VÞ cosðp=4Þ

(43)

experiments or to some type of mechanistic/heuristic analogy between fluid friction and mass  transfer。

where ‘‘h’’ is the corrugation inclination angle in radians measured from the vertical。 The adjustment for correlation inclination angle in Eq。 43 allows us to develop a single set of fitting coefficients for all inclination angles rather than develop- ing inpidual correlating expressions for each inclination angle。

The mass-transfer coefficient correlation for vapor flow

Churchill28 presented a detailed discussion of several of the gas-side mass-transfer correlations derived from classical hydrau- lic analogies。 One such analogy is that of Chilton and  Colburn29

Final expression for the hHETPi

jD ¼

ShV

1

f

1=3  ¼ 2 (48)

Substituting rearranged versions of Eqs。 31, 32, and 42 into Eq。 28 for hHETPi yields (for random packings  and metal gauze ‘‘X’’ style packings; a further adjustment for corrugation inclination angle appears in the general formula- tion for sheet metal structured packings, as discussed   above)

Gde

ReVScV

f ¼ FðReVÞ (49)

where ‘‘f’’ is the friction factor。 Although the correlation is at odds with some theoretical findings, it is reasonably accurate for flows in which no form drag is present。 The packings we are considering here—metal Pall rings, metal IMTP, and sheet

hHETPi ¼ 。 A B

。 metal structured packings with crimp geometries  similar

AM。qV。  。lV。  ðReX D E U

qL lL

L ÞðFrL ÞðWeLÞðReVÞad

MELLAPAK—have   open   structures;   therefore,   form drag

。 Cy

  Cx 。

44Þ

should be small。 Rather than using the Chilton–Colburn analogy in its ‘‘strong’’  form, we shall instead use a    ‘‘weak’’

× AVRemScn  cVDV  þ ALReb Scc cLDL ð

V      V L     L

We immediately see that the Eq。 44 for the hHETPi expressed in terms of independent expressions for ky, kx, and am (opposed to expressions for the combined quantities kyam and kxam) is not unique。 It is possible to factor out the front factor AL (for example) and define two new relative front factors for  ky  and am

Gde

form of Eq。  48

jD / JDðReVÞ (50)

For vapor flow through Pall rings, IMTP, and sheet metal structured packings, the dry friction factor is often found to be weakly dependent on the Reynolds number (often f ! ReV )。  Therefore,  we assume  that  the vapor-phase Sherwood number scales like

hHETPi ¼ 。 A B