Download Sample Test 2 Part2

Part 2
King Saud University
Department of Chemical Engineering
Test 2
ChE 316
Time: 60 min
Total Pages: 1
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Question 2a
From a single stage membrane separation, compositions (mole%) of streams is as follows:
• Feed: CO2 (A) =7, CH4 (B) = 93
• Permeate: CO2 = 40, CH4 = 60
• Retentate: CO2 = 3, CH4 = 97
I. Determine the separation factor (αCO2, CH4).
II. If Feed= 100 mol/h, Permeate= 10 mole/h and the Retentate= 90 mol/h. Determine the cut and the
%recovery of CH4 in the retentate.
Question 2b:
The wet sample (dry solid + water) weight of a solid material is 10 kg. And, the bone dry sample (dry solid
only) weight is 5 kg. The wet sample is dried with the flow of air. At equilibrium after a long period, the wet
sample weight is found to be 6 kg. Determine its
•
•
•
equilibrium moisture content, X* (kg water/kg dry solid)
free moisture content, X (kg water/kg dry solid)
total moisture content on wet basis (kg water/kg wet solid)
Question 2c (use given figure)
i.
ii.
iii.
iv.
v.
5
Rate of Drying, (kg
water/h.m2)
The air at a temperature of 40°C and having a
humidity H=0.015 kg water/kg dry air is used
to dry a sample of solids saturated with
water. Its rate of drying curve is given below.
The heat transfer is by convection only.
Rate of Drying Curve (Ls/A=20.24 kg/m2)
4
3
What is the critical moisture content,
2
Xc, of the solid.
What is the rate of drying in the
1
constant rate period, Rc.
What is the temperature of the solid
0
surface when X=0.6
0
If the rate of drying in the falling rate
period can be assumed to be linear as
R=aX, determine the constant ‘a’.
What is the heat transfer coefficient, h, in this case.
0.2
0.4
0.6
0.8
Free Moisture
Question 3a
A rotary dryer is fed with wet feed at a rate of 1 kg dry solid/s. The feed contains 50% water per kg dry solid
and the product is discharged with 3% water per kg dry solid. The entering air is at 107 C and an absolute
humidity of 0.007 kg/kg. The solid feed enters at 21 C and leaves at 36 C. The air leaves at 37 C. Allow a
radiation heat loss of 25 kJ/kg of dry air. Calculate
• mass of air passing through dryer
• humidity of the air leaving dryer
(Cp data: in kJ/kg K: dry solid= 1.5, dry air = 1.005, water vapor = 1.88, liquid water = 4.19)
Question 3b
In a drying experiment, what will be the % reduction in the value of the heat transfer coefficient if the
velocity of the air is reduced by half (i.e. 50%) for following cases.
• The flow of air is parallel to the drying surface
• The flow of air is perpendicular to the drying surface
1