DE202007008307U1 - Device for determining the moisture movement in porous materials - Google Patents

Abstract

The Facility for Determination of moisture transport in porous materials consisting of a moisture container 1 and a suspension for the sample, characterized in that further comprising a positioning mechanism (3) for height adjustment of the container (2), and thus also the liquid level exists, with the suspension (4) at the top is attached to a digital scale (5), which is above it is attached, being over the container (2) a transmit waveguide (8) of the microwave radiation is arranged is, at its edge, which is averted from the container (2), a Microwave radiation source (15) is arranged, which is connected to a voltage source (6) is connected, being on the other side opposite to the Transmission waveguide (8) a receiving waveguide (9) in the same Height arranged is, wherein the two waveguides as a unit on a support frame via a Adjustment device (14) are arranged adjustably, and the Waveguides are made of a hollow metal profile, and the sample (16) between the mutually facing ends of the waveguides (8, 9) is arranged, whereby ...

Description

Technical area

invention concerns the device for determining the movement of moisture in porous Substances, in particular on the principle of the use of electromagnetic Microwave radiation.

State of the art

The Most wall constructions are made of masonry constructions piece-shaped building materials with mortar as a binder. A considerable one Part of the structural damage is unwanted Moisture is caused and accompanied. The current ones Trends in construction are aimed at the use of new, lightweight building materials with ever increasing requirements to a faultless function of building structures, in particular at thermal insulation ability the outer wall be placed. The determination of the characteristic material parameters for the Assessment of the moisture content of building structures is still an insufficiently clarified topic in the study of Material properties of porous Building materials. The required size is the Capillary transport coefficient, which depends on the measurement of the saturation and desaturation curve (Course of moisture absorption and dehydration) according to the movement the location of the moisture profile in the nonstationary state (i.e., before reaching full moisture).

For this Purpose becomes common applied the gravimetric method, which is the basic procedure for the quantitative determination of the moisture content in substances represents. It consists in that the sample to be examined of a certain length moistened at the front. The water rises during a certain time in the sample. After that, the sample is divided into several Segments - Samples split, which have a different degree of moisture penetration. In the individual segments, the moisture is measured, and due The results will be the moisture distribution curve of the sample certainly. This method is generally due to inaccuracy in handling the samples loaded, and for repeated measurements on a particular sample for assertion the integral method for determining the capillary transport coefficient it is unsuitable.

In 7 the course of the moisture absorption curve in the gravimetric method is shown graphically. It is the sample from the fired piece of broken glass.

For moisture measurement could applied the method of measuring the absorption of neutron radiation which is based on the principle of magnetic resonance. This Procedure is very expensive and places high demands on machine Equipment and protection against hazardous radiation. by virtue of that's it for the construction practice not suitable.

The solution has the goal of a device for determining the movement of moisture in porous Presenting a precise and repeatable measurement enable would, about the integral method in determining the capillary transport coefficient to be able to apply which would be relatively easy and inexpensive.

Disclosure of the invention

The mentioned above Disadvantages are caused by a device for determining the movement of moisture in porous Fabrics according to the invention whose principle is that they also consist of a positioning mechanism for the height adjustment a container, and thus also the liquid level, being the suspension attached in its upper part to a digital scale, which extends over the suspension is located, over the container a transmission waveguide of the microwave radiation is arranged at the Rand, which is averted from the sample to be examined, a microwave radiation source is arranged, which is connected to a power source, wherein a receiving waveguide at the same height on the other side, opposite to the Transmitting waveguide is arranged, wherein the two waveguides as a unit on a support frame over an adjusting device are adjustably arranged, and the waveguides are made of a hollow metal profile, and the sample between arranged the two mutually facing ends of the waveguide is, wherein at the receiving waveguide to a connected to a multimeter microwave receiver the side facing away from the sample to be examined arranged is.

In an advantageous embodiment, the positioning mechanism of the waveguide with an electric provided with the control of the speed of the waveguide adjustment along the sample.

