Internal Heating Effect and Enhancement of Drying of Ceramics by Microwave Heating with Dynamic Control

The effectiveness of internal heating for enhancing the drying of molded ceramics is evaluated by both modeling and experiments. In the theoretical analysis, three dimensional drying-induced strain–stress are modeled, and the numerical solutions show that the internal heating generates lower internal stress than continuous convective heating or intermittent convective heating. Microwave drying is examined experimentally to study the effect of internal heating on the drying behavior of a wet sample of a kaolin slab. The drying behavior is compared among three modes: microwave heating, hot air heating and radiation heating. The transient behavior of temperatures in microwave drying is quite different from conventional drying by external heating. In particular, the temperature of the slab drops once in the progress of drying. This phenomenon cannot be predicted adequately by a simple model of one-dimensional heat conduction and moisture diffusion accompanied with an internal heat generation rate given as a linear function of the moisture content. It should be noted that the temperature behavior takes place due to the combined interactions with internal evaporation of moisture by rise in internal vapor pressure and shift of impedance or interference in the applicator. Microwave heating with a constant power above 100 W results in sample breakage due to the internal vapor pressure. However, if the power is dynamically controlled so as to maintain the temperature less than the boiling point of water, the drying succeeds without any crack generation until completion with a significantly faster drying rate than drying in convective heating or in the oven.     

Drying of suspensions and solutions on inert particle surface in mechanically spouted bed dryer

To eliminate some disadvantages of the conventional spouted bed dryers the mechanically spouted bed （MSB） system was developed. This dryer type is convenient to use inert particles providing an increased surface area for drying of materials of high-moisture content and heat sensitive materials. On three different drying tasks are demonstrated the experimental optimization of process parameters to obtain products of demanded quality. The main object was at drying of AIO（OH） suspension to preserve the particle size under 2.5μm and to obtain product with a moisture content of about 0.05 kg/kg （d.b.）. For this reason a very thin particle coating and intensive abrasion had to be assured. At drying of tomato concentrates the thermoplasticity makes the process very difficult. To jump over the deliquescent and sticky state developed at the critical temperature-moisture content values a very short drying time （8-10 s） must be provided. The third task was to form powder-like product from bovine serum albumin （BSA） solution having very low solid content （2-4%）. The selected process parameters given in this paper resulted in a mean particle size of less than 20 μm while the soluble oreserved orotein content was higher than 90%.     

Size Effect on Onset and Subsequent Evolution of Adiabatic Shear Band: Theoretical and Numerical Analysis

The adiabatic shear instability of ductile materials has attracted more and more attentions of researchers and groups,who have been sparing no effort in further...     

桩-土接触效应及对桥梁结构地震反应的影响

目前有关涉及桥梁桩基础地震反应的研究大多是基于桩与桩侧土体之间无相对滑动、位移保持协调的假定。本文针对地震作用下桥梁桩基础的接触面效应及其对结构地震反应的影响问题,以某桥梁工程为背景,通过在桩-土交界面处设置接触单元来模拟桩-土间的接触非线性,建立了土-桩-桥梁结构相互作用体系的三维分析模型。利用这一模型,分析了地震作用下桩-土交界面处的动力反应形态,探讨了桩-土间的接触非线性及其对桥梁结构地震反应的影响。初步分析结果表明：在强震作用下,桩-土间会产生较强的接触非线性,在本文模型中,这种非线性主要表现为桩-土交界面处的滑移;考虑桩-土间的接触面效应将使结构的位移反应结果较基于桩-土间位移协调的情形有所增大。     

The Effect of Isopropyl Alcohol and Non-Ionic Surfactant Mixtures on the Wetting of Porous Coated Paper

