CN204630880U - A kind of water vapor diffusion coefficient unsteady-state measuring device - Google Patents

Abstract

The utility model discloses a kind of device of water vapor diffusion coefficient measurement of instability.This device comprises: climatic chamber, for providing high relative humidity conditions; Organic glass case, inside holds anhydrous calcium chloride, for providing low relative humidity; Forced convertion device, for making box house relative humidity even; Relative Humidity Sensor, for measuring testing sample inside and envionmental humidity; Data acquisition unit, for gathering the relative humidity and the minute of correspondence that relative humidity sensor measures; And computing machine, representing the Fick second law of water vapor Unsteady Casting and sample interior relative humidity and corresponding minute for combining, utilizing Boltzmann to convert indirect problem process and obtaining water vapor diffusion coefficient under testing sample difference relative humidity.The utility model has the advantages that structure is simple, measuring accuracy is high and the test duration is short.

Description

A kind of water vapor diffusion coefficient unsteady-state measuring device

Technical field

The utility model relates to physical measurement technical field, particularly relates to a kind of water vapor diffusion coefficient unsteady-state measuring device of building field.

Background technology

Along with the develop rapidly of economy and the sustainable growth of population, energy problem becomes the Social Events of whole mankind's facing.At present, building and industry, communications and transportation are listed as China's three large high energy consumption industries.What architectural exterior-protecting construction used is porosint mostly, as concrete, shale brick, timber etc.In hot-humid climate, porous building enclosure also exists very strong wet transition process, and the wet migration of its heat and wet accumulation are to building thermal technique performance, building energy consumption and indoor environment important.Such as, the coefficient of heat conductivity due to water is about 24 times of air, and the small change of porous construction material water capacity all will have an immense impact on to its heat transfer property; Meanwhile, body of wall high water capacity can cause room air water capacity to raise, and causes the microbial growth such as mould, worsens indoor environment.Therefore the wet migration of research porous construction material has very important meaning.

The water vapor diffusion coefficient of porous construction material is the Important Property Parameters characterizing water vapor migration performance in building materials, and being that quantitative solving wets the necessary basic data of migration problem, is also the important content of architectural exterior-protecting construction heat and moisture coupling transfer research.

The water vapor diffusion performance of porous building materials is usually by the dry wet cup Experimental Characterization of stable state, and the method is in many countries standardization.But, under isothermy, the water vapor diffusion performance of porous building materials depends on the relative humidity of its inside, in typical building envionmental humidity scope (40-95%), between the maximal value of water vapor diffusion coefficient and minimum value, differ about order of magnitude.Because the mathematical model of architectural exterior-protecting construction heat and moisture coupling transfer is day by day complicated, day by day improve the requirement of input data accuracy, water vapor diffusion performance need characterize on the basis of existing standard in wider humidity range.But because water vapor transmits slowly in porous building materials, one time Steady Experimental needs several weeks consuming time, and a Steady Experimental can only record a water vapor diffusion coefficient, the water vapor of complete characterization porous building materials transmits performance may need the several months consuming time, so development is efficient, unstable state method of testing has reliably have very important meaning for scientific research and engineer applied.

The people such as Arfvidsson are at " Building and Environment " 3 phases in 2000 (A transient technique for determining diffusion coefficients in hygroscopic materials, 2000, 35 (3): 239-249) the porous building material quality test experimental bed when envionmental humidity step variation has been built in, and experimentally data propose a kind of with the method for the Kirchhoff gesture calculating water vapor diffusion coefficient that is driving force, result of calculation and Steady Experimental result are coincide, but the method need try to achieve the sucting wet curve of material by Steady Experimental, still consuming time longer.The people such as Pavl í k are at " Journal of Building Physics " 3 interim (A Boltzmann transformation method for investigation of water vapor transport in building materials in 2012, 2012, 35 (3): 213-223) the porous building materials water vapor diffusion coefficient unstable state test experimental bed that utilized time-domain reflectomer to build, but author records corresponding relative humidity on the diffusivity curve that water vapor diffusion coefficient records at cold store enclosure by stable state method of " cheers " is about 64%, be 0/50% not to be inconsistent with " cheers " method relative humidities, reliability is not high, and time-domain reflectomer is expensive.

