Study of Particle Motion in He II Counterflow Across a Wide Heat Flux Range

Abstract

Some discrepancy exists in the results of He II counterflow experiments obtained using particle image velocimetry (PIV) when compared with those obtained using particle tracking velocimetry (PTV): using PIV, it was observed that tracer particles move at roughly half the expected normal fluid velocity, $v_n/2$, while tracer particles observed using PTV moved at approximately $v_n$. A suggested explanation is that two different flow regimes were examined since the range of heat flux applied in each experiment was adjacent but non-overlapping. Another PTV experiment attempted to test this model, but the applied heat flux did not overlap with any PIV experiments. We report on the beginnings of a study of solid $\hbox {D}_2$ particle motion in counterflow using PTV, and the heat flux range overlaps that of all previous visualization studies. The observed particle velocity distribution transitions from a two-peak structure to a single peak as the heat flux is increased. Furthermore, the mean value of one peak in the bi-modal distributions grows at approximately the same rate as $v_n$, while the mean value of the single-peak distributions grows at roughly $0.4v_n$, in reasonable agreement with both previous experiments and with the suggested model.