The influence of isopropyl alcohol and non-ionic surfactant solutions on aqueous droplet wetting behaviour on porous coated paper was determined. Paper coatings provide a micro- and nano-porous surface structure, which strictly speaking cannot be described in simple roughness terms as sub-surface lateral absorption directly impacts on the apparent contact angle. It is this very deviation from an idealised system that leads to novel wetting phenomena. Isopropyl alcohol and surfactant-based systems, both of which are commonly used in the printing industry, show differences in wetting behaviour, on both short and long timescales, with changes in the relative composition of the mixtures. Small variations of 0.1?wt% in surfactant concentration have a dramatic influence on the dynamic surface tension, and thus the wetting. It was observed that the wetting kinetics for isopropyl alcohol and surfactant solutions were different in terms of both wetting area and the penetration rate, even in cases where the dynamic surface tension of the solutions was kept the same. Different stages in the wetting and following drying processes could be observed with near infrared spectral imaging. In addition, the surfactant chemistries such as their degrees of hydrophilicity and molecular weights generated comparative differences in the wetting kinetics. The dominating factor affecting the wetting was, as expected, the solid?Cliquid interfacial energy defined on the practical porous substrate, which differed from the direct comparison with dynamic surface tension, thus exemplifying the deviation from idealised surface roughness behaviour when considering porous materials. An apparent ??equivalent?? surface roughness value for the porous material was determined, and it was seen that an increase in this equivalent parameter enhanced the rate of wetting behaviour with decreasing solution surface tension, and so also affected the wetting evolution. The wetting was enhanced by cavities in the coating layer, which were enlarged by the penetrating liquids.     

Phase Change in a Heterogeneous Medium: Comparison Between the Vaporisation of Water and Heptane in an Unsaturated Soil at Two Temperatures

A theoretical and experimental analysis of the phase change of a volatile liquid in an unsaturated soil is presented. Expression of the rate of phase change of the pore liquid is developed within the framework of nonequilibrium thermodynamics. An experiment is proposed in which the value of the phenomenological coefficient associated with this expression is measured. Two examples of results concerning the volatilisation of water and of a volatile hydrocarbon in a silty clayey sand illustrate the potentiality of the experiment. Variation of the phase change coefficient was determined at 30°C for both fluids and at 80°C for heptane, versus the liquid content of the soil.     

Suction Induced Effects on the Fabric of a Structured Soil

This paper presents the mathematical modelling of the modification of the pore space geometry of a structured soil subjected to suction increase. Structured soil concepts are first introduced considering different fabric units, such as aggregates and fissures. The numerical modelling of the structural evolution is based on experimental test results in which the evolution of the structure of the samples subjected to different suctions is determined using the mercury intrusion porosimetry technique. From this information, the macro and micropore volume evolutions are determined. The results show that drying produces a reduction in the soil total porosity which mainly corresponds to a reduction of the macropore volume. Associated with this phenomenon, an increase in micropore volume is also observed. The proposed model divides pore size distribution into three pore classes (micropores, macropores and non-affected areas). Using the concept of a suction-influenced domain, the proposed model is able to reproduce the main observed fabric evolution between the saturated and dry states.     

Water Redistribution in Irrigated Soil Profiles: Invariant Solutions of the Governing Equation

Exact solutions for a class of nonlinear partial differential equations modelling soil water infiltration and redistribution in irrigation systems are studied. These solutions are invariant under two-parameter symmetry groups obtained by the group classification of the governing equation. A general procedure for constructing invariant solutions is presented in a way convenient for investigating numerous new exact solutions.     

Influence of leakage flow through labyrinth seals on rotordynamics: numerical calculations and experimental measurements

An extensive investigation of the influence of the leakage flow through a labyrinth seal at supply pressure of 12 bar on the rotordynamics was performed by using numerical calculations and experimental measurements. Toward this end, an experimental rotor setup was established in Shanghai Jiao Tong University. Two labyrinth seals were chosen for comparison, e.g., an interlocking seal and a stepped one. The numerical calculations based on the bulk-flow theory and the perturbation analysis were accomplished. Simultaneous acquisitions of the fluctuating static pressure at the stator wall and the displacement of the whirling rotor were made. The influence of the aerodynamic forcing on the rotor was analyzed in terms of the axial distribution of the mean static pressure, the circumferential distribution of the fluctuating pressure, the fist critical speed and the destabilization rotating speed of the rotor. The experimental results demonstrated that the sinusoidal distribution of the fluctuating static pressure on the stator wall was closely related to the whirling motion of the rotor. The first critical speed of the rotor was reduced by the aerodynamic forcing, resulting in intensified destabilization of the rotor system. Furthermore, the numerical analyses were in good agreement to the experimental measurements.     

Simulation of the Effect of Water Injection on Volcanic Conduit Flow

The effect on the eruption process of water or steam injection into a volcanic conduit from an adjacent water-saturated stratum is studied. Both steady-state and unsteady processes are considered. The physical characteristics of these eruptions are identified. A mathematical model of such an eruption is proposed for the first time.     

