CN102507394B - Method for measuring effective diffusion coefficient and porosity of porous medium - Google Patents

Abstract

A method for measuring the effective diffusion coefficient and the porosity of a porous medium includes steps as follows: using an evaporation tube method to measure the binary gas diffusion coefficient DAB of component A in component B and the effective diffusion coefficient DABP of component A in the measured porous medium, utilizing the relation between DAB and DABP to work out the ratio epsilon/tau of the measured porous medium porosity to the tortuosity factor, and obtaining the porosity of the measured porous medium according to the tortuosity factor tau. The invention has the advantage of rapidly and accurately measuring the porosity of the porous medium and the effective diffusion coefficient of a gas in the porous medium, thereby providing conditions for chemical engineering and scientific research practice.

Description

A kind of mensuration porous medium effective diffusion cofficient and porosity method

Technical field

The invention belongs to technical field of measurement and test, relate in particular to porous medium effective diffusion cofficient and measurement method of porosity method.

Background technology

Diffusion process spreads all over the chemical engineering every field, for example catalysis, absorption and processes such as film separates, and the diffusion of fluid mixture in porous medium is the deciding factor of decision process performance.Gas spreads to be different from free medium in porous medium and spreads, owing to be subjected to the resistance of solid dielectric, its corresponding coefficient of diffusion will reduce to some extent.Different porosints has different porositys and tortuosity.Therefore porosity and the effective diffusion cofficient of gas in porous medium of measuring porosint quickly and accurately all have great importance in chemical industry and research work.The method of measuring porosity of porous material in the prior art generally is to use the pressure-volume method, the shortcoming of this method is to measure more loaded down with trivial detailsly, is not easy to measure fast and accurately, can not adapt to the actual needs of chemical industry and scientific research, and test gas is toxic, and human body and environment are had harm.

One, summary of the invention

The objective of the invention is to propose the effective diffusion cofficient of a kind of mensuration gas, particularly steam in porous medium, and then obtain the method for porosity of porous material according to the diffusion principle of a component by another static component.

Technical scheme of the present invention is: a kind of mensuration porous medium effective diffusion cofficient and porosity method comprise and measure the binary gas diffusion coefficient D of component A in B component _ABThe evaporation tube method, be about to liquid component A and inject the evaporation tube bottom, evaporation tube is put into convection oven perpendicular to surface level, gassy B component in the convection oven keeps temperature T and pressure p in the convection oven constant; The original liquid level position of record air blast temperature of oven T, evaporation tube bottom liquid component A is apart from the distance z of the evaporation tube mouth of pipe ₀With the distance z of the position that drops to through evaporation tube bottom liquid component A liquid level behind the certain hour θ apart from the evaporation tube mouth of pipe; T, p, z with record ₀Bring formula into z

$D_{\mathrm{AB}}=\frac{{\mathrm{RTp}}_{\mathrm{BM}}{\mathrm{\ρ}}_{\mathrm{AL}}(z^2-z_0^2)}{2p{M}_A\mathrm{\θ}(p_{A1}-p_{A2})}---\left(1\right)$

Calculate the diffusion coefficient D of component A in B component _AB, in the formula

p _A1---the saturated vapor pressure of liquid component A under the condition determination (from " chemical industry solvent handbook is discovered and seized), Pa;

p _A2---liquid component A is at the dividing potential drop (learning by calculating) at mouth of pipe place, Pa;

D _AB---liquid component A steam is at the coefficient of diffusion of B component, m ²/ s;

P---general pressure, 1.0134 * 10 ⁵Pa;

R---gas law constant, 8.314 * 10 ³Nm/ (kmolK);

T---thermodynamic temperature, K;

The position that the evaporation tube bottom liquid component A liquid level of z---record descends is apart from the distance of the evaporation tube mouth of pipe, m;

z ₀---the original liquid level position of the evaporation tube bottom liquid component A of record is apart from the distance of the evaporation tube mouth of pipe, m;

ρ _AL---the density of liquid component A, kg/m ³

M _A---the molal weight of liquid component A, kg/kmol;

