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In this paper, ultrasonic dispersion and surface chemical modification were used to prepare the modified multi-walled carbon nanotubes (MWNTs)/paraffin composite phase-change materials (PCMs). The surface modification of MWNTs was developed via coating MWNTs with silica dioxide. The modified MWNTs were marked as SiO2@MWNTs. The phase-change properties, thermal stability and chemical functional groups of the MWNTs/paraffin composite PCMs were measured by differential scanning calorimetry, thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy, respectively. The results indicated that paraffin and MWNTs were compound physically. The diameter and content of MWNTs had influence on the phase-change temperature and the latent heat of the MWNTs/paraffin composite PCMs. The smaller the diameter or larger content of the SiO2@MWNTs, the greater the influence was. The reduction degree of PCM1(the diameter of the SiO2@MWNTs is 20–30 nm) in latent heat is about 4.5 times of that of PCM3(the diameter of the SiO2@MWNTs is larger than 50 nm). The thermal stability and the thermal conductivity of the composite PCMs were improved with the addition of the SiO2@MWNTs. When the content of SiO2@MWNTs is 5 mass%, the thermal conductivity of the paraffin PCMs is 0.383 W m−1 K−1). [ABSTRACT FROM AUTHOR]

Hybrid nanofluid can be considered as a new generation of nanofluids. Despite the success of the researchers in the field of hybrid nanofluids, no acceptable model has been proposed yet that can accurately predict the thermal conductivity of these nanofluids. The nanofluids, containing carbon nanotubes, are not excluded. This research to provide a model based on previous models to predict the thermal conductivity of hybrid nanofluids containing carbon nanotubes. For this reason, the thermal conductivity of MWCNT-MgO/water-EG nanofluids was experimentally measured. The experimental data were in seven solid volume fractions from 0.015 to 0.96%, in which the tests have been done at the temperature range 30-50 °C. A modified conventional model (as a proposed correlation in present study) can produce better results in forecasting the experimental data. The predicted data error by modified Jang-Choi model as proposed correlation was less than 3%. In addition, the price-performance analysis of the thermal conductivity data shows that hybrid nanofluids are better than single particle nanofluids. [ABSTRACT FROM AUTHOR]