holds for metal Pall rings, metal IMTP, sheet metal structured packings, and metal gauze structured packings。 Equation 63 can be taken to imply that a form of the Chilton–Colburn analogy holds for turbulent liquid film flow。
Analysis Methodology
The variation of the hHETPi with liquid and vapor flow
Penetration/surface renewal theory, on the other hand, pre- dicts that the liquid-side mass-transfer coefficient is propor- tional to the square root of the liquid diffusivity, so that
ShL / Re1 Sc1=2f ðReLÞ (56)
rates can be quite complex。 Figure 4 is an illustration of ‘‘typical’’ hHETPi behavior for a binary distillation at total reflux。 For low liquid rates, there is a deterioration in col- umn efficiency due to underwetting of the packing。 The effi- ciency also deteriorates near flood。 Sometimes, there is also a region near loading with enhanced column efficiency。38
L L
The simple power-law expressions that we have proposed
Assuming that the friction factor is nearly independent of Reynolds number, Eq。 56 reduces to
for ky, kx, and am cannot reproduce the complexity of this typical hHETPi behavior。 Therefore, we have limited our analysis to the intermediate regions of the hHETPi function,
where the variations of the hHETPi with flow rate are more
L L amenable to description with simple power-law expressions
for ky, kx, and am。
Turning now to the experiment, Sherwood and Holloway33 correlated absorption and desorption data for various gases in water with the expression
Because the contribution of the liquid-side resistance has been found to be small in the great majority of binary distil- lations, we will proceed by setting the front factor, AL, in Eq。 44 to unity (this is equivalent to using Eq。 45)。 This
then fixes the contribution of the small liquid-side resistance to the hHETPi。 As the small contribution of the liquid-phase resistance is now completely specified, we can curve fit ex-
with the exponent ‘‘n’’ ranging from 0。22 to 0。46 for Raschig rings and saddles。 Koch et al。34 measured liquid-film mass-
perimental hHETPi data to Eq。 45 to determine the power- law exponents on the various dimensionless groups and to
Figure 4。 Schematic showing the potentially complicated variation of hHETPi with density-corrected
exponents in the fits。 For all but the BX style gauze struc- tured packing power-law exponents were limited to the range
—0。2 to 0。2。 In the case of BX, the range was expanded to be —0。25 to 0。25。 The reasons for limiting the ranges of the power-law coefficients are difficult to elucidate。 Part of the explanation lies in the fact that data fitting becomes more problematic when the same physical quantity appears in more than one dimensionless grouping。26 For example, fit- ting the data with no imposed restrictions would often lead power-law exponents with large magnitudes but whose net effect on some variable, usually the liquid velocity, would be small to negligible。 A further consideration was the fact that many other reported mass-transfer correlations have power-law exponents on dimensionless groupings whose magnitudes are less than 1。64 The final reason was a prag- matic one—limiting the range on these coefficients resulted in correlations whose predictions were generally better in ev- ery situation, and which turned out to be more robust in the simulator。 填料塔的新传质相关性英文文献和中文翻译(14):http://www.youerw.com/fanyi/lunwen_81699.html