Bulk viscosity of stirred xenon near the critical point

Simulation of transport around the coexistence region of a binary fluid

We use Monte Carlo and molecular dynamics simulations to study phase behavior and transport properties in a symmetric binary fluid where particles interact via Lennard-Jones potential. Our results for the critical behavior of collective transport properties, with particular emphasis on bulk viscosity, is understood via appropriate application of finite-size scaling technique. It appears that the critical enhancements in these quantities are visible far above the critical point. This result is consistent with an earlier report from computer simulations where, however, the authors do not quantify the critical singularity.

Predrying transition on a hydrophobic surface: statics and dynamics

For one-component fluids, we examine the predrying phase transition between a thin and thick low-density layer in liquid on a wall repelling the fluid. This is the case of a hydrophobic wall for water. A predrying line starts from the coexistence curve and ends at a surface critical point in the phase diagram. We calculate this line numerically using the van der Waals model and analytically using the free-energy expansion up to the quartic order. We also examine the predrying dynamics of a layer created on a hydrophobic spot on a heterogeneous wall. It is from a thin to thick layer during decompression and from a thick to thin layer during compression. Upon the transition, a liquid region above the film is cooled for decompression and heated for compression due to latent heat convection, and a small pressure pulse is emitted from the film into the liquid.

Calculation of the bulk viscosity in SU(3) gluodynamics

We perform a lattice Monte Carlo calculation of the trace-anomaly two-point function at finite temperature in the SU(3) gauge theory. We obtain the long distance properties of the correlator in the continuum limit and extract the bulk viscosity zeta via a Kubo formula. Unlike the tensor correlator relevant to the shear viscosity, the scalar correlator depends strongly on temperature. If s is the entropy density, we find that zeta/s becomes rapidly small at high T, zeta/s<0.15 at 1.65T(c), and zeta/s<0.015 at 3.2T(c). However, zeta/s rises dramatically just above T(c), with 0.5<zeta/s<2.0 at 1.02T(c).

Thermoacoustic effects in supercritical fluids near the critical point: Resonance, piston effect, and acoustic emission and reflection

We present a general theory of thermoacoustic phenomena in one phase states of one-component fluids. Singular behavior is predicted in supercritical fluids near the critical point. In a one-dimensional geometry we start with linearized hydrodynamic equations taking into account the effects of heat conduction in the boundary walls and the bulk viscosity. We introduce a coefficient Z(omega) characterizing reflection of sound with frequency omega at the boundary in a rigid cell. As applications, we examine acoustic eigenmodes, response to time-dependent perturbations, and sound emission and reflection. Resonance and rapid adiabatic changes are noteworthy. In these processes, the role of the thermal diffusion layers is enhanced near the critical point because of the strong critical divergence of the thermal expansion.

Thermoconvectional phenomena induced by vibrations in supercritical SF6 under weightlessness

The effect of a linear harmonic vibration on heat propagation is investigated in near-critical SF6 under weightlessness conditions in space. Heat was issued from a pointlike source (thermistor), a situation representative of an industrial use of pressurized supercritical fluid storage. Two kinds of vibrations were used, large amplitude (64 mm) at 0.2 Hz and low amplitude (0.8 mm) at 1.6 Hz, with temperatures from 5 K to 20 mK from the critical temperature. The vibrations are seen to strongly affect the evolution and shape of the hot boundary layer (HBL), the heat exchange between the heat source and the fluid, and the bulk thermalization process by the adiabatic piston-effect process. The HBL is initially convected as symmetrical plumes over a distance that only depends on the vibration velocity and which corresponds to a Rayleigh-Bénard-like instability where the vibration acceleration acts as the earth gravity. Then the extremities of the plumes are convected perpendicularly to the direction of oscillation as two "pancakes," a process encountered in the vibrational Rayleigh-Bénard instability. When the vibration velocity is small, only one pancake centered at the hot source is observed. Temperature evolutions of the hot source and the fluid are studied in different locations. Convection flows and adiabatic piston effect compete to determine the thermal dynamics, with the latter being the most efficient near the critical point. The experimental results are compared with a two-dimensional numerical simulation that highlights the similarities and differences between the very compressible van der Waals gas and an ideal gas.

Bulk viscosity, thermoacoustic boundary layers, and adsorption near the critical point of xenon

We present an improved model for the dissipation and dispersion in an acoustic resonator filled with xenon near its critical temperature Tc. We test the model with acoustic measurements in stirred xenon that have a temperature resolution of (T - Tc)/Tc approximately 7 x 10(-6). The model includes the frequency-dependent bulk viscosity calculated numerically from renormalization-group theory and it includes critical-point adsorption. Because the density of adsorbed xenon exceeds the critical density, the bulk viscosity's effect on surface dissipation is reduced, thereby improving the agreement between theory and experiment.

High-speed observation of the piston effect near the gas-liquid critical point

We investigated adiabatic changes in a near-critical fluid on acoustic time scales using an ultrasensitive interferometer. A sound emitted by very weak continuous heating caused a stepwise adiabatic change at its front with a density change of order 10(-7) g/cm(3) and a temperature change of order 10(-5) K. Very small heat inputs at a heater produced short acoustic pulses with width of order 10 micros, which were broadened as they moved through the cell and interacted with the boundaries. The pulse broadening became enhanced near the critical point. We also examined theoretically how sounds are emitted from a heater and how applied heat is transformed into mechanical work. Our predictions agree well with our data.