Vertical Shock Tube Research Articles

Wave propagation in porous media containing a dilute gas–liquid mixture: theory and experiments

The influence of a small amount of gas within the saturating liquid of a porous medium on acoustic wave propagation is investigated. It is assumed that the gas volumes are spherical, homogeneously distributed, and that they are within a very narrow range of bubble sizes. It is shown that the compressibility of the saturating fluid is determined by viscous, thermal, and a newly introduced Biot-type damping of the oscillating gas bubbles, with mean gas bubble size and concentration as important parameters. Using a super-saturation technique, a homogeneous gas–liquid mixture within a porous test column is obtained. Gas bubble size and concentration are measured by means of compressibility experiments. Wave reflection and propagation experiments carried out in a vertical shock tube show pore pressure oscillations, which can be explained by incorporating a dynamic gas bubble behaviour in the linear Biot theory for plane wave propagation.

Sound and weak shock wave propagation in gas-liquid foams

Propagation of sound and weak shock waves in gas-liquid foams is investigated theoretically and experimentally. An original physical model is developed to describe the evolution of small perturbations in a foam of polyhedral structure. The model developed takes into account both peculiarities of interface heat transfer in foam and liquid motion through the system of Plateau-Gibbs borders which results in the appearance of an additional hydrodynamic dissipative force. The Rayleigh equation analog, which takes into account the latter phenomenon, is obtained. Structure and dynamics of weak shock waves are investigated. A vertical shock tube was constructed and used to measure the parameters of weak shock wave propagation in gas-liquid foams of polyhedral structure. Spectral analysis of the data obtained shows that there are weak dispersion and strong dissipation of the initial signal. Comparison of the evolution of experimental and theoretical profiles permits to conclude that the suggested model allows to describe the peculiarities of acoustical perturbations in gas-liquid foam more precisely than it follows from the standard models.

X-ray measurements of growth rates at a gas interface accelerated by shock waves

A new experimental technique to measure the density of a high atomic number gas at a shock-accelerated interface has been developed and demonstrated. It is based on the absorption of x rays by the high atomic number gas, and it was implemented in a vertical square shock tube. The object of the study was the turbulent entrainment and mixing of shock-accelerated air/xenon interfaces prepared by retracting a metal plate, initially separating the two gases, prior to the release of the shock wave. Interfaces of two types, quasi-sinusoidal and nominally flat, were examined. The amplitude of large wavelength (25–100 mm) perturbations on the interface, and the thickness of the interface were measured. An integral definition for the interface mean line was adopted, making it possible to study and time evolution of the individual Fourier modes of the perturbations. A new integral definition for the interface thickness was proposed, making it feasible to study for the first time the time evolution of the thickness of quasi-sinusoidal interfaces. Images of interfaces after interacting with a series of weak waves reverberating between the interface and the shock tube end wall were obtained. The perturbations are studied at the late stages of their evolution, when their amplitude is no longer small compared to their wavelength. Consequently, the measured growth rates of the modal amplitudes are smaller than those predicted by the impulsive model based on the small amplitude approximation. In the case of nominally flat interfaces, the thickness is observed to grow linearly at rates comparable to values previously reported.

Liquid-Metal/Water Interactions in a Shock Tube

To investigate liquid-metal (fuel)/water (coolant) interactions, a vertical shock tube has been designed and constructed. A series of tests was conducted with gallium, indium, lead, and tin as the fuel materials at either low (T f ∼ 300°C) or high fuel temperature (T f ∼ 600°C), with water at room temperature (low T c ) and in the range of T c = 56 to 67° C (high T c ), and with driving pressures from 0.25 to 1.22 MPa. These materials were tested to determine their compatibility for potential use in liquid-metal divertor systems for fusion power plants. The increase in fuel and water temperature, as well as the increase of driving pressure, caused more energetic interactions to occur. High T f tin and lead interactions, and high T f and T c gallium and indium interactions were the most energetic. Stronger interactions produced finer debris fragments. In high T f gallium and indium interactions, small superficial oxidation was observed. For the first two pulses, larger ratios of compression- (compression of expansion vessel gas) to-expansion work correspond to the experiments with higher fuel and coolant temperatures. For the first pulse, only work ratio values of the most energetic experiments are larger than those of isothermal experiments. Consequently, for such experiments, the impulse values of second pulses are the largest. Higher values of the conversion ratio for the first pulse correspond to more energetic interactions. Even for the most energetic experiments, the conversion ratio is no higher than 1.2%, and no more than 15% (or a few millimetres-thick surface layer) of the initially loaded fuel participated in the interaction, assuming equal initial volumes of fuel and coolant.