Multiscale Model for Assessing the Effect of Bacterial Growth on Intrinsic Permeability of Soil: Column Experiment Simulation

A multiscale model was proposed in a companion paper for assessing the impact of bacterial growth attached to soil particles on the intrinsic permeability of soil. In this paper, this model is used to simulate a column experiment. The simulation conditions are described and the results of the simulation runs are presented. Various possible explanations for the observed reduction in permeability in the column experiment are analyzed using the model and it is concluded that the reduction in the metabolic activity of the attached biomass at the bottom of the column is mainly responsible for the reduction in the intrinsic permeability near the top of the column. Based on the set of parameter values used in the simulations, upper and lower bounds on the reduction in metabolic activity are estimated.     

Interval stochastic matrices: A combinatorial lemma and the computation of invariant measures of dynamical systems

The concept of an interval stochastic matrix is introduced. We prove a combinatorial theorem which describes the network flow associated with an interval matrix. The semi-invariant vectors of are characterized in terms of eigenvectors with unit eigenvalue of stochastic matrices . These results are then applied to the approximation and machine computation of invariant measures of dynamical systems.Funded under Australian Research Council Grant A 8913 2609.     

Effect of an Anomalous Temperature Dependence of the Water Density on Circular Jet Propagation

It is shown experimentally that an originally circular jet with a temperature greater than 4°C transforms into a thin sheet when propagating in water at a temperature of about 0°C and sinks rather than ascends. At large times, a peculiar fine structure of the hydrophysical fields is detected. This is due to the difference between the molecular diffusivities of heat and dissolved salts, as well as the breakdown of large-scale to small-scale vortices.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 39–47.Original Russian Text Copyright © 2005 by Bukreev.     

The experimental investigation of heat transport and water infiltration in granular packed bed due to supplied hot water from the top: Influence of supplied water flux, particle sizes and supplied water temperature

In the present study an experimental investigation of heat transport and water infiltration in granular packed bed (unsaturated porous media) due to supplied water flux is carried out. The study is focus on the one-dimensional flow in a vertical granular packed bed column assuming local thermal equilibrium between water and particles at any specific space. This experimental study described the dynamics of heat transport and water infiltration in various testing condition. Experimentally, the influences of particle sizes, supplied water flux and supplied water temperature on heat transport and water infiltration during unsaturated flow are clarified in details. The results showed that the granular packed bed with larger particle size results in faster infiltration rate and form a wider infiltration depth. Furthermore, the increase of the supplied water flux and supplied water temperature corresponds to faster infiltration rate, but the results not linearly related to the interference between the heat transport and hydrodynamics characteristics in granular packed bed.     

Effect of the Nonmonotonic Temperature Dependence of Water Density on the Propagation of a Vertical Plane Jet

This paper gives results of two experiments in which warmer water in the form of a vertical plane jet was let into colder water. In one experiment, the temperature of inflowing and initially quiescent water exceeded 4°C and warm water propagated only along the free surface. In the other experiment, the temperature of inflowing water was above 4°C and that of quiescent water was below 4°C. In this case, two jets — surface and bottom — first formed, and then the inflowing liquid was entirely concentrated in the bottom jet. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 2, pp. 23–29, March–April, 2006.     

Effect of the Nonmonotonic Temperature Dependence of Water Density on the Decay of an Initial Density Discontinuity

The effect of the nonmonotonic temperature dependence of water density on gravity current flow after removal of the shield which separated warm and cold water was studied experimentally. If the temperature of water of maximum density was in the interval between the initial temperatures on the different sides of the shield, Rayleigh-Taylor instability developed along with shear instability under normal conditions. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 66–73, January–February, 2006.     

Effect of rotation direction of a rotary tiller on draft and power requirements in a Bangkok clay soil

Experiments were conducted in a Bangkok clay soil to evaluate the performance of a rotary tiller equipped with reverse or conventional blades. The conventional rotary tiller was equipped with C-type blades whereas the reverse-rotary tiller had new types of blades. Tests were conducted on wet land as well as in dry land. Tests were conducted at tractor forward speeds of 1.0, 1.5 and 2.0 km/h. A power-take-off (PTO) power consumed was calculated from the PTO torque and speed. The results indicated that the PTO power consumption was less for the reverse-rotary tiller compared to the conventional tiller for all passes and forward speeds. For both rotary tillers, power consumption decreased as the number of passes increased, whereas power consumption increased when the forward speed was increased. At all forward speeds, the power consumption was the highest during the first pass and lowest during the third pass. The maximum difference of PTO power requirement was after the first pass at 1.0 km/h forward speed. The reverse-rotary tiller consumed about 34% less PTO power under this condition.     

