We measured high-speed sound propagation in a near-critical fluid using a ultra-sensitive interferometer to investigate adiabatic changes of fluids on acoustic timescales. 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 deg. Very small heat inputs at a heater produced short acoustic pulses with width of order 10µsec, which were broadened as they moved through the cell and encountered 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 well agree with our data. Thermal equilibration in one-component fluids takes place increasingly faster near the gas-liquid critical point at fixed volume [1,2,3,4,5,6,7,8,9,10], despite the fact that the thermal diffusion constant D tends to zero at the criticality. This is because the thermal diffusion layer at the boundary expands and sounds emitted cause adiabatic compression and heating in the whole cell after many traversals in the container. This heating mechanism is much intensified near the critical point due to the critical enhancement of thermal expansion of the layer. If the boundary temperature T w is fixed, the interior temperature approaches T w on the timescale of the piston time [2],where L is the cell length and γ = C p /C V is the specificheat ratio growing near the critical point. This time is much shorter than the isobaric equilibration time L 2 /4D by the very small factor (γ − 1) −2 [11]. The previous experiments have detected only slow temperature and density changes in the interior region on timescales of order 1 sec. The aim of this letter is to report ultra-sensitive, high-speed observation of sound propagation through a cell filled with CO 2 on the critical isochore close to the critical point T c = 304.12K. We can detect density changes of order 10

Experimental investigation and characterization of the departure from local thermodynamic equilibrium along a surfacewavesustained discharge at atmospheric pressure An examination of the axisymmetric equilibrium configurations of fluid systems in cylindrical containers in an arbitrary gravity field has been undertaken. The derived theory allows the effects of gravity on an interface shape to be quantified. When these effects may be neglected, the resulting predictions for equilibrium are contrary to those of previous theories. The theoretical approach adopted herein leads to the prediction that the equilibrium configuration is dependent on the contact angle and on the amount of fluid in the container. These predictions have been examined through a series of experiments conducted in a drop shaft, and the results support the new theoretical approach.

Three-dimensional large-amplitude oscillations of a mercury drop were obtained by electrical excitation in low gravity using a drop tower. Multi-lobed (from three to six lobes) and polyhedral (including tetrahedral, hexahedral, octahedral and dodecahedral) oscillations were obtained as well as axisymmetric oscillation patterns. The relationship between the oscillation patterns and their frequencies was obtained, and it was found that polyhedral oscillations are due to the nonlinear interaction of waves.A mathematical model of three-dimensional forced oscillations of a liquid drop is proposed and compared with experimental results. The equations of drop motion are derived by applying the variation principle to the Lagrangian of the drop motion, assuming moderate deformation. The model takes the form of a nonlinear Mathieu equation, which expresses the relationships between deformation amplitude and the driving force's magnitude and frequency. IntroductionLiquid drop oscillation has attracted the attention of many scientists since the 19th century, since it is not only an interesting basic phenomenon but is also important in such diverse areas as nuclear physics, cloud physics and chemical engineering. Since it has become possible to conduct experiments in microgravity, understanding liquid drop oscillation has become more important, not only from an academic viewpoint but also for the practical aspects of material processing in containerless levitation and measurement of the physical properties of molten materials in space. In a microgravity environment, a free liquid assumes a spherical shape due to surface tension and it is easy to levitate and manipulate a relatively large liquid drop without a container. This is one of the advantages of the space environment. Understanding the nature of drop oscillations is indispensable for future applications of containerless processing. In addition, nonlinear effects resulting from the interaction of finite-amplitude waves are of interest from physical and mathematical points of view, and experimental realization of large-amplitude oscillations is useful for the study of these effects.The first large-amplitude drop oscillation experiments were conducted by acoustically exciting a drop suspended in an immiscible liquid (a mixture of silicone oil and carbon tetrachloride suspended in distilled water) in 1 g conditions (Trinh & Wang 1982). These experiments showed oscillating patterns in the l = 2, 3, 4 axisymmetric (m = 0) modes and also showed the dependence of the amplitude of oscillation of the second mode on oscillation frequency.

Temperature propagation near the critical point of a classical fluid is investigated theoretically. The governing equations of thermal energy transfer near the critical point are introduced and a linear analysis is carried out. The dispersion relation between the angular frequency and the wave number is obtained and the wave characteristics are discussed. The effect of gravitational acceleration on the temperature wave propagation is made clear. Through this analysis, the following results were obtained; (1) The propagation speed of temperature waves is γ/(ρ0κT),where γ, ρ0, and κT are, respectively, the ratio of specific heats, the density, and the isothermal compressibility, with or without gravity if the wavelength is larger than 10−3.(2) The amplitude of wave increases with time in the antigravitational direction and decreases in the gravitational direction but the decay time is long if the wave number is small. (3) Waves decay quickly if the wave number is larger than 104.

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