TED-AJ03-134 INVESTIGATION ON HEAT TRANSFER CHARACTERISTICS OF DRAG-REDUCING FLOW WITH SURFACTANT ADDITIVE BY SIMULTANEOUS MEASUREMENTS OF TEMPERATURE AND VELOCITYFLUCTUATIONS IN THERMAL BOUNDARY LAYER

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The characteristics of drag-reduction (DR) and heat transfer reduction (HTR) of a dilute aqueous CTAC solution with 30ppm of concentration at different inlet temperature and different Reynolds number were studied. Hydrodynamic and thermal turbulence structures and turbulence transport characteristics were investigated by simultaneously measured velocity and temperature fluctuations in thermal boundary layer in a drag-reducing surfactant solution flow. The test section is schematically shown in Fig.A-1. A two-component three-beam mode LDV and a fine-wire thermocouple probe were used for measuring velocity and temperature fluctuations respectively.[figure] Two critical upper limits of DR and HTR effectiveness in temperature and Reynolds number existed for drag-reducing surfactant solution flow, which implies that the threadlike micellar structure or "stress-induced structure" is destructed. At high DR or HTR level, a large temperature gradient appeared when y^+<30 in the measuring range. Similar to the enhancement of u′^+, θ′^+ was also enhanced in thermal boundary layer region in the drag-reducing flow. The streamwise turbulent heat flux normalized by friction velocity and temperature was larger for drag-reducing flow than for Newtonian flow whereas the turbulent heat flux in the wall-normal direction was depressed. In addition, the depression of wall-normal turbulent heat flux showed similar behavior to that of Reynolds stress, i.e., decorrelation between ν and θ vs. decorrelation between u and ν, which was testified by the cross-correlation coefficients of u-ν and ν-θ, as shown in Fig.A-2. It is then conjectured that heat transfer reduction is due to the decrease of-νθ^^^-.[figure]
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TED-AJ03-134 INVESTIGATION ON HEAT TRANSFER CHARACTERISTICS OF DRAG-REDUCING FLOW WITH SURFACTANT ADDITIVE BY SIMULTANEOUS MEASUREMENTS OF TEMPERATURE AND VELOCITYFLUCTUATIONS IN THERMAL BOUNDARY LAYER

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