On this way can be a continuous movement of the waveguides, and therefore ensures a continuous measurement become.

In another advantageous embodiment represents the Gunn diode is the microwave radiation source.

In a further advantageous embodiment are in the two waveguides Apertures for the regulation of the radiation intensity installed. In this manner and way you can see the radiation intensity according to the character simply change the sample.

In In another advantageous embodiment, all elements are on a frame arranged. In this way can be a compact Facility are formed.

In another advantageous embodiment is the multimeter to a personal computer for a digital visualization and transmission the results in the form of curves and to register the measured values the intensity change the electromagnetic microwave radiation in dependence connected by the mass humidity.

In Another advantageous embodiment is the digital scale also connected to a personal computer to the displayed Sizes as continuous detection of the weight of the sample during the Moisture absorption to transfer.

Brief description of the drawings

The Invention will be presented below with the aid of drawings. Show it:

1 The construction scheme of the device according to the invention,

2 The basic graph with the parameters required to determine the capillary transport coefficient,

3 the graph that was formed on the basis of the examination of a concrete sample at the present institution,

4 the graph formed by measuring the weight of the sample during the moisture uptake with the subject device;

5 the graph of the determination of the coordinate of the position of the profile of the moisture front in a selected time interval from the beginning of the moisture absorption,

6 the measurement outputs processed in the Maple program

7 represents the graph of the moisture absorption curve determined by gravimetric method, ie with the decomposition, which is described in the prior art.

Embodiment of the invention

From the construction scheme in the 1 it can be seen that the device 1 for determining the moisture movement in porous materials according to the invention from a container 2 for the liquid, from a positioning mechanism 3 , which adjusts the height of the container 2 , and thus also serves the liquid level exists. Above the container 2 is the sample to be examined 16 which is hung on a suspension attached to a digital scale 5 collected over the sample. In the area above the container 2 is a broadcasting waveguide 8th arranged the microwave radiation, at the end of the container 2 remote edge is a source of radiation 15 In our case it is the Gunn diode connected to a voltage source 6 connected, which is required for the function of the Gunn diode. On the other side of the tank is opposite the broadcasting waveguide 8th a reception waveguide 9 arranged. The dashed arrows indicate the radiation flow. The two waveguides are as a unit with an adjustment 14 height adjustable arranged on a support frame, not shown. The adjusting device 14 is shown schematically with a bidirectional arrow. The waveguides 8th and 9 are made of a metal executed hollow profile. Also the scales 5 is arranged on the frame, not shown. At the two waveguides 8th and 9 are dazzles 12 and 13 installed, with the help of which the radiation intensity can be regulated. The sample 16 is between the mutually facing ends of the waveguides 8th and 9 arranged. At the reception waveguide 9 is on the tank 2 averted side of a microwave receiver 10 arranged, attached to the multimeter 11 is connected, in which the values of the changes of the radiation intensity can be read off.

The multimeter is connected to the computer, in which with the help of an appropriate software program the results, eg in the form of curves can be indicated. The communication program for reading the data from the screen of the digital scale and the software program to the multimeter also serves to transmit the displayed variables 11 ,

Before further describing the function of the device according to the invention, it makes sense to recall general characteristics of the materials investigated. When moistening the front of the sample 76 By contact with the liquid level, it comes at a certain time to absorb the moisture in a certain height of the sample. It is a so-called profile of the moisture front. The moisture in the sample is highest at the liquid level and goes back up along the sample. This changing humidity is the object of investigation.

First is the moisture gradient to investigate. If the temporal and spatial distribution of moisture, i.e. The so-called moisture gradient, known, can be out The values of the capillary transport coefficient K are determined from the measured values become.

In 2 the parameters required to determine the capillary transport coefficient are shown. A - start of the moisture front, B - length of the moisture front, C - length to the dry area, D - position of the x-coordinate

At the Use of a non-stationary Method of determining the capillary transport coefficient it makes sense several curves of moisture absorption for different times from Beginning of the experiment for to have one and the same sample (integral method). For the Matan method only one moisture absorption curve is sufficient, the non-stationary state formed and useful from the measurements in selected time intervals selected has been.

