Experimental And Model Research Of Nanorefrigerants' Thermal Conductivity, Stability And Nanofluids' Electrical Conductivity

As a new type of heat-transfer fluid, nanofluid has gained increased interest. Nanorefrigerant is one kind of nanofluid and the host fluid of nanorefrigerant is refrigerant. The thermal conductivity of nanorefrigerant should be researched in order to improve the performance of refrigeration systems. The stability of nanorefrigerant should be known in order to keep the nanorefrigerant's long-term operation in the system. The nanopowders would diffuse and enter the fluid in the system because of the application of nanorefrigerant. So the electrical conductivity of nanofluid in the system will increase because of the nanopowder's high electrical conductivity. The nanofluid's electrical conductivity should be researched to ensure the insulating properties of system. For this purpose, the experimental and model research is given to nanorefrigerant's thermal conductivity, stability and nanofluids'electrical conductivity. The main contents include:1) Thermal conductivity of nanorefrigerants containing Cu, Al, Ni, CuO, Al₂O₃ and CNT are measured. Experimental results show that the nanorefrigerant's thermal conductivity increases enormously with the increase of nanoparticle volume fraction. The influences of nanopowder's material and physical dimension on nanorefrigerants'thermal conductivity are analyzed.2) The thermal conductivity model for nanorefrigerants containing nanoparticles, the thermal conductivity model for nanorefrigerants containing nanotubes and the general thermal conductivity model for nanofluids are proposed. Such three models are verified by experimental results. It shows that the three models are better than the other existing models and can be recommended for nanofluids, especially for nanorefrigerant.3) The stabilities of nanorefrigerants with three kinds of dispersion method, nine kinds of nanopowders and three kinds of nanopowders volume fraction are evaluated by measuring the nanorefrigerant's transmissivity. It shows that nanopowders can be uniformly dispersed in the nanorefrigerants for long time. Span 80 is recommended as a dispersant for nanorefrigerants.4) The stability model for nanofluids is proposed. In the model the nanofluids'transmissivity can be yielded through the calculation of nanopowders'speed. The model is verified by experimental results. It shows that the model can predict the transmissivities of some nanorefrigerants quantificationally and predict the transmissivit-ies of other nanorefrigerants qualitatively.5) Electrical conductivity of nanofluid, i.e. nanorefrigerants and nano-oils containing Cu, Al, Ni, Al₂O₃ and CNT, are measured. Experimental results show that the nanofluids'electrical conductivity increases with the increase of nanopowder volume fraction. However, the nanorefrigerants'and nano-oils'electrical conductivity is still in line with the national standards and the nanorefrigerants and nano-oils have excellent insulating performance. The influences of nanopowder's material and physical dimension on nanofluid's electrical conductivity are analyzed.6) The electrical conductivity model for nanofluids containing nanoparticles, the electrical conductivity model for nanofluids containing nanotubes and the general electrical conductivity model for nanofluids are proposed. Such three models are verified by experimental results.At last, some deficiencies were pointed out in the paper and some further researches were planned.