Abstract
Unsteady measurement of convective heat transfer was performed to a water flow in a horizontal acrylic circular pipe with inner diameter of D = 20.4 mm for Reynolds number from 1000 to 30000. The velocity distribution in the pipe measured by LDV was laminar at Re ≤ 2000 and turbulent at Re ≥ 3000. The test surface for the heat transfer measurement was fabricated from a titanium foil of 22 μm thick coated with black paint. The titanium foil 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 (~800 Hz ). 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 streak in a circular pipe was revealed, which elongated along the streamwise direction and flowed downstream with some meanderings. The statistic values of the spatio-temporal characteristics, such as the mean spanwise wavelength of the thermal streak and the rms value of the fluctuating heat transfer, were investigated and compared with those of the previously published literature.
