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Thermal unit operation exercise questions (1).pptx
- 1. Thermal unit operationexercise questions Adama Science and Technology University School of Mechanical, Chemical & Materials Engineering Department of Chemical Engineering Thermal Unit Operation exercise questions (ChEg3212) 05/29/2025 Tutor questions 1
- 2. 2 1. Which typeof heat exchanger consists of two concentric pipes for heat transfer? A)Shell and tube heat exchanger B) Plate heat exchanger C)Double pipe heat exchanger D)Extended plate-type heat exchanger 05/29/2025 Tutor questions
- 3. 2. What isthe primary advantage of a plate heat exchanger? A)Low cost B)High-pressure drop C)large footprint D) Compact size 05/29/2025 Tutor questions 3
- 4. 3. In ashell and tube heat exchanger, which fluid typically flows through the shell? A)Hot fluid B)Cold fluid C)Both fluids interchangeably D)None of the above 05/29/2025 4 Tutor questions
- 5. 4. What distinguishesan extended plate type heat exchanger from a regular plate heat exchanger? A)Increased number of plates B)Addition of fins on plates C)larger plate size D)Higher operating pressure 05/29/2025 Tutor questions 5
- 6. 5. What isthe purpose of baffles in a shell and tube heat exchanger? A) To enhance heat transfer B) To increase pressure drop C) To reduce fouling D) To control fluid flow 05/29/2025 Tutor questions 6
- 7. 6. What isthe purpose of using fins in extended plate-type heat exchangers? A)To increase the surface area for heat transfer B)To reduce the pressure drop C)To decrease the temperature difference between fluids D)To prevent fouling 05/29/2025 Tutor questions 7
- 8. 05/29/2025 Tutor questions8 7. In the given figure below:
- 9. Letters a, andd represent: A) Front header and Bundle B)Front header and Shell C)Front header and Rear header D)Rear header and Bundle 05/29/2025 Tutor questions 9
- 10. 8. In theabove question no 7, letters c and b represent respectively: A)Bundle and shell B)Shell and Bundle C)Rear header and bundle D)Front header and shell 05/29/2025 Tutor questions 10
- 11. 9. ________is aniterative process that is normally carried out using computer programs from organizations such as the Heat Transfer and Fluid Flow Service (HTFS) or Heat Transfer Research Incorporated (HTRI). A)Thermal design B)Hydraulic design C)Mechanical Design D)All 05/29/2025 Tutor questions 11
- 12. 10. ______ typeof baffle is used to obtain a lower shell side velocity and pressure drop. A)Disc and Doughnut B)Single Segmental C)Double Segmental D)Orifice type 05/29/2025 Tutor questions 12
- 13. 11. In theequation Q = UAΔt; Δt is A) Geometric mean temperature difference. B) Arithmetic mean temperature difference. C) Logarithmic mean temperature difference. D) The difference in average bulk temperatures of hot and cold fluids 05/29/2025 Tutor questions 13
- 14. 12. Fouling factor A)is a dimensionless quantity. B) does not provide a safety factor for design. C) accounts for additional resistance to heat flow. D) none of these. 05/29/2025 Tutor questions 14
- 15. 13. Hot water(0.01 m3 /min) enters the tube side of a counter-current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3 /min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately, using the density of water, 998 kg/m3 , and Cpw = 4.2KJ/kg.K. A) 32°C B) 37°C C) 45°C D) 50°C 05/29/2025 Tutor questions 15
- 16. 14. In aheat exchanger, a floating head is provided to A) facilitates the cleaning of the exchanger. B) Increase the heat transfer area. C) relieves stresses caused by thermal expansion. D) Increase log mean temperature gradient. 05/29/2025 Tutor questions 16
- 17. 15. Convective heattransfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio if the flow is in the __________ zone. A)Laminar B) Transition C) both 'a' & ‘b’ D) highly turbulent 05/29/2025 Tutor questions 17
- 18. 16. The actualtemperature drop across the heating surface in an evaporator depends on the A) feed. B) depth of liquid overheating surface. C) the pressure difference between the steam chest and vapor space. D) all 05/29/2025 Tutor questions 18