Interaction of rarefaction waves with wet foam

The interaction of rarefaction waves of different shapes with wet water foams is studied experimentally. It is found that the observed values of the pressure are greater, while the surface velocity is lower than the corresponding values predicted by the pseudogas model. The foam breakdown starts as the pressure decreases by 0.3 atm relative to the initial pressure. During downstream propagation of the rarefaction-wave leading edge the propagation velocity decreases. Using of water-based foams as effective screens for damping blast waves in different technological processes has caused considerable interest in studying wave propagation in such systems. The pressure wave dynamics in a foam have been investigated in much detail, both experimentally and theoretically [1–3]. However, the interaction of rarefaction waves with foam has practically never been studied, although it was mentioned in [4] that the unloading phase following the compression wave phase is one of the factors defining the damaging action of blast waves. Besides blast-wave damping, rarefaction wave propagation takes place if such waves are used to breakup foam in oil-producing wells [5]. Below, the interaction of rarefaction waves of different shapes with wet water foams is studied. The vertical shock tube described in detail in [3] was used in these experiments.

Transient film boiling under transient conditions related to vapor explosion (effects of transient flow and fragmentation under a shock pressure)

Two fundamental phenomena are significant when a shock pressure interacts with the large scale coarse mixing state. One is an intensive flow and the other is the surface area enhancement due to the disintegration of the hot drops. The effects of these phenomena on the transient heat transfer and behavior of vapor film under a shock pressure are investigated. Transient heat transfer of film boiling from an electrically heated platinum ribbon 2.5 mm wide and 0.15 mm thick was measured immediately after passage of a shock pressure from 0.1 to 0.7 MPa. The heater was set horizontally in a vertical shock tube which was filled with vapor liquid bubbly mixture and kept initially in the film boiling state. That is, the heater corresponds to a typical hot drop and the bubbles around it correspond to the coarse mixture around the drop. The liquid was Freon-113 with an initial void fraction in the range from 0 to 3%. When the shock wave arrives at the heater, intensive transient flow occurs due to collapse of bubbles around the heater. First, the effects of the initial void fraction, the intensity of the shock and the heated wall temperature on the transient heat fluxes and collapse of the vapor film were investigated experimentally and analytically under the shock pressure. Compared with a heated wall in the liquid alone, the transient heat flux at the heated wall increases and the collapse of the vapor film becomes easier in the bubbly mixture due to the transient flow. Effects of surface enhancement during the fragmentation process on the heat transfer rate and transient behavior of vapor film are investigated analytically by application of the newly proposed surface stretch model. It is made clear when the surface area is increasing, the vapor film is apt to collapse and the transient heat transfer is enhanced by the surface stretch.

Interaction of a shock wave with a two-phase interface

The acceleration by an incident shock of a planar interface between a gas and a particle-gas mixture has been investigated experimentally and numerically. The experiments were conducted in a newly developed vertical shock tube in which the planar interface of the particle-gas mixture was generated and its particle concentration history was measured. Polydisperse corn starch particles with a mean diameter of 10μm were used. We recorded the motion of the interface, as well as of the incident and reflected shock by using a 4 channel spark shadowgraph. The experimental conditions were Mach numberM s=5.15 and initial pressurep 1=50kPa for various particle concentrations in nitrogen. The reflected shock appears with a delay after the incident shock enters the particle-gas mixture. Numerical methods were employed to solve the two-phase governing equations. Experiments and numerical solutions are in good agreement.

Modeling the process of shock-wave attenuation by a foam screen

In a one-dimensional formulation, we consider the problem of decay of the discontinuity in a vertical shock tube when a gaseous suspension of water droplets is present in the channel. Such an approach is used for numerical modeling of the conditions of the physical experiment in a shock tube containing a foam screen. We discuss the dynamics of the wave processes involved in passage of the shock wave through the screen, the damping properties of the screen, and the mechanism for attenuation of the shock wave in the foam. We compare the calculated pressure diagram with the measurement results.

