Chilton—Colburn factor

This can be written in terms of correlations for the coefficients of heat and mass transfer. The Chilton-Colburn factors are... 

In packed beds, mass transfer coefficients are often correlated by means of a Chilton—Colburn factor, Ju, analogous to their Jh heat transfer (Sect. 4.4.4)... 

Chilton-Colburn factor), (Sherwood number), (Schmidt number), (Reynolds number). 

Here / h is the Chilton-Colburn factor for mass transport, i th mass transport coefficient, u the linear flow velocity. Sc = V/D is the Schmidt number and / is the friction coefficient. As a consequence, a higher shear stress also means a higher mass transport rate and vice versa. 

Frequently the mass transfer coefficient is expressed as a Chilton-Colburn factor, which is defined as... 

On occasion one will find that heat-transfer-rate data are available for a system in which mass-transfer-rate data are not readily available. The Chilton-Colburn analogy provides a procedure for developing estimates of the mass-transfer rates based on heat-transfer data. Extrapolation of experimental or Jh data obtained with gases to predict hquid systems (and vice versa) should be approached with caution, however. When pressure-drop or friction-factor data are available, one may be able to place an upper bound on the rates of heat and mass transfer, according to Eq. (5-308). 

The most convenient mathematical form for correlating mass transfer data is in terms of the well-known Chilton-Colburn (75, 76) jD factor. 

For the conditions cited, it was shown that jD was 0.235 and, by the Chilton-Colburn analogy Jh = 0.235. From the definition of the heat transfer factor jH, it follows that... 

The correlation due to Kelly (1965) indicates relatively modest coefficients below 200Wm-2K i for particles up to about 8mm in diameter. The equations proposed by Vazquez and Calvelo, based on the Chilton-Colburn j-factor model, suggest rather higher coefficients of fhe order of 300-400for the fluidization of particles up to 20mm in diameter at gas velocities reasonably in excess of those required for minimum fluidization. 

To characterize the mass transport, Wilson and Geankopolis (1966) used the /-factor according to Chilton-Colburn (Bird et al., 2003) which is defined as follows... 

The heat transfer coefficient can be calculated from the mass transfer coefficient by means of the Chilton-Colburn analogy, also called the factor analogy. The factors are defined as ... 

In case of perfect Chilton-Colburn analogy, both factors are equal ... 

AG Free energy change AGt Free energy of activation ff Critical humidity Ji Chilton-Colburn mass transfer factor... 

Jd = Chilton-Colburn j-factor for mass transfer, dimensionless... 

Here the Chilton-Colburn j-factors and the Reynolds number Re are defined by... 

Figure 10.4. Stanton number, (St) as a function of Schmidt number (Sc) from the von Karman velocity profile and the Chilton-Colburn analogy. The friction factor is maintained at 0.073 for this illustration.

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