CN103852402A - Measuring apparatus and measuring method for MacMullin number of porous mediums - Google Patents

Abstract

A measuring apparatus for MacMullin number of porous mediums is disclosed, a self-breathing unit fuel cell is utilized as a main measuring device, oxygen in air is utilized as a probe, and by comparing the concentration of oxygen penetrating a to-be measured porous medium sample and a standard sample, the MacMullin number of the to-be measured porous medium sample is calculated, and further the effective diffusion coefficient of a substance in the to-be measured porous medium sample is calculated. Compared with conventional measuring of effective diffusion coefficient of a substance in a porous medium by employing a Loschmidt diffusion cell, the method has the advantages of simple measuring apparatus, simple and convenient measuring steps, simple data processing and the like, and also the method does not need high-purity gases, so that a measuring result cannot be changed and further influenced because of influence of environment to gas concentration during measuring.

Description

Proving installation and the method for testing of porous medium MacMullin number

Technical field

The invention belongs to porosint characterization technique field, be specifically related to a kind of proving installation and method of determinator and material effective diffusion cofficient in porous medium of porous medium MacMullin number.

Background technology

Porosint is widely used in the every field of the energy and environment, understands material transmittance process therein for the design of material and uses very important.Material spreads the impact that is mainly subject to porosity ε and tortuosity τ in porosint, and its effective diffusion cofficient can be calculated by following formula.

$D_{\mathrm{eff}}=\frac{D_0}{f(T,\mathrm{\ϵ})}=\frac{D_0}{N_M}$

$N_M=f(T,\mathrm{\ϵ})=\frac{T}{\mathrm{\ϵ}}$

N _mbeing called MacMullin number, is an important parameter of characterizing porous materials.Know that it just can draw the effective diffusion cofficient of material (gas, liquid, ion etc.) in this porosint.

The invention provides a kind of method and device of simple and easy to do mensuration MacMullin number.This device is mainly a self-respiration type fuel battery, utilizes airborne oxygen to measure the MacMullin number of porous medium as probe.Its cathode plate is fluted in order to place standard model and porous medium sample to be measured.When test 1) first allow fuel cell constant-current discharge under a certain electric current, record its voltage V ₀, 2) and standard model is positioned in groove to recording voltage V ₁; 2) porous medium sample to be measured is put in groove, records now voltage V again ₂.Because voltage with the pass of oxygen concentration is:

$E=E_0+\frac{\mathrm{RT}}{\mathrm{nF}}\ln C_s$

It is carried out to Taylor expansion, can obtain

C _s=A+B·F+C·E ²+…

Ignore higher order term, only retain once item, concentration difference is linear with voltage difference, is △ C ∞ △ E, and the ratio of the concentration difference of porous medium sample to be measured like this and standard model both sides oxygen equals the ratio of the voltage difference of twice measurement,

$\frac{\mathrm{\Δ}{C}_0}{\mathrm{\Δ}{C}_1}=\frac{\mathrm{\Δ}{V}_0}{\mathrm{\Δ}{V}_1}=\frac{V_1-V_0}{V_2-V_1}$

In addition, due to the MacMullin number of porous medium sample to be measured can be calculated by following formula,

$\frac{h_s{N}_M^s}{h_t{N}_M^t}=\frac{\mathrm{\Δ}{C}_0}{\mathrm{\Δ}{C}_1}$

Wherein h is thickness of sample, and s represents standard sample, and test sample is treated in t representative, standard sample

known.

And the effective diffusion cofficient D of material in porous medium _effcan be calculated by following formula:

Wherein D ₀for material is at the coefficient of diffusion of open space (not having porous medium), by porous medium sample to be measured

just can try to achieve the effective diffusion cofficient D of material in this porous medium _eff.The method only needs to record twice voltage difference, just can try to achieve effective diffusion cofficient through simple operation.Avoided traditional Loschmidt diffusion cell to measure effective diffusion cofficient complicated processes, also avoided in test process, needing high-purity gas simultaneously and in test test gas volumetric molar concentration variable and affect the problem of test result.

Summary of the invention

For above problem, the object of the invention is to provide method and the device of a kind of simple and easy to do test porous medium MacMullin number and material effective diffusion cofficient in porous medium.