Although existing researcher has carried out the research of porous construction material water vapor diffusion coefficient measurement of instability technology, still there is the problems such as length consuming time, accuracy are not high, expensive in these methods.

Summary of the invention

The purpose of this utility model is the water vapor diffusion coefficient in order to measure porous construction material material, there is provided a kind of water vapor diffusion coefficient unsteady-state measuring device of porous construction material, this apparatus structure is simple, measuring accuracy is high and can determine the relation of water vapor diffusion coefficient and relative humidity by once experiment.

The utility model is achieved through the following technical solutions:

A kind of water vapor diffusion coefficient unsteady-state measuring device comprises climatic chamber, organic glass case, forced convertion device, Relative Humidity Sensor, data acquisition unit, computing machine; The layout of device is as follows:

The part burying the testing sample of Relative Humidity Sensor underground is fixed in organic glass case, organic glass case is placed in climatic chamber, respectively a forced convertion device is placed in climatic chamber and organic glass case, Relative Humidity Sensor is connected to data acquisition unit by climatic chamber lateral opening hole, and data acquisition unit connects computing machine.

Compared with prior art, water vapor diffusion coefficient unsteady-state measuring device of the present utility model and method utilize high precision and cheap Relative Humidity Sensor measures the relative humidity distribution of water vapor in porous construction material during one-dimensional and unsteady state transmission, goes out water vapor diffusion coefficient based on the accurate inverse of inverse problem principle.Therefore, overcome the shortcomings such as traditional steady state measurement method and other measurement of instability methods length consuming time, accuracy be not high, expensive, characterize porous construction material water vapor with being conducive to high efficient and reliable transmitting performance, and then promote the application of architectural exterior-protecting construction heat and moisture coupling transfer model in engineering.

Accompanying drawing explanation

Fig. 1 is the utility model water vapor diffusion coefficient unsteady-state measuring device schematic diagram;

Fig. 2 is that the utility model Relative Humidity Sensor buries schematic diagram underground;

Fig. 3 is the utility model testing sample wiring layout.

Embodiment

Below in conjunction with embodiment and accompanying drawing, the utility model is described in further detail, but should not limit protection domain of the present utility model with this.

First with reference to figure 1, it gives the utility model water vapor diffusion coefficient unsteady-state measuring device schematic diagram.

As shown in Figure 1, the utility model water vapor diffusion coefficient unsteady-state measuring device comprises climatic chamber 1, organic glass case 2, forced convertion device 3, Relative Humidity Sensor 4, data acquisition unit 5, computing machine 6.Described forced convertion device can select any device that can play the effect of forced convertion, as selected fan.Climatic chamber 1 is for providing high relative humidity conditions, anhydrous calcium chloride is held for providing low relative humidity in organic glass case 2, forced convertion device 3 is for making box house relative humidity even, Relative Humidity Sensor 4 is for measuring testing sample inside and envionmental humidity, data acquisition unit 5 is for the relative humidity that gathers relative humidity sensor and measure and the minute of correspondence, and computing machine 6 is for combining the Fick second law and sample interior relative humidity and corresponding minute that represent water vapor Unsteady Casting, utilize Boltzmann to convert indirect problem process and obtain water vapor diffusion coefficient under the different relative humidity of testing sample.

Porous construction material to be measured requires rectangular parallelepiped cutting, at the surrounding of longitudinal direction epoxy sealing waterproof, guarantees the one dimension transmission of water vapor.Testing sample needs drying, and inner initial temperature is consistent with environment and even.

Suppose that porous construction material sample is even, the specimen temperature that water vapor diffusion causes changes ignores, then in isothermal environment, the available Fick second law of the transmission of water vapor in porous building materials represents:

$\frac{\∂{\mathrm{\ρ}}_v}{\∂t}=\frac{\∂}{\∂x}\left(D\right({\mathrm{\ρ}}_v\left)\frac{\∂{\mathrm{\ρ}}_v}{\∂x}\right)---\left(1\right)$

Boundary condition:

ρ _v(0,t)＝ρ _v1(2)

ρ _v(∞,t)＝ρ _v2(3)

Starting condition:

ρ _v(x,0)＝ρ _v2(4)

Wherein, ρ _vfor partial water vapour density, kg/m ³; X is the distance on distance sample high humility surface, m; D is water vapor diffusion coefficient, m ²/ s; T is diffusion time, s.

