Pool boiling in seawater, NaCl solution and de-ionized water

Highlights: • The bubble coalescence is almost absent for boiling in sodium chloride solution or seawater. • The sodium chloride solution shows the best heat transfer performance in this study. • In seawater, some magnesium salt may deposit on the heating wire and deteriorate heat transfer. • Sodium chloride solution at same concentration may not simulate natural seawater for boiling. • Subcooling demonstrates significant effects on bubble dynamics. - Abstract: The present study investigates experimentally steady-state pool boiling of seawater, sodium chloride at seawater concentration, and deionized water on a coated platinum wire heater. The wall temperature is acquired by the Kelvin 4-wire measurement method. The results demonstrate that the bubbles for boiling in deionized water are usually much bigger than that in seawater or sodium chloride solution at the same heat flux. As the heating power is increased, the bubbles in deionized water may merge each other frequently and become larger, while bubble coalescence in sodium chloride solution or seawater is almost absent. In sodium chloride solution, lack of bubble coalescence and high bubble departure frequency may induce significant disturbance to the liquid near the wire surface. This agitation effect together with the possible zeta potential and Marangoni flow effect, due to the surface tension of the NaCl solution increasing slightly with concentration, result in the best heat transfer performance among the three fluids employed in this study. In seawater, however, some salt deposit on the heating wire possibly due to presence of magnesium ions, especially near the cathode, is revealed and deteriorates heat transfer. The present work indicates that boiling in natural seawater may not be simulated using sodium chloride solution with similar concentration. Liquid subcooling shows significant effects on boiling phenomena of the three working fluids under study.