Transfer units empirical correlations

Based on their data, Hoffmann et al. (2011) proposed for the mass transfer in ProCell units empirical correlations of the type... 

Rate of Mass Transfer in Bubble Plates. The Murphree vapor efficiency, much like the height of a transfer unit in packed absorbers, characterizes the rate of mass transfer in the equipment. The value of the efficiency depends on a large number of parameters not normally known, and its prediction is therefore difficult and involved. Correlations have led to widely used empirical relationships, which can be used for rough estimates (109,110). The most fundamental approach for tray efficiency estimation, however, summarizing intensive research on this topic, may be found in reference 111. 

To estimate the number of transfer units for design, the following empirical correlations which were derived from efficiency measurements employing a variety of trays and operating conditions under the aforementioned assumptions are recommended (111) ... 

Results of diying tests can be correlated empirically in terms of overall heat-transfer coefficient or length of a transfer unit as a function of operating variables. The former is generally apphcable to all types of dryers, while the latter applies only in the case of continuous diyers. The relationship between these quantities is as follows. 

Hughmark [181] has proposed empirical correlations for better fit of experimental data to transfer units and thus tray efficiency comparison with the AIChE method [2]. 

The above correlation is valid for a bioreactor size of less than 3000 litres and a gassed power per unit volume of 0.5-10 kW. For non-coalescing (non-sticky) air-electrolyte dispersion, the exponent of the gassed power per unit volume in the correlation of mass transfer coefficient changes slightly. The empirical correlation with defined coefficients may come from the experimental data with a well-defined bioreactor with a working volume of less than 5000 litres and a gassed power per unit volume of 0.5-10 kW. The defined correlation is ... 

Again referring to Fig. 13, the same general trend is apparent in both the pressure-drop and number-of-transfer-unit curves. This suggests that another empirical correlating procedure could be arrived at for example, an approximate relationship exists between the length of a transfer unit (LTU) and the Lockhart-Martinelli parameters, X. 

Numbers of Transfer Units from Empirical Correlations... 

In any case the undetermined model parameters are determined from ap>-propriate empirical correlations [78, 79, 81, 82]. The mass transfer coefficients, all based on unit bubble volume, can be obtained from ... 

In order to calculate the number of mass transfer units, the mass transfer coefficients must be estimated, either based on experimental data or from empirical correlations. The following correlation (Chan and Fair, 1984) was developed for binary systems, and specifically applies to sieve trays. In this correlation Nq and N are expressed in terms of residence time and interfacial area instead of the standard forms of Equations 14.26 ... 

Bolles and Pair (1979) estimate the HETP from vapor and liquid heights of transfer units (HTU). The vapor phase Hq and liquid phase are first calculated separately from empirical correlations. The overall HTU is then calculated as follows ... 

The overall height of a transfer unit can be defined as the height of a packed section required to accomplish a change in concentration equal to the average driving force in that section. Values of for a particular system are sometimes available directly from the literature or from pilot-plant tests, but often they must be estimated from empirical correlations for the individual coefficients or the individual heights of a transfer unit. Just as there are four basic types of mass-transfer coefficients, there are four kinds of transfer units, those based on individual or overall driving forces for the gas and liquid phases. These are as follows ... 

We have employed some rather simple kinetics, conventional pressure drop and heat transfer formulae, ideal film calculations and some basic empirical correlations to develop a reactor model that quite adequately relates the cracking severity of small bench scale units and commercial furnaces. Thus, evaluation of feedstocks using the bench unit has significantly more meaning. Optimization of operating conditions can be calculated for various cracking coil configurations. 

Having set the factual effects of liquid velocity, gas velocity and particle size on mass transfer coefficients and interfacial area for Hg -=84mm, correlations were attempted for these characteristic parameters by non-linear regression analysis of the experimental results. Empirical correlations in S.I. units,obtained for... 

Empirical dimensionless group correlations have been used in the scale-up process. In particular, the correlation for the inside film heat transfer coefficient for agitated, jacketed vessels has been employed for the scale-up to a larger vessel. Reaction calorimeters are often used to give some indication of heat transfer coefficients compared to water in the same unit. Correlation for plant heat transfer is of the general form... 

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