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1.
R. P. Behringer 《Journal of Low Temperature Physics》1986,62(1-2):15-26
The superfluid hydrodynamics of heat flow is examined for very small mass concentrationsc of3He in4He in an effort to better understand recent results for the effective heat conductivity eff, which appear to be in conflict with predictions. The full hydrodynamics contains a thermal boundary layer; within this layer the temperature and concentration gradients differ from those in the bulk fluid. An examination of finite heating effects based on the ansatz eff c
–p
for smallc shows distinctly different behavior for experimental determinations of eff whenp<1,p=1, andp>1. Thus, finite heating can be used as a probe to evaluate the exponentp. 相似文献
2.
An experimental study is presented for the thermal conductivity and the thermal relaxation for dilute mixtures of3He in4He with concentration 9×10–4X(3He)5×10–2 at saturated vapor pressure and in the normal phase near the superfluid transition. The conductivity results for are compared with predictions by Dohm and Folk from field-theoretic renormalization group(RG) theory. The conductivity
s
=[–1(T)––1(T)]–1, is compared with Ahlers' phenomenological arguments, and also with predictions by Dohm and Folk and by Onuki. The temperature difference transient T(t) across the fluid, measured as a function of timet after switching on and off the heat current, is analyzed. The thermal diffusion ratiok
T and the mass diffusion coefficientD are obtained by fitting the calculated transient to the experimental one. The results are compared with the predictions that follow from the RG approach by Dohm and Folk. Very good agreement is obtained fork
T. The transient is not very sensitive toD, and hence the determination is not accurate. Yet within the uncertainty, the deducedD also agrees with predictions. Appendices give (1) the corrections to from finite heat effects, (2) the calculation of the concentration susceptibility (X/)
T,P
, and (3) the calculation procedure for ,k
T, andD using the RG approach of Dohm and Folk. 相似文献
3.
R. P. Behringer 《Journal of Low Temperature Physics》1990,81(1-2):1-17
The response of a layer of superfluid mixture to an ac heat source,Q(t)=Q
0
exp(it), is determined. In the low-frequency regime, the temperature response at the heated side of a superfluid layer is essentially identical to that of an ordinary fluid having a thermal conductivity eff and a thermal diffusion coefficient
0
/2. Here eff is the effective conductivity of Khalatnikov, and
0
is the diffusion coefficient of Griffin. At much higher frequencies, the results are more complicated. The low-frequency regime is defined in terms of the second sound velocityu
2
by u
2
2
/
0
. The ac response function is valuable in a number of ways. It can be used to obtain the system response to more complicated time-dependent variations inQ such as step changes inQ. A knowledge of the response function in the low-frequency regime provides a mechanism for directly determining the Kapitza resistance in mixtures. Finally, a knowledge of the response function provides an additional opportunity to test two-fluid hydrodynamics. Alternative tests of superfluid hydrodynamics are of particular interest in light of recent experiments that show anomalous values for eff in the low
3
He concentration limit 相似文献
4.
Measurements of the average thermal conductivity exp hQ/T and of the thermal relaxation time to reach steady-state equilibrium conditions are reported in the superfluid phase for dilute mixtures of3He in4He. Hereh is the cell height,Q is the heat flux, andT is the temperature difference across the fluid layer. The measurements were made over the impurity range 2×10–9<X(3He)<3×10–2 and with heat fluxes 0.3<Q<160 µW/cm2. Assuming the boundary resistanceR
b
, measured forX<10–5, to be independent ofX over the whole range ofX, a calculation is given for exp. ForQ smaller than a well-defined critical heat fluxQ
c
(X) X
0.9, exp is independent of Q and can be identified with the local conductivity eff, which is found to be independent of the reduced temperature = (T–T)/T for –10–2. Its extrapolated value at T is found to depart forX10–3 from the prediction X
–1
, tending instead to a weaker divergence X
–a
witha0.08. A finite conductivity asX tends to zero is not excluded by the data, however. ForQ >Q
c
(X), a nonlinear regime is entered. ForX10–6, the measurements with the available temperature resolution are limited to the nonlinear conditions, but can be extrapolated into the linear regime forX2×10–7. The results for exp(Q),Q
c
(X), and eff(XX) are found to be internally consistent, as shown by comparison with a theory by Behringer based on Khalatnikov's transport equations. Furthermore, the observed relaxation times (X) in the linear regime are found to be consistent forX>10–5 with the hydrodynamic calculations using the measured eff(X). ForX<10–5, a faster relaxation mechanism than predicted seems to dominate. The transport properties in the nonlinear regimes are presented and unexplained observations are discussed. 相似文献
5.
