Modelling of Rigid-Frame Porous Materials: A Simple Approach

2000 ◽  
Author(s):  
M. J. Brennan ◽  
W. M. To
Keyword(s):  
Porous Material ◽  
Porous Materials ◽  
Characteristic Impedance ◽  
Simple Approach ◽  
Middle Ground ◽  
Acoustic Behaviour ◽  
Rigid Frame ◽  
Flow Resistivity ◽  
Stiffness And Damping ◽  
Optimum Flow

Abstract This paper is concerned with the modelling of rigid-frame porous materials. Currently there are very simple models which describe the acoustic behaviour of such materials, and there are also very complicated models. The aim of this paper is to present a model which occupies the “middle ground”, but is simple enough to be used by practising noise control engineers. Using concepts of acoustic mass, stiffness and damping, non-dimensional expressions for the acoustic wavenumber and the characteristic impedance of a rigid-frame porous material are derived. These expressions are used to give a “rule of thumb” for the optimum flow resistivity for a given thickness of material.

Research on Stiffness and Damping Characteristics of Fixed Oily Porous Materials Joint Interface

2011 ◽  
Vol 422 ◽  
pp. 575-579
Author(s):  
Chong Nian Qu ◽  
Liang Sheng Wu ◽  
Jian Feng Ma ◽  
Yi Chuan Xiao
Keyword(s):  
Porous Material ◽  
Porous Materials ◽  
Parallel Plate ◽  
Joint Interface ◽  
Force Model ◽  
Equivalent Stiffness ◽  
Contact State ◽  
Damping Characteristics ◽  
Stiffness And Damping ◽  
Damping Model

In this document, using the anti-squeezed force model in the narrow parallel plate when fluid is squeezed, the equivalent stiffness and damping model is derived. It is further verified that it can increase the stiffness and damping while there are oil between the joint interfaces theoretically. Because the contact state of oily porous material can divide into liquid and solid parts, the document supposes that it is correct and effective to think the stiffness and damping of the two parts as shunt connection.

Flow resistivity, characteristic impedance and complex wave number assessment of coconut fiber with thin thickness samples.

2017 ◽  
Author(s):  
Key Fonseca de Lima ◽  
Nilson Barbieri ◽  
Fernando Jun Hattori Terashima ◽  
Vinicius Antonio Grossl ◽  
Nelson Legat Filho
Keyword(s):  
Characteristic Impedance ◽  
Wave Number ◽  
Coconut Fiber ◽  
Complex Wave ◽  
Flow Resistivity ◽  
Complex Wave Number

scholarly journals Diffuse Sound Absorptive Properties of Parallel-Arranged Perforated Plates with Extended Tubes and Porous Materials

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1091 ◽  
Author(s):  
Dengke Li ◽  
Daoqing Chang ◽  
Bilong Liu
Keyword(s):  
Boundary Condition ◽  
Porous Material ◽  
Porous Materials ◽  
Sound Absorption ◽  
Azimuthal Angle ◽  
Octave Band ◽  
Frequency Range ◽  
Absorption Coefficients ◽  
Perforated Plates ◽  
Absorption Performance

The diffuse sound absorption was investigated theoretically and experimentally for a periodically arranged sound absorber composed of perforated plates with extended tubes (PPETs) and porous materials. The calculation formulae related to the boundary condition are derived for the periodic absorbers, and then the equations are solved numerically. The influences of the incidence and azimuthal angle, and the period of absorber arrangement are investigated on the sound absorption. The sound-absorption coefficients are tested in a standard reverberation room for a periodic absorber composed of units of three parallel-arranged PPETs and porous material. The measured 1/3-octave band sound-absorption coefficients agree well with the theoretical prediction. Both theoretical and measured results suggest that the periodic PPET absorbers have good sound-absorption performance in the low- to mid-frequency range in diffuse field.

