Initiation of explosive boiling of a droplet with a shock wave

The role of incident shock waves in the initiation of vapor explosions in volatile liquid hydrocarbons has been investigated. Experiments were carried out on single droplets (1–2 mm diameter) immersed in a host fluid and heated to temperatures at or near the limit of superheat. Shocks generated by spark discharge were directed at previously nonevaporating drops as well as at drops boiling stably at high pressure. Explosive boiling is triggered in previously nonevaporating drops only if the drop temperature is above a threshold temperature that is near the superheat limit. Interaction of a shock with a stably boiling drop immediately causes a transition to violent unstable boiling in which fine droplets are torn from the evaporating interface, generating a two-phase flow downstream. On the previously nonevaporating interface between the drop and the host liquid, multiple nucleation sites appear which grow rapidly and coalesce. Overpressures generated in the surrounding fluid during bubble collapse may reach values on the same level as the pressure jump across the shock wave that initiated the explosive boiling. A simple calculation is given, which suggests that shock focusing may influence the location at which unstable boiling is initiated.     

Kinetic theory analysis of explosive boiling of a liquid droplet

The process of rapid phase transition from highly superheated liquid to vapor is frequently so fast and violent that it is called explosive boiling. The paper uses the kinetic theory of evaporation to study growth of an internal vapor bubble produced by homogeneous nucleation within a highly superheated liquid droplet boiling explosively in a hot medium. Evaporation/condensation coefficient is estimated by comparing the predictions of the theory with available experimental data. We show that the value of the evaporation coefficient can be very low for high reduced temperatures (0.06 for butane at 378 K), in agreement with recent molecular dynamic simulations.     

Specific features of explosive boiling of liquids on a film microheater

Explosive boiling of liquids on film heaters under the action of pulsed heat fluxes q = 10⁸–10⁹ W/m ² is considered. A technique of stroboscopic visualization of boiling stages with a time resolution of 100 nsec is used. Numerous scenarios of evolution of explosive boiling are demonstrated. Conditions of the thermal effect (magnitude of the heat flux, duration and repetition frequency of heat pulses) are found, which ensure single and repeated boiling, intermittent boiling, and boiling with formation of complicated multi-bubble structures. It is noted that homogeneous nucleation is a dominating mechanism of incipience of examined liquids for q > 10⁸ W/m ². __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 81–89, March–April, 2007.     

Microscope activation near the wall during explosive boiling

The inception process of nucleation in explosive boiling systems is theoretically investigated. With the effect of pulse heating or sudden cooling, the temperature distribution near the surface during explosive boiling is calculated. The liquid near the wall can maintain a stable layer induced by strong attractive force, and there exists maximum supersaturation beyond this stable layer. As the surface temperature and temperature gradient are high enough, the critical distance of maximum supersaturation can be larger than the radius of critical bubble, and the homogeneous nucleation will dominate the inception boiling process. For explosive boiling induced by pulse heating, homogeneous nucleation forms after a short time; while homogeneous nucleation can dominate the initial explosive boiling induced by sudden cooling.     

Shape of the vapor bubble upon explosive boiling

A relation for the shape of a vapor bubble forming during propagation of a vaporization front is proposed. Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 122–123, March–April, 2000.     

Dynamics of explosive boiling of drops at the superheat limit

A physical model for explosive boiling of drops is presented. Loss of stability of the liquid-vapor interface results in occurrence of evaporation fronts. Their propagation in a metastable liquid is determined by the vapor recoil momentum. Detachment of drops from the interface is due to thermocapillary forces. The validity of the model is supported by comparison of calculations with experimental data. Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Science, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 83–91, November–December, 1999.     

Model of explosive pulsed vaporization of dielectric liquids by intense laser irradiation of their surfaces

The mechanism of explosive vaporization interaction of laser radiation with matter is studied theoretically. It is shown that, in dielectric liquids with a free surface, periodic explosive boiling is possible if the laser radiation intensity exceeds the rate of heat transfer from the region of laser radiation absorption. Analytical expressions are obtained to estimate the pulsating boiling period and the thickness of the surface liquid layer dispersed by fluctuation vapor bubbles during each boiling. The degree of absorption of laser radiation by the aerosol formed above the liquid surface is estimated. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 17–24, November–December, 2008.     