R. Nomura H. H. Hensley T. Matsushita T. Mizusaki 《Journal of Low Temperature Physics》1994,94(5-6):377-383
We have measured the growth rate of single crystal U2D2 solid3He in the superfluid B phase as a function of chemical potential difference between the solid and liquid for temperatures between 0.4 and 0.9 TN. The growth rate was not proportional to , with very slow growth rates for less than about 10 erg/cm3. For larger values of the growth rate depended weakly on temperature and the growth was attributed to a quantum growth mechanism due to screw dislocations. The melting rate was too fast to be measured quantitatively, but was slower at higher temperatures. 相似文献
6.
A recent formula for the heat transfer coefficient between
3He quasiparticles and phonons of a sintered metallic powder is evaluated using the phonon density of states of a microscopic model of a granular structure. The microscopic model describes a simple crystalline granular structure and contains extended modes only. When the dominant phonon wavelength is less than a typical grain size, possesses a low-temperature enhancement typical of a sintered metallic powder and over a limited range exhibits a linear variation with temperature. 相似文献
7.
Relaxation times are reported from the transients observed during thermal conductivity eff and thermal diffusionk
T
*
measurements in superfluid mixtures of3He in4He with a layer thickness of 1.81 mm. The experiments extend from 1.7 K toT
and over a3He concentration range 10–6X<5×10–2. The agreement between the measured and the predicted from the two-fluid thermohydrodynamic equations is satisfactory forX>10–3 but deteriorates for smaller3He concentrations. This situation is similar to that for eff andk
T
*
results and indicates that the transport properties in very dilute mixtures with layers of finite thickness are not well understood. ForX>10–3, the mass diffusion coefficientD
iso for isolated3He in4He has been determined from and from eff measurements. There is an inconsistency by a constant numerical factor between these determinations. This problem might be related to the observations that in the superfluid phase, the relaxation times for different cell heightsh do not scale withh
2. FromD
iso derived via the eff data, the3He impurity-roton scattering cross section is determined. Comparisons with previous work are made. 相似文献
8.
J. Li A. Pflaum F. Pobell P. Sekowski U. Stuhr H. Wipf 《Journal of Low Temperature Physics》1992,88(3-4):309-315
We have measured the thermal conductivity and the heat capacity C of Ti, TiH
0.82
, TiH
1.7
, and TiH
2
at 0.35 K T 4 K. Whereas (TiH
0.82
) and (TiH
1.7
) are substantially smaller than (Ti), we find (TiH
2
) – 3 (Ti). This latter remarkable result may arise from the enhanced electronic density of states — which is shown by the heat capacity data — and from a rather large electronic mean free path in this stoichiometric compound. 相似文献
9.
The thermal conductivity of solid H2 and the NMR absorption signal of isolated o-H2 were measured simultaneously along isotherms 0.07<T<1.5 K as a function of time after a rapid cooldown from 2 K. The o-H2 concentration ranged from 3.4% to 0.4%, and the pressure was 90 atm. During the measurements, clustering of o-H2 particles occurred as seen from the changes both of the NMR signal amplitude and of with time t. The difference
–1
=
–1
()–
–1(0) between the thermal resistivity
–1
(t=0) just after cool down and in equilibrium,
–1
(), was found to change sign near 0.23 K, and this result is discussed with respect to previous experiments. The equilibrium resistivity attributed to the o-H2 impurities,
, is derived and is compared with previous determinations and with predictions. An analysis of the equilibration process for
–1
and for the NMR signal amplitude is presented. It shows that the characteristic times are of comparable but not equal magnitude. Comparison of the derived from NMR data atP=90 and 0 atm favors resonant ortho-para conversion over quantum tunneling as the leading mechanism for quantum diffusion. 相似文献
10.
