Assignment 1
submitted via moodle within 31 Aug 11
Problem 1. 50 kg of food at a moisture content of 400 % dry
basis is dried to 25 % wet basis. Calculate the amount of water
removed
Water removed
F = 50 kg of raw
product
Drying
process
(400 % d.b.)
Solution P = 13.33 kg , W = 36.67 kg
Product
(25 % w.b.)
Problem 2. A membrane separation system is used to concentrate the liquid
food from 12 % to 45 % total solid (TS). The process is accomplished in two
stages, in the first stage a low total solid liquid stream is released. For the
second stage, there are two streams released. The first stream is final
product with 45% TS and the others is coming out with 1.5% TS and recycled
to the first stage. Determine the magnitude of the recycle stream, the waste
stream from first stage contains 0.25 % TS and the stream between stages 1
and 2 contains 30 % TS . The flow rate of 45 % TS final product stream is at
120 kg/min.
W , 0.25 % TS
Feed
12 % TS
first stage
B
30 % TS
Second stage
120 kg/ min of
product
45 % TS
R
1.5 % TS
Solution F = 457.02 kg/min , W = 337.02 kg/min and R = 63.16 kg / min
Problem 3. Steam is used for peeling of potatoes in a semicontinuous operation . Steam is supplied at the rate of 5 kg per
80 kg of unpeeled potatoes. The unpeeled potatoes enter the
system with a temperature of 22 C and the peeled potatoes
leave at 35 C . A waste stream from the system leaves at 65 C .
The specific heats of unpeeled potato, waste stream and peeled
potatoes are 3.7 , 4.2 and 3.5 kJ/ (kg K ) , respectively. If the heat
content of steam is 2800 kJ /kg , determine the quantities of the
waste stream and the peeled potatoes from the process
Solution P = 17.89 kg and W = 67.11 kg
Problem 4. Potato flakes ( 62 % w.b.) are being dried in a concurrent
flow dries. The moisture content of the air entering the drier is 0.05 kg
of water per 1 kg of dry air. The moisture content of air leaving the
drier is 0.125 kg water per 1 kg of dry air. The air flow rate in the drier
is 150 kg dried air per hour. As show in a picture , 80 kg of wet potato
flakes enter the drier per hour. At steady state , Calculate the following
A. What is the mass flow rate of dried patatoes.
B. What is the moisture content , dry basis , of “ dried potatoes ”
exiting the drier
Air in
Exit Air
Feed
Product
Solution mass flow rate = 68.75 kg/h and MC = 126 %db