Way Of Energy Transfer Research Articles

Investigation of Shock Wave Loading and Crater Creation by Means of Single and Double Targets in the PALS-Laser Experiment

The efficiency of crater creation for different types of Al targets, namely, single massive targets and double targets consisting of a foil or a disk placed before the massive target at a chosen distance (300 and 500 µm), is studied. Targets were irradiated by the PALS facility laser beam with E L = 100 – 400 J at the first harmonic λ = 1315 nm, a focal spot radius of 125 µm, and pulse duration of 400 ps. Velocities of the accelerated foil’s fragments or disks and electron density distributions of the plasma streams are determined by means of three-frame interferometry. Shapes and volumes of craters are obtained using the crater replica technology and microscopy measurements. It is shown that direct laser action is the most efficient way of energy transfer to the massive target and the most efficient method of crater creation. Somewhat lower efficiencies of shock wave loading and crater creation in comparison with direct laser action are found in the case of double targets where the energy is transferred to the massive target by colliding laser-driven foils or disks. The efficiencies of such a colliding energy transfer are close to 60% for foils and 40% for disks. The experimental results are in a good agreement with two-dimensional hydrodynamic models of shock wave generation under direct laser action and laser-driven macroparticle impact.

Influence of mechanical activation on synthesis of zinc metatitanate

Investigations of a ZnO-TiO2 binary oxide mixture during mechanical treatment were mainly focused on obtaining orthotitanate Zn2TiO4 with a spinel structure. Due to the specific way of energy transfer during mechanical treatment using a high-energy ball mill, the system passes through low temperature ZnTiO3 metatitanate phase formation. Mechanical activation was performed on an equimolar ratio mixture of ZnO and TiO2. The anatase phase was previously submitted to heat treatment for achieving a starting mixture rich in a rutile phase. Milling conditions were preset for observing the formation of a low temperature ZnTiO3 phase with a perovskite structure. The powder microstructure was characterized using scanning electron microscopy. A nitrogen gas sorption analyzer with the BET method was used to determine the specific surface area and porosity, indicating changes of powder sample properties during mechanical activation. Also, X ray powder diffractometry was applied to obtain the phase composition. Powders were then pressed into pellets and their compressibility was observed through density changes. According to microstructures obtained by scanning electron microscopy analysis, the system underwent a primary and secondary agglomeration process. Specific surface area measurements supported that conclusion. Compressibility investigations established the difference between compressibility of the non-activated mixture and activated powders. X-ray diffraction analysis revealed that a perovskite structure forms simultaneously with a spinel phase during the process of mechanical activation.

Aeroacoustical coupling in a ducted shallow cavity and fluid/structure effects on a steam line

A pure tone phenomenon has been observed at 460 Hz in a piping steam line. The acoustical energy has been identified to be generated in an open gate valve and to be of cavity noise type. This energy is then transmitted to the main pipe by fluid/structure coupling. The objectives here are to display the mechanism of the flow acoustic coupling in the cavity and in the duct through an aeroacoustical analysis and to understand the way of energy transfer from the fluid to the main pipe through a vibroacoustical analysis. Concerning the first objective, an experimental study by means of 2/7 scale models in air is analysed by means of numerical flow simulation. The flow acoustic phenomena are modelled by computing the Euler equations. Two different computations are carried out: in the first one, a pure Euler modelling is used, in the second one, a boundary layer obtained from experimental data is introduced in the computation in order to have a realistic flow profile upstream the cavity. The boundary layer flow profile appears to be essential to recover the experimentally observed coupling between the shear-layer instability and the acoustical transverse mode of the pipe. The numerical results confirm that the second aerodynamic mode is responsible for the oscillation. While the predicted frequency agrees about 1% with the scale model experiments, the predicted amplitude is approximately 15 dB too low. For the second objective, fluid/structure coupling in the main pipe is studied using two fully coupled methods. The first method consists in a modal analysis of the line using a fluid–structure finite element model. The second one is based on the analysis of dispersion diagrams derived from the local equations of cylindrical shells filled with fluid. The way of energy transfer in transverse acoustical waves coupled with flexion-ovalization deformations of the pipe is highlighted using both methods. The dispersion diagrams allow a fast and accurate analysis. The modal analysis using a finite-element model may complete the first one with quantitative data. The link between the fluid/acoustic and the fluid/structure analysis is then the excitation of the transverse acoustical mode of the duct.

Classification of instabilities in parallel two-phase flow

There is extensive literature on the stability of parallel two-phase flow, both in the context of liquid-liquid as well as gas-liquid flow. Aimed at making this literature more transparent, this paper presents a classification,scheme for the various instabilities arising in parallel two-phase flow. To achieve such a classification, the equation governing the rate of change of the linetic energy of the disturbances is evaluated for relevant values of the physical parameters. This shows the existence of five different ways of energy transfer from the primary to the disturbed flow, which have their origin in density stratification, velocity profile curvature, viscosity stratification or shear effects. Each class is discussed on the basis of references covering the developments over the last 35 years.

Classification of instabilities in parallel two-phase flow

There is extensive literature on the stability of parallel two-phase flow, both in the context of liquid-liquid as well as gas-liquid flow. Aimed at making this literature more transparent, this paper presents a classification,scheme for the various instabilities arising in parallel two-phase flow. To achieve such a classification, the equation governing the rate of change of the linetic energy of the disturbances is evaluated for relevant values of the physical parameters. This shows the existence of five different ways of energy transfer from the primary to the disturbed flow, which have their origin in density stratification, velocity profile curvature, viscosity stratification or shear effects. Each class is discussed on the basis of references covering the developments over the last 35 years.

TESTING THE DRYING PROCESS OF SHELLED MAIZE ON ASPECTS OF NUTRITIONAL QUALITY AND THERMAL EFFICIENCY

ABSTRACT Interactions between technology parameters of shelled maize drying and the most important characters of drying material were analysed partly on the basis of the results appeared in written literature also on the basis of the authors' test research not published yet. Theorems describing the most important physical limit of drying were published also the change of nutritional values as a function of drying technology parameters were analysed. Most important laws of different ways of energy transfer also their effect on the process of water removal besides the common ways of drying process simulation, especially considering their applicability within agricultural circumstances were discussed. One part of questions mainly not answered yet - which arise because of the specific parameters of the drying material - have been drawn up. Practically applicable results, on the basis of theoretical research activities also experimental measurements have been shortly presented.

Variations of the dielectric properties of epoxy resins during microwave curing

The curing of a particular epoxy resin (diglycidylether of bisphenol-A) by three amino hardeners (4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulphone and 4,4′-diaminodiphenylether) is followed by dielectric measurements performed under microwave heating. The formation on heating of a molecular association, is suggested by the analysis of the dielectric variations on the basis of an additive contribution of all the known constituents in the mixture. The reversibility of this molecular association is demonstrated. Two possible interpretations are proposed and discussed. Dielectric constant variations during curing provide evidence that microwave heating is a very efficient way of energy transfer and for monitoring chemical processes, such as the cross-linking of epoxy resins.