For achieving the above object, the technical solution used in the present invention is:

A determinator for porous medium MacMullin number, comprises a membrane electrode, an anode end plate and a cathode end plate, one or more standard models;

The side that anode end plate is close to membrane electrode has the runner for fuel flow; Cathode end plate is away from membrane electrode one side and is vertically installed with the groove of placing for sample, and bottom portion of groove offers the through hole perpendicular to the supplied gas circulation of membrane electrode;

Anode end plate, membrane electrode, cathode end plate be superimposed setting successively, and assembling is fixing, forms a self-respiration type fuel battery;

Described standard model is fine and close flat board, and its housing shape is identical with the groove in cathode end plate with size, and edge and the groove madial wall of standard model closely cooperates while inserting;

The hole that the hole of offering on standard model is offered with bottom portion of groove is corresponding one by one; And in the projection of the hole that the projection of the hole of offering on standard model on membrane electrode offered in bottom portion of groove on membrane electrode;

Between one or more standard models and groove in cathode end plate, detachably coordinate, with the common determinator that forms a porous medium MacMullin number of self-respiration type fuel battery.

In described device, there is an anode diffusion layer and a cathode diffusion layer simultaneously; Described self-respiration type fuel battery is superimposed successively by anode end plate, anode diffusion layer, membrane electrode, cathode diffusion layer and cathode end plate, and the fixing formation of assembling.

Described determinator is for the mensuration of porous medium sample MacMullin number to be measured;

Described porous medium sample to be measured is tabular, and the shape of its plate face is identical with the surface of standard model with size, and edge and the groove madial wall of porous medium sample to be measured closely cooperates while inserting;

Depth of groove in cathode end plate is greater than the thickness sum of standard model and porous medium sample to be measured.

Described bottom portion of groove offers one or more hole, and perforated area summation is 0.5-0.9 with the ratio of electrode useful area; In the hole that described bottom portion of groove is offered, the area in each hole is 1:400-1:2 with the ratio of electrode useful area; One or more the hole that described bottom portion of groove is offered, its vertical projection falls within on electrode useful area.

The ratio of the total area in the hole that the total area of the lap in the hole that the hole that described standard model is offered and bottom portion of groove are offered is offered with bottom portion of groove is 0.5-1.

The hole that described bottom portion of groove is offered is uniformly distributed in bottom portion of groove.

Described anode end plate is respectively arranged with the first and second afflux points that can be connected with external loading with cathode end plate; On described anode end plate, have and there is the air intake opening and the gas outlet that communicate with anode flow channel; Its material of described anode end plate and cathode end plate is the one in stainless steel, gold-plated or silver-plated stainless steel, gold-plated aluminium sheet, gold-plated titanium plate, gold-plated or sheffield plate, graphite, graphite/polymkeric substance composite plate.

Adopt device described in claim 1 to measure a method for porous medium MacMullin number, comprise the following steps,

1) assembling one self-respiration type fuel battery monocell;

2) galvanic anode is passed into fuel, and adopt electronic load to measure its constant current discharge performance, get the average voltage in 1-10min, be denoted as V ₀;

3) standard model is placed in to the groove of self-respiration type cell cathode end plate, guarantee the perforate of standard model and the corresponding placement of the perforate of groove, adopting step 2) identical test condition measures its constant current discharge performance, gets the average voltage in 1-10min, is denoted as V ₁;

4) standard model and porous medium sample to be measured are fitted tightly, and be jointly placed in the groove of self-respiration type cell cathode end plate, guarantee the perforate of standard model and the corresponding placement of the perforate of groove, and guarantee closely to amplexiform between porous medium sample to be measured and groove inwall, adopting step 2) identical test condition measures its constant current discharge performance, the average voltage of getting 1-10min, is denoted as V ₂;

5) thickness of difference bioassay standard sample and porous medium sample to be measured, and be denoted as respectively h _sand h _t; The MacMullin number of standard model and porous medium sample to be measured is denoted as respectively simultaneously

with

according to the relation of measuring voltage and oxygen concentration, known:

$\frac{\mathrm{\Δ}{C}_0}{\mathrm{\Δ}{C}_1}=\frac{\mathrm{\Δ}{V}_0}{\mathrm{\Δ}{V}_1}=\frac{V_1-V_0}{V_2-V_1}=\frac{h_s{N}_M^s}{h_t{N}_M^t}$

Wherein △ C ₀, △ C ₁the oxygen concentration that is respectively standard model and testing sample both sides is poor, △ V ₀, △ V ₁be respectively and insert the voltage difference causing after standard model and testing sample.For standard model, its duct is straight, its MacMullin number

in formula, ε is porosity, and τ is tortuosity; Therefore, the MacMullin number of porous medium sample to be measured can calculate by following formula,

$N_M^t=N_M^s\frac{h_s}{h_t}\frac{V_2-V_1}{V_1-V_0}$

According to the MacMullin number of porous medium sample to be measured

effective diffusion cofficient D according to material in porous medium _effthe effective diffusion cofficient of the known a certain material of computing formula in porous medium sample to be measured,

$D_{\mathrm{eff}}=\frac{D_0}{N_M^t}=D_0\frac{1}{N_M^s}\frac{h_t}{h_s}\frac{V_1-V_0}{V_2-V_1}$

D in formula ₀for the coefficient of diffusion at a certain material of open space.

