Experimental verification of the autoregressive method for determining the decrement and frequency of natural oscillations of the gas in a combustion chamber

Conclusions The workability of the autoregression method for determining the logarithmic decrement and frequency of the natural oscillations of the gas in a model and in a full-scale combustion chamber at stable operating regimes has been confirmed. In order to distinguish random narrow-band oscillations of the gas from almost-harmonic self-sustained oscillations, when formal application of the method can lead to invalid results concerning the stability of the combustion process, a quantitative recognition criterion has been proposed and tested. It consists of an estimation of the probability of the occurrence of intrachamber noise exceeding 0.85 times the root-mean-square value of gas-pressure oscillations. With the goal of increasing the reliability of estimates of the logarithmic decrement, recommedations as to the choice of the location for recording oscillations of the gas pressure in the chamber have been made.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 24, No. 2, pp. 65–70, March–April, 1988.     

Combustion of Energetic Materials in an Acoustic Field (Review)

The review summarizes the long-term experience in theoretical research of combustion of gasifying condensed systems with periodically varied pressure. Most results are obtained within the framework of the Zel'dovich-Novozhilov theory. The main properties of the linear function of the burning rate response to harmonically varied pressure are discussed. The concept of nonlinear response functions is introduced, which is illustrated by the explicit form of a number of second-order response functions. A new phenomenon is described: bifurcations of response functions with a varied amplitude or frequency of pressure oscillations. For the simplest gunpowder model containing three parameters only, the sequence of bifurcations of doubling of the burning rate oscillation period is studied, which finally leads to a random combustion regime. An analytical relation between the linear response functions to harmonically varied pressure and to an oscillating radiant heat flux is noted. An example of calculating the response function with allowance for thermal inertia of the gas phase is presented. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 116–136, November–December, 2005.     

Specific features of combustion in a variable-section narrow channel with a periodically changing gas flow

Results of numerical and theoretical research of flame behavior in a periodically changing gas flow during combustion in a variable-section narrow channel are presented. The influence of the mean mass flow of the gas and amplitude and frequency of periodic oscillations of the flow on the mean position and temperature of the flame front is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 16–24, September–October, 2008.     

Special features of the combustion process in a channel with a supersonic velocity at the entrance

Results of combustion studies in channels are presented. These researches deal with anomalous phenomena in steady turbulent flows: unsteady heat transfer, two-layer flow, oscillations of a gas column of different intensity and frequency. Under certain conditions, these phenomena lead to substantial redistributions of enthalphy and stagnation pressure at the exit of the combustion chamber, which significantly affects the integral characteristics of the combustor. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 24–32, July–August 1999.     

轧辊磨损度线阵CCD非接触式在线检测系统的研究

基于激光-线阵CCD检测原理,通过对反射光信号的检测,提出了一种用于轧辊磨损度非接触式检测的高精度检测方法.阐述了线阵CCD工作原理、检测系统组成与检测过程.利用插值法和数值滤波法对信号进行处理,有效降低了轴承振动和随机噪声的影响,提高了检测系统的可靠性和分辨率.同时针对检测过程中易出现的轧辊轴线偏移情况,采用相应的补...     

Estimation of the parameters of the signal of a random process

The basic mathematical characteristics for processing the signal of a random process and the preferred characteristics for evaluating information in different cases applied to production of chemical fibres are indicated. The possibility of evaluating the effect of the operational parameters and different factors on the product quality indexes and isolating important and unimportant parameters and factors is examined by correlation analysis. Mathematical models for calculating the autocorrelation coefficients and reciprocal correlation function are reported. Altai State Technical University, Baranaul. Translated fromKhimicheskie Volokna, No. 1, pp. 44–47, January–February, 1999.     

Rapid method for determination of the thermostability of refractory products

A method for estimating the thermostability of refractories by the change in the frequency of natural oscillations of a specimen after a single thermal shock is presented. The method has been tested in estimating the thermostability of silicon carbide plates on silica binder produced by the Volzhskii Abrasive Plant. At the same time, a direct dependence of the apparent density on the frequency of natural oscillations of a specimen is established, the method is quicker and less laborious than the conventional one. Translated from Ogneupory, No. 4, pp. 18 – 19, April, 1994.     

