Deterioration of heat transfer in turbulent channel flows due to nanoparticles

Custom-designed nanoparticles offer the possibility of influencing the thermo-physical properties of heat carriers, such as water and transformer oil. The present study aims to clarify to what extent such nanofluids may improve convective heat transfer under turbulent flow conditions. The applied assessment methodology is based on wall-resolving large eddy simulations and analytical considerations, exemplified by diamond-water nanofluids of different particle concentrations. It is observed that a change in heat transfer due to nanoparticles is affected by two competing mechanisms. On the one hand, the modified thermo-physical properties of the suspension obviously favor heat transfer. On the other hand, an addition of particles drastically dampens turbulence which causes the opposite effect. At fixed energy input by the pump, the second effect usually dominates, so that the performance of the nanofluid deteriorates compared to the carrier fluid without particles. In other words, increasing the turbulence intensity of the carrier fluid is more efficient to transfer a certain amount of thermal energy than using nanofluids. However, if a specific turbulence level shall not be exceeded in a technical system, nanoparticles can help to further improve convective heat transfer. (C) 2021 Elsevier Ltd. All rights reserved.