θ---the liquid level of evaporation tube bottom liquid component A descends the used time s;

p _BM---the logarithmic mean dividing potential drop of B component, Pa; Computing formula is

p _B2＝p-p _A2

p _B1＝p-p _A1

p _B2-p _B1＝p _A1-p _A2

$p_{\mathrm{BM}}=\frac{P_{B2}-p_{B1}}{\ln \frac{p_{B2}}{p_{B1}}}---\left(2\right)$

It is characterized in that described mensuration porous medium effective diffusion cofficient and porosity method are further comprising the steps of:

1) liquid component A is injected the evaporation tube bottom, tested porous medium is made film, tested porous Jie's film is covered at evaporation tube mouth of pipe place and air-dry with fluid sealant, the tube wall at tested porous dielectric film and evaporation tube mouth of pipe place is sealed;

2) will seal good evaporation tube and put into convection oven perpendicular to surface level, gassy B component in the convection oven keeps temperature T and pressure p in the baking oven constant;

3) with measuring the binary gas diffusion coefficient D of component A in B component _ABThe evaporation tube method calculate component A that the mouth of pipe covers tested porous Jie's film locates component A below porous dielectric film dividing potential drop P _Ax, utilize the P that obtains _Ax, by component A mass balance in porous Jie film, getting component A by the binary gas coefficient of diffusion of diffusion B component in porous Jie film, this coefficient of diffusion is the effective diffusion cofficient D of A component in tested porous Jie's film _ABPEffective diffusion cofficient D _ABPSpecifically be calculated as follows: because component A is by the diffusion flux N of free section and perforated membrane section _AEquate, namely

$N_A=\frac{{\mathrm{\ρ}}_{\mathrm{AL}}}{M_A}\·\frac{\mathrm{dz}}{\mathrm{d\θ}}=\frac{D_{\mathrm{ABP}}p}{\mathrm{RTl}{p}_{\mathrm{BM}}^{,}}\·(p_{\mathrm{AX}}-p_{A2})---\left(3\right)$

The arrangement following formula gets

$D_{\mathrm{ABP}}=\frac{{\mathrm{\ρ}}_{\mathrm{AL}}\mathrm{RTl}{p}_{\mathrm{BM}}^{,}}{p{M}_A\mathrm{\θ}}\·\frac{z-z_0}{p_{\mathrm{AX}}-p_{A2}}---\left(4\right)$

This computing formula is that the evaporation tube method is measured the binary gas of component A in B component by the effective diffusion cofficient D of porous dielectric film _ABPComputing formula.

4) use diffusion coefficient D _ABWith effective diffusion cofficient D _ABPBetween reduction formula:

$D_{\mathrm{ABP}}=\frac{\mathrm{\ϵ}{D}_{\mathrm{AB}}}{\mathrm{\τ}}---\left(5\right)$

Calculate tested porous medium porosity, namely

$\mathrm{\ϵ}=\frac{\mathrm{\τ}{D}_{\mathrm{ABP}}}{D_{\mathrm{AB}}}---\left(6\right)$

The porosity of ε in the formula---porosu solid, m ³/ m ³

τ---tortuous factor.

A kind of mensuration porous medium effective diffusion cofficient of the present invention and porosity method is characterized in that: the thickness of tested porous dielectric film is 0.1-0.5mm;

Evaporation tube bottom liquid component A is water or ethanol, and described gas B is air; Temperature T in the baking oven is 293K≤T≤323K, and described pressure p is normal pressure.

Principle of the present invention is:

