水平円柱に並行して流れるヘリウムガスの強制対流過渡熱伝達

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The knowledge of forced convection transient heat transfer at various periods of exponential increase of heat input to a heater is important as a database for safety assessment of the transient heat transfer process in a high temperature gas cooled reactor (HTGR) due to an accident in excess reactivity and in a heat exchanger with unsteady-state flow. The transient heat transfer coefficient for helium gas flowing parallel to a horizontal cylinder was measured at relatively large Reynolds numbers (Re=7.3×10^3〜1.9×10^4). The platinum cylinder with a diameter of 1.0 mm was used as a test heater and heated by electric current with an exponential function of Q_0exp(t/τ). The experiments were carried out at a pressure of 0.5 MPa. The periods ranged from 50 ms to 15 s, the gas flow velocities ranged from 4 to 10 m/s, and the gas temperatures was 303 K(30℃). The surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period i longer than about 1 s, and it becomes higher for the period shorter than around 1 s. The dependence of transient heat transfer on the gas flowing velocity becomes weak when the period becomes very shorter. The heat transfer shifts to the quasi-steady-state one for longer periods and shifts to the transient one for shorter periods at the same flow velocity. It also approaches the quasi-steady-state one for higher flow velocity at the same period. The quasi-steady-state heat transfer correlation was obtained based on the experimental data, and it shows higher values than those by the previous correlation for parallel flow to a plate and author's previous correlation for cross flow to a cylinder. It was clarified that the correlation for transient heat transfer can be correlated by the correlation for quasi-steady-state one and the non-dimensional parameter composed of period, velocity, and heater length.
2004-07-31

水平円柱に並行して流れるヘリウムガスの強制対流過渡熱伝達

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