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Thermal osmosis in liquids
Journal of Membrane Scrence, l(l976)
149-164
149
o Rlsevrer Screntffic Pubhshmg Company, Amsterdam - Prmted m The Netherlands
THERMAL OSMOSIS IN LIQUIDS
H. VINK and S A.A CHISHTI
Institute of Physzcal Chemistry, (Sweden) (Recerved November 17,1975,
Unruers~ty of Uppsala. P 0 Box 532, 751 21 Uppsala m revrsed form January 8,1976)
Summary A new type of thermo-osmotrc cell, provrded wrth magnetuxlly operated stnrers, has been constructed. With the strrrers, temperature gradients within the liquid compartments can be ehminated and thus the effective temperature gradient m the membrane determined. The instrument has been used to determine thermo-osmotrc transport parameters for cellophane and cellulose acetate membranes in water and m a number of orgamc hqmds and liquid mixtures.
Introduction Material flow through membranes under the influence of a temperature gradient is known as thermal osmosis. If the material flows are confined to closed compartments on both sides of the membrane, a pressure difference is built up across the membrane and the material flows eventually stop. The resulting stationary pressure difference is called the thermo-osmotic pressure. In multicomponent solutions, concentration differences are also estabhshed between the two sides of the membrane. Thermal osmosis is related to the phenomenon of thermal diffusion in liquid mixtures, as the membrane lattice may be looked upon as a “solute” component, which is fixed in space by external constraints. Compared with thermal diffusion, there are still rather few investigations of thermal osmosis reported in the literature. With a few exceptions [1,2], these investigations have been concerned with thermal osmosis in pure water and aqueous solutions. In the present work the investigations have been extended to a number of organic liquids and liquid mixtures. It has also been possible to ehmmate the effect of disturbing temperature gradients at the membrane boundaries and thus to determine the real magnitude of the thermo-osmotic effect. TheOI&iCd
A general phenomenological theory of the transport processes in thermal
164
_ 4
=
(
~211---12,
Wl
w2
i&-
)
_
ah aw2 _
87
(A33)
r+w2au)2
In these equations the phenomenolo@cal coefficients Sz, and the derwatives of 7 and pig, which are all functions of temperature, pressure, and composition, are referred to the mean values of these variables (?: 5, and W,).
149-164
149
o Rlsevrer Screntffic Pubhshmg Company, Amsterdam - Prmted m The Netherlands
THERMAL OSMOSIS IN LIQUIDS
H. VINK and S A.A CHISHTI
Institute of Physzcal Chemistry, (Sweden) (Recerved November 17,1975,
Unruers~ty of Uppsala. P 0 Box 532, 751 21 Uppsala m revrsed form January 8,1976)
Summary A new type of thermo-osmotrc cell, provrded wrth magnetuxlly operated stnrers, has been constructed. With the strrrers, temperature gradients within the liquid compartments can be ehminated and thus the effective temperature gradient m the membrane determined. The instrument has been used to determine thermo-osmotrc transport parameters for cellophane and cellulose acetate membranes in water and m a number of orgamc hqmds and liquid mixtures.
Introduction Material flow through membranes under the influence of a temperature gradient is known as thermal osmosis. If the material flows are confined to closed compartments on both sides of the membrane, a pressure difference is built up across the membrane and the material flows eventually stop. The resulting stationary pressure difference is called the thermo-osmotic pressure. In multicomponent solutions, concentration differences are also estabhshed between the two sides of the membrane. Thermal osmosis is related to the phenomenon of thermal diffusion in liquid mixtures, as the membrane lattice may be looked upon as a “solute” component, which is fixed in space by external constraints. Compared with thermal diffusion, there are still rather few investigations of thermal osmosis reported in the literature. With a few exceptions [1,2], these investigations have been concerned with thermal osmosis in pure water and aqueous solutions. In the present work the investigations have been extended to a number of organic liquids and liquid mixtures. It has also been possible to ehmmate the effect of disturbing temperature gradients at the membrane boundaries and thus to determine the real magnitude of the thermo-osmotic effect. TheOI&iCd
A general phenomenological theory of the transport processes in thermal
164
_ 4
=
(
~211---12,
Wl
w2
i&-
)
_
ah aw2 _
87
(A33)
r+w2au)2
In these equations the phenomenolo@cal coefficients Sz, and the derwatives of 7 and pig, which are all functions of temperature, pressure, and composition, are referred to the mean values of these variables (?: 5, and W,).