致密破碎多孔介质渗透率测量方法

基于均匀各向同性多孔介质、达西渗流和理想气体假设,考虑Klinkenberg效应建立了针对具有纳米尺度孔径的低渗透率多孔介质中的渗流模型。针对致密球形破碎样品的压力脉冲实验,建立了相应的边界条件,同时利用有限差分方法获得其实验腔的压力变化曲线的数值解。通过对渗流方程进行量纲1化,引入了与孔隙率、渗透率和滑移参数有关的量纲1参数Z、Z*和bK。通过改变参数Z、Z*和bK研究了样品边界处压力的变化规律,给出了一种数据处理方法,对于致密球形破碎多孔介质的压力脉冲实验,通过对实验测量的样品边界处压力曲线的分析,结合偏微分方程正问题的数值解,可以确定样品的孔隙率、渗透率和滑移参数,从而更为简便地分析压力脉冲衰减曲线实验数据,得到致密多孔介质样品渗透率。     

泡沫薄膜液在变径管内的流变学特性

针对泡沫流体在储层介质内的流动特点,对泡沫薄膜液在变径管内的流变学特性进行实验研究。基于两相流动假设,利用量纲分析法确定量纲1参数ΔpD/δ及（3μU/σ）^2/3。通过CO₂及N₂泡沫的实验结果发现泡沫薄膜液在变径管内流动时需克服启动压力,量纲1参数间呈明显的线性关系,而且N₂泡沫与CO₂泡沫相比具有更大的流动阻力。与直管相比,泡沫薄膜液在变径管内具有更大的流动压差。实验结果表明,对于揭示泡沫液在多孔介质中的流动机理,Herschel-Bulkley模型优于幂律模型。     

悬浮微粒在被加热多孔介质内的沉积与运移特性

通过建立沿管壁恒热流加热的渗流实验系统,实验研究了悬浮颗粒在饱和多孔介质内以及入口界面处的沉积和运移特性。着重研究了有无加热条件,以及不同加热温差,相同多孔介质和进口悬浮液浓度情况下,实验段入口界面处与内部的颗粒沉积量变化,以及沿程不同位置处的压力变化。并对实验过程中的渗流稳定性及各测点温度和多孔介质段渗透系数进行了分析。结果表明:相对渗透率k_t/k₀在不同温差下有明显不同;多孔介质与进口流体界面处的沉积量随温差的增大而增加,沉积结构的稳定性降低;多孔介质段颗粒沉积强度随温差的增大而增大,实验结果可为今后的理论分析提供验证依据。     

低速横流作用下液体射流初次破碎实验

基于专门搭建的射流破碎雾化实验平台,利用高速摄像可视化研究低速横流作用下不同气液量纲为1参数对液体射流初次破碎模式特征和射流穿透轨迹特征的影响规律。实验结果表明,低速横流作用下液体射流破碎存在柱状破碎和袋式破碎两种模式,其中柱状破碎又可以分为鼓包破碎和拱形破碎。从实验得到的液气动量通量比q和液体韦伯数We_j射流破碎模式图可以看出,液气动量通量比q和液体韦伯数We_j共同决定低速横流条件下射流破碎模式,不同破碎模式之间存在明显的过渡边界。结合液气动量通量比q、液体韦伯数We_j、液体雷诺数Re_j等量纲为1参数,拟合得到了射流穿透轨迹曲线对数形式公式,该公式能够很好地预测低速横流作用下液体射流穿透轨迹,其中液气动量通量比q是影响射流穿透轨迹的主要量纲为1参数。     

高温金属熔液在旋转多孔介质内的渗流传热过程

针对转动坐标系中铝熔液在SiC多孔介质内的流动传热现象 ,考虑离心力对渗流传热过程的影响 ,采用局部非热平衡假设建立多孔介质渗流传热数理模型 ,研究不同工况下流体的流速、压力损失及铝熔液和多孔介质的温度变化 .计算结果表明 :在渗透区域 ,液固两相存在温差 ,且液固温差随渗透界面的移动而减小 ;在非渗透区域 ,固体的温度曲线基本不变 .离心转速或孔隙率的增加都使渗透前沿区域液固两相温差增大 .孔隙率对流场和压力损失有较大影响.     

