Cooling with a subsonic flow of quantum fluid

Miniature heaters are immersed in flows of quantum fluid and the efficiency heat transfer is monitored versus velocity, superfluid fraction, time. The $^{4}\mathrm{He}$ helium with a fraction varied from 71% down to 0% an imposed velocity up $3\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s}$, while characteristic sizes range $1.3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ few hundreds microns. At low fluxes, no dependence observed, agreement expectations. In contrast, some emerges at larger flux, as reported previously, three nontrivial properties identified. First, largest (71%), new regime appears non-null velocities it typically $10%$ less conductive than zero velocity. Second, mean compatible square-root observed classical fluids. Surprisingly, prefactor this maximum for intermediate or temperature (around 2 K). Third, time series exhibit highly short-lived events. These cooling glitches have velocity-dependent time, which manifest itself broad energetic peak spectrum series, kHz range. After showing that can be attributed breaking superfluidity within thin shell surrounding heaters, analytical model forced flow developed account above. We argue large scale patterns must form around heater, having size proportional flux (here two decades heater diameter) resulting turbulent wake. spectral peaking quantitatively consistent formation Von K\'arm\'an vortex street wake bluff body nearly but its precise remains unexplained. An alternative interpretation discussed, connection existing predictions bottleneck spectra energy equipartition.