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DEPARTMENT OF CHEMICAL ENGINEERING

Indian Institute of Technology Madras

Chennai 600 036

CH 3080 Process Equipment Design

Problem set IE

1. The mass flow rate of flue gas in a 4-by 6-ft rectangular duct is to be measured using a

thermal meter. The normal gas composition is 76% N2, 3% O2 , 14% CO2 and 7% H2O, and

the average velocity is 40 ft/s at duct conditions of 3000F and 1 atm. (a) If a 5000 W heating

element is centrally mounted in the duct, what is the temperature rise after the heated gas

has mixed with the rest of the gas? What is the accuracy of the flow measurement if the

upstream and the downstream temperatures can be determined to 0.020F? If the meter is

calibrated for the normal gas composition, what is the effect of a change to 12 % CO2?

2. A pneumatic transfer line has 300ft of straight pipe, two long radius elbows, and a lift of 50

ft. A two-stage cyclone is at the receiving end. Solid with a density of 125 lb/cuft is at the

rate of 10 tons/h and the free air is at 5000 ft/min. Inlet condition is 27 psia and 100 0F.

Investigate the relation between line diameter and power requirement.

3. It is desired to concentrate the caustic soda solution from 12.5 to 40 percent in a double

effect evaporator. 50,000 lb/h of feed solution enters the evaporator at 1200 F, and steam

at 15 psig is available for effecting the concentration. Vacuum in the second effect is held

at 24 in. Hg, and water from a cooling tower is available at 850 F. Estimate (a) the quantity

of steam and water required for forward feed operation. (b) the quantity of steam and

condenser water required for backward feed operation. (c) the surface required for

operation in (a), assuming overall coefficient of heat transfer of 400 and 250 Btu/h. ft 2.0F

for the first and second effects; (d) the surface in (b) for values U equal to 450 and 350 in

the two effects respectively; (e) if equal bodies were required for (c) and (d),what steam

economy could be expected? Show the arrangement of flow directions and the mechanical

design.

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4. We are separating an ethanol-water mixture in a column operating at atmospheric pressure

with a total condenser and a partial reboiler. Constant molal overflow can be assumed, and

the reflux is a saturated liquid. The fed rate is 100 lb moles/h of a 30 mole % ethanol

mixture. The feed is subcooled liquid, and 3 mole of feed will condense 1 mole of vapor at

the feed plate. We desire an xD = 0.8; xB = 0.01and use L/D = 2.0. Use plate spacing of 18

in. What diameter is necessary if we operate at 75% flooding? How many real stages are

required, and how tall is the column? What types of plates are suitable for this operation?

Present the mechanical design of the column.

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