Transient and steady-state heat transfer for forced convection of helium gas in minichannels with various inner diameters

Abstract

An experimental research was carried out on steady-state and transient heat transfer characteristics for forced convection of helium gas in minichannels. Platinum minichannels with different inner diameters were heated by an exponential power source with a wide range of e-folding time of heat generation rate and cooled by forced convection of helium gas with different flow velocities, inlet temperatures, and inlet pressures. The diameter effect of minichannels on the transient and steady-state heat transfer was investigated. According to the results, the heat transfer coefficients were improved with a decrease in the inner diameters of minichannels under both transient and quasi-steady states. A significant enhancement was obtained by using a 0.8 mm diameter minichannel. For the steady-state heat transfer, a new correlation was acquired for the 0.8 mm diameter minichannel and the correlation of a 1.8 mm diameter minichannel was appropriate for a 2.8 mm diameter minichannel. The influence of Reynolds number on steady-state Nusselt number for the 0.8 mm diameter minichannel was more significant compared with the 2.8 and 1.8 mm diameter minichannels. The transient heat transfer correlations for the 0.8 and 2.8 mm diameter minichannels were obtained by introducing Fourier number, respectively.