We present steady-state measurements of the thermal diffusion ratiok
T
and of the heat conductivity for three dilute mixtures of3He in4He with concentrations 9×10–3X(3He)5×10–2 at saturated vapor pressure in the normal phase close to the superfluid transition. The data are compared with predictions by Dohm and Folk from the renormalization group (RG) theory. From auxiliary determinations of thermodynamic derivatives for these mixtures, we obtain the separation factor =–(k
T
/T)×(/X)
T,P
/(/T)
X,P
above T over the range wherek
T
is positive. Here is the mass density. From the transients of X(t) as a function of time, we obtain an estimation for the mass diffusion coefficientD and compare the results with predictions by Dohm and Folk and with results from other experiments. 相似文献
11.
We discuss the feasibility and likely results of measurements of the thermal conductivity (Q,t) of4He very nearT
T
(Q = 0) as a function of the heat currentQ and the reduced temperature t [T —T]/T
by heating a sample from above and cooling it from below. Although the expansion coefficient is negative, the experiment should be possible without inducing convection in the HeI layer provided the sample length does not significantly exceed one cm. Fort 10–7(Q 0.2 erg/s cm2), a state of self-organized criticality can be attained. For these conditions, the thermal gradient cancels the gradient inT
induced by gravity, thus permitting measurements extremely close to the transition even in an Earthbound laboratory. However, the data will be only for a unique path in the Q—t plane. For 0.2 Q 0.5 erg/s cm2 (10–7t 10–8) they will be in the range of linear response and give (0,t); for Q between about 0.5 and 10 erg/s cm2 and over a temperature range of about 20 nK, the experimental path samples the regime where the conductivity is expected to be influenced by nonlinear finite-current effects. The small currents and narrow temperature range of the experiment imply that ultra-high resolution thermometry as well as very careful control of stray heat currents will be required. ForQ 10 erg/s cm2 and up to very largeQ, the method can be used to determine the onset temperatureT
c
(Q) of thermal resistance. 相似文献
12.
Measurements are reported of the surface resistance of dirty type-II superconductors driven into the surface-sheath regime by a static magnetic field,H
0 parallel or nearly parallel to the sample surfaces and transverse to the microwave current, in which condition the latter can excite fluctuations of the order parameter. A recent calculation by Maki has suggested that the surface resistance would be influenced by the presence of Kulik's vortex state even when the sample surface is polished and is as nearly as possible parallel toH
0. It is therefore proposed that the sample surface should be decomposed into elements which make different angles withH
0, and the distribution of these angles described by a Gaussian. 2
(t) is deduced from the surface-resistance measurements nearH
c3, so interpreted, and a temperature variation, 2
(t)/2(1), is found which agrees reasonably with theory and with magnetization data, [2(1)=limt 1 (2)]. It is suggested that the anomalously large variation of 2
(t) reported by Fischer and Maki may have resulted from failure to take Kulik's vortices into account. In magnitude, present 2(1) data agree with theory but not with magnetization data. 相似文献
13.
J. Mucha H. Misiorek A. V. Golubkov L. S. Parfenieva I. A. Smirnov 《International Journal of Thermophysics》2003,24(3):859-865
The thermal conductivity () and electrical resistivity () of mixed-valence compound Sm3S4 have been measured in the temperature range 5 to 300 K. The present results and those presented previously [1] for the thermal conductivity between 80 to 850 K are interpreted in terms of the temperature-dependent fluctuating valence of Sm ions. Sm3S4 crystallizes in the cubic Th3P4 structure, and the cations with different valences occupy equivalent lattice sites. Divalent and trivalent Sm ions are randomly distributed in the ratio of 1:2 over all possible crystallographic cation positions (Sm2+
2Sm3+
2S2–
4). The behavior of the Sm3S4 lattice thermal conductivity
ph
is extraordinary since valences of Sm ions are fluctuating (Sm3+Sm2+) with a temperature dependent frequency. In the interval 20 to 50 K (low hopping frequencies),
ph
of Sm3S4 varies as
ph
T
–1 (it is similar to materials with static distribution of cations with different valences): at 95 to 300 K (average hopping frequencies 107 to 1011 Hz),
ph
changes as
ph
T
–0.3 (it is similar to materials with defects). Defects in Sm3S4 appear because of local strains in the lattice by the electrons hopping from Sm2+ ions (with big ionic radii) to Sm3+ ions (with small ionic radii) and back (Sm2+Sm3+), at T>300 K (high hopping frequencies),
ph
becomes similar to materials with homogenous mixed valence states [1]. 相似文献
14.