Turbulent Dispersion in Porous Materials as Modeled by a Mixing Cell with Stagnant Zone

1971 ◽  
Vol 11 (01) ◽  
pp. 57-62
Author(s):  
C.R. Kyle ◽  
R.L. Perrine
Keyword(s):  
Porous Material ◽  
Turbulent Flow ◽  
Porous Materials ◽  
Molecular Diffusion ◽  
Stagnant Zone ◽  
Skewed Distribution ◽  
Capillary Tubes ◽  
Fluid Movement ◽  
The Media ◽  
Flow Through

Abstract This paper reports on a simple theoretical analysis of dispersion in rapid flow through porous materials, giving a comparison of predicted results with experiments. The analytical model considers a pore structure which acts like a sequence of mixing cells, each coupled with a stagnant zone. Computed results compare very favorably with experimental observations on flow through a staggered matrix of cylinders. This, in turn, has been shown to behave the packed beds of spheres with corresponding properties. Agreement requires that values for certain theoretical parameters be fitted from the data The values required for these parameters are very reasonable. Development of parameters are very reasonable. Development of this approach could be useful for a number of related problems. Introduction The dispersion of two dynamically similar miscible liquids in laminar or turbulent flow through a porous material is a very complex process. However, it can be broken down into four process. However, it can be broken down into four basic mixing mechanisms:Molecular diffusion. Where the flow velocity is appreciable, or pore size is larger, diffusion is usually negligible. Molecular diffusion will not be discussed in this paper.Uneven fluid movement due to irregular pore geometry and inhomogeneities in the media. Both of these factors are difficult to treat, and are usually neglected in theoretical analysis.Uneven fluid movement due to velocity differences within the pores and passages. The zero-velocity boundary condition on each solid surface assures this type of mixing in both laminar and turbulent flow.Mixing by rotational flow, or by turbulent eddies within the pores or passages. The last two are both convective mixing processes and depend primarily upon the level of processes and depend primarily upon the level of energy dissipation in the media, as well as on the geometry of the system. In general as the velocity increases and the friction losses rise, so does the efficiency of the mixing process. Dispersion has been reviewed thoroughly by Perkins and Johnston and has been studied Perkins and Johnston and has been studied extensively by others. DIFFUSION MODEL OF DISPERSION The most commonly used mathematical model for dispersion in both laminar and turbulent flow is a diffusion-type equation (Refs. 1 or 5). The solution for a step function input with flow in the x-direction only, and with negligible lateral gradients, shows that an initial sharp interface degenerates into a broad mixing zone which grows approximately as the square root of the distance traveled. The solution also predicts a normal distribution for concentration as a function of distance. However, in most real systems "tailing" occurs, causing a skewed distribution. Usually the deviation is not serious and the diffusion equation may be used as a good approximation for the actual process. process. DISPERSION IN A TUBE Another simple model for laminar dispersion, neglecting molecular diffusion, is to consider a porous material as a bundle of capillary tubes. porous material as a bundle of capillary tubes. Sir Geoffrey Taylor showed that if one fluid in a capillary tube is displaced by another dynamically similar miscible fluid, the average concentration, C, at the tube exit is given by: 2C = (V /2V)p SPEJ P. 57

The Effect of Porous Material on the Improvement of the Micro-Chip Heat Dissipation

2008 ◽  
Author(s):  
Chyouhwu B. Huang ◽  
Hung-Shyong Chen ◽  
Szu-Ming Wu
Keyword(s):  
Heat Transfer ◽  
Porous Material ◽  
Porous Materials ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Dissipation ◽  
Porous Ceramic ◽  
High Heat ◽  
Force Convection ◽  
Uninterruptible Power

Heat dissipation is a very important subject when dealing with industrial application especially in modern semiconductor related applications. Several techniques have been developed to solve the heat generated problem, such as heat dissipation device in IC packaging, high heat conductivity materials, heat tube, force convection, etc. Porous material is used in this study. Porous material is known to have large interior surface, therefore, with proper force convection; it can easily carry heat away. Micro porous ceramic (porous size: 490 μm) is attached to uninterruptible power supply (UPS) power chips. The increase of the heat dissipation rate improves UPS performance. Heat transfer properties comparisons for power chip with and without micro porous materials attached are studies. Also, heat transfer rate under different fan speeds (force convection) is studied. The results show that, heat transfer increases with the use of micro porous materials, the effectiveness ranges between 2–22%. Also, the heat transfer rate varies with air flow rate, the increase of heat transfer is about 4–6%. The dust effect was also performed; experimental results show that heat transfer rate will not be affected by the accumulated dust if a micro porous material is applied.

Deterministic and statistical characterization of rigid frame porous materials from impedance tube measurements

2017 ◽  
Vol 142 (4) ◽  
pp. 2407-2418 ◽  
Author(s):  
M. Niskanen ◽  
J.-P. Groby ◽  
A. Duclos ◽  
O. Dazel ◽  
J. C. Le Roux ◽  
...  
Keyword(s):  
Porous Materials ◽  
Statistical Characterization ◽  
Impedance Tube ◽  
Rigid Frame
Sign in / Sign up

Export Citation Format

Share Document