Abstract
Unsteady measurements of convective heat transfer was performed to a water flow in a horizontal circular pipe with inner diameter of D = 20.4 mm for Reynolds number from 1000 to 30000. The test surface for the heat transfer measurement was fabricated from a titanium foil of 22 μm thick coated with black paint, which was heated electrically under conditions of constant heat flux. The time-spatial distribution of the heat transfer coefficient was evaluated from the temperature fluctuation on the test surface measured using a high-speed infrared thermograph (〜800Hz). The time-averaged heat transfer coefficient measured here agreed well to the conventional empirical correlation. As a result of the present measurement, the dynamic feature of the thermal streaks in a circular pipe was revealed, which elongated along the streamwise direction and flows downstream with some meanderings. The statistic values of the spatio-temporal characteristics, such as the mean spanwise wavelength of thermal streaks, was investigated and compared with those of the previously published literature.
