Abstract
The motion of micro-spheres in He II thermal counterflow has been measured using the Particle Image Velocimetry (PIV) technique. Although the tracer particles are able to track the motion of the normal fluid component, a significant discrepancy between the measured particle velocity and theoretical normal fluid velocity is observed. Further analysis of this velocity discrepancy suggests that it may be caused by the interaction between particles and vortex lines in the superfluid component. A semi-empirical correlation for the interaction force is developed and compared to the experimental results, from which new dynamic behavior of particles in He II is presented in the form of an effective kinematic viscosity of the superfluid.
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