Water Vapor Adsorption in Porous Building Materials: Experimental Measurement and Theoretical Analysis

An experimental and theoretical analysis of the water vapor adsorption in several types of porous building materials is presented. For the measurement of adsorption isotherms, a DVS-Advantage water sorption device is used. The experimental data is analyzed using theoretical formulas based on the BET, BSB, BDDT, and FHH isotherms, assuming a mono as well as multi-layer water vapor adsorption. The BSB equation is found to provide a good approximation for the relative humidities below 0.6–0.7, whereas the FHH equation shows a sufficient accuracy for the relative humidities above 0.4–0.5. Based on a combination of BSB and FHH isotherms, a semi-empirical formula is proposed that allows one to obtain a very accurate approximation of experimental data for all analyzed materials and all values of the relative humidity.     

Correlation of Water Vapor Permeability with Microstructure Characteristics of Building Materials Using Robust Chemometrics

This paper studies various microstructure parameters of natural and artificial building materials and aims to their correlation to the water vapor permeability. Three categories of building materials were investigated: stones, bricks, and plasters. Mercury intrusion porosimetry was applied in order to obtain the materials microstructure characteristics, a variety of pore size distributions and pore structure measurements, such as total porosity. The water vapor permeability of materials was determined experimentally according to ASTM standard E96-00. A robust principal component regression approach, coupled with multiple outlier detection, was applied in order to correlate water vapor permeability values to pore size distributions. A good quality correlation model was found by utilizing relative specific pore volume and relative specific pore surface distributions, whereas using pore structure measurements, such as total porosity, the correlation results were very poor. From the results, specific ranges of pore size distribution, corresponding to pores radius sizes greater than $10\,\upmu \text{ m }$ 10 μ m and between 1.778 and $0.421\,\upmu \text{ m }$ 0.421 μ m , contribute to the water vapor permeability of the materials.     

水下环向双周期加肋圆柱壳体的自由振动

以浸没于水中的弹性环向双周期加肋薄圆柱壳为研究对象，考虑介质与结构振动的耦合效应，研究流固耦合系统的自由振动。基于Kennard薄壳理论、Helmholtz方程以及壳壁外表面的运动协调条件，并借助Dirac-δ函数引进肋骨对壳体的作用，从而建立耦合系统的运动方程。通过富氏积分变换、引进算子，并利用算子的周期性，得到系统的频率方程。采用沿实波数轴搜索求根的方法，重点计算了水下无限长环向双周期加肋柱壳的自由传播波频率系数，并进一步研究了流场和肋参数对壳体固有频率的影响。     

The Linear Vortex Instability of the Near-vertical Line Source Plume in Porous Media

Free convection plumes usually rise vertically, but do not do so when in an asymmetrical environment. In such cases they are susceptible to a thermoconvective instability because warmer fluid lies below cooler fluid in the upper half of the plume. We analyse the behaviour of streamwise vortex disturbances in plumes that are close to being vertical. The linearised equations subject to the boundary layer approximation are parabolic and are solved using a marching method. Our computations indicate that disturbances tend to be centred in the upper half of the plume. A neutral curve is determined and an asymptotic theory is developed to describe the right hand branch of this curve. The left hand branch is not amenable to an asymptotic analysis, and it is found that the onset of convection for small wavenumbers is very sensitively dependent on both the profile of the initiating disturbance and where it is introduced.     

Formation of Supersonic Zones and Local Separation Zones in Transonic Steady-State Flow Past Surface Roughness in the Free Interaction Regime

Within the framework of free interaction theory numerical methods are used to investigate the occurrence of supersonic zones with shocks in the outer inviscid region for flow past roughness in the lower viscous sublayer, with and without the formation of local separation zones.     

Self-Gravitating Relativistic Fluids: The Formation of a Free Phase Boundary in the Phase Transition from Hard to Soft

In the 1990s Christodoulou introduced an idealized fluid model intended to capture some of the features of the gravitational collapse of a massive star to form a neutron star or a black hole. This was the two-phase model introduced in ‘Self-gravitating relativistic fluids: a two phase model’ (Demeterios, Arch Ration Mech Anal 130:343–400, 1995). The present work deals with the formation of a free phase boundary in the phase transition from hard to soft in this model. In this case the phase boundary has corners at the null points; the points which separate the timelike and spacelike components of the interface between the two phases. We prove the existence and uniqueness of a free phase boundary. Also the local form of the shock near the null point is established.     

The Relevance of Water Vapour Transport for Water Vapour Sorption Experiments on Small Wooden Samples

Transport in Porous Media - To characterise the sorption behaviour of wood or other hygroscopic materials with the use of water vapour sorption experiments, an accurate understanding of water...     

