Study on boiling heat transfer of surfactant solution on grooved surface

Abstract

In the present study, the coupling effect of wire-cutting grooved surface and surfactant (Sodium dodecyl sulfate, SDS) in pool boiling heat transfer is studied experimentally. Based on visualization, the bubble growth at the onset of bubble formation is measured, and the results are found to yield the reported empiric laws in the functional form of heat diffusion growth. In addition, the surfactant is found to improve the bubble nucleation on the heated surface with a shorter growth time and smaller departure diameter. Moreover, the grooved surface is also easier to nucleate than the smooth one, that is, the onset of bubble formation on the grooved surface is advanced, and thus the coupling effect further enhances the bubble nucleation. For the heat transfer, the SDS solution presents good heat transfer performance at low and medium heat flux in comparison to the DI water, and the coupling effect with the grooved surface would lead to further enhancement, by which the heat transfer coefficient (HTC) is maximally increased by about 238%. In addition, there are three main forms of bubbles found during the boiling of SDS solution, including small bubbles, discrete bubbles and large bubbles. The discrete bubbles are found to be formed by the entrainment of the upper foam due to the liquid convection. At relatively high heat flux, there is bubble crowding in the boiling of surfactant solution, accompanied by the expansion and contraction of bubble clusters and significant fluctuation of near-wall temperature. Furthermore, the bubble crowding seems to cause the premature dryout and the low critical heat flux (CHF), and could be attributed to the good nucleation ability and the repulsion between bubbles, which also result in the heat transfer enhancement of SDS solution in low and medium heat flux. Therefore, the enhancement of HTC and CHF cannot be achieved simultaneously in the present method.