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....

Realtime online exam - subject: Food engineering. Exam is on May 17 (next Monday), starts at 2pm (GMT +8), last for 3 hours till 5pm (GMT+8). I need help with an exam that looks very much like the one I attached (attached is exam paper from same course last year). There will be 20 multiple choice questions and 4 structure questions (choose 4 out of 5 questions). Thank you :)


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. 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 Page 2 of 10 Section A: Multiple Choice Questions (20 marks @ 1 mark) Answer ALL questions in this section. Page 3 of 10 Page 4 of 10 Page 5 of 10 Page 6 of 10 Page 8 of 10 (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. (5 marks) 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. (12 marks) Page 9 of 10 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). (12 marks) (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. (8 marks) 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. (15 marks) Page 10 of 10 (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. (5 marks) 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. (13 marks) (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) --- End of Paper ---