Drag of a Plate Planing on the Shallow Water with Formation of Waves

The plane problem of the plate planing at a constant velocity on the surface of a heavy, ideal, incompressible, finite-depth fluid is considered. The approximate, depth-independent expression for the force acting on the plate is derived from the linear distribution of the fluid velocity along the plate and the height of the flow stagnation point, without regard for jet formation near the leading edge. In this approximate formulation the plate drag depends on its velocity and the trailing edge immersion and does not depend on the planing angle. Experiments and numerical calculations in the exact formulation are performed in the near-critical flow regimes. It is shown that the wave patterns in the experiments and numerical calculations coincide, the formula for the drag being in agreement with the numerical experiments. An approximate criterion of the formation of waves going away from the plate in the forward direction is proposed.     

Direct Numerical Simulation of the Puffing Phenomenon of an Axisymmetric Thermal Plume

A spatial direct numerical simulation of an axisymmetric buoyant thermal plume is presented. The governing flow field equations at the centerline are put into a special form to circumvent the axis singularity associated with the cylindrical coordinates and the high order accuracy of the numerical scheme is preserved at the centerline. Boundary conditions associated with the spatial DNS of open-boundary buoyant flows and compatible with the modern nondissipative high-order finite difference schemes have been developed. The fluid exhibits a periodic oscillatory motion known as the puffing phenomenon, which is the formation and convection of vortex at the near field of the plume. Budgets of the vorticity transport are determined to examine the mechanisms leading to the puffing phenomenon. The analysis on vorticity transport shows that vorticity is created mainly by the gravitational term which is due to the interaction between the radial density gradients and gravity at the initial stage of the establishment of the puffing structure, while the baroclinic torque dominates the vorticity transport when the flow is established. Density stratification in the radial direction close to the plume base is found to be essential to the development of the buoyant flow instability. Simulations with different initial temperature ratios reveal that entrainment close to the plume base is enhanced at a higher temperature ratio despite the fact that the puffing structures and the plume pulsation frequency only vary very weakly with the initial temperature ratio. The predicted puffing frequencies are in agreement with the values from experimental correlations for fire and isothermal helium/air plumes. Received 12 May 1999 and accepted 9 December 1999     

Falling of a Spherical Particle in Fine-Bubble Plume and Fine-Bubble Behavior around the Particle

Fluid Dynamics - In this study, the interaction between a spherical solid particle descending in a fine-bubble plume and the fine-bubbles around the particle is investigated experimentally. The...     

Investigation of CO<Subscript>2</Subscript> Plume Behavior for a Large-Scale Pilot Test of Geologic Carbon Storage in a Saline Formation

The hydrodynamic behavior of carbon dioxide (CO₂) injected into a deep saline formation is investigated, focusing on trapping mechanisms that lead to CO₂ plume stabilization. A numerical model of the subsurface at a proposed power plant with CO₂ capture is developed to simulate a planned pilot test, in which 1,000,000 metric tons of CO₂ is injected over a 4-year period, and the subsequent evolution of the CO₂ plume for hundreds of years. Key measures are plume migration distance and the time evolution of the partitioning of CO₂ between dissolved, immobile free-phase, and mobile free-phase forms. Model results indicate that the injected CO₂ plume is effectively immobilized at 25 years. At that time, 38% of the CO₂ is in dissolved form, 59% is immobile free phase, and 3% is mobile free phase. The plume footprint is roughly elliptical, and extends much farther up-dip of the injection well than down-dip. The pressure increase extends far beyond the plume footprint, but the pressure response decreases rapidly with distance from the injection well, and decays rapidly in time once injection ceases. Sensitivity studies that were carried out to investigate the effect of poorly constrained model parameters permeability, permeability anisotropy, and residual CO₂ saturation indicate that small changes in properties can have a large impact on plume evolution, causing significant trade-offs between different trapping mechanisms.     

Large Eddy Simulations of the Flow in the Near-Field Region of a Turbulent Buoyant Helium Plume

Large eddy simulations are conducted in the near-field region of a large turbulent buoyant helium plume. The CFD package FireFOAM is applied to that purpose. The transient and mean flow dynamics are discussed as a function of grid resolution, with and without the use of the standard Smagorinsky subgrid scale (SGS) model. Small scale structures, formed at the edge of the plume inlet due to baroclinic and gravitational mechanisms and subject to flow instabilities, interact with large scale features of the flow, resulting in a puffing cycle. In general, the LES calculations reproduce the main features of the turbulent plume, with better agreement when the Smagorinsky type SGS model is applied. In particular, the puffing cycle is recovered in the simulations with correct frequency. The mean and rms values of the velocity components are well predicted with use of the SGS model, even on relatively coarse meshes. Agreement for the species mass fraction (mean and rms values) is less satisfactory, but in line with results found in the literature.     

Formation of Regions with High Energy and Pressure Gradients at the Free Surface of Liquid Dielectric in a Tangential Electric Field

The nonlinear dynamics of the free surface of an ideal incompressible non-conducting fluid with a high dielectric constant subjected to a strong horizontal electric field is simulated using the method of conformal transformations. It is shown that in the initial stage of interaction of counter-propagating periodic waves of significant amplitude, there is a direct energy cascade leading to energy transfer to small scales. This results in the formation of regions with a steep wave front at the fluid surface, in which the dynamic pressure and the pressure exerted by the electric field undergo a discontinuity. It has been demonstrated that the formation of regions with high gradients of the electric field and fluid velocity is accompanied by breaking of surface waves; the boundary inclination angle tends to 90?, and the surface curvature increases without bound.     

