Page 49 - Chemical engineering design

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CHEMICAL ENGINEERING
1.13 PROBLEMS
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1.1. Given that 1 in D 25.4mm; 1lbm D 0.4536 kg; 1 F D 0.556 C; 1 cal D 4.1868 J;
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g D 9.807 m s , calculate conversion factors to SI units for the following
terms:
i. feet
ii. pounds mass
iii. pounds force
iv. horse power (1 HP D 550 foot pounds per second)
v. psi (pounds per square inch)
vi. lb ft 1 s 1 (viscosity)
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vii. poise (gm cm 1 s )
viii. Btu (British Thermal Unit)
ix. CHU (Centigrade Heat Unit) also known as PCU (Pound Centigrade Unit)
x. Btu ft 2 h 1 Ž 1 (heat transfer coefficient).
F
1.2. Determine the degrees of freedom available in the design of a simple heat
exchanger. Take the exchanger as a double-pipe exchanger transferring heat
between two single-phase streams.

1.3. A separator divides a process stream into three phases: a liquid organic stream, a
liquid aqueous stream, and a gas stream. The feed stream contains three compo-
nents, all of which are present to some extent in the separated steams. The compo-
sition and flowrate of the feed stream are known. All the streams will be at the same
temperature and pressure. The phase equilibria for the three phases is available.
How many design variables need to be specified in order to calculate the output
stream compositions and flow rates?
1.4. A rectangular tank with a square base is constructed from 5 mm steel plates. If
the capacity required is eight cubic metres determine the optimum dimensions if
the tank has:
i. a closed top
ii. an open top.
1.5. Estimate the optimum thickness of insulation for the roof of a house, given the
following information. The insulation will be installed flat on the attic floor.
Overall heat transfer coefficient for the insulation as a function of thickness, U
values (see Chapter 12):
thickness, mm 0 25 50 100 150 200 250
U, Wm 2 Ž C 1 20 0.9 0.7 0.3 0.25 0.20 0.15
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Average temperature difference between inside and outside of house 10 C; heating
period 200 days in a year.
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Cost of insulation, including installation, £70/m . Capital charges (see Chapter 6)
15 per cent per year. Cost of fuel, allowing for the efficiency of the heating
system, 6p/MJ.
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Note: the rate at which heat is being lost is given by U ð T, W/m ,where U
is the overall coefficient and T the temperature difference; see Chapter 12.