The aspect-ratio effect of He II channels on the heat transport characteristics

The critical heat flux qλ at which normal-fluid (He I) sets in at the center of a heated surface distributed along the inner wall of a He II channel can be smaller than the value calculated from the theory of Gorter-Mellink heat conduction. The reduction in qλ becomes noticeable as the ratio of channel gap d to channel length L increases. The effect may be explained by the presence of a temperature gradient across the channel gap, so that the temperature at the heated side reaches the λ-point at an earlier qλ than the other side