Effect of temperature. transport properties J. FOŘT, Z. PAVLÍK, J. ŽUMÁR,, M. PAVLÍKOVA & R. ČERNÝ Č CTU PRAGUE, CZECH REPUBLIC

Transkript

1 Effect of temperature on water vapour transport properties J. FOŘT, Z. PAVLÍK, J. ŽUMÁR,, M. PAVLÍKOVA & R. ČERNÝ Č CTU PRAGUE, CZECH REPUBLIC

2 Outline Introduction motivation, water vapour transport Experimental Measured Sorption Cup material description and desorption experiment method experiment Results Conclusions

3 Introduction Water present in building materials represent always a problem for their durability and also reduces thermal insulation properties of insulation boards. Humidity in buildings interior can cause several healthy negative effects. Measurements of water vapour tranport in isothermal conditions are not sufficient for building material description. Its convenient for material comparation, but not for real enviroment of buidings. Because buildings are exposed to the variation of temperature from -30 to +50 C. Diffusion of water vapour may be enhanced as compared to the isothermal conditions. In this contribute we demonstrate effect of temperature on water vapour transport properties. And try to answer on question: question Is there any relation between temperature and water vapour transport?

4 Introduction effect of temperature on water vapour transport Temperamenture is one of main forces which strongly influences moisture movement (Arrhenius equation). Increase of temperature induces greater mobility of molecules in any form of moisture. Under temperature gradient a vapour pressure gradient develops in the gas phase and caused water to evaporate from one side on liquid islands and diffuse to a liquid islands, where its condenses. This process is then repeated on the other sides of liquid islands, causing the consequent increase of diffusive flux in porous material. Mechanism related to the use of an average temperature gradient in Fick s law. Thermal conductivity of the solid phase is greater than that of liquid phase, which is greater than air phase. Water vapour moves through the porous system of material where is temperature gradient, which provide driving force for the diffusion.

5 Experimental Studied material calcium silicate Basic physical properties Particle size distribution Sorption and desorption isothems measurement Cup method

6 Basic physical properties Bulk density measured on cubic samples - side 50mm 260kg/m3 Matrix density measured by helium pyknometry 2280kg/m3 Total open porosity calculated on the basis of the knowledge bulk and matrix density 0,88

7 Particle size distribution The particle size distribution was measured also on laser diffraction principle using the device Analysette 22 Micro Tec plus (Fritsch), measuring range µm.

8 Particle size distribution Q3(X) [%] D [MM] , ,000.00

9 Sorption and desorption Measured by DVS Advantage device Particular samples were exposed to partial water vapour pressure profiles : 0, 20, 40, 60, 80 and 98% of RH. dm/dt mode to get equillibrium, dm/dt of 0,00004% per minute was selected. Original samples and milled samples were measured.

10 Sorption and desorption isotherm original samples and dust CHANGE IN MASS (%) - REF 16 Calc.Silica - Sorp - dust Calc.Silica - Desorp - dust Calc.Silica - Sorp - 2pcs Calc.Silica - Desorp - 2pcs TARGET % P/PO

11 Cup method Modified cup method was used Sample size 100 x 100 mm Sample thicknesses 20, 30 and 50mm Isothermal conditions Temperature levels 10, 20, 30, 40 and 50 C Cup contain sorption material - silica gel Spheric presure sensor was placed Samples were placed in the climatic chamber Measurement of mass gain or mass loss for determination of water vapour properties

12 Relative humidity variation within measurement at 20 C C 70 TEMPERATURE [ C] C] TIME [H]

13 TEMPERATURE [ C] C] Temperature conditions in the climatic chamber at 50RH 10 C 20 C 30 C C 50 C TIME [H]

14 WATER VAPOR DIFFUSION COEFICIENT [M2/S] Results: Water vapour diffusion coeficient 2cm 3cm 5cm 1.8E E E E E E E E E E TEMPERATURE [ C] [

15 Water vapour diffusion resistance factor at 50RH WATER VAPOR DIFFUSIVITY RESISTANCE FACTOR [[-] 2cm 3cm 5cm TEMPERATURE [ C] [

16 Water vapour diffusion resistance factor in dependency on sample thickness at 50 RH Water vapor diffusion resintace factor [[-] Sample thickness [mm] µ (10 C) µ (20 C) µ (30 C) µ (40 C) (40 µ (50 C)

17 WATER VAPOUR DIFFUSIVITY RESISTANCE FACTOR [-] Water diffusivity resistance factor in dependency on RH 5cm sample 10 C 20 C 30 C C 50 C RH [%]

18 Mass gain at 50 C 2cm 3cm 5cm 8,000 10,000 TIME [S] 12, ,000 4,000 6,000 14,000 16,000 18,000 20,000

19 Conclusions Important effect of temperature on water vapour transport were revealed in studied material Similar performance can be expected also for other porous building materials Water vapour diffusion was increased by increasing temperature Highest water vapout transport resistivity were calculated for lower temperatures This effect was revealed also at 30, 75 and 91RH

20 Folie 19 JF1 Jan Fořt;

21 Thank you for your attention.