Measuring the binary gas coefficient of diffusion of component A in B component with the evaporation tube method is to measure component A at the coefficient of diffusion of free media components B, after covering tested porous Jie's film at evaporation tube mouth of pipe place, component A is divided into two sections by the diffusion of B component, one section is freely to spread, another section is to spread by porous medium, two sections are carried out mass balance at component A respectively, in B component under the free coefficient of diffusion situation, the unknown number of free section mass balance is the component A dividing potential drop P of porous Jie film below at known component A _Ax, obtaining P _AxBe exactly effective diffusion cofficient in the porous medium to second section unknown number that carries out in the mass balance later on.The component A that records use the same method again at the coefficient of diffusion of B component, increased the process that component A spreads in tested porous dielectric film.The process that component A spreads in tested porous Jie's film and component A exist the difference of diffusion length and diffusion area in the process of the diffusion of free media components B: diffusion length is greater than the diffusion length at free media components B in tested porous Jie's film, spread in the space in tested porous Jie's film because be, the passage that links to each other between the space has tortuosity, so diffusion length increases; Diffusion area is greater than the diffusion area at free media components B in tested porous Jie's film, because be to spread in the space in tested porous Jie's film, the total area in space is greater than the sectional area of tested porous dielectric film.So the component A that measures with the evaporation tube method in B component the binary gas coefficient of diffusion and effective diffusion cofficient between have a correction coefficient, this correction coefficient and diffusion length are inverse relation, with the proportional relation of diffusion area, under the identical situation of test condition, diffusion length depends on the tortuous factor of tested porous medium, diffusion area depends on the porosity of tested porous medium, namely

Can get thus

$D_{\mathrm{ABP}}=\frac{\mathrm{\ϵ}{D}_{\mathrm{AB}}}{\mathrm{\τ}}$

The arrangement following formula gets

$\mathrm{\ϵ}=\frac{\mathrm{\τ}{D}_{\mathrm{ABP}}}{D_{\mathrm{AB}}}$

The process that the evaporation tube method is measured the binary gas coefficient of diffusion of component A in B component is the vaporization of liquid A component and spreads by gas-bearing formation B.When component A is diffused into mouth of pipe place, namely taken away by gas B, make that the dividing potential drop of the component A of mouth of pipe place is very low, can think p _A2≈ 0, the dividing potential drop p of the component A of liquid level place _A1Saturated vapor pressure for component A under condition determination.In diffusion process, the consumption because the A component is constantly vaporized, liquid level constantly descends in time, diffusion length z time to time change, process is transient.But because vaporization and the rate of diffusion of liquid A are very slow, so that in long-time, the distance that liquid level descends is compared very little with whole diffusion length, can be used as the quasi-stable state process and handle.In diffusion process, gas B can not be dissolved among the liquid component A, process for component A by stagnating the quasi-stable state diffusion process of B component, its diffusion flux represents with following formula,

$N_A=\frac{D_{\mathrm{AB}}p}{\mathrm{RT\Δz}{p}_{\mathrm{BM}}}(p_{A1}-p_{A2})$

In the formula, D _ABBe the coefficient of diffusion of component A steam by B component, p is mixture pressure, and R is universal gas constant, and T is absolute temperature, Δ z=z-z ₀, p _BMBe the logarithmic mean dividing potential drop of B component,

$p_{\mathrm{BM}}=\frac{P_{B2}-p_{B1}}{\ln \frac{p_{B2}}{p_{B1}}}$

In the d θ time, under the liquid level decline dz condition, the diffusion flux N of component A _AThe computing formula of mass balance is

ρ _AL·dz·A＝N _A·A·dθ·M _A

The arrangement following formula gets

$N_A=\frac{{\mathrm{\ρ}}_{\mathrm{AL}}}{M_A}\·\frac{\mathrm{dz}}{\mathrm{d\θ}}$

ρ in the formula _AL---the density of component A, kg/m ³

M _A---the molal weight of component A, kg/kmol;

The cross-sectional area of A---evaporation tube, m ²

Under the quasi-stable state spread condition, the diffusion flux N of component A _AAbove-mentioned two calculating formulas equate, namely

$\frac{D_{\mathrm{AB}}p}{\mathrm{RTz}{p}_{\mathrm{BM}}}(p_{A1}-p_{A2})=\frac{{\mathrm{\ρ}}_{\mathrm{AL}}}{M_A}\·\frac{\mathrm{dz}}{\mathrm{d\θ}}$

To following formula through variables separation and integration

${\∫}_0^{\mathrm{\θ}}\mathrm{d\θ}=\frac{{\mathrm{\ρ}}_{\mathrm{AL}}\mathrm{RT}{p}_{\mathrm{BM}}}{D_{\mathrm{AB}}p{M}_A(p_{A1}-p_{A2})}\·{\∫}_{z_0}^z\mathrm{zdz}$

obtain

$\mathrm{\θ}=\frac{{\mathrm{\ρ}}_{\mathrm{AL}}\mathrm{RT}{p}_{\mathrm{BM}}}{D_{\mathrm{AB}}p{M}_A(p_{A1}-p_{A2})}\·\frac{z^2-z_0^2}{2}$