For the calculation Capillary transport coefficient is the method of Matan usual. at This method is sufficient to provide a moisture absorption curve have the time from the beginning of the experiment and the coordinates of the Course of the moisture front, which correspond to this curve. The Matan's method applies the Boltzmann transformation that occurs at short times is applicable where the boundary condition at the dry end the sample does not yet come into its own.

(u(x,t) = ω(η), u(0,t) = u1, u(x,0) = u2) (2)wird die Lösung der partialen Differentialgleichung zur Lösung einer gewöhnlichen Differentialgleichung in einer neuen Variablen η:

mit Randbedingungen ω(0) = u₁, ω(∞) = u₂,
wo

Ω

Neue Variable unter der Voraussetzung, daß t ein ausgewählter Zeitintervall ist

H

Transformation, bezeichnet als Boltzmannkoordinate [m·s-1/2]

u₁

Bestimmter zeitbedingter erreichter Wert der Massenfeuchtigkeit [-]

u₂

Massenfeuchtigkeit des Materials im stationären Zustand als relative Feuchtigkeit [-]

For simplification of the calculation, the function transformation of two variables u, t has been applied to the function of a variable η:
Through a Boltzmann transformation:

(u (x, t) = ω (η), u (0, t) = u 1 , u (x, 0) = u 2 ) (2) becomes the solution of the partial differential equation for solving an ordinary differential equation in a new variable η:

with boundary conditions ω (0) = u ₁ , ω (∞) = u ₂ ,
Where

Ω

New variable, provided that t is a selected time interval

H

Transformation, referred to as Boltzmann coordinate [m · s-1/2]

u ₁

Specific time-related value of mass moisture reached [-]

u ₂

Mass moisture of the material in the stationary state as relative humidity [-]

κ(u(x))

Kapillartransportkoeffizient, als Funktion der Feuchtigkeit von der Länge untersuchten Materialprobe in der Länge der Feuchtigkeitsfront [m²·s^{– 1}]

T

Zeitintervall, in dem die Feuchtigkeit als Funktion der Kurve u(x) in der Länge des Profils der Feuchtigkeitsfront gemessen wird [s]

Z

Substitution des entlang der Probe gemessenen Abstands vom Punkt an der Feuchtigkeitsaufnahmekurve du, die in der Gleichung bis ∞ ausgedrückt ist, für praktische Anwendung ist sie als Tor zum Intervall an der gemessnen Probe bis zum Abstand, wo die Feuchtigkeit den stationären Zustand erreichte, d.h. u₂, als Wert der relativen Feuchtigkeit des gemessenen Materials [-]

X

Koordinaten in der Länge der Probe und zur Identifizierung ihrer genauen Lage sind die Messwerte des Fortgangs der Feuchtigkeitsfront erforderlich, die ab der Ebene der unteren Fläche der gemessenen Probe feststellbar ist [m]

u'

Derivation der Feuchtigkeit gemäß der Raumkoordinate, anfangs wird sie ∞ sein und mit zunehmender Zeit wird sie zu 0 gehen. Durch die Substitution x durch ζ ist u' eine Derivation gemäß ζ [-]

Given a known distribution of moisture u (x) in the given time t, (ie t is a constant and u (x) is the function of a variable x) we can further transform equation (2) and find the capillary transport coefficient:

κ (u (x))

Capillary transport coefficient, as a function of moisture of the length of the examined material sample in the length of the moisture front [m ² · s ^{- 1} ]

T

Time interval in which the moisture is measured as a function of the curve u (x) in the length of the profile of the moisture front [s]

Z

Substitution of the distance measured along the sample from the point on the moisture uptake curve you expressed in the equation to ∞, for practical application it is as a gate to the interval at the measured sample to the distance where the moisture reached the stationary state, ie u ₂ , as the value of the relative humidity of the measured material [-]

