Abstract
It is found that, in liquid—helium-II pure counterflow, the dimensionless number A=ρsAw¯l (where A is the Gorter-Mellink constant, w¯ is the mean relative velocity between the two fluids, and l is a characteristic dimension of the geometry) scales the mutual friction between the two fluids. Critical relative velocities in cylindrical channels are shown to be correlated by the rule AcρsAw¯cπd1.