Abstract
Heat transfer fluctuation between a fluid and a solid may cause problems related to wall temperature fluctuation, such as high cycle thermal fatigue in materials. Moreover, heat transfer enhancement due to flow turbulence is similar to mass transfer enhancement, which leads to flow accelerated corrosion (FAC) downstream of an orifice in pipe flows. In order to avoid and/or predict these phenomena, quantitative information on the spatio-temporal fluctuation of the heat transfer is necessary. In the present study, a technique using high-speed infrared thermography was used to measure the spatio-temporal heat transfer to a turbulent water pipe flow around an orifice plate (bore ratio: d/D = 0.49, Re_D ≈ 12,000). The spatio-temporal distribution of the heat transfer coefficient was evaluated based on the temperature fluctuation of a heated thin-foil measured using high-speed infrared thermography (at approximately 800 Hz). As a result, it was revealed that the heat transfer downstream of the orifice fluctuated violently, and the instantaneous structure of the heat transfer was remarkably finer than the streaky structure for the fully developed pipe flow. The time-averaged value of the heat transfer had a maximum at approximately two diameters downstream of the orifice, where the rms value of the fluctuation and its characteristic frequency also became much higher than those for the fully developed pipe flow.