X

Coordinates in the length of the sample and in order to identify their exact location require measurements of the progress of the moisture front, which can be observed from the level of the lower surface of the measured sample [m]

u '

Derivation of moisture according to the space coordinate, initially it will be ∞ and with time it will go to 0. By the substitution x by ζ, u 'is a derivation according to ζ [-]

to Determination of the position of the weight moisture in the porous structure an inert substance, the electromagnetic radiation is applied, which allows a non-destructive and continuous measurement points a high sensitivity, and the measurement result is more chemical Composition of the substance or the amount of chemically bound Water is not affected.

The microwaves penetrate through the material regardless of its properties. For measuring the Kapillartransportkoeffizienten in porous building materials, a frequency of 10 ¹⁰ Hz is suitable.

When working with the device according to the invention, the procedure is as follows:
When the moisture movement is detected, the determination of the intensity change of the electromagnetic microwave radiation is applied as a function of the mass moisture in the porous material. It involves the detection of the one-dimensional transport process in laboratory conditions in samples of building materials in their direct contact with the water level. The detection of the changes in the intensity of the electromagnetic microwave radiation passing through the sample serves to detect the position and amount of moisture contained in the porous material due to a synchronized time-dependent movement of the waveguide - the transmitting and receiving antenna along the examined building material sample. The values of the positioning mechanism of the waveguides expressed in time can be transmitted by converting the speed of the drive into length values, see 5 ,

The Measuring equipment is connected to a personal computer. For transmission the displayed sizes a communication program for reading data from the screen of the digital scale and the software program to the multimeter.

The 3 contains a graph, which was formed by examining a concrete sample from the gas silicate with the objective device and which depicts the dependence of the change in the intensity of the electromagnetic microwave radiation on the mass moisture in mV in the fired piece of broken glass. It is a functional dependence of the change in the intensity of the electromagnetic microwave radiation on the mass moisture.

The 4 contains a graph that was formed by examining another concrete sample from the fired body with the objective device and represents a curve of the moisture absorption of a Galkalkbetonprobe as a function of time.

In the 5 the position of the profile of the moisture front in the selected time interval from the beginning of the moisture absorption as well as the transmission of the time information in length data using a synchronized drive unit and using the Linregrese Exel program is shown graphically.

The Values acquired during the measurement can be used to determine the capillary transport coefficient be used by procedures other than the determination of Moisture distribution (u / x, t) along the sample at selected time intervals, i.e. from the determination of the moisture absorption curves in the non-stationary state emerge. For moisture determination at the given place It makes sense to use the microwave radiation measurement of the sample. The higher the moisture of the material is, the smaller amount of microwave radiation can penetrate through the material, because the hydrogen nuclei of water molecules absorb the microwave radiation. Due to the measurement by means of Microwave radiation can determines the moisture at the given location of the material and the moisture intake curves are formed for the Determination of Kapillartransportkoeffizienten K are required.

The simplest dependency type is the linear dependency. The measured values obtained with the assembled apparatus in approximation by a k-th degree polynomial enable the processing of the results in the Linregrese Exel program. For further calculations from the measured values it makes sense to use the mathematical program system Maple, which makes it possible to work with almost arbitrarily large numbers, to easily define function dependencies, sets, etc., to represent point data, curves, surfaces in different ways. solve algebraic and differential equations and perform calculations using numerical methods. In the 6 the Maple program outputs are shown.

Industrial application

The invention makes it possible to determine input data for the determination of the capillary transport coefficient of porous building materials using the properties of the electromagnetic microwave radiation. The method is given by the initial and boundary conditions of moisture uptake before steady state, which corresponds to the state of complete water saturation for a number of building materials. In comparison to known laboratory methods, it has a comparable accuracy, lower technical requirements for equipment and protection against side effects. The assembled measuring apparatus allows not only to determine the movement of the moisture profile but also the determination of the amount of water that penetrates into the porous material at capillary rise, as well as the determination of the calibration dependency for the transfer of the measured values of the electric potential to represent the functional dependence of the change in intensity electromagnetic microwave radiation into energy units in mV, optionally as damping in decibels with inserted calibrated diaphragms 12 and 13 depending on the mass humidity of the examined sample.

