Page 288 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10G 5/30/2001 4:40 PM Page 250

250 Applied Process Design for Chemical and Petrochemical Plants

The liquid phase resistance, h la , is considered low when
Ackerman correction factor, dimensionless, source
unknown.
compared to the overall resistance; therefore, the h ga
should give a reasonable approximation to the overall resis-
tance for the system, 242, 247 because 1/U a 1/h ga 1/h la . For little or no condensation in the system:

B. Random Packed Columns 1>U a 1>h g a 1>h l a
Fair 242 recommends the correlating relations from For condensation:
Huang 250 as shown in Table 10-49, which satisfies the rela-
tion. 1>U a 1>
h g a 11>h l a2 1Q s >Q T 2
m
Coefficient h g a, or h l a, or U a C 1 G L n
Sc Schmidt number, dimensionless
where h g a volumetric gas-phase heat transfer coefficient, Pr Prandtl number, dimensionless
3
Btu/(hr) ( ft )(°F) c g gas specific heat, Btu/lb-°F
2
h l a liquid-phase heat transfer coefficient, a interfacial area, ft /ft 3
3
Btu/(hr) (ft )(°F) Q s sensible heat transfer duty, Btu/hr
U a volumetric overall heat transfer coefficient, Q T total heat transfer duty, Btu/hr
3
Btu/(hr) (ft )(°F)
2
G superficial gas mass velocity, lb/(hr) (ft ) C. Sieve Tray Columns
2
L superficial liquid mass velocity, lb/(hr) (ft )
The thesis of Stewart 249 indicates that the overall liquid
film and mass transfer coefficients were functions of the gas
Table 10-49 flow rate and the column pressure and are independent of
Heat Transfer Coefficients for Packed Columns the liquid flow rate and inlet air temperature. The gas film
heat transfer coefficient was found to be a function only of
m
Coefficient* C 1 G L n the air flow rate.
From Fair 242 the gas phase coefficient is
Packing System Coefficient C 1 m n
RR—1 in. Air/water h l a 0.774 0.51 0.63 c g G1Sc g 2 2>3
Air/water h g a 0.230 1.10 0.02 h g a H g,d 1Pr g 2 (10-276)
Air/oil U a 0.00026 1.69 0.51
RR—1.5 in. Air/water h l a 0.738 0.48 0.75 and the heat transfer efficiencies range from 60–100%.
Air/water h g a 0.008 1.45 0.16 Based on the gas phase, the height of a transfer unit, H g ,
Air/oil U a 0.0016 1.49 0.38 is 242
IS—1 in. Air/water h l a 2.075 0.20 0.84
Air/water h g a 0.095 1.01 0.25
Air/oil U a 0.0045 1.32 0.43 H g,d G (10-277)
IS—1.5 in. Air/water h l a 6.430 0.20 0.69 k g a M g P
Air/water h g a 0.019 1.38 0.10
Air/oil U a 0.003 1.44 0.36 For nitrogen data: 242 U a 0.213G 1.0
PR—1 in. Air/water h l a 0.296 0.45 0.87 For helium data: 242 U a 1.05G 1.0
Air/water h g a 0.019 1.12 0.33
Air/oil U a 0.0013 1.47 0.46 D. Baffle Tray Column 242
PR—1.5 in. Air/water h la 1.164 0.31 0.80
Air/water h ga 0.011 1.28 0.26 The contacting counterflow action provides a depen-
Air/oil U a 0.027 1.07 0.36 dence on the liquid rate, similar in concept for packed
*h g a or h l a or U a , Btu/(hr-ft -°F) columns:
3
Symbols
m n
H g a C 1 G L (10-277A)
RR 1 in. } Ceramic Raschig rings, 1-in. and 1.5-in. nominal size
RR 1.5 in.
where C 1 coefficient which depends on the system used, for
IS 1 in. } Ceramic Intalox saddles, 1-in. and 1.5-in. nominal size example, C 1 2.058 for nitrogen/absorption oil
IS 1.5 in. 3
h g heat transfer coefficient, J/m sk
2
2
PR 1 in. } Metal Pall rings, 1-in. and 1.5-in. normal size a interfacial area, n /m , or ft /ft 3
3
PR 1.5 in. c specific heat, Btu/(lb) (°F)
2
Used by permission: Fair, J. R. ASME Solar Energy Division Conference, G superficial gas mass velocity, lb/(hr) (ft )
2
April 1989. ©American Society of Mechanical Engineers, San Diego, CA. h heat transfer coefficient, Btu/(hr) (ft )(°F)