Page 1 of 10 Faculty of Science and Technology SFS5321 Elements of Food Engineering End-of-Semester Examination Semester Two 2019/20 Date : Time : Time Allowed : 3 hours INSTRUCTIONS TO CANDIDATES 1....

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Faculty of
Science and Technology

SFS5321
Elements of Food
Engineering

End-of-Semester Examination
Semester Two 2019/20
Date :
Time :
Time
Allowed
: 3 hours
INSTRUCTIONS TO CANDIDATES
1. This question paper contains
Section A and Section B.
2. Answer ALL questions in Section
A.
3. Answer ANY FOUR OUT OF FIVE
questions in Section B. Each
question carries same marks.
4. This question paper has 10 pages.
DO NOT TURN THIS PAGE OVER
UNTIL YOU ARE TOLD TO DO SO
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Section A: Multiple Choice Questions (20 marks @ 1 mark)
Answer ALL questions in this section.
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(d) Ethanol can be produced by either chemical or
biological process in industry. Compare the two
methods by stating the relative raw materials, reaction
conditions and yield of production XXXXXXXXXXmarks)
Q.2 (a) Milk with 3.8% fat and 8.1% fat-free solids is used to
produce canned concentrated milk. The process
includes separation of the cream in a centrifuge and
concentration of the partially defatted milk in an
evaporator. If the cream that is produced in the
centrifuge contains 55% water, 40% fat, and 5% fat-free
solids, determine the amount of milk (in g) that is
required for producing a can of concentrated milk in 410
g which contains 7.8% fat and 18.1% fat-free solids.
How much cream and how much water must be
removed in the centrifuge and the evaporator
respectively? Assume steady state is applied. Support
your answers with the aid of process diagram. (8 marks)
(b) In a process of concentration, 3000 kg of freshly
extracted orange juice which containing 20.5 wt% solids
is strained, yielding 2400 kg of strained juice and 600 kg
of pulpy juice. The strained juice is concentrated in a
vacuum evaporator to give an evaporated juice of 65%
solids. The 600 kg of pulpy juice is bypassed around the
evaporator and mixed with the evaporated juice in a
mixer to improve the flavor. This final concentrated juice
contains 45 wt% solids. With the aid of a complete
process flow chart, determine the concentration of solids
in the strained juice, the kg of final concentrated juice
and the concentration of solids in the pulpy juice
bypassed XXXXXXXXXXmarks)
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Q3 (a) A food mix containing 62% non-fat solids, 28% fat and
10% water is pasteurized at 90 oC by direct injection of
270.1 kPa, 80% quality steam. The food mix is fed to the
pasteurizer at 100 kg/h and 10 oC. The final food product
is a mixture of the food mix and steam condensate.
Calculate the amount (kg/h) of steam used, and the final
composition of the pasteurized food product (wt% of
solids, fat and water XXXXXXXXXXmarks)
(b) 1000 kg/h of milk is heated in a heat exchanger from
458oC to 728oC. Water is used as the heating medium. It
enters the heat exchanger at 908oC and leaves at 758oC.
Determine the mass flow rate of the heating medium, if
the heat losses to the environment are equal to 1 kW. The
heat capacity of water is given equal to 4.2 kJ/kg-oC and
that of milk 3.9 kJ/kg-oC. Illustrate your answer with the
aid of a process diagram XXXXXXXXXXmarks)
Q4 (a) Water at 20oC is being pumped from a tank to an elevated
tank at the rate of 5.0 × 10-3 m3/s. All of the piping in the
following figure is 4-in. schedule 40 pipe. The pump has
an efficiency of 65%. Calculate the kW power needed for
the pump XXXXXXXXXXmarks)
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(b) Saturated steam at 150oC is flowing in a steel pipe of 2
in nominal diameter, schedule No. 80. If the average
velocity of the steam is 10 m/s, calculate the mass flow
rate of the steam XXXXXXXXXXmarks)
Q5 (a) A liquid food having a Cpm = 2.85 kJ/kg⋅K is flowing at
a rate of 7260 kg/h and is to be cooled from 377.6 K to
344.3 K. Cooling water at 288.8 K is available and the
flow rate is 4536 kg/h. The overall Uo is 653 W/m2⋅K and
mean heat capacity of water is 4.181 kJ/kg⋅K. Calculate
the outlet water temperature and the area Ao of the
exchanger for
(i) Counter-flow;
(ii) Co-current flow XXXXXXXXXXmarks)

(b) Hot water is transferred through a stainless-steel pipe of
0.04 m inside diameter and 5 m length. The inside wall
temperature is 90oC, the outside surface temperature is
88oC, the thermal conductivity of stainless steel is 16
W/m-oC, and the wall thickness is 2 mm. Evaluate the
heat losses if the system is at steady state. (7 marks)
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May 10, 2021

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