Heat Transfer Enhancement in Thermal Processing of Tomato Juice by Application of Nanofluids

In this research, our chief aim was to survey possible improvements in thermophysical properties of nanofluids when they are used as heating mediums for time reduction and energy saving in food industries for the first time. Accordingly, three different variables of temperature (70, 80, and 90 °C), alumina nanoparticle concentration (0, 2, and 4 %), and time (30, 60, and 90 s) were selected for thermal processing of tomato juice by a shell and tube heat exchanger. Our results revealed that incorporation of nanoparticles could raise density, viscosity, and thermal conductivity and decrease heat capacity, but this increasing/decreasing trend was linear or non-linear depending on the diameter of the nanoparticles. Four percent Al₂O₃–water, compared with 2 % nanofluid and pure water (0 % nanofluid), had the highest overall heat transfer coefficients for all Re numbers. Incorporating nanoparticles into the base heating fluid of water could augment the effectiveness of the heat exchanger by 49 %. Thermal processing time of tomato juice was shorter for 2 and 4 % nanofluids, compared with water, by 22.23 and 46.29 %, respectively; this time reduction caused energy saving rates for 2 and 4 % nanofluids to be improved by 22.3 and 48.76 %, respectively.