Or

$D_{\mathrm{AB}}=\frac{\mathrm{RT}{p}_{\mathrm{BM}}{\mathrm{\ρ}}_{\mathrm{AL}}(z^2-z_0^2)}{2p{M}_A\mathrm{\θ}(p_{A1}-p_{A2})}$

Record the corresponding relation of a series of time intervals and z, can calculate the binary gas diffusion coefficient D of component A in B component by following formula (formula 1) _AB

When measuring component A in porous medium in the B component during effective diffusion cofficient, component A is divided into two sections by the diffusion of B component, and one section is freely to spread, and another section is to spread by porous medium, two sections are carried out mass balance at component A respectively, by first section mass balance obtained

$p_{\mathrm{Ax}}=p_{A1}-\frac{{\mathrm{\ρ}}_{\mathrm{AL}}\mathrm{RT}{p}_{\mathrm{BM}}}{D_{\mathrm{AB}}p{M}_A}\·\frac{z^2-z_0^2}{2}---\left(7\right)$

The P that obtain this moment _AXBe liquid A component dividing potential drop under porous Jie film.

Under the quasi-stable state spread condition, component A is by the diffusion flux N of free section and perforated membrane section _AEquate, namely

$N_A=\frac{{\mathrm{\ρ}}_{\mathrm{AL}}}{M_A}\·\frac{\mathrm{dz}}{\mathrm{d\θ}}=\frac{D_{\mathrm{ABP}}p}{\mathrm{RTl}{p}_{\mathrm{BM}}^{,}}\·(p_{\mathrm{AX}}-p_{A2})$

The arrangement following formula gets

$D_{\mathrm{ABP}}=\frac{{\mathrm{\&rho;}}_{\mathrm{AL}}\mathrm{RTl}{p}_{\mathrm{BM}}^{,}}{p{M}_A\mathrm{\&theta;}}\&CenterDot;\frac{z-z_0}{p_{\mathrm{AX}}-{\mathrm{<figure-callout\; id="2"\; label="p\; A"\; filenames="HDA0000109518910000021.png"\; state="\{\{state\}\}">p</figure-callout>}}_A}$

This computing formula is that the evaporation tube method is measured the binary gas of component A in B component by the effective diffusion cofficient D of porous dielectric film _ABPComputing formula.

The invention has the beneficial effects as follows:

Can measure porosity and the effective diffusion cofficient of gas in porous medium of porosint fast and accurately, for chemical industry and research practice provide condition.

Description of drawings

The present invention has accompanying drawing two width of cloth, wherein

Fig. 1 is the evaporation tube subtraction unit synoptic diagram of measuring the binary gas coefficient of diffusion,

Fig. 2 is mensuration porous medium effective diffusion cofficient device synoptic diagram of the present invention.

Among the figure 1, evaporation tube, 2, component A liquid, 3, tested porous medium, 4, p _A2The interface, i.e. evaporation tube mouth of pipe interface, 5, p _XThe interface, i.e. tested porous dielectric film lower surface interface, 6, liquid A liquid level original position, 7, the position that drops to of liquid A liquid level, the position that z drops to for the liquid A liquid level is to evaporation tube mouth of pipe distance, z ₀For arriving evaporation tube mouth of pipe distance in liquid A liquid level original position.

