ACCURATE SURFACE TEMPERATURE PREDICTION AT HIGH SPEEDS

Computational tools of turbulent combustion have practical applications for various fields including liquid rocket engines, but some numerical issues are still presented for solving supercritical combustion. In the present study, several of these numerical issues are studied and discussed. Turbulent flow and thermal fields of gaseous hydrogen/cryogenic liquid oxygen flame at supercritical pressure are simulated by a turbulence model. To realize real-fluid combustions, the modified Soave-Redlich-Kwong (SRK) equations of state (EOS) are implemented into the flamelet model with a look-up table as functions of mean and variance of mixture fraction, scalar dissipation rate, enthalpy, and pressure. For supercritical combustion flows, modified forms of the pressure implicit with splitting of operator (PISO) algorithm for solving the pressure-velocity linked equation are introduced. From a comparison of instantaneous temperature distributions for gaseous hydrogen/cryogenic liquid oxygen flame at supercritical pressure, the capability of each method based on the different solution sequence is examined and the effective sequence is explored. The results show that the updated mixture fraction reflected in the pressure correction loop is a critical factor for numerical stability. Also, the relative performance of six convection schemes for supercritical combustion is discussed.     

On consensus algorithms design for double integrator dynamics

This paper considers the consensus problem of double integrator multi-agent systems where: (i) each agent is subject to input saturations, and (ii) the velocity (second state) of each agent is not available for feedback. We present new consensus algorithms that handle simultaneously the above mentioned situations. Sufficient conditions are derived such that consensus algorithms developed for first- and second-order multi-agent systems in ideal situations can be used to account for input saturations and remove the requirement of velocity measurements. To illustrate the effectiveness of the proposed approach, we propose solutions to two different second-order consensus problems in the case where the input is saturated and the velocity states are not available for feedback and simulation results are provided in each case.     

Electron Charge Density Distribution from X-ray Diffraction Study of the M-Nitrophenol Compound in the Monoclinic Form

At room temperature, the m-Nitrophenol (m-NPH) appears in two polymorphic structures: orthorhombic and monoclinic forms. In the present work, we shall focus on the monoclinic form of this compound which has a centrosymmetric structure with the space group P2₁/n. The molecular dipole moment has been estimated experimentally. High resolution single crystal diffraction experiment was performed at low temperature with MoKα radiation. The crystal structure was refined using the multipolar model of Hansen and Coppens (1978). The molecular electron charge density distribution is described accurately. The study reveals the nature of inter-molecular interactions including charge transfer and hydrogen bonds. In this crystal, hydrogen bonds of moderate strength occur between the hydroxyl group and the O atom in the nitro one.     

New separation method of metal/plastic micronized particles using travelling wave conveyors

The paper reports an experimental investigation for studying the movement dynamics and the separation of micronized particles on a poly-phase travelling wave conveyor (TWC). A digital balance and a sensitive electrometer controlled by Labview software were used to analyse the velocity and the material flow rate on a three-phase conveyor with respect to the variation of both the amplitude and the frequency of the applied voltage. It was found that about 80% of the particles mass move together in one single wave and that the electric charge gained by the particles increases with the intensity of the electric field. Moreover, preliminary experiments showed that it is possible to separate a granular mixture of plastic and copper micronized particles using a TWC. Successful experiments were carried out on micronized samples of both electric cable and electronic card wastes. High purity metal was recovered.     

An improved spectral analysis of the stray flux component for the detection of air-gap irregularities in squirrel cage motors

For machines? monitoring purpose, the classical motor current signature analysis has shown its weakness in distinguishing the eccentricity occurrence in presence of others mechanical faults. Although Park?s vector approach can cover this drawback, the high cost due to the requirement to use three current sensors associated with an advanced processing technique, makes it less desired by industrialists. In this paper, we suggest an alternative diagnosis method based on a suitable processing of the stray flux data. The experimental results have revealed the potential of a simple search coil for the detection and the distinction of the accurate eccentricity nature even in presence of similar mechanical faults.     

Efficiency of granulated blast furnace slag replacement of cement according to the equivalent binder concept

The strength development of slag cement has a great consideration for the scheduling of formwork removal, prestressing operations, and other practical aspects of slag cement usage. The prediction of slag concrete strength, using the Feret’s model has been studied by introducing the concept of the equivalent binder. This has led to define an efficiency coefficient of slag which distinguishes the latter with the regard to the cement. Thus, this obtained coefficient characterizes well the slag and lets to predict the slag concrete strength from strength values of a normal concrete made without slag for a given age and replacement rate. At 90 days age, the test results show that for 15% replacement rate, the slag is activated completely and gives 67% of efficiency more than the cement. For higher replacement rate, the efficiency of the slag decreases and becomes similar to that of cement for 50% replacement rate.     

Influence of acoustic streaming on thermo-diffusion in a binary mixture under microgravity

An analytical and numerical study of the influence of acoustic streaming on species separation of a binary mixture under microgravity is presented. A rectangular cell filled with binary fluid is submitted to an ultrasonic propagating wave along a portion of one of its small walls while the opposite wall is perfectly absorbing. A temperature gradient is applied between the two other walls. The unicellular flow induced by the Eckart streaming may lead to significant species separation. In a first part, the hypothesis of parallel flow is used to determine the analytical solution which describes the unicellular flow and the separation is calculated analytically based on the acoustic streaming parameter, A, the acoustic beam width, ?, and the Schmidt number, Sc. Theses analytical results are corroborated by direct numerical simulations. In a second part, a linear stability analysis of the unicellular flow is performed. The eigenvalue problem resulting from the temporal stability analysis is solved by the Galerkin method, a spectral Tau–Chebychev method and by a finite element method. The thresholds for the stationary and oscillatory instability depend on the normalized acoustic beam width.     

Synthesis and Characterization of Some Nonionic Bolaamphiphiles

A series of nonionic bolaamphiphiles were synthesized from the reaction of fluoroalkylene (dimercaptoacetates) with maleate crown ethers. Surface activity of the new surfactants was evaluated on the basis of surface tension measurements. The new fluorinated bolamphiphiles exhibit a remarkable lowering of surface tension in comparison with nonfluorinated analogues.