Study on a thermal boundary layer of drag reducing surfactant solution - Measurements of temperature fluctuation

In order to clarify the mechanism of turbulent heat transfer in drag reducing flow by surfactant additives, temperature in thermal boundary layer in two dimensional channel has been experimentally investigated. Time mean temperature and temperature fluctuation were examined at the Reynolds number of 1.2×10 ⁴ using a fine wire thermocouple probe. The surfactant system tested was CTAC/NaSal/water. A high diffusivity layer near the wall was found in the thermal boundary layer of surfactant solution. The layer is formed by micellar phase change. Time scales of the temperature fluctuation in surfactant solution flow became large compared to the water flow. It suggests the role of the fluid elasticity to suppress the coherent structure near the wall. As the drag reducing additives have a direct effect on the flow structure in the buffer layer at 10<y ⁺<100, reductions of drag and heat transfer are not recovered nevertheless of high diffusivity layer.