Plate exchange efficiency

If contact time is not enough for each stage to reach equilibrium, one may calculate the number of actual plates NAP by incorporating contacting efficiency. Two principal types of efficiency may be employed overall and stage. The overall exchanger efficiency, rj , can be used to relate NAP tind NTP as follows... 

In conjunction with membrane-based blood oxygenators for example, microchannels offer improved gas exchange efficiency and reduce the volume of blood required for initial priming. A device developed by Himg et al. [281] involves a stack of 16 plate units incorporating 110 pm deep by 230 pm wide microchannels sandwiched with oxygen permeable membranes (Fig. 7.22). Experimental results not only show improved gas exchange efficiency over both macrochannels and theoretical predictions, but also a reduction in apparent blood viscosity. 

Traditional heat recovery included the recovery of heat fron a dryer outlet, the hot dried product, and/or the outlet gas. Typical devices for heat recovery are presented in Figure 54.5. Conventional heat exchangers have the following efficiency indices thermal wheel, 75%-90% plate exchanger, =70% heat pipe, =60% scrubber, =60% and two-section exchanger, =50%. 

The gasketed plate exchanger is highly efficient and can be used in a cost-effective manner. Gasketed plates should be considered when heat exchange opportunities exist. 

Hausen H (1953) A definition of exchange efficiency of rectifying plates for binary and ternary mixtures. Chem Ind Tech 25 595... 

Fig. 10. Plate-—coil heat exchangers. Plate—coil is a very efficient and versatile prime surface-type heat exchanger.

Figure 10-7C. The patented COMPABLOG welded plate heat exchanger is technologically advanced, compact, and efficient. The fully welded design (but totally accessible on both sides) combines the best in performance, safety maintenance, and capital/maintenance costs. (Used by permission Vicarb Inc., Canada, publication VNT-3110 1997.)...

For those condensing duties where permissible pressure loss is less than 0.07kpf/cm there is no doubt but that the tubular unit is most efficient. Under such pressure-drop conditions only a portion of the length of a plate heat exchanger plate would be used and a substantial surface area would be wasted. However, when less restrictive pressure drops are available the plate heat exchanger becomes an excellent condenser, since very high heat transfer coefficients are obtained and the condensation can be carried out in a single pass across the plate. 

Higher overall heat transfer coefficients are obtained with the plate heat exchanger compared with a tubular for a similar loss of pressure because the shell side of a tubular exchanger is basically a poor design from a thermal point of view. Considerable pressure drop is used without much benefit in heat transfer efficiency. This is due to the turbulence in the separated region at the rear of the tube. Additionally, large areas of tubes even in a well-designed tubular unit are partially bypassed by liquid and low heat transfer areas are thus created. 

The peak capacity is not pertinent as the separation was developed by a solvent program. The expected efficiency of the column when operated at the optimum velocity would be about 5,500 theoretical plates. This is not a particularly high efficiency and so the separation depended heavily on the phases selected and the gradient employed. The separation was achieved by a complex mixture of ionic and dispersive interactions between the solutes and the stationary phase and ionic, polar and dispersive forces between the solutes and the mobile phase. The initial solvent was a 1% acetic acid and 1 mM tetrabutyl ammonium phosphate buffered to a pH of 2.8. Initially the tetrabutyl ammonium salt would be adsorbed strongly on the reverse phase and thus acted as an adsorbed ion exchanger. During the program, acetonitrile was added to the solvent and initially this increased the dispersive interactions between the solute and the mobile phase. 

The column, designated as TSKgel DEAE-NPR a weak anion exchanger, was 3.5 cm long and 4.6 mm in diameter packed with non-porous resin beads 2.5 ji in diameter. Thus, the maximum efficiency available at the optimum mobile phase velocity would be about 7,000 theoretical plates. The sample was a crude hexokinase product and an... 

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