Described anode fuel is hydrogen, methyl alcohol, ethanol or formic acid.

Adopt apparatus and method of the present invention to measure porous medium effective diffusion cofficient, have the following advantages:

1. proving installation is simple and easy;

2. testing procedure is easy;

3. after test, data processing is simple.

Accompanying drawing explanation

Fig. 1 is the assay device structures schematic diagram of porous medium MacMullin number of the present invention.

Wherein, 1 is anode end plate; 2 is membrane electrode (MEA); 3 is cathode end plate; 4 is standard model; 5 is porous medium sample to be measured.

Embodiment

Below in conjunction with embodiment, the present invention is explained in detail.Certainly the present invention is not limited in following specific embodiment.

Embodiment 1:

Membrane electrode preparation: gases used diffusion layer is TGP-060.On it, be coated with 0.6mg/cm ²carbon dust, PTFE potpourri, wherein the massfraction of PTFE is 30%.Blade coating catalyst slurry thereon more afterwards.Nafion solution, ethanol that slurries are 5% by Pt/C (60%wt.JM company), concentration form; Wherein Nafion, Pt/C, ethanol mass ratio are 1:4:20.In the present embodiment, cathode and anode preparation technology and structure are identical, all use the electrode of above-mentioned preparation.Above-mentioned prepared two plate electrodes are placed in respectively to Nafion-115 film both sides, and under 120 ℃, 2000 pounds pressure, the integrated film electrode with diffusion layer is made in hot pressing for one minute.The present embodiment electrode used therein is of a size of 2cm × 2cm.

The inside surface that anode end plate is close to membrane electrode side has point-like flow field, and on end plate, has and point-like smooth identical fuel inlet and fuel outlet.

The outside surface that cathode end plate is away from membrane electrode side has the square indentations of 3cm × 3cm, depth of groove is 1cm, bottom portion of groove offers the circular hole that 25 central shaft diameters vertical with cathode end plate inside surface are 3mm, above-mentioned 25 circular holes are uniformly distributed in (5 holes of every row, totally 5 row) on the region of bottom portion of groove with 2cm × 2cm corresponding to electrode area.

The membrane electrode of above-mentioned preparation and anode end plate and cathode end plate, according to Fig. 1 order, are assembled into monocell according to the order of anode end plate, integrated film electrode, cathode end plate.

Standard model is made up of ABS, its big or small 3cm × 3cm, offers the circular hole that 25 diameters are 3mm on it, and position of opening is corresponding one by one with the position of opening of cathode end plate bottom portion of groove, in the time that standard model is inserted to cathode end plate bottom portion of groove, the central shaft in hole is vertical with standard model simultaneously.

Porous medium sample to be measured is made up of ABS equally, its size is 3cm × 3cm, on it, offer the circular hole that 25 diameters are 2.47mm, and position of opening is corresponding one by one with the position of opening of cathode end plate bottom portion of groove, in the time that testing sample and standard model are inserted to cathode end plate bottom portion of groove simultaneously, the center of gravity in the hole on hole, the standard model of bottom portion of groove and the hole on testing sample is overlapping in the projection of groove floor simultaneously.

Because standard model is straight hole in porous medium emptying aperture that sample is opened to be measured, therefore its theoretical N _mvalue can be by calculating, the N that relatively adopts the method for the invention to measure _mvalue and theoretical N _mvalue, can check the whether accurate and effective of MacMullin number of measuring porous medium with said method.

Pass into H at anode end plate air intake opening ₂, flow velocity is 50mLmin ^-1, and discharged by gas outlet.The afflux point of anode end plate is connected with Arbin electronic load negative pole, and cathode end plate afflux point is connected with load is anodal, and at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 702.4mV that gets last minute, is designated as V ₀.

In groove, put into standard model, battery is equally at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 686.3mV that gets last minute, is designated as V ₁.Standard model perforate size position and shape are consistent with groove, aperture 3mm, and thickness is 2.68mm.Its N _m=1.

In groove, put into porous medium sample to be measured, battery is equally at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 663.0mV that gets last minute, is designated as V ₂.Treat that test sample hole shape, position are consistent with groove, its aperture 2.47mm, thickness is 2.68mm.Can be calculated its N _m=1.45, and its theoretical value is 1.48, both approach.