Growth induced by multiple shock waves normally incident on plane gaseous interfaces

Experiments to measure the visual thickness of the mixing region produced by shock waves incident on continous and discontinous interfaces between gases of different densities have been carried out in a new vertical shock tube. The generation of vortical structures by shock-wave boundary layer interaction at the interface is observed and the need for experimental methods to distinguish the effects of resulting jets on the walls and windows of the shock tube is emphasized. Initially thick interfaces, smoothed by molecular diffusion, exhibit growth after being perturbed by acoustic noise induced during wave reverberation. Thin interfaces, whose perturbations are introduced by the rupture of the supporting plastic membrane, have a more rapid initial growth but the late time growth is comparable to that of the thicker interfaces. In both cases the rate of increase of the thickness of the interfaces is an order of magnitude less than reported by previous investigators.

Effects of gas and liquid properties on detonation-wave parameters in liquid-bubble systems

This paper considers shock wave existence conditions and the effects from component properties (gas composition, type of liquid, and viscosity) on the detonation-propagation limits in liquid-bubble systems. A vertical shock tube was used. The detonation-wave parameters were recorded by piezoelectric pressure sensors and the emission by a photomultiplier. The following systems were used: water-glycerol solutions with bubbles of oxygen mixed with acetylene, hydrogen, and propane or air with acetylene, and a vacuum oil containing oxygen-nitrogen bubbles.

Study on a shock wave in liquid metal two-phase mixture with and without magnetic field

Propagating phenomena of a pressure wave in a liquid metal two-phase flow with and without magnetic field have been investigated theoretically and experimentally by using a vertical shock tube. First, the pressure rise time at the shock front in the mercury-nitrogen medium without magnetic field was measured and compared with that in water-nitrogen mixture. These results show that the pressure rise time is determined by the inertia of the radial motion of bubbles regardless of whether the medium was the liquid metal two-phase medium or the conventional one. Secondly, the effect of magnetic field on the shock wave speed in liquid metal two-phase medium was studied by changing the electrical wall condition. Under the insulating wall condition, the shock speed was not affected by the magnetic field; however, under the conducting wall condition, it was reduced with an increase of the magnetic flux density by the Lorentz force.

Vapor pressure and sensitization effects in detonation of a decane spray

The effect of an additive and the vapor pressure on the detonability and critical initiation energy for the detonation of a decane spray of 400 μm diameter monodisperse droplets was studied experimentally in a vertical shock tube. The effect of an additive on the ignition delay and the nature of the transition from purely liquid to purely vapor detonation behavior were also investigated. The wave position was sensed by eleven pressure switches located along the tube. The pressure profiles behind the wave were measured using two pressure transducers. A photocell was used to measure the ignition delay. The vapor pressure was increased by heating the whole shock tube through the use of heating tapes. Both air and oxygen were used as oxidizers and the additive used was normal propyl nitrate (NPN), a monopropellant with a high vapor pressure. Two different fuel additive combinations were tested, 75% decane +25% NPN and 88% decane +12% NPN (by volume). The equivalence ratio ranges tested were 0.68–2.83 for (75% decane +25% NPN) + air mixtures, 0.20–0.64 for (75% decane +25% NPN) +O 2 mixtures, and 0.86–0.98 for (88% decane +12% NPN) + air mixtures. For studying the effect of the vapor pressure, the equivalence ratios of 0.92–3.29 for decane + air mixtures and 0.24–0.74 for decane +O 2 mixtures were tested. The temperatures ranged from 15°C. to 58°C. The results showed that addition of NPN to the decane increased the sensitivity of the mixture. The higher sensitivity led to enhanced detonability, to shorter ignition delay, to lower critical initiation energy, and to wider detonation limits. The results for higher vapor pressure showed these same trends.

Bulk cavitation in a vertical water filled shock tube

A one dimensional lumped parameter theoretical model is developed to predict the occurrence of recompaction waves associated with bulk cavitation following the reflection of a pressure pulse from a free surface. Experimental data is obtained from a simple shock tube for comparison with the theoretical model and with that of Cushing whose work covers the classic explosion pulse. It is concluded that the model presented here predicts the occurrence of recompaction waves reasonably well and can have significant advantages over previously published work.

