Effect of ammonium chloride as a surfactant additive on bubble dynamics during nucleate boiling of water

摘要

Temperature in vicinity of heating element varies according to pool boiling curve at applied heat flux. In this study, all experiments were performed by keeping a cylindrical hypodermic needle as single active nucleation site. Inner cylindrical area of needle was kept in contact with saturated water and heat was applied to outer area. Single bubble was generated inside saturated water by controlled heating of needle. Boiling phenomena was recorded by high speed camera at heat flux 601 kW/m² and 950 kW/m². Ammonium chloride surfactant in water was maintained at 2600 ppm throughout the experiment. Vapor bubbles originating from the nucleation site were observed while corresponding wall temperature was measured by a thermocouple. Bubble parameters were plotted at two heat fluxes with respect to excess wall temperature, without and with surfactant. With addition of surfactant, average measured values of bubble departure diameter and terminal velocity was decreased, while detachment frequency was increased as compared to that in saturated water. With increase in excess wall temperature, departure diameter was decreased at 601 kW/m² and increased at 950 kW/m². Detachment frequency increases and terminal velocity was independent for applied heat fluxes with increase in excess wall temperature.