Anomalous dissipation nearTλunder a large heat flux

Abstract

We report on thermal transport experiments in liquid 4 He near T using heat fluxes 8рQр55 W/cm 2 . We have confirmed the presence of a region near the superfluid transition, reported by Liu and Ahlers ͓Phys. Rev. Lett 76, 1300 ͑1996͔͒, in which thermal dissipation is anomalously small. The temperature transients for reaching a steady state upon entering this region from the superfluid side or cooling back into the superfluid have been studied, and are found to be quite different from each other; one possible explanation for this behavior is proposed which implies that the region of anomalous dissipation has a low thermal diffusivity. We discuss the location of this region in the phase diagram of liquid 4 He.

Liquid4Henear the superfluid transition in the presence of a heat current and gravity

“…From the slopes of the lines in the double-logarithmic plot we obtain effective power laws ∆T 1 (Q) ∼ −Q x and ∆T c (Q) ∼ −Q x with nearly the same exponent x, which varies between x ≈ 0.9 for 0.1 µW/cm 2 < ∼ Q < ∼ 1 µW/cm 2 and x ≈ 1.25 for Q > ∼ 10 µW/cm 2 . While our theoretical predictions for the dissipative region agree qualitatively with the experimental observations 5,6,8 , there are three major quantitative disagreements. First of all, the experimentally observed dissipation is much larger than the theoretically predicted, because for ∆T c (Q) < ∆T < ∆T λ (Q) the measured thermal resistivity ρ T = 1/λ T of Ref.…”

“…Then suddenly, when the temperature ∆T approaches and drops below the second transition temperature ∆T c (Q), the experimentally observed thermal resistivity is so small, that it was not detected any more in the experiment 6 . Our theory does not predict the second transition temperature ∆T c (Q), which has been found in the experiments 5,6,8 . While the solid line in Fig.…”

“…The force density (9.1) was added to the hydrodynamic equations of the two-fluid model (see (8) and (9) …”

Enhanced Heat Capacity and a New Temperature Instability in SuperfluidH4ein the Presence of a Constant Heat Flux NearHarter1, Lee2, Chatto3 et al. 2000Phys. Rev. Lett.24170View full textAdd to dashboardCite

“…Furthermore, they report the observation of a region of small but finite resistivity that they believe lies between T DAS ͑Q͒ and T c ͑Q͒. An experiment by Murphy and Meyer [7] confirmed the existence of this anomalous dissipative region, but called LA's placement of the region into question. An alternative explanation is given in the theory by Haussmann [3].…”

“…There has been intense recent interest in the superfluid transition of liquid 4 He in the presence of a constant heat flux Q because it provides an ideal testing ground for the study of phase transitions under dynamical conditions [1][2][3][4][5][6][7][8][9][10][11]. A heat flux induces a counterflow between the superfluid and the normal fluid, which gives the system an extra degree of thermodynamic freedom and depresses the superfluid density r s .…”