Investigation On Boiling Heat Transfer Characteristics And Bubble Behaviors Of Surfactant Solution On Grooved Surface

Boiling heat transfer,as an efficient phase transfer heat form,is widely used in refrigeration,air conditioning,seawater desalination,electronic component cooling,nuclear power generation and other fields.For more efficient heat transfer,scholars have conducted researches and explorations on boiling heat transfer enhancement methods.In pool boiling heat transfer system,commonly used methods include improving heat transfer surface（Chemical modification,laser ablation,wire cutting,etc.）and using additives（Nanofluids,surfactants,etc.）.The aims are to advance the onset of nucleate boiling（ONB）,improve bubble nucleation ability and surface wettability,etc.In this study,the grooved surface which is convenient for processing is adopted,and the cheap surfactant sodium dodecyl sulfate（SDS）is used as additive to investigate the boiling heat transfer characteristics and bubble behaviors under coupled action.The bubble nucleation,growth and departure characteristics,under the low and medium heat fluxes（q<43 W/cm~2）,are observed based on visualization.The results are found to yield the reported empiric laws in the functional form of diffusion controlled growth,i.e.,D_eq∝t^0.5,for both deionized water and surfactant solution.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.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 fluxes 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 238%.For the surfactant boiling curve,the wall superheat will be stable near a certain value within a certain range of heat fluxes,that is,the surfactant solution can maintain a relatively stable heat transfer effect within a certain thermal conditions.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）.It could be attributed to the good nucleation ability and the repulsion between bubbles,which also result in the heat transfer enhancement of SDS solution at low and medium heat fluxes.Finally,the surfactant boiling model is constructed based on Freundlich adsorption isotherm,where molecular transport,adsorption rate and adsorption quantity factors are considered,and also compared with the existing experimental results for verification.It is found that the adsorption and diffusion of surfactant molecules are a determinant.Moreover,since the surfactant molecular adsorption and diffusion mechanism may change,different surfactant solution concentrations would lead to significant differences in the boiling curves.