Internal sweep design

Third, Morgan etal.[ teach the use of a plurality of passages (fibres, tubes, or other conduits) embedded in the retentate end tube sheet that allow fluid communication between the retentate header and the shell. The pressure difference between the header and shell drives a portion of the retentate product back into the shell. The sweep flow rate is determined by the number and size of the passages and cannot be regulated externally. This internal sweep design is used extensively. Durban et al. [12] describe a modification in which a diffuser is used to distribute the sweep more uniformly in the shell. A channel or conduit extends from the retentate header through the tube sheet into the fibre bundle. The channel end in the header is left as an open orifice while the channel end in the fibre bundle is capped by a porous diffuser. 

A capillary-tube method to analyze binary liquid diffusivity was reported in Mickley et al. (1957) a straight, narrow bore capillary tube of known internal length has one end sealed and is filled with a binary solution of known composition. The capillary is maintained in a vertical position with the open end pointed upward. A slow stream of pure solvent is allowed to continuously sweep past the open mouth of the capillary tube. We shall designate species A as solute and species B as solvent. After an elapsed time, t, the capillary is removed and the solution it contains is well mixed and then analyzed for composition, to find how much solute A was extracted. Generally, several such experiments are conducted at different values of r. 

Potentiometric pH sensors are probably the most employed in corrosion studies. The simplest design is based on the introduction of the selected ionophore after silanization of the tip of the pulled capillary in which a silver chlorinated wire is immersed to serve as the internal reference electrode. This kind of microelectrodes can be mounted on the X-Y-Z positioning system to control the position and program the sweeping of the microelectrode. " " ... 

In some module designs, sweep gas is internally generated by modifying the membranes in the module.The amount of sweep gas required varies with the saturation temperature of the feed gas, pressure of operation and moisture contents desired in the dry product gas. The sweep air used in the membrane systems to achieve a -40 °C dew point air can be as high as 15-20% of the feed air. Lower amounts of purge may be needed for producing less dry air. Another way to move water vapor away from the permeate surface is the use of vacuum on the permeate side. Very moderate vacuum is needed and generally can be provided with water seal vacuum pumps or steam ejectors. 

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