信息理论在气固流化床颗粒碰撞压力波动信号分析中的应用

用信息理论中信源熵或信息流率的概念来判断气固流化床中颗粒碰撞压力信号中存在的混沌现象 ,确定信号中噪声的干扰情况 ,同时计算了不同操作条件下体系的KS熵。     

Determining the unsteady combustion behavior of propellants from results of closed-bomb testing

Two methods for processing the results of closed-bomb tests of propellants are proposed: a method for determining the force of propellant, the covolume of propellant gas, and the pressure dependence of the degree of propellant combustion that takes into account the heat exchange between the combustion products and the walls of the closed bomb; a procedure for determining the linear behavior of unsteady combustion in the form justified by Ya. B. Zel’dovich. It is shown that accounting for heat losses is necessary not only to determine the force of propellant and the covolume of propellant gas but also to determine the combustion behavior. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 29–38, March–April, 2006.     

Determination of the concentration of aromatic polyamide in a spinning solution

A method for determining the concentration of polymer in a spinning solution based on potentiometric titration of hydrochloric acid bound by the tertiary nitrogen of the benzimidazole group in the polymer was developed. The method allows reducing the time of analysis by 2–2.5 times in comparison to the dry residue method of analysis. The method was metrologically certified in an active enterprise. The possibility of using the method of linear regression analysis for processing the spinning solution titration curves without plotting them was demonstrated. Moscow State Textile Academy. Translated fromKhimicheskie Volokna, No. 1, pp. 47–49, January–February, 1999.     

Parametric study of shock-wave formation in a spatially inhomogeneous self-igniting medium for arrhenius combustion kinetics

An approach to describing the formation and propagation of small gas-dynamic perturbations in a spatially inhomogeneous self-igniting medium for arbitrary chemical reaction kinetics was developed in a previous paper. In the present paper, the proposed approach is illustrated by studying the problem for a simple reaction with an Arrhenius reaction rate. A comparison of calculation results with the solution of the complete system of gas dynamics equations shows that the approach provides good accuracy of quantitative estimates. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 76–83, March–April, 2008.     

Flow behavior of wakes in a three-phase slurry bubble column with viscous liquid medium

Flow behavior of wakes has been investigated in a three-phase slurry bubble column of 0.102 m ID and 1.5 m in height. The dependence of wake characteristics such as rising velocity, frequency, holdup and equivalent size on the operating variables was examined by employing an electric resistivity probe method. The gas velocity, liquid viscosity and solid content in the slurry phase were chosen as independent parameters. The rising velocity of wake region increased with an increase in the gas velocity (4.0–12.0 cm/s), liquid viscosity (1.0–50.0 mPa·s) or solid content (0–25 wt%) in the slurry phase. The frequency and holdup of wake phase increased with increasing gas velocity, but decreased with increasing liquid viscosity or solid content in the slurry phase. The equivalent size of wake phase increased with increasing gas velocity, liquid viscosity or solid content in the slurry phase. The wake properties and holdup were well correlated with operation variables within these experimental conditions.     

Theory of thermohydrodynamic instability of the front of filtration combustion of gases

Based on the filtration equations with account of heat transfer in the heating region, the problem of instability of small perturbations of the wave front of filtration combustion of a gas is solved. Expressions for the growth decrement and critical transverse size of a perturbation are obtained. The problem of the wave-front stability is solved with account of the macroscopic redistribution of filtration in the system. The solution includes macroscopic characteristics such as the transverse size, the width of the high-temperature zone, etc. A method is proposed for taking into account the influence of the characteristics of the system on the evolution of perturbations. It is shown that small deformation perturbations of the front always increase to a certain amplitude; their subsequent development— continuation of their growth or stabilization—is determined by the characteristics of the system. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 3–5, September–October 1999.     

Stability of a Spontaneous Vortex Structure in Flame under Gas Oscillations

The stability of a spontaneous vortex structure formed during combustion of a gas injected through a round hole in a flat horizontal plate onto its lower surface was studied. The unsteady velocity, vorticity, temperature, and pressure fields in the vortex structure were studied experimentally and numerically. It is established that for Reynolds numbers Re 10–75 and Rayleigh numbers Ra 10³ – 10⁴, the vortex structure is stable against single velocity perturbations and changes under acoustic oscillations with a frequency of 100 – 150 Hz. Small cells whose dimensions are comparable with the flame front thickness are destroyed, and the velocity of the vortex gas flow in large cells changes with the frequency of forced oscillations. The amplitude of linear gas velocity oscillations in the vortex is larger than that of gas velocity oscillations in the burner nozzle. It is assumed that the observed increase in the amplitude of gas velocity oscillations in the vortex is due to both acceleration of the combustion products in the gravity field and their thermal expansion. The gas velocity oscillations in the vortex structure lag behind the gas flow rate oscillations by a quarter of the period.     