非弯折织物渗透率的数值预测

采用多孔介质模型替代纤维束区域的方法,数值计算预制件单胞模型的渗透率。平行和垂直方向纤维束分别用平行和垂直多孔介质区域替代,多孔介质阻力系数由最小二乘法拟合得出。首先验证了四方排列平行及垂直方向纤维单胞模型流场计算方法的可靠性;其次验证了纤维单胞多孔介质模型的可靠性;然后通过预制件单胞模型的研究,发现考虑束内渗透率的误差远小于不考虑束内的误差,说明考虑束内流动对准确模拟渗透率是有必要的;最后研究了预制件结构参数对渗透率和孔隙率的影响。纤维束宽度增大,预制件渗透率减小,孔隙率减小。纤维束高度增大,预制件渗透率增大,孔隙率不变。纤维束间距增大,预制件渗透率增大,孔隙率增大。     

液化条件对多孔介质中CO2水合物生成过程的影响

为了研究液化条件对多孔介质中CO₂水合物生成过程的影响机制及其规律,在初始压力为3.9、4.2、4.5、4.8和5.1 MPa,温度为273.5、274.5和275.5 K条件下研究粒径为700μm的石英砂介质中CO₂水合物的生成过程。结果表明：在相同条件下,随着初始压力的增加,多孔介质中CO₂水合物的生成速率逐渐增大;当压力低于液化压力时,随着初始压力的增加,CO₂水合物的生成速率逐渐增大,且温度越高,水合物生成速率增加的趋势越明显;当CO₂气体压力达到液化压力时,随着初始压力的不断升高,CO₂水合物的生成速率明显增大;多孔介质中CO₂水合物的最大生成速率达到了9.297×10^-3 mol·s^-1。研究结果进一步表明：液化可有效强化多孔介质中CO₂水合物的生成过程,提高CO₂水合物的生成速率。     

孔隙分布对多孔介质内流动和传热的影响

采用Sierpinski地毯分形技术建立多孔介质内流动和传热模型,通过改变固体基质位置研究了孔隙分布结构对多孔介质内流动特性和热效率的影响,3种孔隙分布为每分形一次固体基质分布在中心位置(A)、分布在中上方(B)和分布在右上方(C),当流体稳定流过多孔介质时,不同的孔隙分布表现出不同流动和传热特性. 结果表明,孔隙分布是影响多孔介质传输特性和传热效率的重要因素,无量纲渗透率k*C>k*B>k*A,多孔介质孔隙率大于0.8时更明显;流体流过不同孔隙分布的多孔介质时,相同孔隙率时与流体接触的固体基质面积A>B>C,传热效果A最佳、C最差. 孔隙分布影响了无量纲局部熵产率,在3种孔隙分布下用Be表示的热传导引起的熵产率占主导.     

K2CO3和CaCO3对低温制备SiC多孔陶瓷性能的影响

采用固相反应法制备SiC多孔陶瓷,通过添加二元复合烧结助剂K₂CO₃和CaCO₃与SiC在空气气氛下氧化生成的SiO₂在较低温度下生成低共融相,促进SiC多孔陶瓷在1100℃-1200℃温度下烧成。研究烧成温度、K₂CO₃和CaCO₃添加量对SiC多孔陶瓷的抗弯强度、显气孔率、气体渗透率、相组成和显微结构的影响。结果表明：当K₂CO₃和CaCO₃添加量分别为1wt%和1wt%,在空气气氛下1100℃保温3h制备的样品综合性能较佳,抗弯强度为33.6MPa,显气孔率为36.3%,气体渗透率为728m³/(m²·h·KPa)。     

毛细吸液芯冷却顶板流动阻力及制冷特性

基于现有空调系统耗能高,舒适性不够均匀,提出了多孔介质柠檬酸钾-石膏配制而成的毛细吸液芯辐射-冷却顶板,在用水作冷却介质时毛细吸液芯辐射-冷却顶板就成了一块内含多孔介质的均布流道。对以多孔介质孔隙率为55.3%的毛细吸液芯为例,水作为载冷剂流过毛细吸液芯冷却顶板进行了实验研究。介绍了毛细吸液芯冷却顶板的结构和内部配置,并通过搭建实验模型在维持室内温度（26±1）℃分布的情况下对其换热量进行了测试,分析了不同流量条件下流量与阻力的关系。结果表明,在冷水进口温度为10～16℃的条件下,相比常规蛇形辐射管,制冷量提高了36.6%～57.7%,当水流量从4 L·h^-1变化到28 L·h^-1时,黏性力减弱,摩擦因子逐渐减小,渗透率逐渐增大,但当流量从28 L·h^-1变化到40 L·h^-1时,渗透率开始减小。     