O ₂at N ₂in binary diffusion coefficient D ₀=0.181cm ²s ^-1(when temperature is 273.2K), oxygen effective diffusion cofficient in porous medium sample to be measured:

$D_{\mathrm{eff}}=\frac{D_o}{N_M}=\frac{0.181}{1.45}=0.125$

Embodiment 2:

Assemble with embodiment 1 in electrode preparation and single pond.Standard model perforate aperture is 2.98mm, and all the other situations are with embodiment 1.

Treat that test sample is carbon paper, model is TGP-H060.Single thickness is 180 μ m.

Pass into H at anode end plate air intake opening ₂, flow velocity is 50mLmin ^-1, and have gas outlet to discharge.The afflux point of anode end plate is connected with Arbin electronic load negative pole, and cathode end plate afflux electricity is connected with load is anodal, and at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 697.6mV that gets last minute is V ₀

In groove, put into standard model, battery is at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 672.7mV that gets last minute is V ₁.Standard sample perforate size position and shape are consistent with groove, aperture 3mm, and thickness is 2.68mm.

In groove, put into porous medium sample to be measured (8 TGP-H060), battery is at 700mA/cm ²constant-current discharge three minutes, recorded primary voltage every one second.The mean value 647.4mV that gets last minute is V ₂.

According to $\frac{h_s{N}_M^s}{h_t{N}_M^t}=\frac{\mathrm{\Δ}{C}_0}{\mathrm{\Δ}{C}_1}=\frac{V_1-V_0}{V_2-V_1},$ Calculate and treat test sample N _m=1.93.

Repeat above testing procedure, only change single tank discharge current density into 800mAcm ^-2, record data are as follows: V ₀=677.6, V ₁=643.7, V ₂=611.1, calculate to such an extent that treat test sample N _m=1.83.

Embodiment 3:

Assemble with embodiment 1 in electrode preparation and single pond.Standard model perforate aperture is 2.98mm, and all the other situations are with embodiment 1.

Treat that test sample is through hydrophobic treatments carbon paper (TGP-H060).Single thickness is 185 μ m.

Pass into H at anode end plate air intake opening ₂, flow velocity is 50mLmin ^-1, and have gas outlet to discharge.The afflux point of anode end plate is connected with Arbin electronic load negative pole, and cathode end plate afflux electricity is connected with load is anodal, and at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 689.7mV that gets last minute is V ₀

In groove, put into two standard samples, battery is at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 639.5mV that gets last minute is V ₁.Standard sample perforate size position and shape are consistent with groove, aperture 3mm, and thickness is 2.68mm.

In groove, put into and treat test sample (8 hydrophobic carbon papers), treat that test sample is clipped between two standard samples.Battery is at 700mAcm ^-2constant-current discharge three minutes, recorded primary voltage every one second.The mean value 611.4mV that gets last minute is V ₂.

According to $\frac{h_s{N}_M^s}{h_t{N}_M^t}=\frac{\mathrm{\Δ}{C}_0}{\mathrm{\Δ}{C}_1}=\frac{V_1-V_0}{V_2-V_1},$ Calculate and treat test sample N _m=2.13.

Claims (10)

1. a determinator for porous medium MacMullin number, is characterized in that:

Comprise a membrane electrode, an anode end plate and a cathode end plate, one or more standard models;

The side that anode end plate is close to membrane electrode has the runner for fuel flow; Cathode end plate is away from membrane electrode one side and is vertically installed with the groove of placing for sample, and bottom portion of groove offers the through hole perpendicular to the supplied gas circulation of membrane electrode;

Anode end plate, membrane electrode, cathode end plate be superimposed setting successively, and assembling is fixing, forms a self-respiration type fuel battery;

Described standard model is fine and close flat board, and its housing shape is identical with the groove in cathode end plate with size, and edge and the groove madial wall of standard model closely cooperates while inserting;

The hole that the hole of offering on standard model is offered with bottom portion of groove is corresponding one by one; And in the projection of the hole that the projection of the hole of offering on standard model on membrane electrode offered in bottom portion of groove on membrane electrode;

Between one or more standard models and groove in cathode end plate, detachably coordinate, with the common determinator that forms a porous medium MacMullin number of self-respiration type fuel battery.

2. the determinator of porous medium MacMullin number as claimed in claim 1 is characterized in that: in described device, have an anode diffusion layer and a cathode diffusion layer simultaneously; Described self-respiration type fuel battery is superimposed successively by anode end plate, anode diffusion layer, membrane electrode, cathode diffusion layer and cathode end plate, and the fixing formation of assembling.

