Hydrodynamic aspects in the problems of theory of superfluid turbulence

Nemirovskii, Sergey K.; Kondaurova, L. P.; Nedoboiko, M. V.

doi:10.1016/s0011-2275(05)80068-2

Cited by 5 publications

(2 citation statements)

References 2 publications

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“…The problem of unsteady heat transfer in He-II is rather complicated. To be solved accurately, this problem requires superfluid turbulence hydrodynamics to be invoked [9,10]. The temperature difference T i −T b that arises in liquid helium can be evaluated using the Gorter-Mellink semi-empirical theory.…”

Section: Formula (2) Is Valid Provided Thatmentioning

confidence: 99%

Experimental study of HE-II boiling on a sphere

Kryukov

Mednikov

2006

J Appl Mech Tech Phys

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Regimes of superfluid-helium boiling on structural-steel spheres 4.8 and 6.0 mm in diameter, with heaters installed inside, are examined. Experimental data on the evolution of vapor films formed on the spherical surfaces are obtained.Introduction. Knowing the features of vapor-film formation and development on heater surfaces is important both for basic research of transfer processes across interfaces and for solving many applied problems. In particular, elucidation of conditions for vapor-phase generation and development in superfluid-helium film boiling is necessary for working out measures providing for reliable cryostatting of superconducting magnets, cables, and other devices, and also for substantiating methods preventing equipment faults.The majority of He-II boiling studies were performed on cylindrical samples and flat heaters [1][2][3][4]. On the other hand, studying the evolution of the vapor film in He-II on spherical surfaces is capable of providing useful information for further development of the theory of heat and mass transfer and for various applications.Experimental Setup. To examine He-II boiling on a sphere, we used an experimental setup that comprised a cryostatting system, an optical system, a video-recording system, and also a system for generating the thermal load and temperature measurement (Fig. 1). The experimental assembly was a glass helium pair consisting of two Dewar flasks of different diameters: An inner flask filled by helium and an outer flask filled by nitrogen. The helium flask (whose inner diameter was 55 mm) was hermetically connected to the pipeline vapor evacuation. The outer flask was open (directly contacting the atmosphere) and was filled by liquid nitrogen serving as a protecting thermal shield. Both flasks had vision slots 20 mm wide, which were used for video recording of the experimental processes. The flasks were aligned so that the slots coincided with each other, which allowed visual observations and video recording of the experimental cell installed in the inner flask. The desired temperature in the helium bath was maintained by vapor evacuation. The liquid temperature was monitored on the basis of the saturation pressure measured with a mercury manometer. The cryostat was filled by liquid helium from an STG-40 liquid-helium transport vessel through an overflow siphon.The processes on the sphere were recorded using an optical system consisting of an MBS-9 microscope placed onto the optical axis of the two Dewar flasks, a video camera coupled with the microscope eyepiece, and a videotape recorder.The experimental sample is schematically shown in Fig. 2. A hole was drilled in a ball bearing to insert a fluoroplastic-insulated carbon heater. Samples 4.8 and 6.0 mm in diameter were used. The heat supplied to the heater was measured by a four-wire circuit. The electric current in the supply circuit was determined from the voltage drop across a reference coil with a nominal resistance of 0.1 Ω. The depth of sphere penetration below the superfluid-helium level was mea...

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Section: Formula (2) Is Valid Provided Thatmentioning

confidence: 99%

Experimental study of HE-II boiling on a sphere

Kryukov

Mednikov

2006

J Appl Mech Tech Phys

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“…Skrbek et al first realized that the t −3/2 behavior at large decay times indicated the decay of a quasiclassical turbulence in the coupled two fluids, similar to those generated by a towed grid [7]. However, the underlying mechanism for the appearance of the bump and the switching to the t −3/2 decay was unclear for many years despite various theoretical efforts [48][49][50]. With the aid of our flow visualization, we have recently elucidated that the energy spectrum transition in the coupled turbulence is responsible for the observed complex L(t) behavior [9].…”

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confidence: 99%

Determination of the effective kinematic viscosity for the decay of quasiclassical turbulence in superfluidHe4

2016

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The energy dissipation of quasiclassical homogeneous turbulence in superfluid 4 He (He II) is controlled by an effective kinematic viscosity ν ′ , which relates the energy decay rate dE/dt to the density of quantized vortex lines L as dE/dt = −ν ′ (κL) 2 . The precise value of ν ′ is of fundamental importance in developing our understanding of the dissipation mechanism in He II, and it is also needed in many high Reynolds number turbulence experiments and model testing that use He II as the working fluid. However, a reliable determination of ν ′ requires the measurements of both E(t) and L(t), which was never achieved. Here we discuss our study of the quasiclassical turbulence that emerges in the decay of thermal counterflow in He II at above 1 K. We were able to measure E(t) using a recently developed flow visualization technique and L(t) via second sound attenuation. We report the ν ′ values in a wide temperature range determined for the first time from a comparison of the time evolution of E(t) and L(t).PACS numbers: 67.25.dk, 29.40.Gx, Below about 2.17 K, liquid 4 He transits to the superfluid phase (He II) in which an inviscid irrotational superfluid component (i.e. the condensate) coexists with a viscous normal-fluid component (i.e. the thermal excitations) [1]. The fraction of the normal fluid drops drastically with decreasing temperature and only amounts to about 0.7% of the total density at 1 K [2]. This quantum fluid system exhibits fascinating hydrodynamic properties. For instance, the rotational motion of the superfluid in a simply-connected volume can occur with the formation of topological defects in the form of vortex lines. These vortex lines all have identical cores with a radius a 0 ≃1Å and they each carry a single quantum of circulation κ=10 −3 cm 2 /s [3]. Turbulence in the superfluid therefore takes the form of an irregular tangle of vortex lines (quantum turbulence). Turbulence in the normal fluid is expected to be more similar to that in a classical fluid, but a force of mutual friction between the two fluids, arising from the scattering of thermal excitations by the vortex lines, can affect the flows in both fluids [4].At above 1 K, despite being a two-fluid system with many properties restricted by quantum effects, He II is observed to behave very similarly to classical fluids when a turbulent flow is generated by methods conventionally used in classical fluid research, such as by a towed grid [5] or a rotating propeller [6]. Even in a non-classical thermal counterflow induced by an applied heat current in He II, it has been revealed that quasiclassical turbulence can emerge during the decay of counterflow after the heat current is switched off [7][8][9]. The quasiclassical behavior * Corresponding: wguo@magnet.fsu.edu of He II is interpreted as the consequence of a strong coupling of the two fluids by mutual friction at large scales [10]. It is suggested that the turbulent eddies in the normal fluid are matched by eddies in the superfluid produced by polarized vortices [11,12], although ...

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Dynamics of intense heat pulses in HeII interacting with vortices they generate

Kondaurova

Nemirovskii

1996

Czech J Phys

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Hydrodynamic aspects in the problems of theory of superfluid turbulence

Cited by 5 publications

References 2 publications

Experimental study of HE-II boiling on a sphere

Experimental study of HE-II boiling on a sphere

Determination of the effective kinematic viscosity for the decay of quasiclassical turbulence in superfluidHe4

Dynamics of intense heat pulses in HeII interacting with vortices they generate

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