Effect of nanofluid sedimentation on heat transfer and critical heat flux in boiling flows

Nanofluids have gained considerable attention as potential alternatives to pure fluids in cooling systems, particularly in boiling flow systems operating in two-phase vapor–liquid conditions. While nanofluids enhance heat transfer in cooling systems, a significant challenge associated with their implementation is the issue of nanoparticle deposition and sedimentation. Numerical analyses often neglect the deposition layer formed on the walls of pipes and channels. Disregarding this layer in simulations can lead to significant errors in estimating fluid flow and heat transfer parameters. This study investigates the boiling flow of four different nanofluids (nickel–water, gold–water, aluminum–water, and titanium oxide–water) with a volume fraction of 0.03% and pure water in a vertical tube with a diameter of 1.45 mm using a two-dimensional simulation in MATLAB software. In the simulation, five mass transfer mechanisms including evaporation, condensation, deposition, entrainment, and fluid entry into the sedimentary area are considered. To simulate the sedimentary layer, the rules of the porous media have been used. In addition, Brownian motion of particles and Kapitza resistance are also considered in the calculations. The primary objective is to demonstrate the impact of deposition layer simulation on the heat transfer coefficient (HTC) and critical heat flux (CHF) in various nanofluids. The results indicate that the deposition layer causes an average reduction of 31% in the HTC and 16% in the CHF. The findings emphasize the importance of incorporating deposition layer simulation in analyzing boiling nanofluids. Ignoring sediment phenomenon can result in substantial errors in predicting heat transfer and CHF, with significant implications for the design and optimization of nanofluid-based cooling systems.