Performance of Packed Columns

Similar relationships are apparent for heat transfer for the case oftnrbulent flow through tubes. Since 

A comparison of Equations 6.31 and 6.33 shows that the /-factors for mass and heat transfer are exactly equal in this case. Thus, it is possible to estimate heat transfer coefficients from mass transfer coefficients, and vice versa. 

So far, we have considered only mass transfer within a single phase - that is, mass transfer between fluids and solid surfaces. For gas absorption and desorption, in which mass transfer takes place between a gas and a liquid, packed columns are extensively used, while bubble columns and sparged stirred vessels are used mainly for gas-liquid reactions or aerobic fermentation. As the latter types of equipment are discussed fully in Chapter 7, we shall, at this point, describe only the performance of packed columns. 

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Shulman, H. L., C. F. Ullrich and N. Wells, Performance of Packed Columns, Total, Static and Operating Holdups, Amer. Inst. Chem. Engr. four. 1, No. 2, 247 (1955). 

The concept of the effective plate number was introduced and employed in the late nineteen fifties by Purnell (7), Desty (8) and others. Its introduction arose directly as a result of the development of the capillary column, which, even in 1960, could be made to produce efficiencies of up to a million theoretical plates (9). It was noted, however, that these high efficiencies were were only realized for solutes eluted close to the column dead volume, that is, at very low k values. Furthermore, they in no way reflected the increase in resolving power that would be expected from such high efficiencies on the basis of the performance of packed columns. This poor performance, relative to the high efficiencies produced, can be shown theoretically ( and Indeed will be, later in this book) to result from the high phase ratio of capillary columns made at that time. That is the ratio of the mobile phase to the stationary phase in the column. The high phase ratio was... 

Although the performance of packed columns is more modest than capillary columns, they are still usually employed for many routine analyses. Easy to manufacture and with a large choice of stationary phases available, they are not however, well adapted to trace analyses. 

Hoek, P. J., and F. J. Zuiderweg, "The Influence of Channelling on the Mass Transfer Performance of Packed Columns, Paper presented at the AIChE Annual Meeting, Chicago, Nov., 1985. 

Shulman.H.L., Ullrich,C.F. and N.Wells. Performance of packed columns. I. Total, static and operating hold-ups". 

The performance of packed columns should be compared with that of packed column HPLC. As the diffusion coefficients are > 20 times greater, depending on the density, higher than in HPLC, SFC should in theory be more rapid and/or efficient than HPLC. The examples given here indicate... 

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