Perfecting a method of micro-analysis of water and acetic acid in a cocoa bean in the course of drying: applying to determine transportation coefficients

This article is about the study of the diffusion of water and acetic acid in a grain of cocoa in course of drying. The authors present a method of microanalysis which enables the analysis of each little slice of the grain : a precise measurement of each slice is realised in view of the analysis from the centre to the surface of the grain with the aid of a cutting apparatus, designed and realised to this effect. At each instant of the drying process, the profiles of water and acetic acid contents are then determined. A one dimensional diffusion model enables a shell by shell evaluation of the diffusion of water and acid in the cocoa grain. The results obtained show an augmentation of transport coefficients in course of drying. We however observe a decrease of the diffusion coefficient of water to the low moisture content : what makes us think of the appearance of crusting phenomenon.     

Effect of buoyancy on the wakes of circular and square cylinders: a schlieren-interferometric study

Wakes behind heated cylinders, circular, and square have been experimentally investigated at low-Reynolds numbers. The electrically heated cylinder is mounted in a vertical airflow facility such that buoyancy aids the inertia of main flow. The operating parameters, i.e., Reynolds number and Richardson number are varied to examine flow behavior over a range of experimental conditions from forced to mixed convection regime. Laser schlieren-interferometry has been used for visualization and analysis of flow structures. Complete vortex shedding sequence has been recorded using a high-speed camera. The results on detailed dynamical characteristics of vortical structures, i.e., their size, shape and phase, Strouhal number, power spectra, convection velocity, phase shift, vortex inception length, and fluctuations are reported. On heating, alteration of organized (coherent) structures with respect to shape, size and their movement is readily perceived from instantaneous Schlieren images before they reduce to a steady plume. For both cylinders, Strouhal number shows a slow increase with an increase in Richardson number. At a critical value, there is complete disappearance of vortex shedding and a drop in Strouhal number to zero. The corresponding spectra evolve from being highly peaked at the vortex shedding frequency to a broadband appearance when vortex shedding is suppressed. The geometry of vortex structures transforms to a slender shape before shedding is suppressed. At this heating level, absence of multiple peaks in power spectra at cylinder centerline indicates absence of interaction between opposite shear layers. The convection velocity of vortices increases in stream wise direction to an asymptotic value and its variation is a function of Richardson number. The convection speed abruptly falls to zero at critical Richardson number. The phase difference of shed vortices between upstream and downstream location increases with an increase in Richardson number. Velocity profiles show an increase in fluid speed and beyond the critical point, buoyancy forces add enough momentum to cancel momentum deficit due to the cylinder. Overall, the combined effect of temperature gradient on the separating shear layer velocity profile in near field and vortical structures interaction in far field influences wake instability of a heated cylinder. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Prediction of the Compressible Stage Slamming Force on Rigid and Elastic Systems Impacting on the Water Surface

In this paper some models focusing on hydrodynamic and elasticforces arising during the impact of rigid and elastic systems on thewater surface are investigated. In particular, the supersoniccompressible stage of the impact is considered by modelling the slammingphenomenon through the Skalk–Feit acoustic approximation. The dynamicequations of the dropping system are coupled to those of the fluid and anonlinear fluid-solid interaction problem is stated. Generalrelationships between the body's shape, slamming force and body motionare determined. These equations are applied to the wedge water entrycases, and a closed-form expression for the maximum hydrodynamic forceis found. Moreover the theoretical correlation between the hydrodynamicforce and the body geometry allows us to control the inverse problem andthe shape associated to a constant slamming force is determined.Due to some simplifications allowed in the supersonic compressibleimpact, the results of the hydrodynamic analysis hold in closed form.This permits us to focus on the basic result of the paper addressed to asystematic correlation between hydrodynamic and elastic maximum forcesin terms of some characteristic dimensionless quantities involved influid-solid interaction.In particular, critical conditionscorresponding to those hydorelastic parameters combinations areinvestigated, leading to severe elastic response of the impactingsystem.