The effect of sedimentation phenomenon of the additives silver nano particles on water pool boiling heat transfer coefficient: A comprehensive experimental study

Abstract

Nowadays, the increase in the number of nanoparticles in base fluids is considered as one of the most significant causes of change in thermodynamic properties and boiling heat transfer coefficient. Hence, the present study aims to examine the effects of different concentrations of silver nanoparticles on pool boiling inside deionized water. Five different nanoparticle concentrations were tested, namely (0.2, 0.4, 0.6, 0.8, 1) gr/lit. The nanoparticles were synthesized using the two-step method in an aqueous base fluid. A magnetic stirrer was first used to suspend the nanoparticles, and then the stabilization was performed using an ultrasonic stirrer. The average diameter of the nanoparticles is approximately 20 nm, and the stability results indicate that the nanofluids are highly stable. The stability results from the DLS test show that changing the pH of the base fluid by 9 at a concentration of 0.4 gr/lit results in stability of −40 mV. The boiling results of the deionized water were recorded in three steps and were compared to the Rohsenow curve. The variations were very similar to the Rohsenow curve, and the change in the wall superheat and the shifting of the curve can be due to the different conditions of the experimental apparatus. The results indicate that adding silver nanoparticles leads to a decrease in the boiling heat transfer coefficient provided that the roughness parameter is smaller than or equal to unity. Increasing the concentration can reduce the deviation in the boiling heat transfer coefficient at low heat fluxes and increase it at high heat fluxes. Furthermore, boiling heat transfer on sedimentation surfaces was examined in three sedimentation steps. The results show that an increase in sedimentation and a decrease in the roughness parameter cause a reduction in the boiling heat transfer coefficient.