3. the determinator of porous medium MacMullin number as claimed in claim 1, is characterized in that:

Described determinator is for the mensuration of porous medium sample MacMullin number to be measured;

Described porous medium sample to be measured is tabular, and the shape of its plate face is identical with the surface of standard model with size, and edge and the groove madial wall of porous medium sample to be measured closely cooperates while inserting;

Depth of groove in cathode end plate is greater than the thickness sum of standard model and porous medium sample to be measured.

4. the determinator of porous medium MacMullin number as claimed in claim 1, it is characterized in that: described bottom portion of groove offers one or more hole, and perforated area summation is 0.5-0.9 with the ratio of electrode useful area; In the hole that described bottom portion of groove is offered, the area in each hole is 1:400-1:2 with the ratio of electrode useful area; One or more the hole that described bottom portion of groove is offered, its vertical projection falls within on electrode useful area.

5. the determinator of porous medium MacMullin number as claimed in claim 1, is characterized in that: the ratio of the total area in the hole that the total area of the lap in the hole that the hole that described standard model is offered and bottom portion of groove are offered is offered with bottom portion of groove is 0.5-1.

6. the determinator of porous medium MacMullin number as claimed in claim 1, is characterized in that: the hole that described bottom portion of groove is offered is uniformly distributed in bottom portion of groove.

7. the determinator of porous medium MacMullin number as claimed in claim 1, is characterized in that: described anode end plate is respectively arranged with the first and second afflux points that can be connected with external loading with cathode end plate; On described anode end plate, have and there is the air intake opening and the gas outlet that communicate with anode flow channel; Its material of described anode end plate and cathode end plate is the one in stainless steel, gold-plated or silver-plated stainless steel, gold-plated aluminium sheet, gold-plated titanium plate, gold-plated or sheffield plate, graphite, graphite/polymkeric substance composite plate.

8. adopt device described in claim 1 to measure a method for porous medium MacMullin number, it is characterized in that: comprise the following steps,

1) assembling one self-respiration type fuel battery monocell;

2) galvanic anode is passed into fuel, and adopt electronic load to measure its constant current discharge performance, get the average voltage in 1-10min, be denoted as V ₀;

3) standard model is placed in to the groove of self-respiration type cell cathode end plate, guarantee the perforate of standard model and the corresponding placement of the perforate of groove, adopting step 2) identical test condition measures its constant current discharge performance, gets the average voltage in 1-10min, is denoted as V ₁;

4) standard model and porous medium sample to be measured are fitted tightly, and be jointly placed in the groove of self-respiration type cell cathode end plate, guarantee the perforate of standard model and the corresponding placement of the perforate of groove, and guarantee closely to amplexiform between porous medium sample to be measured and groove inwall, adopting step 2) identical test condition measures its constant current discharge performance, the average voltage of getting 1-10min, is denoted as V ₂;

5) thickness of difference bioassay standard sample and porous medium sample to be measured, and be denoted as respectively h _sand h _t; The MacMullin number of standard model and porous medium sample to be measured is denoted as respectively simultaneously

with

according to the relation of measuring voltage and oxygen concentration, known:

$\frac{\mathrm{\Δ}{C}_0}{\mathrm{\Δ}{C}_1}=\frac{\mathrm{\Δ}{V}_0}{\mathrm{\Δ}{V}_1}=\frac{V_1-V_0}{V_2-V_1}=\frac{h_s{N}_M^s}{h_t{N}_M^t}$

Wherein △ C ₀, △ C ₁the oxygen concentration that is respectively standard model and testing sample both sides is poor, △ V ₀, △ V ₁be respectively and insert the voltage difference causing after standard model and testing sample.For standard model, its duct is straight, its MacMullin number

in formula, ε is porosity, and τ is tortuosity;

Therefore, the MacMullin number of porous medium sample to be measured can calculate by following formula,

$N_M^t=N_M^s\frac{h_s}{h_t}\frac{V_2-V_1}{V_1-V_0}.$

9. method as claimed in claim 8, is characterized in that: according to the MacMullin number of porous medium sample to be measured

effective diffusion cofficient D according to material in porous medium _effthe effective diffusion cofficient of the known a certain material of computing formula in porous medium sample to be measured,

$D_{\mathrm{eff}}=\frac{D_0}{N_M^t}=D_0\frac{1}{N_M^s}\frac{h_t}{h_s}\frac{V_1-V_0}{V_2-V_1}$

D in formula ₀for the coefficient of diffusion at a certain material of open space.

10. method as claimed in claim 8, is characterized in that: described anode fuel is hydrogen, methyl alcohol, ethanol or formic acid.