VISUALIZATION OF TURBULENT HEAT TRANSFER TO A WATER FLOW IN A CIRCULAR PIPE USING HIGH-SPEED INFRARED THERMOGRAPHY

摘要

Visualization and measurement of the spatial-temporal heat transfer characteristics of a turbulent water flow were conducted in a horizontal acrylic circular pipe, using a high-speed infrared thermograph (frame rate of up to 800 Hz). The inner diameter of the pipe was D = 20.4 mm and the Reynolds number varied from 1000 to 38,700. The test surface for the heat transfer measurement was fabricated from 22-μm-thick titanium foil coated with black paint, which was heated electrically with a constant heat flux. The heat transfer coefficient was evaluated quantitatively through heat conduction calculations for the heated surface considering the thermal inertia and diffusion. From the results of the present measurements, the convection pattern of high heat transfer spots was elucidated through frame-by-frame imaging of the instantaneous distribution. Also, the convection velocity was estimated from a 2D autocorrelation of the streamwise-temporal distribution. The convection velocity normalized by the mean velocity in the pipe was u_c/u_m = 0.5-0.8 and that normalized by the friction velocity was u_c~+ = 10-14.