Surfactant survey

Conclusions This study emphasizes the differences in properties required of surfactants for various application, the large and growing number of uses requiring more than 500,000 pounds per year, and the constantly changing pattern of use, making most of the recent estimates of volume distribution obsolete. For some time it has been customary to estimate the household market as 75–80% of the total. This study shows that this estimate is certainly high as household use is now probably only 50–55% of the total. This fact may be important in releasing our energies for the creative development of markets in the industrial fields. There is a rich potential market in such applications as ore flotation, agriculture, road building, and petroleum processing.     

Interaction of weak shock waves with a layer of a powdered medium

Results of analytical and numerical studies of the interaction of linear and weakly nonlinear air shock waves with an infinite layer of a powdered medium and with a finite-thickness layer are presented. Approximate analytical expressions for phase-pressure distributions in the powdered medium are obtained. It is found that the gas pressure at the “gas-powder” interface is continuous for linear waves and experiences a sudden change for nonlinear waves. The dependences of phase pressures on a shielded solid wall obtained by solving a general nonlinear system of equations of motion of a powdered medium and an approximate analytical solution of linear equations are compared. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 131–140, March–April, 2000.     

Controlling the thickness of a fluoroplastic coating for polyimide films

The order of developing instruments for process control proposed in [3] was confirmed on a concrete example. The ITP-1 instrument allows controlling the thickness of a fluoroplastic coating on a polyimide film directly in process equipment by a contactless method of measurement. The technical solutions for controlling the thickness of film and fibre materials when the object measured exhibits transverse mechanical oscillations are reported. A method is proposed for checking the ITP-1 instrument using a calculation equation. A possible area of application of these process solutions is indicated. __________ Translated from Khimicheskie Volokna, No. 6, pp. 61–63, November–December, 2006.     

Compensation Effect of Benzene Hydrogenation on Pt(111) and Pt(100) Analyzed by the Selective Energy Transfer Model

Kinetic measurements at low temperatures (310–360 K) using gas chromatography (GC) for benzene hydrogenation on Pt(100) and Pt(111) single crystal surfaces have been carried out at Torr pressures. These kinetic measurements demonstrated a linear compensation effect for the production of cyclohexane. A detailed application of the model of selective energy transfer to the experimentally obtained results yields the vibrational frequency of the adsorbate leading to reaction. This frequency is attributed to ring distortion modes. The vibrational frequency of the heat bath, or catalyst, is ascribed to a Pt-H mode. An approximate heat of adsorption of the reacting molecule is also calculated from the model.     

Improving the resolution of ultrasonic echoes from thin bondlines using cepstral processing

The measurement of the transit time of an ultrasonic pulse through the adhesive layer of a bonded joint can be an important indicator of the cohesive strength of the bond. However, when the pulse length is long in comparison with its transit time through the adhesive, it becomes impossible to resolve the echoes from the front and back faces of the bondline, and hence to deduce the transit time. In such cases, it is possible to improve the resolution by deconvolving the pulse shape from the impulse response of the adhesive layer. Standard deconvolution techniques are dependent on an accurate knowledge of the pulse shape in order to facilitate this deconvolution, whereas cepstral processing is a deconvolution technique for which no a priori pulse shape information is required. Using this technique it is found that it is possible to resolve the echoes of typical broadband ultrasonic pulses from layers of half the thickness that it is possible to resolve without signal processing. The line spacing of the cepstrum determines the digital accuracy of the transit time measurement. This line spacing is inversely proportional to the time domain sampling frequency. Hence, in order to obtain good time domain resolution, a high sampling frequency is required. However, it is found that it is essential that the signal contains significant energy up to the Nyquist frequency (half the sampling frequency) to minimize cepstral noise. This limits the improvement in resolution which can be obtained with a given transducer.     

Optimum estimation of process parameters using pseudo-random binary signals with application to mixing inside a packed tower

A technique is described for the design of a test signal such that the parameters, defined by the axial mixing model for a packed tower, can be estimated with the greatest accuracy from experimental records. Methods for calculating the effect of additive noise, usually associated with small amplitude signals, on computed correlation-, spectral-and amplitude ratio estimates are discussed. Designed experiments were performed on a 10-in. I.D. packed tower by the injection of a radioactive tracer into the gas phase. Peclet numbers for both dry and irrigated beds are reported.