Height, of transfer unit

Ht s. In connection with the data on this figure, it should be noted that economical values of m Vp Vp will usually lie in the range between 1 and 2, so that overall heights of transfer units are not too unreasonable even for this high-interfacial-tension system. For lower interfacial tensions, Htoc will ordinarily be appreciably less. 

The system of Fig. 15-38 is one of high interfacial tension, so that the heights of transfer units are relatively high and stage efficiency low. For systems of low interfacial tension, on the other hand, stage efficiencies may be very much improved. Table 15-8 lists sources of mass-transfer data. 

The dominant mechanism of purification for column ciystallization of sohd-solution systems is reciystallization. The rate of mass transfer resulting from reciystallization is related to the concentrations of the solid phase and free hquid which are in intimate contac t. A model based on height-of-transfer-unit (HTU) concepts representing the composition profQe in the purification sec tion for the high-melting component of a binaiy solid-solution system has been reported by Powers et al. (in Zief and Wilcox, op. cit., p. 363) for total-reflux operation. Typical data for the purification of a solid-solution system, azobenzene-stilbene, are shown in Fig. 22-10. The column ciystallizer was operated... 

Hog, Hql = Height of transfer unit based on overall gas or liquid film coefficients, ft Gm, Ljn = Gas or liquid mass velocity, lb mols/(hr) (ft ) Kga, Kla = Gas or liquid mass transfer coefficients, consistent units... 

A packed column is used in the desulfurization operation described in the previous problem. The overall height of transfer unit based on the gas phase is 0.7 m. WTien the flowrate of water is twice the minimum, what height of packing is needed ... 

Overall height of transfer unit based on the liquid phase is given by... 

Hog = height of transfer units, based on overall gas film, coefficients, ft... 

Correcting Height of Transfer Unit for Inert Gases in System T / Vi/Ma + 1/Mb... 

The principal applications of mass transfer are in the fields of distillation, gas absorption and the other separation processes involving mass transfer which are discussed in Volume 2, In particular, mass transfer coefficients and heights of transfer units in distillation, and in gas absorption are discussed in Volume 2,. In this section an account is given of some of the experimental studies of mass transfer in equipment of simple geometry, in order to provide a historical perspective. 

The methods for estimating the heights of transfer units, HTU, given in Section 11.14.3 can be used for distillation. The relationship between transfer units and the height of an equivalent theoretical plate, HETP is given by ... 

Chen, N.H. New Equation Gives Tower Diameter, Chemical Engineering, Feb. 5, 1962, p. 109. Chart for Height of Transfer Unit in Wetted Wall Columns, Chemical Engineering, May 10, 1965, p. 193. 

Hol Height of transfer unit — overall (liquid concentration) m L... 

Figure 12.8. Effect of liquid rate on height of transfer unit Hol- Comparison of the results of Sherwood and...

In this analysis, it is assumed that the total number of moles of gas and liquid remain the same. This is true in absorption only when a small change in concentration takes place. With distillation, the total number of moles of gas and liquid does remain more nearly constant so that no difficulty then arises. In Chapter 11, the following relationships between individual and overall heights of transfer units are obtained and methods of obtaining the values of HG and HL are discussed ... 

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