Numerical and experimental study of a micro-blast wave generated by pulsed-laser beam focusing

This paper describes a numerical and experimental study of a micro-blast wave which is produced from the source of several tens microns in dia. and propagates in the length scale of a few centimeter in diameter. The micro-blast wave was generated by focusing a Nd:Glass pulsed-laser beam in ambient air. Its propagation and reflection were visualized by using double exposure holographic interferometry and simulated numerically using the dispersion-controlled scheme to solve the Euler and Navier-Stokes equations with initial conditions of a point-source explosion specified with the Taylor similarity law. Good agreement was obtained between numerical solutions and experimental results, and this spherical micro-blast wave was shown to be a handy model of blast waves created in large scale explosions. Received 28 October 1997 / Accepted 30 April 1998     

爆炸自紧残余应力及对构件疲劳强度的影响

用贴腻子炸药法和动液压法两种爆轰工艺对不同类型厚壁构件实施了爆炸自增强处理,并对爆炸处理形成的残余应力进行了实验测定。对内壁有缺口和裂缝的厚壁圆环以及带缺口的超高压圆筒和四通构件进行了爆炸自紧处理并进行了疲劳实验检验,结果是:在高周疲劳阶段,经爆炸处理的构件缺口根部疲劳裂纹萌生寿命可提高5倍,内压疲劳开裂寿命可提高8~10倍。在低周塑性疲劳阶段构件的疲劳开裂寿命仍可提高1倍左右。由于用贴腻子炸药方法可使构件表面硬度增加从而获得更高的残余压应力,故其自增强效果优于动液压法。     

An experimental investigation of thermally induced flow instabilities in a convective boiling upflow system

The two-phase flow instabilities in a single channel, forced convection, open loop, up-flow system have been investigated experimentally using R-11 as the working fluid. The effects of mass flow rate, heat input, inlet liquid temperature and upstream compressible volume on two-phase flow instabilities have been investigated. Two heater surfaces were tested at five different heat inputs with constant inlet temperature, and four different inlet temperatures with constant heat input. For each case, the mass flow rate was varied over a wide range covering the entire scope for boiling two-phase flows. Experiments were also conducted at different compressible volumes, with constant heat input, inlet fluid temperature, and average mass flow rate. The oscillations of inlet mass flow rate, heater inlet pressure, and heater wall temperature were recorded. The effects of mass flow rate, inlet liquid temperature and heat input on the amplitudes and periods of inlet pressure and thermal oscillations are presented in tabular and graphical forms.

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Experimentelle Untersuchung der thermisch bedingten Strömungsinstabilitäten bei konvektiven Sieden in einer Aufwärtsströmung

Zusammenfassung Mit R-11 als Arbeitsfluid werden Zweiphasen-Strömungsinstabilitäten im Einzelkanal bei erzwungener Aufwärtsströmung ohne Rückführung experimentell untersucht, und zwar besonders im Hinblick auf den Einfluß der Massenstromdichte, der Wärmezufuhr, der Eintrittstemperatur und des in Strömungsrichtung zunehmenden kompressiblen Volumenanteils. Zwei Heizflächen wurden einmal mit fünf verschiedenen Heizflächenbelastungen und konstanter Eintrittstemperatur getestet und dann bei vier verschiedenen Wärmeeinträgen und konstanter Eintrittstemperatur. In jedem der Fälle erfolgte die Variation der Massenstromdichte in einem so weiten Bereich, daß das gesamte Feld der Zweiphasen-Siedeströmungen durchfahren werden konnte. Es wurden auch Experimente mit verschiedenen kompressiblen Volumenanteilen bei konstanter Wärmezufuhr, Fluideintrittstemperatur und mittlerer Massenstromdichte durchgeführt. Die Oszillationen der Massenstromdichte und des Druckes am Eintritt in die Heizstrecke sowie deren Wandtemperatur wurden aufgezeichnet. Die Enflüsse der Massenstromdichte, der Fluideintrittstemperatur und der Wärmezufuhr auf Amplituden und Perioden der Druck- und Temperaturoszillationen sind tabellarisch und in Diagrammform dargestellt.

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Dedicated to Prof. Dr.-Ing. F. Mayinger's 60th birthday     

Mesoscale analysis of volumetric and surface dissipation in granular explosive induced by uniaxial deformation waves

