nusselt number and Rayleigh number increase with increasing the heating power. What’s more, the presence of Zn O nanoparticles deteriorates the natural convec tive heat transfer capability under the condition of this study.Finally, an experimental platform for boiling heat transfer was established, the effective of ethylene glycol aqueous solution and particles concentrations on boiling heat transfer characteristics of Zn O nanofluid were researched. Results show that for Zn O-EG/DW nanofluids with a mass fraction of 5.25%, the heat flux decreases with decreasing the ratio of EG(i.e., increasinig the ratio of DW). Only the nanofluids with Zn O fraction less than ~7.25% could enhance the bolling heat transfer capability, further loading of nanoparticles result s in the deterioration of bolling heat transfer capability.