Investigations on Minichannel Gas Cooling

Experimental Investigations of Pressure Drop and Heat Transfer in an annular Minichannel

Axial pressure profiles and temperature profiles numbers have been measured with a heatable annular minichannel with a hydraulic diameter of 1.23mm and a channel length of 94mm. The measured data has been reduced to local friction factors and Nusselt numbers, covering 1500 < Re < 14000 and 0.0005 < q+ < 0.004 . It was found, that the friction factors for the adiabatic experiments matched very well the correlation of Chen, taking in account the measured channel surface roughness. For the heated cases, a pronounced effect of the heating intensity q+ (a nondimensional quantity proportional to the temperature increment of the gas) was proven, where higher heating rates effected a deterioration of the heat transfer, especially in the transition range 6000 < Re < 10000 of this configuration. It could be shown, that this is due to the increased gas viscosity near the wall, while acceleration effects do not yet play a significant role. Influence of the pressure (0.1-0.4MPa) and the gas species (N2, He, Ar) were not evident.

ITHEX annular laminarization
Plots of the local Fanning friction factor and local Nusselt number at two Reynolds numbers, measured in the ITHEX annular duct minichannel experiment. A clear effect of laminarization is visible for high heating rates q+

Flow Velocity Profile