PEO/聚吡咯中空纳米微球混合基质膜的制备及其CO2渗透分离性能

采用壳层具有介孔结构的聚吡咯中空纳米微球作为填料，和聚氧化乙烯单体共混自由基聚合制备了混合基质膜。结果表明，聚吡咯微球与基质相容性较好，未见明显团聚现象和缺陷。混合基质膜的渗透系数随填料含量的增加先增大后减少，在0.5%处达到最大值，CO₂渗透系数增长31%；CO₂/N₂分离系数有所降低，CO₂/CH₄分离系数则变化不大。研究表明，由于聚合物链段对微球壳层的介孔填充，气体在膜内的扩散系数不升反降，渗透系数的提高主要是由于溶解度系数的变化，而这也导致了溶解选择性的变化，进而影响了分离系数。     

Influence of Air Compressibility on the Permeability Evaluation of Refractory Castables

Air compressibility is important in attaining an accurate quantification of the permeability parameters for refractory castables. Nevertheless, this effect is often neglected in the permeability equations that are found in ceramics literature. The consequences of omitting the compressibility effect in two of the main permeability equations are highlighted and discussed. The permeability to air flow of high-Al₂O₃ ultra-low-cement refractory castables has been quantified by Darcy's law according to U.S. ASTM C577–96 and European PRE-16th permeability methods, which propose distinct approaches for air compressibility. Forchheimer's equation, which establishes a more realistic dependence between fluid pressure and fluid velocity, also has been used to obtain the permeability constants k ₁ and k ₂. Results show that equations proposed by the ASTM and the PRE methods may yield very distinct values of Darcian permeability k ₁ for the same sample. Forchheimer's equation for compressible fluids provides the best fitting with experimental data.     

High-Temperature Active Oxidation of Chemically Vapor-Deposited Silicon Carbide in CO─CO2 Atmosphere

Active oxidation behavior of CVD-SiC in CO─CO₂ atmospheres was investigated using a thermogravimetric technique in the temperature range between 1823 and 1923 K. The gas pressure ratio, P _CO2/ P _CO, was controlled between 10⁻⁴ and 10⁻¹ at 0.1 MPa. Active oxidation rates (mass loss rates) showed maxima at a certain value of P _CO2/ P _CO, ( P _CO2/ P _CO )^*, In a P _CO2/ P _CO region lower than the ( P _CO2/ P _CO)^* a carbon layer was formed on the SiC surface. In a P _CO2/ P _CO region higher than the ( P _CO2/ P _CO)^*, silica particles or a porous silica layer was observed on the SiC surface.     

Use of Stabilized ZrO2 to Measure O2 Permeation

The rate of permeation of CaO-stabilized ZrO₂ (CSZ) by O₂ gas was measured from 640° to 1200°C with the CSZ tubing used simultaneously as the sample and the O₂ pressure detector. The apparent permeation rate depended significantly on the O₂ pressure at the low-pressure side. The rate measured by this method was orders of magnitude smaller than that measured under steady-state conditions, except when the O₂ partial pressure was high (>10⁻⁴ atm), in which case the agreement was good. The difference between steady-state permeability and non-steady-state permeability is related to the deviation in stoichiometry in a sample or detector. The transient response (measured under variable pressure difference) may be very different from steady-state permeation (measured under constant differential pressures across the membranes). To apply CSZ to typical O₂ gas permeability measurements, the O₂ pressure must be kept above ∼ 10^−3.5 atm. In this range, the permeability of CSZ may be regarded as a temperature-dependent material property which is governed by the electron-hole mobility. At lower O₂ pressures the permeation rate is a more complex function of the pressure difference and level.     

Assessment of Forchheimer's Equation to Predict the Permeability of Ceramic Foams

Correct estimation of the pressure drop in filtration processes that involve fluid velocity variations is of major importance, because it allows the filtration rate and/or the energy consumed on fluid flow to be more accurately controlled. Permeability of porous filters has been often described by Forchheimer's equation, which establishes a nonlinear dependence between pressure drop and fluid velocity. Two constants, k ₁ and k ₂, dependent only on the medium, quantify the viscous and inertial effects on the pressure drop curve. In this work, experimental data of airflow through 10 pores per linear inch ceramic foam filters are used to show that a single sample may have completely distinct permeability constants depending on the data range chosen for analysis. The Darcian permeability constant k ₁ displays higher variation than the non-Darcian permeability constant k ₂. The conclusion is that special attention must be taken to represent permeability of highly porous structures in a large velocity range. The predictability of Forchheimer's equation generally worsens when less data are included in the curve fitting, particularly at low velocities. Careful consideration should be made if constants k ₁ and k ₂ are intended to be used for permeability estimation beyond the fitting range.     

