Number of transfer units for

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) ... 

The second (integral) terms represent the numbers of transfer units for an infinitely dilute gas. The first terms, frequently amounting to only small corrections, give the effect of a finite level of gas concen-t rati on. 

Since the term (1 -i- k i)/k approaches unity for large /c -value, the number of plates is equal to one half the number of transfer units for a strongly retained component. For these conditions, when Np = N/2, Eq. (16-174) and Eq. (16-161) produce the same peak retention time, peak spreading, ana predict essentially the same peak profile. 

Number of Transfer Units. For dilute solutions the number of transfer units Nqg is obtained by... 

Equation 3 Is quite accurate for calculating the number of transfer units for the example cooling tower... 

Calculate N,og and Table 1, from Predict the number of Transfer Units for Cooling Towers, by Kamal Adham Khodaparast, Chemical Engineering Progress, Vol. 88, No. 4, pp. 67-68 (1992). Reproduced by permission of the American Institute of Chemical Engineers. 1992 AlChE. ... 

Example 9 Number of Transfer Units for Dilute Solutions... 

Figure 9-72. Graphical integration number of transfer units for Example 9-11.

It is easy to define the number of transfer units for equimolar counter-diffusion (distillation) and for dilute systems, when the mole fraction of the solute is so small that the... 

As for the values of HTU (see Equation 6.1-37), it is possible to write the equations that express the addition of individual resistances in terms of the number of transfer units. For example, when m, the slope of the equilibrium curve, is constant, the equations applicable to either dilute or concentrated systems are ... 

It may be helpful to remember the genesis of the concept of the number of transfer units. For a gas or a vapour, it is essentially the change in concentration of the gas stream, dy, divided by the driving force (y-y ) or (y-yj. Similar considerations hold for the liquid. 

The variable flow rate G is used here instead of the constant G because the mass transfer coefficient kG depends more directly on G. As used in Eqs. (13.176) and (13.177), a mean value of the coefficient is preferred in practice in preference to accounting for its variation within the integral. The integrals are defined as numbers of transfer units for absorption or stripping, ... 

There are two key variables that are difficult to calculate NG and NL (gas phase transfer units and liquid phase transfer units, respectively). The number of transfer units for each phase is calculated in terms of contact time and vapor rate. The contact times are determined... 

Calculate the number of transfer units. For dilute systems in which the equilibrium and operating lines are both straight, the equations for the number of individual liquid-phase transfer units Ni... 

Related Calculation. When the equilibrium and/or operating lines are curved, Eqs. (11.27) and (11.28) do not apply exactly. In this case, it is necessary to base the design on the individual number of transfer units for the liquid resistance and integrate graphically to determine Nt. This is illustrated in the following example. 

The number of transfer units for packed columns is defined by ... 

Number of Transfer Units. For relatively dilute systems the ratios involvingjg y, and 1 — y approach unity so that the computation of... 

The integrals are defined as numbers of transfer units for absorption or stripping. 

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