Assignment 1
submitted via email within 29 Aug 12
mmeang@gmail.com
Problem 1. 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
Problem 2. 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
Problem 3. How much saturated steam with 120.8 kPa pressure
is required to heat 1000 g/h of juice from 58C to 95C? Assume
that the heat capacity of the juice is 4 kJ/kgC.
Problem 4. For quick preparation of a cup of hot chocolate in a
cafeteria, cocoa powder and sugar are added in a cup of water
and the solution is heated by direct steam injection. If the initial
temperature of all the ingredients is 15 C, the final temperature
is 95C, the mass of the solution is 150 g initially, and the heat
capacity of the solution is 3.8 kJ/kg  C, calculate how much
saturated steam at 110 C will be used. State your assumptions.