An experimental study on resuspension, thermostability and migration phenomenon of nanoparticles in pool boiling

Abstract

Nanoparticles have proven to be effective in sensible and latent heat exchanges alike. Applications of nanoparticles in phase change processes are associated with migration and resuspension of nanoparticles upon which our existing knowledge is very limited. This work experimentally investigates the migration ratio, stability and resuspension of nanoparticles during phase change. Knowledge on migration ratio is essential to gauge the thermal and lubricative enhancements in the subsequent processes. Al2O3/Water & CuO/Water nanofluids were prepared in four mass fractions (0.05, 0.1, 0.2, 0.4) using ultrasonic agitation technique. Nanofluids with mass fraction higher than 0.5% displayed poor stability over time also, agglomeration and sedimentation were pronounced and inevitable. Nanofluid destabilises and agglomerates rapidly at temperatures closer to saturation temperature. Resuspension of agglomerated chunks were observed during nucleate boiling where the test fluid became extremely nonhomogeneous. Migration ratio was found to commensurate with volume fraction where CuO/water nanofluid exhibited 23% lesser migration ratio than Al2O3/water nanofluid. Maximum migration ratio of 17.8% was observed for Al2O3/water with 0.05 wt%. Maximum migration was found when the molecular dimensions of nanoparticles and the base fluid are of similar magnitudes. It is inadvisable to involve nanoparticles in phase change systems.