PHOTOGRAPHIC STUDY OF BUBBLE DEPARTURE DIAMETER IN SATURATED POOL BOILING TO ELECTROLYTE SOLUTIONS Article Highlights

• Larger bubbles are generated in electrolyte solutions compared with water at similar conditions • Increasing the salt concentrations makes the bubbles slightly larger • Bubble diameter decreases with increasing heat flux in all three electrolyte solutions • Larger bubbles appear during boiling of NaCl solutions since it has higher surface tension Bubble departure diameters during saturated pool boiling to pure water and three different electrolyte solutions including NaCl, KNO3 and KCl aqueous solutions are experimentally measured. Variable heat fluxes up to 90 kW/m2 and different salt concentrations from 10.6 to 69.6 kg/m3 are applied in order to investigate their effects on the bubble size during pool boiling around the hori-zontal rod heater. Visual observations demonstrate that larger vapor bubbles generate on the heat transfer surface at higher salt concentrations and lower heat fluxes in all of the solutions tested while in distilled water bubbles become slightly larger with increasing heat flux. Furthermore, the effects of different important physical properties like surface tension, viscosity, and density of the solutions on the bubble departure diameter are also discussed. NaCl solutions have surface tension higher than the other electrolyte solutions. Furthermore, the addition of NaCl to distilled water slightly increases the viscosity of the solution whereas other salts have no measurable effect on the viscosity. Therefore, larger bubbles are expected to appear on the heat transfer surface during the boiling of NaCl solutions, which is in agreement with the experi-mental results