Experimental study of electrochemical mass transfer in an annular duct with the electrolyte nanofluid

Abstract

The paper shows experimental studies on mass transfer phenomena in the nanofluid flowing through an annular channel. The effect of aluminium oxide nanoparticles on mass transfer was investigated in the channel with hydraulic diameter 10.5 mm.The experiment was performed using the electrochemical limiting current technique.A classical system for mass transfer measurements, based on ferricyanide ion reduction at the cathode and ferrocyanide ion oxidation at the anode has been applied. The base fluid (base-electrolyte) was composed of equimolar potassium ferri-ferrocyanide solution and sodium hydroxide solution. The nanofluid tested (nano-electrolyte) was composed of the base-electrolyte and spherical, 99.9% pure aluminium oxide nanoparticles, of about 40 nm in diameter. The nano-electrolyte used was characterized by volume particle fractions: 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.04%, 0.05% and 0.06%.Mass transfer processes during the forced transitional and turbulent flow of the nano-electrolyte through the horizontal annular channel were investigated. The fully developed hydrodynamic profile was considered. Mass transfer coefficients at the cathode attached to the inner surface of the channel were measured. The experiment was performed with the Reynolds numbers ranging from 2080 to 10430. Bulk ion concentrations in the electrolyte were measured experimentally during each test which minimized errors resulting from ion concentration decomposition. There occurred changes in the mass transfer coefficients depending both on nanoparticle concentration and the Reynolds number. With an increase in nanoparticle fraction, mass transfer was reduced. Measurements for the transitional and turbulent regime indicated that the mass transfer coefficients achieved their lowest values at the largest value of nanoparticle fraction. However, the reduction in mass transfer was not proportional to an increase in particle fraction. The maximum reduction of about 12% was observed for the largest Re numbers and the maximum particle fraction.