Heat transfer enhancement in a loop thermosyphon using nanoparticles/water nanofluid

This research focuses on two-phase thermal control systems, namely loop thermosyphons (LTS) filled with nanofluids and their use as LED cooling devices. The behavior of the fluid in the thermosyphons and the mechanisms explaining the possible impact of nanoparticles on the thermal properties of the working fluid, as well as the processes in the LTS, are addressed. Nanoparticle distribution in the nano fluid, methods of preparing nanofluids and the nanofluid degradation processes (aging) are studied. The results are obtained from a set of experiments on thermosyphon characteristics depending on the thermophysical properties of the working fluid, filling volume, geometry and nanoparticle mass concentrations. The impact of nanofluids on the heat-transfer process occurring inside the thermosyphon is also studied. The results indicate the strong influence of nanoparticles on the thermal properties of the thermosyphons, with up to a 20-25% increase in the heat transfer coefficient. It is shown that this effect is due to the aggregation of nanoparticles and the formation of a micro nano relief on the vaporization surface. Additionally, a method of calculating the hydrodynamic limit of the LTS is proposed, which allows for estimation of the maximum heat that can be transferred by means of the LTS. The nanofluids are shown to be effective means for enhancing heat transfer in two-phase thermal management systems. (C) 2018 Elsevier Ltd. All rights reserved.