Embodiment

Be component A liquid with water and ethanol, air is B component, measures water vapour and the effective diffusion cofficient of alcohol vapour in the porous carbon paper.At first measure water vapour and alcohol vapour aerial diffusion coefficient D at a certain temperature with the evaporation tube method of binary gas coefficient of diffusion _AB, device as shown in Figure 1.To inject evaporation tube 1 bottom respectively as water and the ethanol of component A, evaporation tube 1 is put into convection oven perpendicular to surface level, the air of gassy B component in the convection oven keeps temperature T and pressure p in the convection oven constant; The original liquid level position of record air blast temperature of oven T, evaporation tube bottom liquid A component is apart from the distance z of the evaporation tube mouth of pipe ₀With the distance z of the position that drops to through evaporation tube bottom liquid A component liquid level behind the certain hour θ apart from the evaporation tube mouth of pipe.Calculate water vapour and alcohol vapour aerial diffusion coefficient D at a certain temperature respectively _ABRecycling Fig. 2 device is measured as the water vapour of A component 2 and alcohol vapour and with the porous carbon paper is being effective diffusion cofficient D in the porous medium 3 _ABP, will inject evaporation tube 1 bottom as the water of A component 2 and ethanol, will cover at evaporation tube mouth of pipe place with fluid sealant as the porous carbon paper of tested porous medium 3 and air-dry, the tube wall at porous carbon paper and evaporation tube 1 mouth of pipe place is sealed; The evaporation tube 1 that sealing is good is put into convection oven perpendicular to surface level, is full of air in the convection oven, keeps temperature T and pressure p in the baking oven constant; With measuring the binary gas diffusion coefficient D of component A in B component _ABThe evaporation tube method calculate water vapour and the aerial binary gas coefficient of diffusion of alcohol vapour that the mouth of pipe covers the porous carbon paper, this coefficient of diffusion is water vapour and the effective diffusion cofficient D of alcohol vapour in the porous carbon paper _ABP, according to formula 5

$\mathrm{\&epsiv;}=\frac{\mathrm{\&tau;}{D}_{\mathrm{ABP}}}{D_{\mathrm{AB}}}$

Determine the ε/τ of porous carbon paper, owing to mainly be straight hole in the porous carbon paper, so τ is approximately 1, can obtain the porosity ε of carbon paper.

Embodiment 1

Be the liquid of component A with ethanol, air is the B component, measures the aerial diffusion coefficient D of alcohol vapour earlier _AB, measure the effective diffusion cofficient D of alcohol vapour in the porous carbon paper again _ABP

$D_{\mathrm{ABP}}=\frac{{\mathrm{\&rho;}}_{\mathrm{AL}}\mathrm{RTl}{p}_{\mathrm{BM}}^{,}}{p{M}_A\mathrm{\&theta;}}\&CenterDot;\frac{z-z_0}{p_{\mathrm{AX}}-{\mathrm{<figure-callout\; id="2"\; label="p\; A"\; filenames="HDA0000109518910000021.png"\; state="\{\{state\}\}">p</figure-callout>}}_A}$

Measure the effective diffusion cofficient D of alcohol vapour in the porous carbon paper _ABPEach parameter as follows:

R---gas law constant, 8.314 * 10 ³Nm/ (kmolK);

M _A---the molal weight of ethanol, 46.07kg/kmol;

θ---component A in evaporation tube liquid level by z ₀Drop to the used time of z, 18000s;

L---the thickness of porous Jie's film, m;

T---thermodynamic temperature is respectively 295K, 300K, 305K, 310K, 315K;

p _A2---liquid component A is at the vapour pressure at mouth of pipe place, Pa;

p _AX---the dividing potential drop of component A under porous Jie film under the different condition, calculate and can get by formula (7);

ρ _AL---the density (as table 1) under the different temperatures, kg/m3;

p _A1---the saturated vapor pressure (as table 1) under the different temperatures, KPa.

The density of ethanol and saturated vapor pressure under table 1 different temperatures

Calculate evaporation tube with formula (14) and cover the aerial diffusion coefficient D of alcohol vapour under the carbon paper condition _AB, this D _ABNamely be the effective diffusion cofficient D of alcohol vapour in carbon paper _ABP, application of formula 5

$\mathrm{\&epsiv;}=\frac{\mathrm{\&tau;}{D}_{\mathrm{ABP}}}{D_{\mathrm{AB}}}$

Calculate ε/τ.

Be example with air-ethanol system under the 295K condition, its computation process is as follows:

The coefficient of diffusion of ethanol component in constituent of air is 0.132 * 10 under the 295K condition ^-4m ²/ s.

