Water vapor diffusion coefficient measuring device and its measuring method
Technical field
The invention belongs to the wet physical measurement field of material, and in particular to a kind of material water vapor diffusion coefficient measuring device and
Measuring method.
Background technology
Energy problem is the major issue of contemporary society, and energy resource consumption has not only triggered energy security problem, also results in
The pollution of environment.Building is as one of high energy consumption industry, so the research to building energy conservation is significant.In Building Heat ring
During border changes, heat transfer and mass transfer are two factors being closely connected, by the heat and mass coupling for studying architectural exterior-protecting construction
Transmission situation, it could accurately weigh the energy-saving effect of building structure.Architectural exterior-protecting construction uses porous material more, in order to preferably
Strengthen building enclosure performance, people the hot moisture migration principle and mathematical procedure of porous construction material have been carried out many experiments and
Research, had difficulties due to determining various hot moisture migration characterisitic parameters, up to the present unification has not yet been formed in various correlative studys
Theory.Wherein, water vapor diffusion coefficient is the important parameter for describing the wet transmission of construction material, is also to solve for moisture migration problem
Fundamental quantity.
Currently used water vapor diffusion coefficient measuring method is mostly when the disperse state of vapor is in steady state
Its flow and the variable quantity of concentration gradient are obtained, diffusion coefficient is calculated to obtain using formula.But time-consuming for this method, to experimental situation
Requirement it is high, it is big using difficulty.So inventing a kind of quick and accurate measurement water vapor diffusion coefficient method is provided with weight
The realistic meaning wanted.
The content of the invention
The present invention provides a kind of water vapor diffusion coefficient measuring device, and in the same of measurement material water vapor diffusion coefficient
When, the Saturated Moisture Content of also measurable material.
The water vapor diffusion coefficient measuring device of the present invention includes:For building the test cabinet of constant-temperature constant-humidity environment and being used for
Collection and the balance system of record testing sample weight change;
The test cabinet is built with fan, humidification device, dehydrating unit, electric calorifie installation, semiconductor cooling device, humiture
Sensor, temperature and humidity control instrument, wind blocking cylinder, the input of temperature and humidity control instrument are connected with Temperature Humidity Sensor, Temperature and Humidity Control
The signal output part of instrument is connected with electric calorifie installation, semiconductor cooling device, and fan is installed on the top and a left side on right side in test cabinet
The bottom of side;
The balance system is made up of electronic balance, level board, balance support, hook and computer, and balance support is built
Contacted outside test cabinet and not with test cabinet, level board is poly (methyl methacrylate) plate, is positioned on balance support, for horizontal support
Electronic balance, electronic balance are positioned on level board, are connected with computer, the real time data that computer recording balance is weighed, and are hung
Hook is suspended on electronic balance bottom.
Preferably, the test indoor top is provided with the hole communicated with the external world, and radius is 2 centimetres;Wind blocking cylinder is arranged on
Below hole, at the top of test cabinet, wind blocking cylinder is cylindrical lucite bucket, and wind blocking cylinder internal diameter is 10 centimetres, wind blocking cylinder bottom surface circle
The heart overlaps with the hole center of circle.
Preferably, described level board is provided with the hole that a radius is 2 centimetres, the hole center of circle and test cabinet top-portion apertures
The hole center of circle overlaps.
Preferably, described hook surface smear has waterproof material, and hook bottom is cross hanging basket shape, is treated for placing
Test sample product.
Preferably, the testing sample is spherical sample.
The invention also discloses a kind of water vapor diffusion coefficient measuring method of described device, step are as follows:
Detected materials to be processed into radius 3cm spherical sample, processing is dried, drying process uses oven drying method,
Drying starts to weigh after 12 hours, and time interval is 2 hours, and when continuously weighing three times, acquired results are not in monotone variation, and are marked
When quasi- difference is no more than the 1% of average value, it is believed that sample is thoroughly dried;
Measurement process:
A) using temperature and humidity control instrument design temperature, relative humidity, while open fan and carry out internal air circulation, make test
Room reaches temperature, relative humidity needed for measurement;
B) balance is opened, calibrated, remove the peel operation;
C) after Temperature Humidity Sensor monitors that temperature, relative humidity are stable, test cabinet is opened, pretreated is treated into test sample
Product are positioned on hook rapidly, sealing test room;
D) the real-time weight data of sample is passed to computer, and every 10 seconds records are once;
E) the weight change of observation in every 30 minutes, it is not in be monotonically changed when continuously observing acquired results three times, and standard
When difference is no more than the 1% of average value, it is believed that sample moisture absorption reaches saturation state;
F) W now obtained∞For the saturation water capacity under the corresponding relative humidity, according to the real-time weight data of sample and
Last saturation water capacity data, you can obtain water vapor diffusion coefficient of the material at the temperature and the relative humidity.
Water vapor diffusion coefficient measuring device provided by the invention is simple in construction, and constant temperature and humidity ring is built using test cabinet
Border, the weight change situation of detected materials is obtained using balance system, measure equation is derived by by Fick second laws, so as to
Water vapor diffusion coefficient is calculated.Testing sample process glomeration, surrounding can moisture absorption, can reach in a short time saturation suction
Wet condition, so as to shorten time of measuring.Testing sample can be obtained under certain temperature, certain relative humidity by carrying out one-shot measurement
Water vapor diffusion coefficient.The present invention while water vapor diffusion coefficient measure, can also obtain testing sample the temperature, this
Saturation water capacity under relative humidity.Balance support does not contact with test cabinet, can effectively prevent test cabinet in the course of the work
The perturbation to electronic balance is shaken, so as to ensure the accuracy of experimental result.Wind blocking cylinder inside test cabinet can effectively prevent from surveying
Sample caused by examination indoor air flows rocks.Hook surface smear has waterproof material, prevents from linking up with surface because of adsorption moisture
Caused by error.
