Page 318 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10H-J 5/30/2001 4:47 PM Page 277

Heat Transfer 277

R oa overall resistance to heat transfer, temperature of condensate film in partial
2
(hr)(ft )(°F)/Btu. condenser calculations, °F.
r b or r o fouling resistance (factor) with fluid on out- t g temperature of dry gas (inerts), °F.
2
side of tube, (hr)(ft )(°F)/Btu. t h caloric temperature of hot fluid, °F.
r h hydraulic radius, ft. t i inside tubes fluid temperature, °F.
r i or r t fouling resistance (factor) associated with t o fluid outside tubes temperature, °F; or, tem-
2
fluid on inside of tube, (hr)(ft )(°F)/Btu. perature of inner surface of insulation °F.
r f,t tube-side fouling resistance, t s boiling fluid temperature, °F; or, tempera-
2
(hr)(ft )(°F)/Btu. ture of outer surface of insulation, °F.
r f,a air-side fouling resistance, t sv temperature of saturation or dew point, °F.
2
(hr)(ft )(°F)/Btu. t v temperature of vapor, °F.
r l longitudinal tube pitch, in./tube O.D., in. t w temperature of tube wall, °F.
for cross-flow pressure drop, in direction of t w temperature of inlet water, °F.
fluid flow; or, outside radius of any (if used) t wo temperature of outside tube wall, °F.
intermediate layer of insulation, in. t 1 inlet dry bulb air temperature to air-cooled
r o inside radius of pipe insulation, in. exchanger, °F.
r s outside radius of pipe insulation, in. t 2 outlet dry bulb air temperature from air-
r t transverse tube pitch, in./tube O.D., in.; for cooled exchanger, °F
cross-flow pressure drop, transverse to direc- T overall temperature difference, °F; or, mean
tion of flow. temperature difference between bulk of
r w resistance of tube wall, L w /k w ; boiling liquid and bulk of heating medium,
2
(hr)(ft )(°F)/Btu. °F; or, temperature difference of fluid, (end
Sc Schmidt number. points),°F; or, (T w T s ), °R, in Levy Boiling
S e weighted flow area [(cross-flow area) equation.
1/2
2 .
(baffle window area)] , ft . T b mean temperature difference between bulk
St Stanton number. of boiling liquid and tube wall, °F; or, tem-
s specific gravity of fluid referred to water; or, perature drop across boiling film, °F.
2
inside surface of pipe, ft . t temperature difference, (t 2 t 1 ),°F; or, log
s f fin surface per ft of length. mean temperature difference based on lim-
s o plain pipe/tube surface per ft of length. its (unless defined otherwise), °F; or, tem-
T temperature of hot fluid, °F; or, absolute perature difference (t 1 t avg ) between
temperature, °R; or, tank diameter, ft. inside surface of pipe insulation and aver-
T ap annulus space temperature, °F. age outside air temperature, °F.
T k temperature absolute, °Kelvin. t b temperature drop across boiling film,
T m pipe temperature, °F. between boiling fluid and wall surface on
T p process temperature, °F. boiling side, °F.
T r absolute radiation temperature, T L actual liquid temperature rise, °F.
°R °F 460. T L,max maximum possible liquid temperature rise
T s saturation temperature of liquid, °R; or, (to vapor inlet temperature).
steam temperature, °F; or, surface tempera- t o overall t between average tube-side bulk
ture of insulated or bare pipe in contact temperature, °F, between average tube-side
with air, °F. bulk temperature and boiling film, °F; or,
T w temperature of heating surface, °R; or, wall critical temperature differential in boiling, °F.
temperature of tube, °F. t m mean temperature difference, (t v t w )/2,
T 1 inlet temperature of hot fluid, °F; or, inlet °F; or, corrected mean temperature differ-
fluid to tubes of air cooled exchanger, °F. ence, °F.
T 2 outlet temperature of hot fluid, °F; or, outlet t ca overall temperature drop from average
process fluid temperature from air-cooled tube-side temperature to shell boiling tem-
exchanger, °F. perature, °F.
T °R (degrees Rankine). T V,max Maximum possible vapor temperature
t temperature , °F; or, tube wall thickness, in.; decrease (to liquid inlet temperature).
or, temperature of cold fluid, °F; or, temper- U, U o, overall heat transfer coefficient corrected
2
ature of a fluid or material, °F; or, air tem- for fouling conditions, Btu/(hr)(ft )(°F).
perature. U a volumetric overall heat transfer coefficient,
3
t a or T a ambient temperature, °F; or, arithmetic Btu/(hr)(ft )(°F).
average tube-side fluid temperature, °F. U L overall coefficient of heat transfer per ft of
t b bulk temperature of fluid, °F. length, Btu/(hr)(lin ft)(°F).
t c temperature of condensate film, °F; or, U 1 single tube overall heat transfer coefficient,
2
caloric temperature of cool fluid, °F; or, Btu/(hr)(ft )(°F).