(z=8.0000cm) locates at the ethanol liquid level, p _A1Be the saturated vapor pressure of ethanol, i.e. p _A1=6698.16862Pa

p _B1＝(1.013-0.06698)×105＝9.4602×104Pa

Dividing potential drop under the porous Jie film of pipe top is p _AX, namely

p _BX＝p-p _AX

So

$p_{\mathrm{BM}}=\frac{p_{\mathrm{BX}}-p_{B1}}{\ln \frac{p_{\mathrm{BX}}}{p_{B1}}}=\frac{(1.013\&times;{10}^5-p_{\mathrm{AX}})-0.946\&times;{10}^5}{\ln \frac{1.013\&times;{10}^5-p_{\mathrm{AX}}}{0.946\&times;{10}^5}}$

Application of formula (7) is calculated the dividing potential drop of ethanol under porous Jie film,

$p_{\mathrm{AX}}=p_{A1}-\frac{{\mathrm{\&rho;}}_{\mathrm{AL}}\mathrm{RT}{p}_{\mathrm{BM}}}{D_{\mathrm{AB}}p{M}_A}\&CenterDot;\frac{z^2-z_0^2}{2}$

$=6698.17-\frac{0.788\&times;8314\&times;295}{0.132\&times;1.013\&times;{10}^5\&times;46.07}\&times;\frac{(1.013\&times;{10}^5-p_{\mathrm{AX}})-0.946\&times;{10}^5}{\ln \frac{1.013\&times;{10}^5-p_{\mathrm{AX}}}{0.946\&times;{10}^5}}\&times;\frac{({8.0811}^2-{8.0000}^2)\&times;{10}^{-4}}{2}$

Following formula is found the solution,

p _AX＝6687.4148Pa

So

p _BX＝p-p _AX＝(1.013-0.066874)×10 ⁵＝9.474×10 ⁴Pa

Component A is diffused into evaporation tube mouth of pipe place, is namely taken away by gas B, makes that the concentration at mouth of pipe place is very low, can think p _A2≈ 0.

p _B2＝p-p _A2＝(1.013-0)×10 ⁵＝1.013×10 ⁵Pa

$p_{\mathrm{BM}}^{,}=\frac{p_{B2}-p_{\mathrm{BX}}}{\ln \frac{p_{B2}}{p_{\mathrm{BX}}}}=\frac{(1.013-0.9474)\&times;{10}^5}{\ln \frac{1.013\&times;{10}^5}{(1.013-0.066874)\&times;{10}^5}}=9.792\&times;{10}^4\mathrm{Pa}$

So the effective diffusion cofficient of ethanol in porous Jie film is

$D_{\mathrm{ABP}}=\frac{{\mathrm{\&rho;}}_{\mathrm{AL}}\mathrm{RTl}{p}_{\mathrm{BM}}^{,}}{p{M}_A\mathrm{\&theta;}}\&CenterDot;\frac{z-z_0}{p_{\mathrm{AX}}-{\mathrm{<figure-callout\; id="2"\; label="p\; A"\; filenames="HDA0000109518910000021.png"\; state="\{\{state\}\}">p</figure-callout>}}_A}=\frac{0.788\&times;8314\&times;295\&times;0.032\&times;9.792\&times;{10}^4}{1.013\&times;{10}^5\&times;46.07\&times;18000}\&times;\frac{(8.0811-8.0000)\&times;{10}^2}{6687.4148}$

$=0.8742\&times;{10}^{-5}{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HDA0000109518910000021.png"\; state="\{\{state\}\}">m</figure-callout>}}^2/s$

Application of formula 5 is calculated the porosity of porous Jie film, so

$\frac{\mathrm{\&epsiv;}}{\mathrm{\&tau;}}=\frac{D_{\mathrm{ABP}}}{D_{\mathrm{AB}}}=\frac{0.8742\&times;{10}^{-5}}{0.132\&times;{10}^{-4}}=66.24\%$

The data of record and the effective diffusion cofficient D of calculating _ABPWith As following table:

Effective diffusion cofficient and porosity under the table 2 air-ethanol 295K of system

Effective diffusion cofficient and porosity under the table 3 air-ethanol 300K of system

Effective diffusion cofficient and porosity under the table 4 air-ethanol 305K of system

Effective diffusion cofficient and porosity under the table 5 air-ethanol 310K of system

Effective diffusion cofficient and porosity under the table 6 air-ethanol 315K of system

Five groups of data

Mean value be about 0.6628, getting τ is 1, obtaining ε is 0.6628.

