scholarly journals Experimental study on the permeability of crushed coal medium based on the Ergun equation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mingkun Pang ◽  
Tianjun Zhang ◽  
Yukai Meng ◽  
Zhiqiang Ling
Keyword(s):  
Reynolds Number ◽  
Porous Medium ◽  
Accurate Determination ◽  
Test System ◽  
Ergun Equation ◽  
Permeability Characteristics ◽  
Number Distribution ◽  
Coal Particles ◽  
Depth Analysis

AbstractAccurate determination of the permeability of crushed coal medium is the basis for the study of their permeability characteristics. To investigate the permeability characteristics of this special porous medium composed of crushed coal particles, the permeability parameters of crushed coal specimens of different initial porosities were measured by designing a lateral-limit compression seepage test system. Parameters were determined separately for specimens of different initial porosities. (1) the Reynolds number distribution region characterising the seepage state was determined and obtained. Specimens with initial porosity distribution between 0.02 and 0.08, and seepage Reynolds number distribution in the low-permeability zone, under Darcy flow; (2) the intrinsic permeability of the crushed coal medium was obtained by using the Ergun equation. The complex inverse proportional relationship between the drag coefficient and Reynolds number was derived; (3) Through the determination of the permeability of the crushed coal medium, the mean value of βK value was obtained to be about 45.7, and the analysis of the permeability of porous medium can determine its critical permeability. The relationship between the Forchheimer number Fo and critical Reynolds number was measured. The results indicate that it conforms to a linear distribution. In-depth analysis of these two parameters can be used to explore the flow transition process between laminar, transition, and turbulent flow. This study provides insight into the permeability characteristics of the media in fractured coal bodies.

The Effect of Inlet and Exit Pressure-Drop on the Determination of Porous Media Permeability and Form Coefficient

2005 ◽  
Author(s):  
Christian Naaktgeboren ◽  
Paul S. Krueger ◽  
Jose´ L. Lage
Keyword(s):  
Reynolds Number ◽  
Porous Medium ◽  
Porous Media ◽  
Pressure Drop ◽  
Turbulent Pipe Flow ◽  
Flow Adjustment ◽  
Medium Length ◽  
Exit Pressure ◽  
Flow Through

The determination of permeability and form coefficient, defined by the Hazen-Dupuit-Darcy (HDD) equation of flow through a porous medium, requires the measurement of the pressure-drop per unit length caused by the medium. The pressure-drop emerging from flow adjustment effects between the porous medium and the surrounding clear fluid, however, is not related to the porous medium length. Hence, for situations in which the entrance and exit pressure-drops are not negligible, as one would expect for short porous media, the determination of the hydraulic parameters using the HDD equation is hindered. A criterion for determining the relative importance of entrance and exit pressure-drop effects, as compared to core effect, is then of practical and fundamental interest. This aspect is investigated analytically and numerically considering flow through a thin planar restriction placed in a circular pipe. Once the pressure-drop across the restriction is found, the results are then compared to the pressure-drop imposed by an obstructive section having the same dimension as the restriction but finite length, playing the role of the least restrictive porous medium core. This comparison yields a conservative estimate of the porous medium length necessary for neglecting entrance and exit pressure-drop effects. Results show that inlet and exit pressure-drop effects become increasingly important compared to core effects as the porosity decreases and Reynolds number increases for both laminar and turbulent flow regimes. (Correlations based on experimental results available in the literature are employed for turbulent pipe flow). The analysis also shows why the HDD equation breaks down when considering flow through porous media where the entrance and exit pressure-drop effects are not negligible, and how modified permeability and form coefficients become necessary to characterize this type of porous media. Curve-fits accurate to within 2.5% were obtained for the modified permeability and form coefficients of the planar restriction with Reynolds number ranging from 0.01 to 100 and porosity from 0.0625 to 0.909.

scholarly journals Investigating the effects of effective stress on pore-dependent permeability measurements of crushed coal

PLoS ONE ◽  
2021 ◽  
Vol 16 (12) ◽  
pp. e0261678
Author(s):  
Mingkun Pang ◽  
Tianjun Zhang ◽  
Lu Gao ◽  
Binfeng Qin
Keyword(s):  
Porous Media ◽  
Effective Stress ◽  
Calculation Method ◽  
Accurate Determination ◽  
Coal Particles ◽  
Exploratory Stage ◽  
Median Particle ◽  
Fractured Coal ◽  
Dependence Relationship

The accurate determination of permeability is one of the parameters essential for the study of fluid flow and transport state. However, a large number of fractured coal bodies are faced during the production of coal mines. The study of permeability of these special media composed of grains of a certain size, whose structure is different from that of raw coal, has been in the exploratory stage. In this paper, inspired by the calculation method of median particle size and the calculation principle of KC’s equation, we calculate the permeability parameters of broken coal particles. It is considered that its permeability is closely related to the compaction and re-crushing process of skeletal grains. The lateral limit compression test of the crushed coal body was designed, and the pore-dominated permeability calculation method was given to reveal the mechanism of the action of the effective stress. The dependence relationship between the effective stress and the pore-correlation permeability is obtained by data analysis, and the force and deformation process of the crushed coal grain media is described. In contrast to the conventional Darcy series of permeability discussions, our approach excludes the influence of fluid factors on the permeability of porous media. The permeability of porous media is considered to be determined only by its own pore structure.