Detonation in oxyhydrogen bubbled liquids

Shock wave propagation in glycerin with 70% Ar+30% (2H 2 +O 2 ) bubbles and associated bubble behaviors were observed in a vertical shock tube where the pressure ratio between the high and low pressure sections was p 4 /p 1 =15. It was found that once a bubble explosion started in the glycerin, it continued propagating, the amplitude and the propagation velocity of the shock wave increased, and the pressure profile changed significantly. On the other hand, there was a limit of such a chain bubble explosion, depending on the initial bubble radius, shock strength, interbubble distance, and exothermicity. These results imply the existence of bubble detonation. A theoretical calculation of bubble dynamics containing realistic oxyhydrogen reaction kinetics was performed, and showed agreement with the observed results. Finally, a phenomenological model of bubble detonation was introduced to explain the mechanism of propagation. This theory leads to a qualitative interpretation of the measured velocity.

Initiation of detonation by steady planar incident shock waves

The initiation of detonation by planar shocks has been studied in a vertical shock tube in which a removable diaphragm allows a shock, generated in a buffer section, to be transmitted, without any reflection at the interface, into the gas mixture under test. Streak schlieren photography confirms that a quasi-steady shock reaction complex is formed prior to the shock acceleration phase. The existence of a steady phase enables the induction delay time to be measured in a direct and unambiguous manner. It is also shown that microwave interferometry, in conjunction with pressure transducers, allows the delay time to be measured with reasonable precision. From the experimentally determined shock acceleration the locus of the exothermic reaction zone is calculated, and it is shown that the time coherence of energy release between particles entering the shock front at different times is a process that leads to the formation of reactive centers which are characteristic of mild ignition. Ignition delay data obtained by the incident shock method for oxyacetylene, diluted with nitrogen, are compared with those obtained by the well-established reflected shock technique. These results indicate that the incident shock method promises to be useful in high heat capacity systems for which the magnitude of the nonideality in the reflection process may be unacceptable.

Propagation of a pressure wave in two-phase flow with very high void fraction

An experimental and theoretical study of a finite amplitude pressure wave propagating through a two-phase media of about 0.9999–0.99999 void fraction is performed. This two-phase media consists of many parallel liquid films in a gas. The films are perpendicular to the wave propagation direction and result in a two-phase fluid of extremely high void fraction. Experiments are done in a vertical shock tube and show that the shock wave is broken down into an initial sharply rising wave and a second gradually rising wave. The velocity of the first wave agrees well with the theoretical prediction assuming an adiabatic thermal equilibrium change, which approaches the gas sonic velocity in the two-phase flow in the low void fraction region. The second wave is caused by the complex reflection and destruction of the waves.

Propagation of pressure waves in two-phase flow

We deal with a pressure wave of finite amplitude propagating in a gas and liquid medium or in the fluid in an elastic tube. We study the effects of pipe elasticity on the propagation velocity of the pressure wave. Pressure waves of finite amplitude progressing in the two-phase flow are treated considering the void fraction change due to pressure rise. The propagation velocity of the two-phase shock wave is also investigated, and the behavior of the reflection of the pressure wave at the rigid wall is analyzed and compared to that in a pure gas or liquid. The results are compared to experimental data of a pressure wave propagating in the two-phase flow in a vertical shock tube.

Thermal decomposition and hydrogenation of coal dust in a shock tube

A vertical shock tube with fluidized coal particles prior to shocking was used for this investigation. The high heating and quenching rates together with the exceedingly short reaction times obtainable with the shock tube were shown to have a marked effect on the product distribution. Additions of iodine were shown to promote the reaction. The reaction conditions were varied over the following ranges: shock temperature, 600–1200 K; maximum reaction time, 1·29–1·89 ms; pressures in shock, 658–1546 kPa. Electron photomicrographs of shocked coal particles are also presented. The distribution of gaseous hydrocarbons produced from coal subjected to high heating rates and short reaction times during hydrogenation is found to differ considerably from that produced by long reaction times, the gases containing a greater proportion of unsaturates (acetylene, ethylene, and propylene). The presence of gaseous iodine has no effect upon the product distribution of the hydrocarbon gases formed, but permits a lower reaction temperature for a given degree of decomposition.