Normal fluid heat-exchange drag in liquid helium II

An examination is made of the modification to Stokes' law for a heated sphere in liquid helium II, as calculated by Springett. His calculation yields an extra term in the drag, over and above the ordinary viscous drag and the Penney--Hunt heat-exchange drag. It is shown that this term is an artifact of the handling of the inertial term in Oseen's approximation to the full Navier--Stokes equation, and thus Springett's result cannot be regarded as valid. The problem is also considered by means of the Stokes theory, and its is shown that in this approximation the extra term is zero. Another approach, boundary layer theory, is mentioned, but not considered; it is cautioned that in the use of this theory careful attention should be paid to the treatment of the inertial terms