水平円柱に直交した低レイノルズ数領域の種々気体の過渡強制対流熱伝達

抄録

The knowledge of forced convection transient heat transfer at various periods of exponentially increasing heat input to a heater is important as a database for understanding the transient heat transfer process in a high temperature gas cooled reactor (HTGR) due to an accident in excess reactivity. In this study, the transient heat transfer coefficients for Helium, Argon, Air, and Nitrogen gases flowing perpendicular to a horizontal cylinder were measured in the low-Reynolds-number region. The platinum heater with a diameter of 1.0 mm was heated by electric current with an exponentially increase of Q₀exp (t/τ) . It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ over around 1 s, and it becomes higher for the period of τ shorter than about 1 s. Though the transient heat transfer region is influenced by both convection and the conductive heat transfer in the quasi-steady state heat transfer region, the conductive heat transfer becomes predominant as the period becomes short, especially in the region of within 200 ms. The transient heat transfer shows less dependent on the gas flowing velocity when the period becomes very short. Based on the experimental data, the ratio of transient heat transfer to the quasi-steady-state one was correlated as a function of Reynolds number of the gas flow and the non-dimensional period of increasing heat input. For the non-dimensional period larger than about 300, the transient heat transfer approaches the quasi-steady-state one, and shows no dependence on the Reynolds number.