Study of enthalpy of evaporation, saturated vapor pressure and evaporation rate of aqueous nanofluids

Al₂O₃ and TiO₂ nanoparticles were added to deionized water to study the effects of enthalpy of evaporation, saturated vapor pressure and evaporation rate. The results show that the enthalpy of evaporation decreased with an increase of nanoparticle concentration and the larger the nanoparticle size, the smaller the enthalpy of evaporation. Two experiments were built to determine the saturated vapor pressure and the evaporation rate of nanofluids. The results show that most of the nanofluids have lower saturated vapor pressure and evaporation rate than those of water, particularly with an increase of nanoparticle concentration, but a few nanofluids with lower volume concentrations show slightly larger values than those of water. Therefore, the evaporation rate of nanofluids as well as their saturated vapor pressure, can be increased or decreased, depending on their volume concentration and the type of nanofluid. Besides, a semi-analytical model for estimating the evaporation rate of water and nanofluids as a function of temperature, humidity and air velocity was developed. After comparing the modeling results with the experiment, the agreement between them is generally good. Lastly, some nanofluids were tested as an adsorbate in an adsorption cooling system, and the results show that using 0.01% TiO₂ nanofluid as the adsorbate enhances the cooling performance by about 9%.