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Transient Heat Transfer From a Horizontal Cylinder in the Low-Reynolds-Number Flow of Various Gases
Qiusheng Liu and Katsuya Fukuda

The knowledge of forced convection transient heat transfer at various periods of exponentially increase of 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-Reynoldsnumber region. The platinum heater with a diameter of 1.0 mm was heated by electric current with an exponentially increasing heat input of Q = Q<sub>0</sub> exp(t/t). It was shown that the heat transfer coefficient approaches a quasi-steady-state for the period t larger than 1 s, and it becomes higher for the period of t shorter than about 1 s. The transient heat transfer shows little dependence on the gas velocity when the period becomes very short. Based on the experimental data, the ratio of transient to the quasi-steady-state heat transfer was correlated as a function of Reynolds number of the gas flow and the non-dimensional period of increasing heat input t*. For the non-dimensional period larger than about 300, the transient heat transfer approaches the steady-state one, and shows no dependence on the Reynolds number.

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