Of the Concrete advantage of the measuring apparatus can not only in the possibility the establishment of a methodology for Determination of moisture transport in porous materials using the described measuring device, but also in their further Use at the for practical purposes Research of the moisture problem seen in building constructions become.

• – Bestimmung des Feuchtigkeitstransports in Baustoffen bei wiederholter Feuchtigkeitsaufnahme und Austrocknung,
• – Bestimmung der Feuchtigkeitsbewegung in Baustoffen unter Einfluss und Einwirkung des mineralsalzhaltigen Wassers,
• – Bestimmung des Feuchtigkeitstransports in Baustoffen bei Anwendung von Verfahren zur Unterdrückung der Feuchtigkeitsverbreitung in Baukonstruktionen durch Trocknungsmethoden,
• – Fassung von direkten Schlussfolgerungen zur Effizienz der vorgeschlagenen elektroosmotischen Methode in der Projektphase für konkrete Beispiele,
• – experimentelle Bestimmung des Kapillaraufstiegs,
• – Feuchtigkeitsverbreitung durch die Schnittstelle zwischen unterschiedlichen Baustoffen.

Further examples of the use of the assembled measuring apparatus are the following:

• - Determination of moisture transport in building materials with repeated moisture absorption and dehydration,
• - Determination of the moisture movement in building materials under the influence and influence of mineral water,
• - Determination of moisture transport in building materials using methods of suppressing the spread of moisture in building structures by means of drying methods,
• - Provide direct conclusions on the efficiency of the proposed electroosmotic method in the project phase for concrete examples,
• - experimental determination of capillary rise,
• - Moisture diffusion through the interface between different building materials.

Claims (8)

The device for determining the moisture transport in porous materials consisting of a moisture container 1 and a suspension for the sample, characterized in that it also consists of a positioning mechanism ( 3 ) for the height adjustment of the container ( 2 ), and thus also of the liquid level, the suspension ( 4 ) at the top of a digital scale ( 5 ) which is fastened above it, wherein above the container ( 2 ) a transmission waveguide ( 8th ) the microwave radiation is arranged, at the edge of which from the container ( 2 ), a microwave radiation source ( 15 ) which is connected to a voltage source ( 6 ), on the other side opposite the transmission waveguide ( 8th ) a receive waveguide ( 9 ) is arranged at the same height, wherein the two waveguides as a unit on a support frame via an adjustment device ( 14 ) are arranged adjustable, and the waveguides are made of a hollow metal profile, and the sample ( 16 ) between the mutually facing ends of the waveguides ( 8th . 9 ) is arranged, wherein at the receiving waveguide ( 9 ) on the container ( 2 ) facing away from a multimeter ( 11 ) connected microwave receiver ( 10 ) is arranged. The device according to claim 1, characterized in that the adjusting mechanism ( 14 ) the waveguide ( 8th . 9 ) is provided with an electric motor with regulation of the adjustment speed. The device according to claim 1, characterized in that the microwave radiation source is a Gunn diode ( 15 ). The device according to claim 1, characterized in that in the two waveguides ( 8th . 9 ) Aperture ( 12 . 13 ) are installed for the regulation of the radiation intensity. The device according to claim 1, characterized in that that all Elements are arranged on a frame. The device according to claim 1, characterized in that the multimeter ( 11 ) to a personal computer ( 17 ) is connected for the visualization of the results, eg in the form of curves. The device according to claim 1, characterized in that the balance ( 5 ) also to a personal computer ( 17 ) is connected to transmit the displayed quantities. The device according to claim 1, characterized in that the positioning mechanism ( 3 ) a precise delimitation and adjustment of the contact of the examined sample ( 16 ) with the level of the liquid in the container ( 2 ).