Characteristics of a vortex-stabilized plasma generator at reduced pressure

The operation of an argon plasma generator at discharge chamber pressures in the region (3–100)·10³ N/m² has been experimentally investigated. Current-voltage characteristics in dimensional complexes have been obtained for stable operating regimes.     

Projectile dynamics at low barrel pressures

A mathematical model for a projectile shot at low pressures in the space behind the projectile space is developed. The pressure rise is limited because of the nonsimultaneity of propellant ignition and combustion and the discharge of the propellant combustion products through the gap between the projectile and the walls of the gun barrel. The kinetic characteristics of flame propagation over the propellant particles are determined. A comparison of calculation and experimental data is performed. The calculation results are used in designing 2A85 self-propelled launchers and upgrading 2A30 self-propelled launchers. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 6, pp. 44–49, November–December, 2007.     

Behavior of detonation waves at low pressures

With respect to stability of gaseous detonations, unsteady behavior of galloping detonations and re-initiation process of hydrogen-oxygen mixtures are studied using a detonation tube of 14 m in length and 45 mm i.d. The arrival of the shock wave and the reaction front is detected individually by a double probe combining of a pressure and an ion probe. The experimental results show that there are two different types of the re-initiation mechanism. One is essentially the same as that of deflagration to detonation transition in the sense that a shock wave generated by flame acceleration causes a local explosion. From calculated values of ignition delay behind the shock wave decoupled from the reaction front, the other is found to be closely related with spontaneous ignition. In this case, the fundamental propagation mode shows a spinning detonation. Received 10 March 1997 / Accepted 8 June 1997     

Projectile acceleration in a single-stage gun at breech pressures below 50 MPa

Experimental studies were carried out to investigate projectile acceleration in a single-stage gun at breech pressures below 50 MPa. The gun was driven by firing either liquid or solid propellant. In-bore projectile velocity was continuously recorded using the well-known, precise VISAR interferometer technique so that accurate projectile acceleration data could be deduced. Both the attained projectile acceleration and muzzle exit velocity depend upon the charge-to-mass ratio and the pressure at which the blow-out disk ruptures. The results obtained from these experiments render information on the interplay between propellant combustion and projectile acceleration for low in-bore pressure regimes, and they provide the input data required for adequate numerical simulation.     

Cylindrical probe in the nitrogen plasma of a glow discharge at average pressures

The results of a study of the nitrogen plasma of a stabilized glow discharge (I_t=40–80 mA, p=1–7 mm Hg) using Langmuir probes 0.004 and 0.03 mm in diameter are presented. Considerable disagreement is found in the plasma parameters n andf() (electron concentration and energy distribution function of electrons) obtained by measurement with probes of =0.004 and 0.03 mm. An analysis of the experimental data made it possible to conclude that the measurements made using the probe of =0.004 mm are correct, and to show the magnitudes of the systematic distortions of the plasma parameters occurring in work with a probe of =0.03 mm.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, pp. 13–20, March–April, 1973.In conclusion the authors thank V. M. Fedorov for useful discussions in the course of the work.     

Motion of inhomogeneities of a developed fluidized bed at small reynolds numbers

The instability of a fluidized system in which the particles are uniformly distributed in space [1–3] leads to the development of local inhomogeneities in the internal structure, these taking the form of more or less stable formations of packets of particles [4]. In accordance with the existing ideas based on experimental data [5–8, 13], the particle concentration within a packet may vary in a wide range from very small values (10^–2–10^–3 [8]) for bubbles to the concentration of the unfluidized bed for bunches of particles in a nearly closely packed state. The paper considers the steady disturbed motion of the fluid and solid phases near an ascending or descending packet of particles in a developed fluidized bed. It is assumed that the motion of the solid phase corresponds to a creeping flow of viscous fluid, and the viscosity of the fluidizing agent is taken into account only in the terms that describe the interphase interaction. The velocity fields and pressure distributions of the phases inside and outside a packet are determined. If the particle concentration within a packet tends to zero, the solution describes the slow motion of a bubble in a fluidized bed. The results of the paper are compared with results obtained earlier for the model of ideal fluids [9] and Batchelor's model [10], in which the fluidized bed is treated in a simplified form as a viscous quasihomogeneous continuum.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 57–65, July–August, 1984.     

Numerical investigation of pyrolysis of a Loy Yang coal in a lab-scale furnace at elevated pressures

A computational fluid dynamics (CFD) model of the pyrolysis of a Loy Yang low-rank coal in a pressurised drop tube furnace (pdtf) was undertaken evaluating Arrhenius reaction rate constants. The paper also presents predictions of an isothermal flow through the drop tube furnace. In this study, a pdtf reactor operated at pressures up to 15 bar and at a temperature of 1,173 K with particle heating rates of approximately 10⁵ K s^?1 was used. The CFD model consists of two geometrical sections; flow straightner and injector. The single reaction and two competing reaction models were employed for this numerical investigation of the pyrolysis process. The results are validated against the available experimental data in terms of velocity profiles for the drop tube furnace and the particle mass loss versus particle residence times. The isothermal flow results showed reasonable agreement with the available experimental data at different locations from the injector tip. The predicted results of both the single reaction and competing reaction modes showed slightly different results. In addition, several reaction rate constants were tested and validated against the available experimental data. The most accurate results were being Badzioch and Hawksley (Ind Eng Chem Process Des Dev 9:521–530, 1970) with a single reaction model and Ubhayakar et al. (Symp (Int) Combust 16:427–436, 1977) for two competing reactions. These numerical results can provide useful information towards future modelling of the behaviour of Loy Yang coal in a full scale tangentially-fired furnace.     

