Environmental Engineering Reference
In-Depth Information
channel will be measured and be considered as proof. This humidity will result from
the surrounding stone [BAS 84; BAS 95]. Analysis using such a process will be
interesting for a hygroscopic stone: from the relative humidity of the air in the
channel, we can deduce the water content of the stone at the available
sorption/desorption isotherm condition of this stone (in the case of hysteresis, it will
be necessary to know whether the stone humidity is increasing or decreasing). More
practical hygrometric probes (regarding size, rapidity, low brittleness) include
capacitance ones: the sensor is a microcondenser with a thin dieletctric layer with a
permittivity depending on the relative humidity of the contact air.
10.2.3.
Phenomenologic parameters and related parameters
There are various parameters appearing, such as proportionality coefficients in
Darcy, Fick's and Fourier's laws, and related parameters. They are present in system
[10.3]. There is for instance λ*(θ, T) [W/m.K], apparent thermal conductivity
resulting from the overlapping of a pure conduction phenomenon (Fourier's law)
and a heat from a phase change linked to vapor transport. There is also D
θ
[m
2
/s],
mass diffusivity in liquid phase, and vapor and K
1
[m/s], hydraulic conductivity.
Coupling terms D
T
and D
Tv
can be calculated [CRA 96] or measured [DAI 93]. They
are relatively low. We do not describe them here.
The development of system [10.3] can be done in two phases:
- conception and experimentation allowing to us determine one parameter each
time (i.e. λ*) in a more or less extended area of stone where the area is characterized
by its water content and humidity;
- eventual subsequent injection of data found for the parameters in a numeric
model resulting from a system such as [10.3] in order to simulate a given heat and
humidity transport.
As the basic principle consists of analyzing the response of a certain rock volume
that was in an initial equilibrium to a thermal and/or hydric disruption, weak
perturbations allowing a linearization of transfer equations will be distinguished
from strong ones. Brief and long perturbations (related to the type of transport) will
also be distinguished. Finally, the types of limiting conditions of the volume
considered will be distinguished. Fluxmetry will be used first in this instance.
10.2.3.1
. Fluxmetry
10.2.3.1.1. Heat
Fluxmetry should probably deserve a better place in thermal discipline. We can
be conducted to measure densities of thermal flux [W/m
2
.K]: the sensor (fluxmeter)
