An experimental investigation and modelling of the thermal and caloric properties of nanofluids isopropyl alcohol - Al2O3 nanoparticles

Highlights: • Influence of nanoparticles on caloric properties of isopropanol is studied. • New model for predicting the molar isobaric heat capacity of nanofluids is proposed. • Fraction of base fluid in interfacial phase is calculated. • Hydrodynamic radius of the nanoparticles with interfacial phase is determined. -- Abstract: An influence of Al₂O₃ nanoparticles on the thermodynamic properties of isopropyl alcohol in the liquid phase has been studied. Experimental measurements of the two-phase specific heat capacity have been performed in the temperature range from 184 to 340 K for samples with the mass fractions of the nanoparticles 0.0201, 0.0511 and 0.0996 kg·kg^-1. The method of monotonic heating in an adiabatic calorimeter of variable temperature has been applied. The saturated vapor pressure of the nanofluids has been measured at the temperatures from 297 to 352 K and concentrations of the nanoparticles in isopropyl alcohol 0.0253, 0.0444, 0.0687, 0.0955 kg·kg^-1. The results obtained have shown that the specific isobaric heat capacity of the nanofluids decreases up to 8.6% at 0.0996 kg·kg^-1 of Al₂O₃ nanoparticles in comparison with pure isopropyl alcohol. In addition, the influence of Al₂O₃ nanoparticles on the specific enthalpy and specific entropy of isopropyl alcohol in the liquid phase has been examined. It is established that both the specific heat capacity of the material of the nanoparticles and structural changes of the base fluid around the nanoparticles are main factors that determine a decrease of the specific isobaric heat capacity of isopropyl alcohol. It was shown that the excess molar volume and excess molar isobaric heat capacity are determined by properties of the interfacial phase of structurally oriented isopropyl alcohol molecules on the surface of nanoparticles. A new three-phase model for prediction the molar isobaric heat capacity of nanofluids is proposed. To predict caloric properties of nanofluids the proposed model requires only data for the molar volume of the investigated samples.