Experience in making rheological measurements at high pressures

Summary We review the difficulties encountered in the design and operation of apparatus for rheological studies on liquids at pressures up to 900 MN m^–2 and temperatures from –30 to 120°C. Such rheological information is required in connection with elastohydrodynamic lubrication in which high pressures and shear rates are encountered.With 3 figures     

Heat transfer in bubble layers at elevated pressures

Heat transfer with steam condensation under moderate pressure on the surface of a horizontal tube immersed in a bubbling layer was experimentally investigated. A copper test section 16 mm in outer diameter and 400 mm in length was placed in a bubbling column 455 mm in diameter. Experiments were made under pressures of 0.14–0.8 MPa, with void fraction 0.04–0.23, vapor superficial velocities 0.05–0.42 m/s, liquid-wall temperature differences 47–105 K, and heat flux densities 0.12–0.8 MW/m². The heat transfer process in the bubbling layer is shown to be of a high intensity: with moderate values of steam content, heat transfer coefficients reach 12–14 kW/(m² · K). Data obtained showed that the known correlations do not consider the influence of pressure on heat transfer. For the first time, data on radial steam content distribution under pressures higher than atmospheric were obtained by an electroprobe method. A table of experimental data is presented.     

Heat transfer in bubble layers at high pressures

An original experimental investigation of heat transfer with steam condensation on a surface of a horizontal cooled tube immersed in a bubbling layer was carried out. A copper test section 16 mm in diameter and 285 mm in length was placed in a bubbling column 295 mm in diameter. Experiments were made under a pressure of 0.72-3.8 MPa with volume steam content 0-0.18, steam superficial velocities 0-0.18 m/s, and liquid-wall temperature difference 38–106 K. The heat transfer process in a bubbling layer under high pressures is shown to be of considerably intensity; with moderate values of steam content heat transfer coefficients reach 10–12 kW/(m²·K). The use of the known correlations assumed for the case of air bubbling under atmospheric pressure results in systematically underestimating heat transfer by 30–80%. Data were obtained on heat transfer with film condensation of steam and natural convection of subcooled water at high temperature differences outside the range investigated earlier. Experimental data table is appended.     

Forced convection heat transfer at the boundary layer of a packed bed

Numerical investigations of the nature of the fluid flow pattern and heat transfer at the boundary layer of a packed bed are reported. A volume averaged Navier-Stokes equation is used to predict the fluid flow and a volume averaged heat balance equation the heat transfer. A variable porosity in the packing is assumed in the region near the wall. Simulations are performed using a modified penalty Galerkin finite element method. The case of fully developed hydrodynamic flow and developing thermal flow is studied. The Nusselt number is found to depend on the Reynolds number, Graetz number and ratio of thermal conductivity of the solid and fluid phases. Comparison is made to some experimental literature values.Nomenclature A constant - [A] Navier-Stokes type matrix - B constant - [B] divergence matrix - C _p constant pressure heat capacity - d characteristic length - D _p particle diameter - D _t tube diameter - {F} solicitation vector - Gz Graetz number, z D _t ^–1 Pr _f Re _p - k permeability term - k _f Thermal conductivity of the fluid phase - k _s Thermal conductivity of the solid phase - [K] coefficient matrix for temperature equation - n normal vector - P pressure - Pr _f Prandtl number for the fluid _f C _p k _f ^-1 - r radial coordinate - R _t tube radius - R residual - R _m residual - Re _p Reynolds number for particle, - t tortuosity factor - T temperature - interstitial velocity - z axial coordinate - effective thermal conductivity - penalty parameter - boundary of solution domain - porosity - viscosity - density - test function - solution domain - test function     

Shock tube study of n-decane ignition at low pressures

Ignition delay times for n-decane/O 2 /Ar mixtures were measured behind reflected shock waves using endwall pressure and CH* emission measurements in a heated shock tube. The initial postshock conditions cover pressures of 0.09-0.26 MPa, temperatures of 1 227-1 536 K, and oxygen mole fractions of 3.9%-20.7% with an equivalence ratio of 1.0. The correlation formula of ignition delay dependence on pressure, temperature, and oxygen mole fraction was obtained. The current data are in good agreement with available low-pressure experimental data, and they are then compared with the prediction of a kinetic mechanism. The current measurements extend the kinetic modeling targets for the n-decane combustion at low pressures.