Hydraulic gradient condensers

The temperature rising in the vicinity of the heaters causes an evaporation of liquid. Due to thermal and pressure gradients it comes to a vapour diffusion, which can lead to a strong modification of the humidity distribution in the barrier system. Modifications in the humidity distribution on the other hand directly affect the hydraulic characteristics, since the permeability depends strongly and nonlinearly on the saturation. By cooling it comes to a condensation of water vapour and thus to the increase of water saturation. For the permeation of water from the adjacent rock into the barrier system the characteristics of the multiphase flow are crucial in the contact area of both materials - the contrast in permeability, relative permeability and capillary pressure. For the water flow into the barrier, the subsequent delivery of water is further important due to regional hydraulic gradients. 

Condensation in a horizontal in-shell partial condenser with liquid outlet at the bottom and vapor outlets at the top was controlled hy vaijdng liquid level in the condenser. Excessive entrainment was caused by condenser pressure drop building a large hydraulic gradient... 

Notwithstanding any particular structural model, water transport in PEMs, in general, should be considered a superposition of diffusion in gradients of activity or concentration and hydraulic permeation in gradients of liquid or capillary pressure. Hydraulic permeation is the predominant mechanism xmder conditions for which water uptake is controlled by capillary condensation, whereas diffusion contributes significantly if water strongly interacts with the polymeric host. The molar flux of liquid water in the membrane, N, is thus given by... 

Under steady-state operation, local mechanical equilibrium prevails at all microscopic and macroscopic interfaces in the membrane. It fixes the stationary distribution of absorbed water. The condition of chemical equilibrium is, however, lifted to allow for the flux of water. Continuity of the net water flux in the PEM and across its interfaces with adjacent media adjusts the gradients in water activity or pressure in the system. Water fluxes occur by diffusion, hydraulic permeation, and electro-osmotic drag. At external interfaces, vaporization and condensation proceed at rates that match the net water flux. These mechanisms apply to PEM operation in a working cell, as well as to ex situ water flux measurements that are conducted in order to investigate the transport properties of PEMs. 

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