A quantitative approach to inner shell losses

1978 ◽  
Vol 36 (1) ◽  
pp. 526-527 ◽  
Author(s):  
R.D. Leapman ◽  
P. Rez ◽  
D.F. Mayers
Keyword(s):  
Energy Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Accurate Determination ◽  
Background Intensity ◽  
Core Excitation ◽  
Quantitative Basis ◽  
Cross Section Differential ◽  
Bound Electrons

Microanalysis by EELS has been developing rapidly and though the general form of the spectrum is now understood there is a need to put the technique on a more quantitative basis (1,2). Certain aspects important for microanalysis include: (i) accurate determination of the partial cross sections, σx(α,ΔE) for core excitation when scattering lies inside collection angle a and energy range ΔE above the edge, (ii) behavior of the background intensity due to excitation of less strongly bound electrons, necessary for extrapolation beneath the signal of interest, (iii) departures from the simple hydrogenic K-edge seen in L and M losses, effecting σx and complicating microanalysis. Such problems might be approached empirically but here we describe how computation can elucidate the spectrum shape.The inelastic cross section differential with respect to energy transfer E and momentum transfer q for electrons of energy E0 and velocity v can be written as

Fast calibration of CBED patterns for quantitative analysis

1993 ◽  
Vol 51 ◽  
pp. 674-675
Author(s):  
M.A. Gribelyuk ◽  
M. Rühle
Keyword(s):  
Reciprocal Lattice ◽  
Accurate Determination ◽  
Incident Beam ◽  
Crystal Thickness ◽  
Structure Model ◽  
Beam Direction ◽  
Transmitted Beam ◽  
Reciprocal Vector ◽  
On Line

A new method is suggested for the accurate determination of the incident beam direction K, crystal thickness t and the coordinates of the basic reciprocal lattice vectors V1 and V2 (Fig. 1) of the ZOLZ plans in pixels of the digitized 2-D CBED pattern. For a given structure model and some estimated values Vest and Kest of some point O in the CBED pattern a set of line scans AkBk is chosen so that all the scans are located within CBED disks.The points on line scans AkBk are conjugate to those on A0B0 since they are shifted by the reciprocal vector gk with respect to each other. As many conjugate scans are considered as CBED disks fall into the energy filtered region of the experimental pattern. Electron intensities of the transmitted beam I0 and diffracted beams Igk for all points on conjugate scans are found as a function of crystal thickness t on the basis of the full dynamical calculation.

Computer-Assisted High-Re Solution TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 162-163
Author(s):  
F.A. Ponce ◽  
H. Hikashi
Keyword(s):  
Signal To Noise Ratio ◽  
Accurate Determination ◽  
Computer Software ◽  
Video Camera ◽  
Image Contrast ◽  
Objective Lens ◽  
Computer Assisted ◽  
Optical Parameters ◽  
Astigmatism Correction

The determination of the atomic positions from HRTEM micrographs is only possible if the optical parameters are known to a certain accuracy, and reliable through-focus series are available to match the experimental images with calculated images of possible atomic models. The main limitation in interpreting images at the atomic level is the knowledge of the optical parameters such as beam alignment, astigmatism correction and defocus value. Under ordinary conditions, the uncertainty in these values is sufficiently large to prevent the accurate determination of the atomic positions. Therefore, in order to achieve the resolution power of the microscope (under 0.2nm) it is necessary to take extraordinary measures. The use of on line computers has been proposed [e.g.: 2-5] and used with certain amount of success.We have built a system that can perform operations in the range of one frame stored and analyzed per second. A schematic diagram of the system is shown in figure 1. A JEOL 4000EX microscope equipped with an external computer interface is directly linked to a SUN-3 computer. All electrical parameters in the microscope can be changed via this interface by the use of a set of commands. The image is received from a video camera. A commercial image processor improves the signal-to-noise ratio by recursively averaging with a time constant, usually set at 0.25 sec. The computer software is based on a multi-window system and is entirely mouse-driven. All operations can be performed by clicking the mouse on the appropiate windows and buttons. This capability leads to extreme friendliness, ease of operation, and high operator speeds. Image analysis can be done in various ways. Here, we have measured the image contrast and used it to optimize certain parameters. The system is designed to have instant access to: (a) x- and y- alignment coils, (b) x- and y- astigmatism correction coils, and (c) objective lens current. The algorithm is shown in figure 2. Figure 3 shows an example taken from a thin CdTe crystal. The image contrast is displayed for changing objective lens current (defocus value). The display is calibrated in angstroms. Images are stored on the disk and are accessible by clicking the data points in the graph. Some of the frame-store images are displayed in Fig. 4.

Sign in / Sign up

Export Citation Format

Share Document