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ABSTRACT
The focus of this paper was to examine the contribution of two key mechanisms—moisture convection and diffusion–on heated air and moisture transfer in porous building envelopes and to define the validity of the sub-models. A numerical simulation was performed and is focused on the one-dimensional problem for drying test boundary conditions. Thereafter, a detailed parametric analysis was carried out in order to investigate the influence of typical nondimensional parameters. Results show that convection is a prominent driving potential with respect to the diffusion process when the hygric state is stable between the environment and the envelope.
Nomenclature
| cq | = | heat capacity (J/kg · K) |
| ca | = | humid air capacity coefficient (kg/kg · Pa) |
| cs | = | surface concentration (Kmol/m2) |
| Dl | = | liquid diffusivity coefficient (m2/s) |
| Dm | = | moisture diffusion coefficient (m2/s) |
| Dv | = | vapor diffusion coefficient (m2/s) |
| = | surface diffusion coefficient (m2/s) | |
| hl | = | specific enthalpy of the liquid (J/kg) |
| hv | = | specific enthalpy of the vapor (J/kg) |
| hlv | = | specific enthalpy of vaporization (J/kg) |
| jvs | = | surface diffusion flux (mol/m · s) |
| kfl | = | liquid filtration coefficient (kg/m · s · Pa) |
| kfv | = | vapor filtration coefficient (kg/m · s · Pa) |
| k | = | thermal conductivity (W/m · K) |
| ka | = | air permeability (m2) |
| kf | = | infiltration coefficient (kg/m · s · Pa) |
| m | = | moisture content (kg/kg) |
| M | = | molecular weight (kg/mol) |
| p | = | total pressure (Pa) |
| rp | = | radius of the passage or capillary |
| t | = | time (s) |
| T | = | temperature (K) |
| δ | = | thermal gradient coefficient (kgmoisture/kg · K) |
| ρs | = | dry density (kg/m3) |
| α | = | thermal diffusivity (m2/s) |
| χ | = | ratio of vapor diffusion coefficient to total moisture diffusion coefficient |
Nomenclature
| cq | = | heat capacity (J/kg · K) |
| ca | = | humid air capacity coefficient (kg/kg · Pa) |
| cs | = | surface concentration (Kmol/m2) |
| Dl | = | liquid diffusivity coefficient (m2/s) |
| Dm | = | moisture diffusion coefficient (m2/s) |
| Dv | = | vapor diffusion coefficient (m2/s) |
| = | surface diffusion coefficient (m2/s) | |
| hl | = | specific enthalpy of the liquid (J/kg) |
| hv | = | specific enthalpy of the vapor (J/kg) |
| hlv | = | specific enthalpy of vaporization (J/kg) |
| jvs | = | surface diffusion flux (mol/m · s) |
| kfl | = | liquid filtration coefficient (kg/m · s · Pa) |
| kfv | = | vapor filtration coefficient (kg/m · s · Pa) |
| k | = | thermal conductivity (W/m · K) |
| ka | = | air permeability (m2) |
| kf | = | infiltration coefficient (kg/m · s · Pa) |
| m | = | moisture content (kg/kg) |
| M | = | molecular weight (kg/mol) |
| p | = | total pressure (Pa) |
| rp | = | radius of the passage or capillary |
| t | = | time (s) |
| T | = | temperature (K) |
| δ | = | thermal gradient coefficient (kgmoisture/kg · K) |
| ρs | = | dry density (kg/m3) |
| α | = | thermal diffusivity (m2/s) |
| χ | = | ratio of vapor diffusion coefficient to total moisture diffusion coefficient |