Introduce Boltzmann variable:

$\mathrm{\η}=\frac{x}{2\sqrt{t}}---\left(5\right)$

ρ _v(x,t)＝ω(η) (6)

Formula (1) can be converted into ordinary differential equation:

$\frac{d}{d\mathrm{\η}}\left(D\right(\mathrm{\ω}\left)\frac{d\mathrm{\ω}}{d\mathrm{\η}}\right)+2\mathrm{\η}\frac{d\mathrm{\ω}}{d\mathrm{\η}}=0---\left(7\right)$

Boundary condition:

ω(0)＝ρ _v1(8)

ω(∞)＝ρ _v2(9)

If the partial water vapour density distribution ρ in certain moment known _v(x, t ₀), be zero by water vapor flux to formula (7) integration and when supposing η → ∞, the function of water vapor diffusion coefficient about partial water vapour density can be obtained:

$D\left({\mathrm{\ρ}}_v\right(x_0,t_0\left)\right)=\frac{1}{2t_0{\left(\frac{{\mathrm{d\ρ}}_v}{dx}\right)}_{x_0}}{\∫}_{x_0}^{\mathrm{\∞}}x\frac{{\mathrm{d\ρ}}_v}{dx}dx---\left(10\right)$

Can be derived the explicit relation of partial water vapour density and relative humidity by the Ideal-Gas Equation and relative humidity definition, then under isothermal conditions, water vapor diffusion coefficient about the function of relative humidity is:

When measuring, concrete operations are as follows:

1, by rectangular parallelepiped testing sample with after the longitudinal surrounding of epoxy sealing, as shown in Figure 2, the h in figure is the length of testing sample, and l is the height of testing sample, longitudinally bores several preformed hole, cool after drying testing sample in certain one side of coating epoxy resin.

2, Embedded capacitance formula relative humidity sensor be fixed with industrial plasticine and seal in preformed hole.

3, use glass cement testing sample to be fixed on the organic glass case that inside is contained with anhydrous calcium chloride, the uncoated surface of testing sample is exposed in the organic glass case of sealing, and another surface is exposed to outside organic glass case, as shown in Figure 3.

4, the organic glass case being fixed with testing sample is positioned in climatic chamber parks one day (climatic chamber design temperature be 25 DEG C, relative humidity be 0%) to guarantee that testing sample internal temperature evenly and consistent with environment temperature.

5, when experiment starts, setting climatic chamber temperature is 25 DEG C, relative humidity is 90%, thus makes water vapor one dimension transmission in testing sample.In whole experimentation, forced convertion device continuous firing is with the relative humidity in even two casings.Several pieces of Relative Humidity Sensor, data acquisition unit and computing machines continue to monitor and record the relative humidity in the inner and climatic chamber of testing sample, organic glass case.

6, combine the Fick second law representing water vapor Unsteady Casting and sample interior relative humidity and corresponding minute, utilize Boltzmann to convert inverse problem calculation and obtain testing sample different relative humidity water vapor diffusion coefficient.

Claims (1)

1. a water vapor diffusion coefficient unsteady-state measuring device, is characterised in that: comprise climatic chamber (1), organic glass case (2), forced convertion device (3), Relative Humidity Sensor (4), data acquisition unit (5), computing machine (6); The layout of device is as follows:

The part burying the testing sample of Relative Humidity Sensor (4) underground is fixed in organic glass case (2), organic glass case (2) is placed in climatic chamber (1), respectively a forced convertion device (3) is placed in climatic chamber (1) and organic glass case (2), Relative Humidity Sensor (4) is connected to data acquisition unit (5) by climatic chamber (1) lateral opening hole, and data acquisition unit (5) connects computing machine (6).