Summary The rupture problem of a thin micropolar liquid film on a horizontal plane is studied. A nonlinear evolution equation is firstly derived for the film thickness,h(x, t), and then solved numerically. The results reveal that the rupture time of the film strongly increases with increase of the magnitude of the parameterR(=/). However, the analysis also shows that the micropolar coefficient, (=h
0
2/), has little influence on the stability of the film. 相似文献
15.
We report ultrasonic dispersion and attenuation measurements near the liquid-gas critical point of 3He at frequencies from 0.5 to 5.0 MHz and densities from 0.89
c
to 1.15
c
. The singular part of the sound attenuation and the dispersion on the critical isochore
c
= 0.0414 g/cm3 are analyzed in terms of the Kawasaki-Mistura theory. If the Ornstein-Zernike order parameter correlation function is assumed in the analysis, good agreement with our data is achieved, except close to the critical temperature T
cin the high-frequency region, where * = /D
1. Here
D
is the characteristic relaxation rate of the critical fluctuations. From a fit of the theory to our data, and assuming the inverse correlation length is expressed by = 0, where = (T–Tc)/Tc with = 0.63, we obtain 0 = (3.9 ± 0.4) × 109 m–1. It is found that a more realistic form of the correlation function, as proposed by Fisher and Langer and calculated by Bray, yields even poorer agreement with out data than does the classical Ornstein-Zernike form for * > 10. The same difficulties appear in the analysis of the available data for xenon. Thus, the present mode coupling theory is unable to satisfactorily describe the acoustic experiments on fluids near the liquid-vapor critical point over a large range of reduced frequencies *. In the appendix, we reanalyze previously reported ultrasonic data in 4He, taking into account the nonsingular term of the thermal conductivity. Using = 0.63, we obtain a good fit of the experiment to the theory in the hydrodynamic region with 0 = (5.5 ± 1) × 109 m–1.Supported by a grant from the National Science Foundation. 相似文献
16.
Experimental magnetic field penetration depths (t, d, H) of the stable and superheated Meissner state were calculated as a function of temperature for various applied magnetic fields and various film thicknesses for two cases: (1) (t)/d and (2) 2(t)/d ( is the Ginzburg-Landau penetration depth,d is the film thickness, is the GL parameter). The results of the first case should be a useful tool for obtaining (0) of amorphous superconducting thin films.1
This work was supported in part by NSF Grant No. INT 8006927. 相似文献
17.
The thermal conductivity and the associated relaxation time to reach steady-state conditions are reported for the normal phase of several very dilute mixtures of3He in4He (X<4 × 10–6) at saturated vapor pressure near T. The measurements were made over the reduced temperature range 2.5 × 10–6<<2×10–1, where (T–T)/T, and are representative for pure4He. The spacing between the cell plates was 0.147 cm. The systematic uncertainty in the conductivity data is estimated to increase from 2% for =0.2 to 4% for =3 × 10–6. The random scatter due to finite temperature resolution increases to 7% at the smallest . The data are in agreement within the combined uncertainty with recent ones by Tam and Ahlers (cell F, spacing 0.20 cm) and with previous ones in this laboratory taken with a different plate spacing. The thermal diffusivity coefficientD
T
= / C
p
obtained from is found to agree within better than 15% with the calculated one using data for , the density , and the specific heatC
p
. Measurements of the effective boundary resistivityR
b
in the superfluid phase are described.R
b
is found to depend on the thermal history of the cell when cycled up to 77 K and above. Also,R
b
shows the beginning of an anomalous increase for ¦¦10–4. The possible reasons for this anomaly are discussed, and their impact on the analysis of conductivity data in the normal phase is appraised. 相似文献
18.
