Evaluation of performance and thermophysical properties of alumina nanofluid as a new heating medium for processing of food products

Abstract

AbstractIncreasing energy consumption and constraints on fossil fuels make it necessary to optimize heat transfer processes. Due to exceptional thermal properties of nanofluids, compared with conventional heating fluids, their usage in heat exchangers has been increased recently. In this research, application of alumina‐water nanofluid for thermal processing of watermelon juice was investigated. Different temperatures of 75, 80, or 85 °C (for durations of 15, 30, or 45 s) and nanoparticles concentrations (0, 2, and 4%) were applied, and changes in thermophysical properties, including density, thermal capacity, viscosity, thermal conductivity and overall heat transfer coefficient, energy consumption rate, and process duration were studied. Our results revealed that, at a constant temperature, density of the nanofluid remained stable until 2% nanoparticle addition, after which it escalated up to 11.47%. Also, heat capacity dwindled by 17.94% as the nanoparticle concentration augmented to 4%. Viscosity of 0 and 4% nanofluids were 0.798 and 3 mPa.s, respectively but it still remained Newtonian due to the low volume concentration of nanoparticles. While increasing the temperature to 77 °C descended viscosity of 2 and 4% nanofluids by 56.07 and 59.35%, compared with the base fluid, respectively, this increased thermal conductivity of nanofluids up to 14.6% (belonging to 4% nanoparticles). The effectiveness of working fluid in heat exchanger was raised by 58.65% after addition of 4% nanoparticle to the base fluid. Duration of watermelon juice processing diminished by 24.88 and 51.63% for 2 and 4% concentrations of nanoparticles, compared with water, respectively, and its energy consumption by 22.74 and 47.48%.Practical applicationsThermal conductivity of conventional fluids is much lower than metals and oxidized metals. Accordingly, fluids with suspended particles of metals or oxidized metals benefit from better heat transfer properties. There is no research dealing with effects of adding nanoparticles to conventional thermal fluids for fruit juices processing. So, the goal of this research was to introduce nanofluid technology for thermal processing of food products for the first time, increasing heat transfer efficiency in shell and tube exchangers by nanofluids and frugality in energy consumption for pasteurization, reducing thermal processing duration and better quality retention of food products.