Embodiment 2

Be the liquid A component with water, B component is air, measures the aerial diffusion coefficient D of water vapour under the different condition earlier _AB, measure the effective diffusion cofficient D of water vapour in the porous carbon paper again _ABP

Measure the effective diffusion cofficient D of water vapour in the porous carbon paper _ABPEach parameter as follows:

R---gas law constant, 8.314 * 10 ³Nm/ (kmolK);

M _A---the molal weight of component A (water), 18.09kg/kmol;

θ---component A (water) in evaporation tube liquid level by z ₀Drop to the used time of z, 18000s;

L---the thickness of porous Jie's film, m;

T---thermodynamic temperature is respectively 310K, 315K, 320K, 325K, 330K;

p _AX---the dividing potential drop (by formula (7) calculate can get) of component A (water) under different condition, Pa;

ρ _AL---the density of component A (water) under the different temperatures, kg/m ³

p _A1---the saturated vapor pressure of component A (water) under the different temperatures, KPa;

The density of water and saturated vapor pressure under table 7 different temperatures

Calculate evaporation tube with formula (11) and covered the aerial diffusion coefficient D of water vapour under the carbon paper condition _AB, this D _ABNamely be the effective diffusion cofficient D of water vapour in carbon paper _ABP, application formula (5) is calculated

The data of record and the effective diffusion cofficient D of calculating _ABPWith

As following table:

Coefficient of diffusion and porosity under the table 8 air-water system 310K

Effective diffusion cofficient and porosity under the table 9 air-water system 315K

Effective diffusion cofficient and porosity under the table 10 air-water system 320K

Effective diffusion cofficient and porosity under the table 11 air-water system 325K

Effective diffusion cofficient and porosity under the table 12 air-water system 330K

Five groups of data

Mean value be about 0.6632.Getting τ is 1, and obtaining ε is 0.6632.

Claims (4)

1. a method of measuring porous medium effective diffusion cofficient and porosity comprises and measures the binary gas diffusion coefficient D of liquid component A in gas composition B _ABThe evaporation tube method, be about to component A and inject the evaporation tube bottom, evaporation tube is put into convection oven perpendicular to surface level, be full of B component in the convection oven, keep temperature T and pressure p in the convection oven constant; The original liquid level position of record air blast temperature of oven T, evaporation tube bottom component A is apart from the distance z of the evaporation tube mouth of pipe ₀With the distance z of the position that drops to through evaporation tube bottom liquid component A liquid level behind the certain hour θ apart from the evaporation tube mouth of pipe; T, p, z with record ₀Bring formula into z

$D_{\mathrm{AB}}=\frac{{\mathrm{RTp}}_{\mathrm{BM}}{\mathrm{\&rho;}}_{\mathrm{AL}}(z^2-z_0^2)}{2p{M}_A\mathrm{\&theta;}(p_{A1}-p_{A2})}---\left(1\right)$

Calculate the diffusion coefficient D of component A in B component _AB, in the formula

p _A1---the saturated vapor pressure of component A under the condition determination, from " chemical industry solvent handbook is discovered and seized Pa;

p _A2---component A learns by calculating in the dividing potential drop at mouth of pipe place, Pa;

D _AB---the coefficient of diffusion of component A in B component, m ²/ s;

P---pressure, 1.0134 * 10 ⁵Pa;

R---gas law constant, 8.314 * 10 ³Nm/ (kmolK);

T---thermodynamic temperature, K;

The position that the evaporation tube bottom component A liquid level of z---record drops to is apart from the distance of the evaporation tube mouth of pipe, m;

z ₀---the original liquid level position of the evaporation tube of record bottom component A is apart from the distance of the evaporation tube mouth of pipe, m;

ρ _AL---the density of component A, kg/m ³

M _A---the molal weight of component A, kg/kmol;

