Device for measuring the activity of a liquid in a complex medium and associated method
AssigneesCentre National De La Recherche Scientifique, Universite Montpellier 2
InventorsJean-Claude Benet, Bruno Cousin, Fabien Cherblanc, Samuel Ouoba
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Abstract
A device for measuring the activity of a liquid in a complex medium and an associated method, the device comprising a sealed enclosure in which the complex medium is intended to be placed and means for maintaining this enclosure at a constant temperature T, characterized in that it comprises: a means (14) for modifying the total volume of the enclosure; a pressure sensor (22) for measuring the total pressure in the enclosure; and means (24) for calculating the activity of the liquid in the complex medium from the temperature T, from the total volume of the enclosure and from the total pressure in the enclosure.
Claims10
A device for measuring the activity of a liquid in a complex medium, comprising a sealed enclosure, said enclosure being also an isotherm enclosure which is therefore capable of maintaining this enclosure at a constant temperature T and in which the complex medium is intended to be placed, wherein the device comprises:
- a means for modifying the total volume of the enclosure;
- a pressure sensor for measuring the total pressure in the enclosure;
- a means for calculating the activity of the liquid in the complex medium, from the temperature T of the enclosure, the total volume of the enclosure and the total pressure in the enclosure.
A method for measuring the activity of a liquid in a complex medium, wherein the method comprises the steps consisting, after having placed the complex medium in a sealed enclosure, said enclosure being also an isotherm enclosure which is therefore capable of maintaining this enclosure at a constant temperature T, in:
- (a) performing a basic increment Δvj of the enclosure volume;
- (b) after having reached the thermodynamic balance between the complex medium and the enclosure, maintaining the total pressure pi, measured in the enclosure;
- (c) determining a relationship (R1) between the total pressure pi, the partial liquid vapor pressure at balance pveq and the partial pressure of the ideal gas not being dissolved, for example air, the latter being expressed using the ideal gas law, such that the relationship (R1) is expressed:
- p
- i
- =
- p
- veq
- +
- n
- a
-
- RT
- v
- i
- (
- R
-
-
- 1
- )
- in which:
- R is the ideal gases constant;
- na is the number of moles of the ideal gas not being dissolved;
- vi is the total volume of the enclosure, defined by the relationship:
- v
- i
- =
- v
- 0
- +
- ∑
- j
- =
- 1
- i
-
-
- Δ
-
-
- v
- j
- with vo being the initial volume of the enclosure
- (d) repeating steps (a) to (c) n times, with n>1 if the initial volume of the enclosure is known or n>2 otherwise, to deduce therefrom the value of the partial balance vapor pressure pveq;
- and
- (e) calculating the activity of the liquid aw in the complex medium by the following relationship (R2):
- a
- w
- =
- p
- veq
- p
- vs
-
- (
- T
- )
- (
- R2
- )
- in which:
- pvs(T) is the saturating vapor pressure of the pure liquid at the temperature T.
Dependencies are inferred from the claim text.