Page 317 - Applied Process Design For Chemical And Petrochemical Plants Volume III

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276 Applied Process Design for Chemical and Petrochemical Plants

N Pr Prandtl number. p pressure loss, lb/in. 2
N Re Reynolds number. p b pressure loss across or through the “win-
Nu Nusselt number. dow” opening of segmental baffles, lb/in. 2
n number of tube passes; also, in Hajek p c pressure loss across the tube bundle in cross
reboiler relation, n log U T/log T; or, flow, lb/in. 2
agitator revolutions/min; or, number of p long. shell-side pressure drop due to longitudinal
horizontal tubes in a vertical bank; or, num- flow, lb/in. 2
ber of equilibrium contact stages; or, expo- p r pressure loss through return ends or chan-
nent for baffle tray columns; or, number of nels of tube side of exchanger, lb/in. 2
tubes/row, per ft of exchanger width, 1/ft. P s pressure drop of fluid, heated or cooled,
2
n number of tubes per pass; or, effective sur- including entrance and exit losses, lb/ft .
face efficiency; or, number of tracers. p s or p shell-side pressure drop, lb/in. 2
n number of rows of tubes between centers of p t pressure drop through tubes, lb/in. 2
gravity of two adjacent segmental baffles, for p tt tube side of exchanger total pressure drop,
finned tubes. lb/in. 2
n b number of baffles. Pe Peclet number.
n c minimum number of tube rows fluid crosses Q total heat load, or transferred, Btu/hr
in flowing from one baffle window to an (see q ); or, heat loss from pipe insulation,
2
adjacent baffle. Btu/(hr)(ft )
n n number of tubes in a row at the exchanger Q ap , Q ia , Q pa , Q ta , Q tp heat transfer related to pipe, annulus and
centerline normal to the direction of flow. pipe tracer.
n s number of fluid streams in shell side of con- Q b heat duty for boiling, Btu/hr.
denser. Q c heat load of overhead condenser (removed
n w number of tubes passing through baffle win- in condenser), Btu/hr.
dow. Q total rate at which a black body emits heat
NPS nominal pipe size. radiation of all wave lengths, Btu/hr.
2
P absolute pressure, lb/in. abs; or, total pres- Q R reboiler duty, or heat added, Btu/hr.
2
sure lb/ft abs. See Appendix A-4 and A-8 Q s sensible heat transfer duty, Btu/hr.
for additional information; also, P factor Q T total heat transfer duty, Btu/hr.
in LMTD correction (t 2 t 1 )/(T 1 t 1 ). q heat transferred, Btu/hr, usually used as
p A total pressure at point A in flow loop, psi, abs. identification for individual heat quantity
2
P B boiling pressure, lb/in. , abs. (see Q); or, heat loss per lin ft of pipe,
P c critical pressure, psi abs. Btu/(hr)(lin ft); or, heat loss through wall,
P r reduced pressure absolute pressure/ Btu/lin ft.
absolute critical pressure. q or q max tube bundle maximum heat flux for boiling,
2
P f or p tube pitch, in. or ft, consistent units. Btu/(hr)(ft ).
p total pressure, psi abs; or, tube pitch, in. q sum of latent and sensible heat duty/load,
p a number of tube passes in exchanger. Btu/hr.
2
p B total pressure at point B in flow loop, lb/in. 2 q s rate of heat transfer per ft of outer surface
2
abs. of insulation, Btu/(hr)(ft ).
2
p c partial pressure of vapor in condensate film, q t heat transfer, Btu/(hr)(ft )(°F).
atm. R factor in LMTD correction (T 1 T 2 )/
p fg log mean pressure difference of the inert (t 2 t 1 ); or, factor from Table 10-46; or,
gas between p g and p g , atm. mean radius of bend, in.; or, reflux ratio,
p g partial pressure of inert gas in the main gas mol condensate returned/mol product
body, atm (P p v ), psi abs or atm. withdrawn; or, volume fraction of phase,
p g partial pressure of one inert at the conden- dimensionless.
sate film, atm or psi, abs. R* asymptotic value for fouling resistance,
2
o
p partial pressure inert gas at condensate film, (hr)(ft )(°F)/Btu; see Figure 10-43C.
atm or psi, abs. R e Reynold’s number, expressed in units suit-
p s static pressure, in. water. able for application.
2
4
p t total pressure, in. water. R f fouling resistance, (hr)(ft )(°F)/(Btu 10 ).
p t total pressure, atm. R g volume fraction of gas phase, dimensionless.
p v velocity pressure, in. water; or, Colburn- R L or R l (1 R g ), volume fraction of liquid phase,
Hougen calculation; or, vapor pressure of dimensionless.
condensate at t g , psia or atm; or, partial pres- R s outside surface resistance,
2
sure condensing vapor, psia, or atm. (ºF)(hr)(ft )/Btu.
P V partial pressure of vapor in gas body, atm. R t total resistance to heat transfer,
2
2
P pressure loss, lb/ft . (hr)(°F)(ft )/Btu.