Experimental investigation on bubble dynamic behaviors in pool boiling of surfactant solutions

Abstract

In this study, pool boiling experiments on copper surfaces with different roughness levels (Ra = 0.61 μm and Ra = 0.15 μm) using sodium dodecyl sulfate (SDS) solutions at various concentrations (0.1 CMC, 1 CMC, 5 CMC, and 10 CMC) are investigated. Our study focuses on the impact of SDS concentration, wall superheat, surface roughness, and bubble behavior on boiling heat transfer. The results show that an increase in SDS concentration could improve the heat transfer. However, when the SDS concentration reaches 10 CMC, there is a deterioration in heat transfer. Additionally, rough surfaces show better heat transfer performance compared to smooth surfaces. The presence of surfactant not only promotes bubble nucleation but also reduces the bubble departure diameter and inhibits bubble coalescence. Multiple bubbles are formed from the same nucleation site in surfactant solutions with high concentrations (5 CMC, 10 CMC). Various bubble dynamic parameters, including instantaneous size, departure diameter, growth time, waiting time, and departure frequency are obtained and compared with existing empirical correlations in the literature. It is found that the bubble growth in both deionized water (DI water) and surfactant solutions is mainly influenced by the near-wall thermal conditions, aligning with the thermal diffusion mechanism. In addition, the bubble departure diameters in both DI water and surfactant solutions gradually increase with increasing Jakob number (Ja). The growth time and waiting time in the surfactant solution both decrease with increasing Ja number, leading to a significant rise in the departure frequency. In contrast, the bubble growth time in DI water increased and the waiting time decreased with increasing Ja number, resulting in a relatively stable departure frequency. A new empirical formula is proposed for fDd0.5 based on the surface tension coefficient, surface roughness, and Ja number, which demonstrates good rationality.