Optical Study of Lithium–Bismuth–Borate Glasses

Glasses with compositions x Bi₂O₃(75− x )B₂O₃25Li₂O₃ for 0≤ x ≤40 mol% have been prepared using the normal melt-quenching technique. The optical absorption and reflection spectra were recorded at room temperature in the wavelength range 190–1100 nm. From the absorption edge studies, the values of the optical band gap ( E _opt) and Urbach energy (Δ E ) have been evaluated. Optical parameters such as refractive index and complex dielectric constant have been determined. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. Color parameters and color difference data L ^*, U ^*, V ^*, C ^*, h _ue, W , Y _e, Δ L ^*, Δ U ^*, Δ V ^*, Δ C ^*, and Δ E have been calculated.     

基于GA-BP神经网络的超临界CO2传热特性预测研究

超临界二氧化碳（S-CO₂）动力循环在能源利用领域中拥有广阔的应用前景,其中超临界CO₂的传热特性对其能量转换效率至关重要。开展了超临界CO₂在水平小圆管内对流传热实验研究,并通过建立遗传算法优化的BP神经网络模型（GA-BP）,对其在不同工况下的传热特性进行预测分析。实验参数范围：系统压力7.5~9.5 MPa,质量流速1100~2100 kg/（m²?s）,热通量120~560 kW/m²。实验结果表明,超临界CO₂传热系数随流体温度的升高先增大后减小,在拟临界温度附近达到最大值。GA-BP神经网络模型能有效地预测超临界CO₂的传热系数,预测数据的决定系数R²为0.99662,超过95%的数据误差位于±10%范围内,平均误差为3.55%,为超临界流体传热预测提供新的思路。     

Data Driven Order Selection for Projection Estimator of the Spectral Density of Time Series with Long Range Dependence

Fractional exponential (FEXP) models have been introduced by Robinson (1991) and Beran (1993) to model the spectral density of a covariance stationary long-range dependent process. In this class of models, the spectral density f ( x ) of the process is decomposed as f ( x ) = |1 − exp( ix )|^{−2 d} f _*( x ), where f _*( x ) accounts for the short-memory component. In this contribution, FEXP models are used to construct semi-parametric estimates of the fractional differencing coefficient and of the spectral density, by considering an infinite Fourier series expansion of log f _*( x ). A data-driven order selection procedure, adapted from the Mallows' C _p procedure, is proposed to determine the order of truncation. The optimality of the data-driven procedure is established, under mild assumptions on the short-memory component f _*( x ). A limited Monte-Carlo experiment is presented to support our claims.     

Field-Property Bounds for Porous Sintered Ceramics

Three sets of equations provide upper and lower values bound ing the experimentally obtained electrical and thermal conduc tivities as well as the magnetic permeabilities (="field properties") of porous ceramics. These equations are as I-order upper bound: φ _p=φ_M (1 -P ) (φ=effective field property of the porous material, φ_M=field property of the nonporous material, P =porosity), and as I-order lower bound: φ_r=φ_M (1- P )⁷. Closer bounds corresponding to isotropic porous materials are the II-order upper bound: φ_P^II ,= φ _M ,[2(1- P)/ (2+P)], and the II-order lower bound: φ_PIII=φ_M(1- P)³ . Even closer bounds, referring to isotropic porous materials containing closed, unconnected pores are the III-order upper bound: φ_P^III = φ _M (1- P)^3/2 , and the III-order lower bound: φ_PIII = φ_M(1- p)3 .     

An experimental, numerical and analytical investigation of gas flow characteristics in concrete

A series of tests are reported which used existing pressure cell apparatus to measure nitrogen gas flow in concrete. A finite difference numerical model is described which is used to investigate the time to reach steady state and the long-term transient response of the experimental system. An analytical solution is derived for the cell-pressure-time function from which a formula is derived for the intrinsic permeability coefficient. The permeabilities calculated from the experimental data have variations consistent with those from other investigations. The analytical solution matches the experimental pressure-time decay curves closely in the range of interest but there is a tendency for the curves to diverge for lower cell pressures. This is attributed to gas slippage and modifications to both the numerical and analytical solutions are described to account for this factor. Revised formulae are derived which give both the intrinsic permeability and Klinkenberg factor. These are then applied to the present experimental data and results compared with those from the literature.