Brief description of the drawings
Fig. 1 is spheroidal material water vapor diffusion coefficient measuring principle figure;
Fig. 2 is the front view of the water vapor diffusion coefficient measuring device of the present invention.
Embodiment
The present invention can complete the measurement to material water vapor diffusion coefficient, also can obtain corresponding saturation water capacity.Measurement
Principle is as follows:
Vapor meets Fick laws in the diffusion of material internal.According to this law, when water vapor diffusion pass through it is a certain
During solid cross section, the diffusion passband of each cross section and concentration gradient and the product of diffusion coefficient are in ratio in medium, concentration
Gradient is the motive force transmitted.When material is spheroid, vapor ecto-entad spreads, such as Fig. 1, and arrow represents vapor in figure
Dispersal direction.Now, diffusion equation can be expressed as:
In formula, D be vapor diffusion coefficient, m2·s-1;C be vapor concentration, molm-2;T is the time, s;R is
Radial distance, m.
Primary condition and boundary condition are respectively
C=C0, 0<r<R, t=0 (2)
C=C∞, r=R, t>0 (3)
C=0, r=0, t>0 (4)
In formula, C0For the adsorption concentration at t=0 moment, molm-2, C∞The adsorption concentration of matter is spread when being adsorption equilibrium,
mol·m-2, R is radius of sphericity, m.
Formula (1) is solved using formula (2) (3) (4), can obtain:
In formula, MtFor the adsorbance of t, molg-1;M∞It is saturated extent of adsorption, molg-1;N is natural number.
Equation (5) is simplified by The Ideal-Gas Equation, the solution equation on water capacity can be obtained:
In formula, WtFor the water capacity of t, gg-1;W∞It is saturation water capacity, gg-1。
W∞For the saturation water capacity under the corresponding relative humidity.When the saturation for measuring different relative humidity at a certain temperature contains
During moisture, using relative humidity as abscissa, the saturation water capacity of material is ordinate, can obtain the material saturation water capacity with
The scatter diagram of relative air humidity relation, these points are connected with a smoothed curve, that is, obtain material in specified temp
Under sorption isotherm curve.
The front view of the measurement apparatus of the present invention is shown in Fig. 2, including test cabinet, balance system.
Test cabinet is by wind blocking cylinder 5, fan 7, humidification device 8, dehydrating unit 9, electric calorifie installation 10, semiconductor cooling device
11st, Temperature Humidity Sensor 12, temperature and humidity control instrument 13 form.Temperature and humidity control instrument 13 is monitored by connecting Temperature Humidity Sensor 12
Indoor temperature, relative humidity are tested, is adjusted by humidification device 8, dehydrating unit 9 of the connection positioned at bottom relative in test cabinet
Humidity, pass through temperature of the connection in the electric calorifie installation 10, the regulation test cabinet of semiconductor cooling device 11 of right flank.Fan 7
The bottom in the top on right side and left side in test cabinet is installed on, makes constant-temperature constant-humidity environment in test cabinet more uniform.In test cabinet
Top is provided with the hole communicated with the external world, and radius is 2 centimetres.Wind blocking cylinder 5 is arranged at the top of test cabinet below hole, test ceiling
Portion, it is cylindrical lucite bucket, internal diameter is 10 centimetres, and the wind blocking cylinder bottom surface center of circle overlaps with the hole center of circle at the top of test cabinet, can
Effectively prevent sample caused by test cabinet internal cause air flow from rocking.
Balance system is made up of electronic balance 1, level board 2, balance support 3, hook 4 and computer 14.Balance support 3 is
Build the stable frame not contacted outside test cabinet and with test cabinet.Level board 2 is poly (methyl methacrylate) plate, is positioned on support,
For horizontal support electronic balance 1.Level board is provided with the hole that a radius is 2 centimetres, the horizontal plate holes center of circle and test
The ceiling portion hole center of circle overlaps.Electronic balance 1 is positioned on level board 2, is connected with computer 14.Computer 14 can record balance
The real time data weighed.Linking up with 4 surface smears has waterproof material, and hook bottom is cross hanging basket shape, and test sample is treated for placing
Product 6.
Testing sample 6 is spherical sample.
Measuring process using the measurement apparatus of the present invention is as follows:
Detected materials are pre-processed first.
Detected materials are processed into radius 3cm spherical sample, processing is dried.Drying process uses oven drying method,
Drying starts to weigh after 12 hours, and time interval is 2 hours.When continuously weighing three times, acquired results are not in monotone variation, and are marked
When quasi- difference is no more than the 1% of average value, it is believed that sample is thoroughly dried.
Measurement process:
A) using the design temperature of temperature and humidity control instrument 13, relative humidity, while open fan 7 and carry out internal air circulation, make
Test cabinet reaches temperature, relative humidity needed for measurement.
B) balance is opened, calibrated, remove the peel operation.
C) after Temperature Humidity Sensor 12 monitors that temperature, relative humidity are stable, survey crew puts on the gloves of hermetically drying
Operated, open test cabinet, pretreated testing sample 6 is positioned on hook rapidly, sealing test room.
D) the real-time weight data of sample is passed to computer 14, and every 10 seconds records are once;
E) the weight change of observation in every 30 minutes.It is not in be monotonically changed when continuously observing acquired results three times, and standard
When difference is no more than the 1% of average value, it is believed that sample moisture absorption reaches saturation state.
F) W now obtained∞For the saturation water capacity under the corresponding relative humidity.Resulting data are substituted into formula
(6) water vapor diffusion coefficient of the material at the temperature and the relative humidity, is calculated.