Yu. M. Kolyano M. M. Semerak I. P. Dmitrash 《Journal of Engineering Physics and Thermophysics》1981,40(3):308-314
The temperature field is determined in a circular plate with a system of thin extrinsic heat sources.Notation T
temperature in the plate with the inclusions
- r
polar radius
-
polar angle
-
time
- (r,)
coefficient of thermal conductivity
-
(r,)
heat transfer coefficient
- C(r,)
volume heat capacity
- W(r,, )
specific intensity of the heat sources
-
half thickness of the plate
-
(x)
Dirac's delta function
- ¯T
finite Fourier cosine transform of the temperature
- p
parameter for this transformation
- T
Laplace transform of the temperature
- s
its parameter
- Iv(x)
Bessel function with imaginary argument of order
- K
v
(x)
the MacDonald function of order
-
and
dimensionless temperature
- Po
Pomerantz number
- Bi
Biot number
- Fo
Fourier's number
-
dimensionless polar radius
- b1
*
dimensionless radius of the circle on which the inclusions are placed
- R*
dimensionless radius of the plate
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 3, pp. 495–502, March, 1981. 相似文献
19.
Temperature gradients in superfluid helium carrying a heat current in a 13.8-mm-wide tube or in a 0.1-mm-wide slit have been measured at 0.09 m°K–T<16 m°K. The results are interpreted in terms of a mutual friction force between the normal component of He II and vortices in its counterflowing superfluid component. This force is found to diverge near T with a mutual friction constant proportional to (T–T)T
0.35±0.06. 相似文献
20.
Previous spin-fluctuation theories yielding the strong coupling corrections \-
i
to the five coefficients of the fourth-order invariants in the free energy functional are extended. First, the superfluid part of the susceptibility is calculated up to order 4 for all momenta and frequencies and the contribution arising from p-wave fluctuations of the order parameter is included. Then the frequency sums yielding the \-
i
are calculated by taking into account the full momentum and frequency dependence of the superfluid susceptibility and the spin fluctuation propagator. The results for the \-
i
are plotted vs. a cutoff qc on the momentum integration for spin-fluctuation parameters N(0)I = 0.75 and = 0.95. The cutoff takes into account in a rough way the effect of additional terms in the free energy functional which were neglected in previous theories. These additional terms are due to the implicit dependence of the superfluid susceptibility on the spin-fluctuation parameter I via the gap parameter . The gap equation providing the relation between and I is derived in the weak coupling approximation. The cutoffs obtained by fitting the experimental values of the three combinations of \-
i
(arising from the measured specific heat discontinuities on the melting curve) are comparable to the cutoff obtained from the spin-fluctuation contribution to the weak coupling freeenergy [q
c
= 0.3(2k
F
) for = 0.75]. The corrections due to the momentum and frequency dependence of the superfluid susceptibility and the spinfluctuation propagator are large and point in the direction of better agreement with experiment: The ratio % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiOuamaaBa% aaleaacaaIXaaabeaakiabg2da9iabfs5aejqbek7aIzaaraWaaSba% aSqaaiaaiwdaaeqaaOGaai4laiaacIcacqqHuoarcuaHYoGygaqeam% aaBaaaleaacaaIYaaabeaakiabgUcaRiabfs5aejqbek7aIzaaraWa% aSbaaSqaaiaaisdaaeqaaOGaaiykaaaa!47E0!\[R_1 = \Delta \bar \beta _5 /(\Delta \bar \beta _2 + \Delta \bar \beta _4 )\]decreases from 2 to about 1.2. However, in view of the large discrepancy with experiment (experimentally, R
1= 0.14), we conclude that spin-fluctuation theory in its present form (without taking into account renormalization effects) cannot account quantitatively for the measured specific heat discontinuities on the melting curve. 相似文献