Heat Exchangers

A.  For the heat exchanger equation, Q = UAF (LMTD), use F = 0.9 when charts for the LMTD correction factor are not available. Charts for LMTD correction can be found in Kern or other textbooks.
B.  Most commonly used tubes are 3/4 in. (1.9 cm) in outer diameter on a 1 in triangular spacing at
16 ft (4.9 m)long.
C.  A 1 ft (30 cm) shell will contains about 100 ft2 (9.3 m2)
A 2 ft (60 cm) shell will contain about 400 ft2 (37.2 m2)
A 3 ft (90 cm) shell will contain about 1100 ft2 (102 m2)
D.  Typical velocities in the tubes should be 3-10 ft/s (1-3 m/s) for liquids and
30-100 ft/s (9-30 m/s) for gases
E.  Flows that are corrosive, fouling, scaling, or under high pressure are usually placed in the tubes
F.  Viscous and condensing fluids are typically placed on the shell side.
G.  Pressure drops are about 1.5 psi (0.1 bar) for vaporization and 3-10 psi (0.2-0.68 bar) for other services
H.  The minimum approach temperature for shell and tube exchangers is about 20 0F (10 0C) for fluids and
10 0F (5 0C) for refrigerants.
I.  Cooling tower water is typically available at a maximum temperature of 90 0F (30 0C) and should be
returned to the tower no higher than 115 0F (45 0C)
J.  Shell and Tube heat transfer coefficient for estimation purposes can be found in many reference books
or an online list can be found at one of the two following addresses:
	http://www.cheresources.com/uexchangers.shtml
	http://www.processassociates.com/process/heat/uvalues1.htm
K.  Double pipe heat exchangers may be a good choice for areas from 100 to 200 ft2 (9.3-18.6 m2)
L.  Spiral heat exchangers are often used to slurry interchangers and other services containing solids
M.  Plate heat exchanger with gaskets can be used up to 320 0F (160 0C) and are often used for interchanging
duties due to their high efficiencies and ability to "cross" temperatures.  More about compact heat exchangers
can be found at:
	http://www.us.thermal.alfalaval.com/