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278 Applied Process Design for Chemical and Petrochemical Plants
V vapor rate, lb/hr; also, used as molecular mass rate of flow of condensate from lowest
volume for component in diffusivity equa- point on condensing surface divided by
tion; or, linear velocity, ft/sec. breadth (unit perimeter), lb/(hr)(ft).
V f superficial flooding velocity of vapor, ft/sec. = acceleration loss group, dimensionless; see
V max maximum vapor velocity in exit from Equation 10-181.
reboiler, m/sec. difference.
V RB vapor formed in reboiler, lb/hr. ( t/ p) s slope of vapor pressure curve.
v tube-side velocity, ft/sec; or, ft/hr. emissivity of a surface, ratio of total rate at
v i specific volume of fluid at inlet to reboiler, which a gray surface emits radiation to the
3
ft /lb. total rate at which a black body at the same
v o specific volume of fluid at outlet of reboiler, temperature would emit radiation of all wave
3
ft /lb. lengths, dimensionless; or, emissivity of the
v s superficial vapor velocity, usually, ft/sec. outside surface of insulated or bare pipe.
W mass rate of flow, lb/hr condensate for con-
fin width at fin base, ft.
densers; or, lb/sec; or, width of air-cooled f fin efficiency, fraction.
exchanger, ft. w e f , weighted fin efficiency, fraction.
W flow rate, lb/sec. tube taper angle (to horizontal), degrees.
2
W tube loading for condensing, lb/hr (ft of effective average (two-phase)/liquid phase
finned tube length). pressure drop ratio corresponding to effec-
W s shaft work done by system, ft liquid. tive average vaporization.
W T total vapor condensed in 1 tube, lb/hr; or, latent heat of vaporization, Btu/lb.
total mass flow rate, lb/sec. viscosity of fluid, lb/(hr)(ft); or, centipoise
w weight rate of fluid flow per tube, (as specified); or, viscosity at the caloric tem-
lb/hr/tube; or, rate of condensation per perature, lb/(ft)(hr).
tube from lowest point of vertical tube(s), viscosity of fluid at film temperature, lb/
lb/(hr)(tube); or, fin height, in. (hr)(ft) (centipoise) 2.42 lb/(hr)(ft).
X N Re /1000. viscosity, centipoise.
X tt correlating parameter, dimensionless for f absolute viscosity, lb/sec (ft) (centipoise)
turbulent-turbulent flow mechanism, Figure (0.000672).
10-113. s viscosity of fluid at film temperature of heat
x vapor quality in fluid, weight fraction, nucle- transfer surface, lb/(hr)(ft).
ate boiling; or distance film has fallen; or, w viscosity of fluid at wall temperature,
weight fraction of vapor or gas, dimension- lb/(hr)(ft); or, centipoise.
less. 3.1416.
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x 2 height of liquid level in column above density, lb/ft .
reboiler bottom tubesheet, ft. t d o for vertical tube perimeter, ft.
x c distance from top (effective) of tube, ft. tp effective average two-phase density, lb.ft 3
3
y mol vol % noncondensables in bulk stream. tph homogeneous two-phase density, kg/m .
Z distance or length, or vertical height, ft or surface tension, lb/ft; or, dynes/cm as speci-
in. as consistent; or, viscosity at flowing tem- fied.
2
perature, centipoise. (Used by permission: surface tension of liquid, Btu/ft ; or,
2
7
Brown Fintube Company.) (dynes/cm)(0.88 10 ) Btu/ft .
Z sp height of individual spray zone, ft. surface tension of liquid, dynes/cm.
Z height (vertical) of driving leg for thermal s or Stefan-Boltzmann constant, 0.173 10 8
4
2
circulation, ft. Btu/(hr)(ft )(°R) .
constant, Gilmour boiling equation; or, sur-
Greek Symbols face condition factor, Equation 10-140; or,
tube density coefficient, Table 10-27.
–
constant, Gilmour boiling equation; or, tube average value of .
–
layout angle, degree coefficient of ther- physical property factor; or, parameter for
mal expansion of fluid, %/°F; or, correction two-phase flow, dimensionless.
factor for convective heat transfer, dimen- p physical property factor for shell-side heat
sionless; or, correction factor for nucleate transfer.
boiling, dimensionless; or, Ackerman cor- s ( / w ) 0.14 , subscript w refers to wall
rection factor, dimensionless. condition.
coefficient of expansion 1/T r , with T r in maximum flux physical property factor,
3
°Rankine °F 460. Btu/(ft )(hr), Equation 10-149.
