Abstract
Transient forced convection heat transfer due to exponentially increasing heat input to a heater is important as a database for safety assessment of the transient heat transfer process in a Very High Temperature Gas-cooled Reactor (VHTR). Forced convection transient heat transfer for helium gas flowing over a cylinder in a narrow channel at various periods of exponential increase of heat input was experimentally studied. The test heater was mounted horizontally along the center part of a circular test channel with a diameter of 5 mm. The heat generation rates of the heater, Q, was raised with exponential function, Q = Q_0 exp(t/τ). By using a narrow channel, relatively high flow velocity was achieved and experiment data at large Reynolds number were obtained. As the results, the surface temperature and heat flux are increasing exponentially with the time. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than about 1 s. The heat transfer coefficients show high dependence on the flow velocity of helium gas and heater diameter.
