Packing-specific constant

The practical advantage of applying Eq. (4-32) Hes in the fact that the geometric packing surface area a is the only variable required to calculate the liquid hold-up. It is possible to determine the liquid hold-up hp in packed columns more accurately using Eq. (4-32), i.e. with a relative error of 5(hL) < 10—15%, if a packing-specific constant... 

In order to determine the pressure drop Ap/Apo, acc. to Eq. (4-7) or (4-9), it is necessary to know the specific geometric data of the packing element a and e as well as the packing-specific constants x and (j) and the total liquid hold-up hp. The latter can be determined by using one of the models found in literature [12, 44], as quoted in Sect. 4.2. 

Co = constant specific to a particular packing Cl = constant specific to a particular packing Cs = 7.4 X 10- ... 

Re, Fr and We are modified dimensionless groups in which the particle size dp is replaced by the inverse of the packing specific area a. The form of this function is suggested by the observed asymptotic approach to a constant value of . Eq. 23 predicts that [Pg.565]

The constant A and the exponent B as well as the numerical values of the packing-specific form factors x were determined on the basis of approx. 10,000 experimental data items from the available database, using the minimisation procedure. The numerical values of the form factors x are listed in Tables 6-la-c. 

The constant is not a tme partition coefficient because of difference, — V, includes the soflds and the fluid associated with the gel or stationary phase. By definition, IV represents only the fluid inside the stationary-phase particles and does not include the volume occupied by the soflds which make up the gel. Thus is a property of the gel, and like it defines solute behavior independently of the bed dimensions. The ratio of to should be a constant for a given gel packed in a specific column (34). 

These methods depend on the fact that at low flowrates the flow through a packed bed is directly proportional to the pressure difference, the proportionality constant being proportional to the square of the specific surface (surface volume ratio) of the powder. From this method it is possible to obtain the diameter of the sphere with the same specific surface as the powder. The reliability of the method is dependent upon the care with which the sample of powder is packed. Further details are given in Chapter 4. 

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