Abstract
The purpose of this work was to study both theoretically and experimentally the process of moisture redistribution and heat transfer due to phase changes during the tests of thermal conductivity in aerated autoclaved concrete (AAC) moist specimens. The different moisture contents of the test samples were obtained in climatic chamber at equilibrium conditions reached with constant air temperature and variable relative humidity. The moist specimens were sealed inside highly impermeable polyethylene bag, as required by UNI 10051, and placed in a heat flow meter apparatus. During the experimental thermal conductivity measurements, the temperature and heat flow rate were measured under transient and steady state conditions. A theoretical analysis of the heat and mass transfer process was performed and then a suitable numerical model was used to predict the moisture redistribution and heat transfer due to the phase changes. The theoretical model has been compared against the experimental data. Substantial agreement between numerical results and experimental data was found. Then several numerical simulations have been performed to study the influence of the errors due to phase changes and non-uniform moisture distribution during the test of thermal conductivity of moist AAC specimens.
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Abbreviations
- \(A\) :
-
Coefficient
- \(a\) :
-
Coefficient
- \(B\) :
-
Coefficient
- \(c\) :
-
Specific heat (J/kg K)
- \(D\) :
-
Diffusion coefficient (m\(^{2}\)/s)
- \(E\) :
-
Error
- \(h\) :
-
Specific enthalpy (J/kg)
- g :
-
Gravity vector (m/s\(^{2}\))
- j :
-
Mass flux vector (kg/m\(^{2}\,\)s)
- \(K\) :
-
Intrinsic permeability (m\(^{2}\))
- \(L\) :
-
Thickness (m)
- M:
-
Molar mass (kg/kmol)
- \(m\) :
-
Mass (kg)
- \(\dot{m}\) :
-
Evaporated water in units of time and volume (kg/m\(^{3}\,\)s)
- \(n\) :
-
Coefficient
- \(p\) :
-
Pressure (Pa)
- q :
-
Heat flux vector (W/m\(^{2}\))
- R:
-
Universal gas constant (J/kmol K)
- \(r\) :
-
Pore radius (m)
- RH:
-
Relative humidity
- \(S\) :
-
Saturation
- \(T\) :
-
Temperature (K)
- \(t\) :
-
Time (s)
- \(u\) :
-
Moisture content mass by mass
- v :
-
Velocity vector (m/s)
- \(w\) :
-
Moisture content mass by volume (kg/m\(^{3}\))
- \(\alpha \) :
-
Coefficient
- \(\beta \) :
-
Coefficient
- \(\delta \) :
-
Coefficient
- \(\varepsilon \) :
-
Porosity
- \(\gamma \) :
-
Surface tension (N/m)
- \(\lambda \) :
-
Thermal conductivity (W/m K)
- \(\mu \) :
-
Viscosity (kg/m s)
- \(\rho \) :
-
Density (kg/m\(^{3}\))
- \(\tau \) :
-
Tortuosity
- \(a\) :
-
Air
- \(c\) :
-
Capillary
- \(d\) :
-
Dry
- \(da\) :
-
Dry air
- \(g\) :
-
Gaseous phase
- \(irr\) :
-
Irreducible
- \(l\) :
-
Liquid phase
- \(r\) :
-
Relative
- \(tot\) :
-
Total
- \(vap\) :
-
Evaporation
- \(w\) :
-
Moist
- \(wv\) :
-
Water vapor
References
Baggio, P., Maiorana, C.E., Schrefler, B.A.: Thermo-hygro-mechanical analysis of concrete. Int. J. Numer. Methods Fluids 20, 573–595 (1995)
Baggio, P., Campanale, M., Moro, L.: Analytical and experimental investigations on the transient heat transfer process in moist wood wool slabs. J. Therm. Envel. Build. Sci. 24, 211–225 (2001)
Degiovanni, A., Moyne, C.: Conductivité thermique de matériaux poreux humides: évaluation théorique et possibilité de mesure. Int. J. Heat Mass Transf. 30(11), 2225–2245 (1987)
Galbraith, G.H., Mclean, R.C., Guo, J., Kelly, D., Lee, C.: The use of differential permeability in moisture transport modelling. In: Proceedings of Building Performance Simulation, Kyoto, vol. 1, pp. 267–271 (1999)
