Capillary Condensation

capillary condensation

[′kap·ə‚ler·ē ‚kän‚den′sā·shən]
(physical chemistry)
Condensation of an adsorbed vapor within the pores of the adsorbate.

Capillary Condensation

 

the condensation of vapor in the capillaries and microcracks of porous bodies or in the interstices between closely packed particles.

A necessary condition for capillary condensation is the wetting of the surface of the material (particles) by the liquid. Capillary condensation starts with the adsorption of vapor molecules by the condensation surface and the formation of liquid menisci. The pressure of the saturated vapor over concave menisci is, according to Kelvin’s equation, lower than the saturated vapor pressure p0 over a flat surface. Capillary condensation proceeds, therefore, at lower vapor pressures than the saturation pressure P0. The volume of liquid condensed in pores attains its limiting value at external vapor pressure p = p0, where the liquid-gas interface has zero curvature (plane, catenoid).

The complex capillary structure of a porous body may be the cause of capillary hysteresis, that is, the dependence of the quantity of liquid condensed in the pores not only on vapor pressure but also on the prehistory of the process, that is, how the given state was attained—by the condensation or by the evaporation of the liquid.

Capillary condensation increases the absorption (sorption) of vapors by porous bodies, particularly near the point of vapor saturation. The phenomenon of capillary condensation is used industrially in trapping liquids by finely porous materials (sorbents). Capillary condensation also has an important role in the processes of drying and moisture retention in soils, construction materials, and other porous materials.

REFERENCE

Kurs fizicheskoi khimii, 2nd ed., vol. 1. Edited by Ia. I. Gerasimov. Moscow, 1969.

N. V. CHURAEV

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Churaev, "Polymolecular Adsorption and Capillary Condensation in Narrow Slit Pores," J.
A Transport Membrane Humidifier (TMH) concept was developed by using a nanoporous membrane that facilitates a capillary condensation separation mechanism which transports water vapor only from furnace combustion flue gas to humidify building air.
The low-temperature, high-flow-rate, dry room air passing over the membrane surfaces provides adequate membrane cooling to facilitate the high-performance capillary condensation water vapor separation mode.
Importantly, the capillary condensation separation mode of the membrane prohibits the transfer of noncondensible gases such as nitrogen, carbon dioxide, etc.
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