The influence of additive molecular weight and ionic nature on the pool boiling performance of aqueous surfactant solutions

Saturated nucleate pool boiling on a horizontal cylindrical heater in aqueous solutions of surfactants, which have different molecular weights and ionic character, has been experimentally investigated. Two anionic surfactants, sodium dodecyl sulphate (SDS) and sodium lauryl ether sulfate (SLES), and two nonionic surfactants, Triton X-100 and Triton X-305, were used; their molecular weights are 288.3, 422, 624 and 1526, respectively. The boiling performance, characterized by an early onset of nucleate boiling, is significantly enhanced, and the maximum enhancement increases with decreasing surfactant molecular weight. Also, the heat transfer coefficient, normalized by dynamic σ (at 50 ms, 80°C), scales as h∝Mn with n=−0.5 and 0 for anionics and nonionics, respectively. This scaling follows from the postulation that the solutionʹs dynamic surface tension is determined by the surfactant concentration and its interfacial activity in the sublayer around the growing bubble. Correspondingly, boiling of these solutions is directly influenced by the ionic character and molecular makeup of this sublayer.