Effectiveness of Acidizing of the Vellbore Zone Taking into Account the Capillary Locking of Formation Water

The results of calculations of immiscible fluid flow to an operating well are compared for various formation parameters and states of the wellbore zone. Steadystate and unsteady filtration regimes are considered. The calculations show that acidizing of the wellbore zone increases the well flow rate.     

Effect of Anisotropy Structure on Plume Entropy and Reactive Mixing in Helical Flows

Plume dilution and reactive mixing can be considerably enhanced by helical flows occurring in three-dimensional anisotropic porous media. In this study, we perform conservative and reactive transport simulations considering different anisotropy structures of a single inclusion with the objective of exploring the effect of the inclusion’s geometry and orientation on the patterns of twisted streamlines and on the overall dilution and reaction of solute plumes. We analyzed 100 different scenarios by varying key parameters such as the angle of the anisotropic structures with respect to the average flow velocity, the spacing between alternated heterogeneous zones of coarse and fine materials, the permeability contrast between such matrices, and the magnitude of the seepage velocity. Entropy conservation equations and entropy-based metrics for both conservative and reactive species were adopted to quantify dilution, reactive mixing and their interactions with the helical flow patterns in the considered three-dimensional anisotropic setups. The results allowed identifying optimal anisotropic configurations maximizing mixing and reactions, and yielding enhancement factors up to 15 times the outcomes of analogous simulations in homogeneous media. Furthermore, the effects of compound-specific diffusive/dispersive properties of the transported species were found to be relevant for both plume dilution and reactive mixing in helical flows.     

深水井控过程中天然气水合物生成区域预测

针对深水井控的特点,建立了多相流控制方程,给出了温度场方程和水合物生成热力学方程,并给出了不同工况下求解上述方程的定解条件和离散方法以及求解步骤.数值计算表明:随着关井时间的增加,环空内的温度越接近环境温度,水合物的生成区域越大;随着压井排量的增加,天然气水合物的生成区域变小,可适当提高流量使水合物的生成区尽量远离海底,减小防喷器管线被水合物阻塞的危险;由于节流管线摩阻的原因,与钻进时相比,压井时水合物的生成区域会变大,且随着节流管线内径的减小,水合物的生成区域会变大;随着抑制荆浓度的提高或钻井液入口温度的升高,天然气水合物的生成区域也随之变小.     

Stability of Periodic Clusters in Globally Coupled Maps

The phenomenon of partial synchronization, or clustering, in a system of globally coupled C ¹-smooth maps is analyzed. We prove the stability of equally populated K-clustered states with n-periodic temporal dynamics, referred to as P _n C _K-states. For this purpose, we first obtain formulas giving a relation between longitudinal and transverse multipliers of the in-cluster periodic orbits, and then, using these formulas, we find exact parameter intervals for transverse stability. We conclude that, typically, for symmetric P _n C _K-states, in-cluster stability implies transverse stability. Moreover, transverse stability can take place even if in-cluster dynamics are unstable.     

无限粘弹介质中圆孔时变问题的解析分析

本文推导粘弹介质中圆孔孔径时变时的应力和位移.由粘弹解与弹性解的对应关系得到粘弹时变应力解.用直接解方程法求径向位移,最终归结为求解关于待定函数的l阶非齐次微分方程.将半径时变函数泰勒展开,用幂级数解法得到一般情况下的解.在寻找定解条件时,采用了对待定函数的光滑化处理,认为在t=0的微小邻域内函数仍满足微分方程,通过积分得到与待定系数数目相同的定解条件,从而获得本问题径向位移解析解.对Maxwell粘弹模型的求解证明了该法的可靠性.文中解适用于任意粘弹模型和孔径任意时变的情况.     

A Film-Flow Model to Describe Free Water Transport during Drying of a Hygroscopic Capillary Porous Medium

In this work, a two-phase film-flow model in a hygroscopic capillary tube is developed and extended to describe the two-phase capillary viscous transport in a network of parallel capillary tubes in terms of relative permeabilities. This film-flow approach is further considered to predict the longitudinal moisture transport in oak wood during drying. Numerical results obtained from this prediction are compared with data of convective drying experiments performed on samples of this wood. The comparison seems to confirm the physical relevance of a film-flow model to correctly represent the moisture transfer until the hygroscopic regime is reached.     

Distinctive Features of the Dynamics of a Bubble Detonation Wave in Tubular Clusters

The distinctive features of the passage of a detonation wave from a tubular body of a bubbly liquid confined by a layer of a “pure” liquid into a region of a homogeneous bubbly liquid are investigated. It is shown that the detonation wave propagating in the tubular bubble cluster can break away on the passage through a region, where the cluster radius increases jumpwise, due to the two-dimensional wave scattering in the expansion zone, despite an increase in the system power-intensity.