A Lagrangian finite and discrete element technique, combined with a finite deformation, thermo-elastic-viscoplastic, and stick-slip friction theory, is used to computationally examine volumetric and surface dissipation within the meso-structure of granular explosive (HMX, C₄H₈N₈O₈) induced by uniaxial deformation waves. Emphasis is placed on characterizing the fraction of mass heated to elevated temperature (referred to as hot-spot mass fraction) by quasi-steady waves due to plastic and friction work and its dependence on wave strength. Predictions for a large, randomly packed ensemble of HMX particles having a solid volume fraction of 0.85 and a mean diameter of 60 μm show that plastic work principally affects the average temperature, whereas friction work affects the high frequency, high-temperature fluctuations that are likely responsible for combustion initiation. Cumulative distributions for hot-spot mass within the wave indicate that most mass (~99.9%) is heated to approximately 330, 400, and 500 K by plastic work for impact speeds of 50, 250, and 500 m/s, respectively, with a small fraction (~0.001%) heated to 600, 1,100, and 1,400 K by friction work. The hot-spot mass fraction induced by plastic work is well described by a Gamma distribution, though significant departures occur in the high-temperature end of the distribution due to friction work, even at higher impact speeds. Consequently, it is not possible to describe hot-spot mass fraction curves by a single classical distribution function. Implications of the predicted hot-spot mass fraction on granular HMX combustion are discussed.     

One-dimensional projection of a liquid shell by an explosive charge

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 6, pp. 90–96, November–December, 1992.     

Loading of obstacles by explosion of a low-density sheet explosive

The dependence of the detonation velocity of aNIL-1 low-density sheet explosive on density is found in the range of charge densities0.1–0.3 g/cm ³. The equation of state of theNIL-1 detonation products with a linear dependence of the effective isentropic exponent of unloading on the density of an explosive that is acceptable for applied calculations is proposed. Calculated estimates of the mechanical action of anNIL-1 explosion on obstacles from several powerful explosive compositions are given. Institute of Experimental Physics, Sarov 607190. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 3, pp. 43–47, May–June, 2000.     

Destabilization of film boiling by means of a thermal resistance

Described is the type of vaporisation which takes place when a thermal resistance, consisting in a film of a substance of low heat conductivity, is placed between the surface of a quenched sample and the cooling liquid. This type of vaporisation, larvate boiling, is characterised by an alternate wetting/non-wetting of the solid surface.Two conditions are necessary for larvate boiling: thermal resistance and surface effusivity.Substituting larvate boiling for film boiling allows the heat flux between a solid surface at high temperature and the cooling liquid to be greatly increased.     

爆炸烧结制备CuCr合金

介绍了铜铬合金的性能、应用及该材料现有的制备方法。提出了采用机械合金化制粉,进而进行爆炸烧结和后续热扩散处理的制取铜铬合金的方法,并初步进行了实验研究。研究结果表明,采用上述方法可以制造出高密度、组织均匀、晶粒细化的CuCr合金。在wCu∶wCr＝1∶1的条件下,可制出密度大于95%理论密度、硬度HV大于217的具有纳米晶粒的CuCr合金,明显优于热等静压、熔渗和电弧熔炼产品。     

Explosive boiling of a liquid droplet

A mathematical model describing growth of an internal vapor bubble produced by homogeneous nucleation within a liquid droplet during explosive boiling is presented. Existing experimental results for explosive boiling of superheated droplets confirm the predictions of the model. The difference between the present model and the classical theories of bubble growth is discussed.     

Long-term shock loading of solids by a combined charge with explosive initiation

A method and results of calculation of parameters of long-term shock loading of solids, generated by a gas-dynamic former containing a combined charge with explosive initiation, are described. A calculation model based on the concepts of the hydrodynamic theory of detonation and on the theory of combustion of condensed substances is considered. The forcing pressure and the physical laws of combustion of the combined charge are determined in calculations and experiments. The dynamics of the process is studied by an example of calculation of parameters of the loaded solid acceleration pulse in the case of initiation and combustion of a charge consisting of two batches of high explosives: black powder and pyroxylin powder. The effect of the combined charge parameters and combustion-chamber size on the parameters of the shock loading pulse is studied. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 3–10, July–August, 2009.     

Analytical calculation of DNB-superheating by a postulated thermo-mechanical effect of nucleate boiling

Observations of stationary subcooled nucleate boiling with forced convection in a glass-pipe at a pressure of 0.1 MPa lead to a new interpretation of the wall. This interpretation applied to the rules of linear non-equilibrium thermodynamics results in framework equations with non-linear heat transfer as indicated by several empirical correlations. Momentum balances at the singular surfaces of a bubble have been combined with a sonic limit for the mass transfer through the interfaces serving as a maximum condition with respect to heat transfer (DNB). The calculation predicts the corresponding wall temperature from properties of state without using empirical coefficients and therefore must be valid independent of coolants' geometries and surface conditions. Documented measurements at pool boiling, forced and free convection with cryogenic liquids, water and liquid metals emphasize this if data are properly selected corresponding to the precondition that void fraction remains low.