Hansen, K.K.: Sorption Isotherms, a Catalogue. Department of Civil Engineering, The Technical University of Denmark, Building Materials Laboratory (1986)
Hassanizadeh, M., Gray, W.G.: General conservation equations for multiphase systems: 1 averaging technique. Adv. Water Res. 2, 131–144 (1979)
Hassanizadeh, M., Gray, W.G.: General conservation equations for multiphase systems: 2 mass, momenta, energy and entropy equations. Adv. Water Res. 2, 191–203 (1979)
Hassanizadeh, M., Gray, W.G.: General conservation equations for multiphase systems: 3 constitutive theory for porous media flow. Adv. Water Res. 3, 25–40 (1980)
ISO 10051: Thermal insulation. Moisture effects on heat transfer. Determination of thermal transmissivity of a moist material (1996)
Kumaran, M.K.: Moisture transport trough glass-fibre insulation in the presence of a thermal gradient. J. Therm. Insulation 10, 243–255 (1987)
Nasrallah, S.B., Perre, P.: Detailed study of a model of heat and mass transfer during convective drying processes. Int. J. Heat Mass Transf. 31(5), 957–967 (1988)
Roels, S., Carmeliet, J., Hens, H., Adan, O., Brocken, H., Cerny, R., Pavlik, Z., Hall, C., Kumaran, K., Pel, L., Plagge, R.: Interlaboratory comparison of hygric properties of porous building materials. J. Therm. Envelope Build. Sci. 27(4), 307–325 (2004)
Sandberg, P.I.: Thermal Resistance of Wet Insulation Materials. Technical Report 29. Swedish National Testing Institute, Boras, Sweden (1986)
Whitaker, S.: Simultaneous heat mass and momentum transfer in porous media: a theory of drying. Adv. Heat Transf. 13, 119–203 (1977)
Whitaker, S.: Heat and mass transfer in granular porous media. Adv. Dry. 1, 23–61 (1980)
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Annex A
Annex A
-
Dry density AAC 450: \(\rho _{d} = 450\,\text{ kg}/\text{ m}^{3}\)
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Dry density AAC 350: \(\rho _{d} = 350 \text{ kg}/\text{ m}^{3}\)
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Dry thermal conductivity AAC 450: \(\lambda _{d} = 0.122\) W/m K
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Dry thermal conductivity AAC 350: \(\lambda _{d} =0.097\) W/m K
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Irreducible saturation: \(S_{irr} = 0.09\)
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Porosity AAC 450: \(\varepsilon = 0.80\)
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Porosity AAC 350: \(\varepsilon = 0.843\)
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Specific heat: \(c_{ps} = 850\) J/kg K
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\(A = 0.920\,\text{ kg}_\mathrm{w}/\text{ kg}_\mathrm{d}\)
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\(a = 0.0004\,\text{ Wm}^{2}\)/kg K
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\(B = 0.123{\,\cdot \,}10^{-3}\)
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\(D_{a} = 2.58{\,\cdot \,}10^{-5}\,\text{ m}^{2}/\text{ s}\)
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\(K = 10^{-12}\,\text{ m}^{2}\)
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\(n = 2.211\)
-
\(\alpha = 0.293\)
-
\(\beta = 1.131\)
-
\(\delta = 20.273\)
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Campanale, M., Deganello, M. & Moro, L. Effect of Moisture Movement on Tested Thermal Conductivity of Moist Aerated Autoclaved Concrete. Transp Porous Med 98, 125–146 (2013). https://doi.org/10.1007/s11242-013-0136-z
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DOI: https://doi.org/10.1007/s11242-013-0136-z