Transient forced convective heat transfer of helium gas in a narrow tube heated by exponential time-varying heat source

Abstract

ABSTRACT The analysis and evaluation of transient heat transfer are essential to predict stability and safety of helium gas cooling fusion blanket due to plasma disruption. In this study, transient turbulent heat transfer characteristics of helium gas flowing in a narrow tube were experimentally investigated by using a forced convection gas loop. A narrow tube with an inner diameter of 1.8 mm was employed as test heater and heated exponentially increasing with time under various e-folding time of heat generation rate (0.04–15 s), flow velocities (101–248 m/s), inlet gas temperatures (293–313 K), and pressures (298–502 kPa). The experimental results showed that the heat transfer process can be separated into transient-state heat transfer and quasi-steady-state one at the e-folding time of near 1.5 s. The dependence of quasi-steady-state heat transfer on gas pressure and flow velocity was significant, but the transient-state one was less dependent on gas pressure and flow velocity. The influence of inlet gas temperature on the heat transfer coefficient was not obvious under both transient and quasi-steady conditions. A semi-empirical correlation of the relationship between transient-state and steady-state heat transfer was developed based on substantial experimental data by employing a nondimensional parameter of Fourier number.