Influence of Counter-Ion Concentration on the Impinging Jet of Surfactant Solutions

An impinging jet is characterized by high heat transfer and thus is widely used in cooling and heating process in industry. On the other hand, surfactant solutions reduce pipe friction in turbulent flow and at the same time reduce heat transfer. In our past study, it was found that the surfactant solution with higher counter-ion concentration did not reduce the heat transfer in the impinging jet. This phenomenon suggested that the high heat transfer was characterized by high shear rate in impinging jet and not by turbulence. However, it has not yet been determined satisfactorily how the heat transfer is influenced by surfactant solutions in the impinging jet. Especially, the influence of the counter-ion concentration is important, because the counter-ion changes not only the heat transfer but also the rheology of the surfactant solutions. In this study, we visualized the impinging jet of the surfactant solutions, and the influence of the counter-ion was investigated. The results indicated that the wall flow was remarkably influenced by the counter-ion concentration in the impinging jet. In the case of the surfactant solution with equi-molar counter-ion, the induced wall flow was continued only near the stagnation point. By contrast, the solution with higher molar counter-ion induced the radial boundary layer flow on the wall similar to the water flow. This difference in flow would cause the different heat transfer, and the solution with higher molar counter-ion produces normal heat transfer. When comparing the visualized results of the impinging jet with the numerically simulated results, the qualitative agreement was not satisfactory for the surfactant solution with counter-ion of equi-molar concentration. The simulation used a Bingham model as the rheological equation, the constants of which were obtained from a cone and a plate rheometer. It was suggested that the surfactant solution indicated different rheological behavior in these viscometric flow and impinging jet.