Plate efficiency typical values

The plate height, and thus the total number of theoretical or effective plates, depends on the average linear carrier gas velocity (van Deemter relationship) and, for a particular carrier gas, the efficiency will maximize at a particular flow rate. Only at the optimum carrier gas flow rate are n, N, and HETP Independent of the column length. The efficiency will also depend on the column diameter (see section 1.7.1) where typical values for n, N, and HETP for different column types can also be found. Values for n, N, and HETP are reasonably independent of temperature but may vary with the substance used for their determination, particularly if the test substance and statioKary phase are not compatible. 

Some typical values of plate efficiency for a range of systems are given in Table 11.1. More extensive compilations of experimental data are given by Vital et al. (1984) and Kister (1992). 

To determine the actual number of plates required, divide the result in step 2 by the overall plate fractional efficiency, typically denoted by E(y Values can range from 0.4 to 0.8. The actual number of plates can be calculated from... 

Some typical values of plate efficiencies are given in Table 18-4 (taken from Perry s 6 edition). 

High collection efficiency of diffuse light. If the incoming radiation is misdirected by arriving under an angle on the plate, the trapped flux is only multiplied by (sin ) which is still 0.9848 for <1> = 80° and 0.9397 for = 70° representing typical values of misdirection. 

An efficient packed gas chromatography column will have several thousand theoretical plates, and capillary columns will have in excess of 10,000 theoretical plates. The H value for a 1-m column with 10,000 theoretical plates would be 100 cm/ 10,000 plates = 0.01 cm/plate. In a high-performance liquid chromatography (below), efficiency on the order of 400 theoretical plates per centimeter is typically achieved, and colunms are 10 to 50 cm in length. 

The efficiencies of these nonevacuated CPCs are to be compared with typical values for flat plates of = 0.70-... 

Figure 2-80 shows a typical absorber tray diagram for the absorption of CO2 in MEA solution. Ibis figure is based on actual plant data from a 16 bubble-cap tray absorber treating atmospheric pressure flue gas for CO2 recovery. Because of the low values of solution loading involved, the equilibrium line is almost coincident with the x-axis and is not shown. A pseudo-equilibrium line (dashed) has been drawn to represent actual gas and liquid compositions from each tray. The plate efficiencies in this column vaiy from about 14% in the bottom of the column to slightly over 16% at the top. 

High productivity separations are described as comprising the bulk of the work in a QC lab. These require moderate efficiencies (typically 10,000-15,000 plates) and can benefit from decreased ran times. In these cases, the goal is to leverage the smaller values of H to reduce column lengths and thus shorten analyses. 

The suitability of gas absorption as a pollution control method is generally dependent on the following factors (1) availability of suitable solvent (2) required removal efficiency (3) pollutant concentration in the inlet vapor (4) capacity required for handling waste gas and (5) recovery value of the pollutant(s) or the disposal cost of the unrecoverable solvent. Impingement plate scrubbers are typically used in the food and agriculture industry, and at gray iron foundries. 

Recent chromatographic data indicate that the interactions between the hydrophobic surface of a molded poly(styrene-co-divinylbenzene) monolith and solutes such as alkylbenzenes do not differ from those observed with beads under similar chromatographic conditions [67]. The average retention increase, which reflects the contribution of one methylene group to the overall retention of a particular solute, has a value of 1.42. This value is close to that published in the literature for typical polystyrene-based beads [115]. However, the efficiency of the monolithic polymer column is only about 13,000 plates/m for the isocratic separation of three alkylbenzenes. This value is much lower than the efficiencies of typical columns packed with small beads. 

Polymer gel GPC columns packed with 10-pm gels can exhibit efficiencies of 12,000 to 16,000 plates depending on the pore size. Single columns of this type produce bandwidths from 160 to 180 pi. As columns are coupled in series, bandwidth increases as the square root of the number of columns, as may be seen from Equation 1. Plate number doubles, but so does the exclusion volume. The 5-pm gel columns typically achieve 20,000 to 24,000 plates, and are represented by the bottom two rows of the table. The implications of the bandwidth values in Table I will be discussed below. 

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