1. Strawberries contain about 15 % Solids and 85 % water.
To make a strawberry jam, crushed
strawberries and sugar are mixed in a 45:55 ratio, and the mixture is heated to evaporate water
until the residue contain one-third water by mass. Calculate how many grams of strawberries are
needed to make a kilogram of jam.
F2, sugar W, H2O
F1, crushed strawberries
15 % Solids Mixer Evaporator P, Jam
85 % water 1/3 water by mass
=
Required: g of F1 per kg P
Basis: 1 kg of P (1000 g)
Solid balance @ whole system
0.15 F1 + F2 = iiiL
F1 =
F2
F1 = 485.83 g of strawberries
2. Fresh feed stream flowing at 100 kg/h contains 20 wt% KNO3 and the balance water. The fresh
feed stream is combined with a recycle stream and is fed to an evaporator. The concentrated
liquid solution leave the evaporator containing 50 wt % KNO3 is fed to a crystallizer. The crystals
obtained from the crystallizer is wet and contains 4 wt % water. The liquid from the crystallizer
constitute the recycle stream and contains 0.6 kg KNO3 per 1 kg water. Calculate:
a) Weight of product crystal collected
b) Weight of water removed in the evaporator.
c) Weight of the recycled stream
F = 100 kg/h W, H2O
20 wt % KNO3
80 wt% water 50 % wt% KNO3
Evaporator Crystallizer
C
P KNO3
4 % H2O
0.6 Kg KNO3 / Kg H2O % H2O
Required: C, W, R
Basis: 1 hr operation
KNO3 balance @ whole system
0.2(100) = (1 – 0.04)(P )
P = 20.83 kg
OMB @ whole system
100 = W + 20.83
W = 79.17 kg
@ crystallizer
OMB: C = 20.83 + R
ith
KNO3 balance: 0.5(C ) = 0.96(20.83) + th
R
R = 76.68 kg
3. A stream of air at 40 oC and 1 atm has a dew point of 20 oC. Determine the following:
a. Molar humidity
b. Absolute humidity
c. Relative Humidity
d. % Humidity
e. % (mole) water vapor
tᄀᄀ
ln (Pv) = 18.3036 -
ᄀt
at 40 oC, Pv = 54.75 mm Hg
at 20 oC, Pv = 17.19 mm Hg
Pp = Pv at 20 oC
t
Hm = hi t
= 0.023
th
Habs = Hm( tᶈ
L = 0.023( L = 0.014
t
RH = t
x 100 = 31.40 %
t t.h2t iti
%H = t th th2 thᶈ
x 100 = t x 100 = 29.62 %
hi t
t
% H2O = hi
x 100 = 2.26 %
4. Dry air containing at 90 oC and 1 atm is humidified by spraying water and gas mixture leaves the
humidifier saturated 60 oC and 1 atm. Calculate the moles of water added per 100 moles of dry air
entering.
Dry air Saturated air
90 oC, 1 atm Humidifier 60 oC, 1 atm
E L
Required: W/100 mole dry air
Hm E = 0
Using Antoine eq. At 60 oC, Pv = 148.39 mm Hg
t
Hm L = hi t
= 0.243
t ii t tᶈ t t
ii t tᶈ
= (0.243 – 0) t tᶈ
x ii t tᶈ
= ii t tᶈ
5. Contaminated air contains 3 mol% acetone and 2 mol% water vapor. The air was sent to an
absorber to completely remove the acetone using water as absorber. The air leaving the absorber
contains 0.5 mol % water and the liquid leaving the system contains 19 wt% acetone and 81 wt %
water. Calculate the weight of water used per 100 mol of contaminated air
Contaminated air E
3 mol % C3H6O
2 mol % H2O air, L
0.5 mol % H2O
Absorber 99.5 mol % dry air
R
19 wt % C3H6O S H2O
81 wt % water
Required: S / 100 mols of E
Basis: 100 mols of E
Dry air balance: (1 – 0.03 - 0.02)(100) = 0.995(L)
L = 95.5 mol
Acetone recovered: 0.03(100) = 3 mols
0.19(R ) = 3(58)
R = 915.8 g
Water balance
S = 0.81(915.8) + 0.005(95.5)(18)
S = 750.4 g
