Channel concentrate

Because surface binding causes bulk concentration depletion, protein solution was flowed continuously through the channels until the bulk concentration became stabile. This required an aliquot roughly equal to 4 or 5 times the channel volume in the microchannels with the lowest protein concentration, while the highest concentration channels required considerably less flow, as expected. A line profile generated from the epifluorescence image of these channels is shown in Fig. 6.10b. The majority of the signal emanated from the bulk. 

Full-column stacking with subsequent sample matrix removed by polarity reversal was achieved using a pre-concentration channel coupled to the separa-... 

An imager in which CCD registers are separated by regions having high impurity concentration (channel stops) and a method of manufacturing the imager is shown in JP-A-58171848 (Fujitsu KK, Japan, 08.10.83). 

The salt solution is pumped through the dialysate and concentrate channels, with salt removed continuously along the length from the dialysate channel and transferred to the concentrate channel. A dialysate and concentrate channel with the associated membranes are termed a cell pair. A typical electrodialysis stack may have 50 to 300 cell pairs between a single pair of electrodes, and a number of stacks may be used in series to achieve the desired level of salt removal. 

Eventually, the diffusion layers fill the channels, and thereafter the ion concentration begins to decrease in the center of the dialysate channel and to increase in the concentrate channel. At infinite channel lengths the concentrations in the dialysate and concentrate channels would tend to limiting values corresponding to the total applied potential drop being taken up by the... 

To model the electrodialysis stack, we assume that since there are many cells in a stack the behaviors in different pairs of adjacent dialysate and concentrate channels are the same. If we neglect the potential drop in the electrode cells adjacent to the electrodes as small compared with that in the rest of the system, the potential drop across a channel pair is constant and equal to the total applied voltage divided by the number of channel pairs. The dialysate and concentrate channels are taken to have the same separation 2h (Fig. 6.2.1). Since there is symmetry about the center plane of each channel, we may model the electrodialysis cell pair of Fig. 6.2.1 by one half of the dialysate channel and one half of the adjacent concentrate channel separated by a membrane, as shown in Fig. 6.2.4. For specificity we choose the cation exchange membrane. Both types of membranes are assumed to have the same resistances and thicknesses and to be perfectly selective. To simplify the problem somewhat further, we take the membrane resistance to be small so that the ohmic drop within the membranes may be neglected. 

Electrolyte concentration Channel Gate area length/width ON/OFF Switch speed Switch speed (ON = OFF)a... 

Fig 5.2 is a schematic diagram of a tubular type gas-diffusion separator. The separator is column shaped, with two concentric channels. The tubular membrane forms the inner channel, usually reserved for the donor stream, and extends beyond the outer channel to be connected to the suppK and waste conduits. The terminals of the outer channel are extended to inlet and outlet ports on the column which are furnished with connectors for the acceptor stream conduits. 

Once the distribution of ion concentration is found, we can obtain the distribution of potential from (7.38). But we should note first that the total potential drop is a sum of the drop in the dialyzate and concentrate channels and the drop at the membrane. The potential drop at the membrane is analogous to concentration overvoltage at the electrode caused by the difference of ion concentrations at membrane surfaces. For a cation-exchange membrane, the potential drop is equal to... 

Spiral heat exchangers are constructed by winding two long strip of plate metal around a center to form a spiral body, which then contains two concentric channels. Each channel is welded closed at alternate sides (see Fig. 27.1). Covers are then bolted over each side of the spiral body to complete the unit. When both of these covers are removed, the entire surface area of the exchanger is available for manual cleaning. 

Two injection units are used in this method, which are joined through a specially designed nozzle. In the Battenfeld design, the nozzle is equipped with two separate concentric channels that can be independently, operated, opened, and closed hydraulically. This allows the process sequence to be carefully controlled. 

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