θ---the liquid level of evaporation tube bottom component A descends the used time s;

p _BM---the logarithmic mean dividing potential drop of B component, Pa; Computing formula is

$\begin{array}{c}{p}_{B2}=p-p_{A2}\\ p_{B1}=p-p_{A1}\\ p_{B2}-p_{B1}=p_{A1}-p_{A2}\\ p_{\mathrm{BM}}=\frac{p_{B2}-p_{B1}}{\ln \frac{p_{B2}}{p_{B1}}}\end{array}---\left(2\right)$

The method that it is characterized in that described mensuration porous medium effective diffusion cofficient and porosity is further comprising the steps of:

1) component A is injected the evaporation tube bottom, tested porous medium is made film, tested porous dielectric film is covered at evaporation tube mouth of pipe place and air-dry with fluid sealant, the tube wall at tested porous dielectric film and evaporation tube mouth of pipe place is sealed;

2) will seal good evaporation tube and put into convection oven perpendicular to surface level, be full of B component in the convection oven, and keep temperature T and pressure p in the convection oven constant;

3) with measuring the binary gas diffusion coefficient D of component A in B component _ABThe evaporation tube method calculate the dividing potential drop P that component A that the mouth of pipe covers tested porous dielectric film locates below porous dielectric film _Ax, utilize the P that obtains _Ax, by component A mass balance in porous dielectric film, getting component A by the binary gas coefficient of diffusion of diffusion B component in porous dielectric film, this coefficient of diffusion is the effective diffusion cofficient D of component A in tested porous dielectric film _ABPEffective diffusion cofficient D _ABPSpecifically be calculated as follows: because component A is by the diffusion flux N of free section and porous dielectric film section _AEquate, namely

$N_A=\frac{{\mathrm{\&rho;}}_{\mathrm{AL}}}{M_A}\&CenterDot;\frac{\mathrm{dz}}{\mathrm{d\&theta;}}=\frac{D_{\mathrm{ABP}}p}{\mathrm{RT}{\mathrm{lp}}_{\mathrm{BM}}^{,}}\&CenterDot;(p_{\mathrm{AX}}-p_{A2})---\left(3\right)$

The arrangement following formula gets

$D_{\mathrm{ABP}}=\frac{{\mathrm{\&rho;}}_{\mathrm{AL}}{\mathrm{RTlp}}_{\mathrm{BM}}^{,}}{p{M}_A\mathrm{\&theta;}}\&CenterDot;\frac{z-z_0}{p_{\mathrm{AX}}-p_{A2}}---\left(4\right)$

This computing formula is that the evaporation tube method is measured the binary gas of component A in B component by the effective diffusion cofficient D of porous dielectric film _ABPComputing formula;

In the formula

$p_{\mathrm{BM}}^{,}=\frac{p_{B2}-p_{\mathrm{BX}}}{\ln \frac{p_{B2}}{p_{\mathrm{BX}}}}$

p _BX＝p-p _AX

The thickness of l---porous dielectric film, m

4) use diffusion coefficient D _ABWith effective diffusion cofficient D _ABPBetween reduction formula:

$D_{\mathrm{ABP}}=\frac{\mathrm{\&epsiv;}{D}_{\mathrm{AB}}}{\mathrm{\&tau;}}---\left(5\right)$

Calculate tested porous medium porosity, namely

$\mathrm{\&epsiv;}=\frac{\mathrm{\&tau;}{D}_{\mathrm{ABP}}}{D_{\mathrm{AB}}}---\left(6\right)$

The porosity of ε in the formula---porous medium, m ³/ m ³

τ---tortuous factor.

2. a kind of method of measuring porous medium effective diffusion cofficient and porosity according to claim 1, it is characterized in that: the thickness of described tested porous dielectric film is 0.1-0.5mm.

3. a kind of method of measuring porous medium effective diffusion cofficient and porosity according to claim 2 is characterized in that: described evaporation tube bottom component A is water or ethanol, and described B component is air.

4. a kind of method of measuring porous medium effective diffusion cofficient and porosity according to claim 1, it is characterized in that: the temperature T in the described convection oven is 293K≤T≤330K, described pressure p is normal pressure.

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