- 19. 17. The unitof heat transfer co-efficient in the SI unit is A) J/M2°.K B) W/m2 °K C) W/m°.K D) J/m°.K 05/29/2025 Tutor questions 19
- 20. 18. The numberof kg vaporized per kg of steam fed to the evaporator is defined as A) Capacity B) rate of evaporation C) Economy D) rate of vaporization 05/29/2025 Tutor questions 20
- 21. 19. One ofthe major problems in thermal unit operation is fouling. Which of the following statements is not true about fouling? A) It is the accumulation of undesirable substances on the surfaces of process equipment B) It changes the geometry of heat exchangers and increases the efficiency of heat exchangers by affecting the pressure drop C) It reduces process equipment service life D) As it has low thermal conductivity, so does increase the resistance to heat transfer 05/29/2025 Tutor questions 21
- 22. 20. A backwardfeed multiple effect evaporator is better than a forward feed for concentrating cold feed because it provides A) higher economy B) Higher capacity C) both (a) & (b) D) lower economy 05/29/2025 Tutor questions 22
- 23. 21. In thefollowing fouling mechanism, which sequence of fouling events is correct? A) Initiation, transport, attachment, transformation, removal B) Attachment, initiation, transformation, transport, removal C) Initiation, attachment, transportation, transport, removal D) Transformation, transport, initiation, attachment, removal 05/29/2025 Tutor questions 23
- 24. 22. If thebaffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid A) remains unchanged. B) increases. C) increases or decreases depending on the number of shell passes. D) decreases. 05/29/2025 Tutor questions 24
- 25. 23. What isthe purpose of more viscous fluid allocated in a shell side A) Decrease resistance B) Reduce the cost C) Improve the rate of heat transfer D) none 05/29/2025 Tutor questions 25
- 26. 24. The tubeside and shell side fluids are separated by a_______________ A) Baffles B) Tube sheet C) Header plate D) Flange 05/29/2025 Tutor questions 26
- 27. 25. What isNusselt number? A) B) C) D) 05/29/2025 Tutor questions 27
- 28. 26. Performance ofthe boiler, like efficiency and evaporation ratio reduces with time, due to__________factors A)Poor combustion B)Heat transfer fouling C)Poor operation and maintenance D)All 05/29/2025 Tutor questions 28
- 29. 27. In boilerefficiency tests the indirect method testing is preferred over than direct method Why? A) Does not give clues to the operator as to why the efficiency of the system is lower B) calculates the various heat losses associated with boiler C) Does not calculate various losses accountable for various efficiency levels D) Evaporation ratio and efficiency may mislead if the steam is highly wet due to water carryover 05/29/2025 Tutor questions 29
- 30. 28. Which oneis the greatest boiler heat loss in indirect method testing? A) Heat loss due to moisture present in the fuel B) Heat loss due to moisture present in the air C) Heat loss due to dry flue gas D) Heat loss due to radiation and convection 05/29/2025 Tutor questions 30
- 31. 29. In aparallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is A) Minimum B) Infinity C) Maximum D) zero 05/29/2025 Tutor questions 31
- 32. 30. In counterflow compared to parallel flow, A) LMTD is greater. B) Less surface area is required for a given heat transfer rate. C) Both (a) and (b). D) More surface area is required for a given heat transfer rate. 05/29/2025 Tutor questions 32
- 33. 31. In evaporatordesign if the concentrated product may degenerate if exposed to high temperature, which feeding arrangement is best? A) Forward feed B) Backward feed C) Mixed feed D) Parallel feed 05/29/2025 Tutor questions 33
- 34. 05/29/2025 34 Compiled examsThermal, Fundamentals of Biochem, & apparatus, Mechanical Unit Operation Course, Reaction Engineering Model Exam, Chemical Engineering Thermodynamic II, Plant design and engineering economics, Heat and mass transfer model questions, Fluid Mechanics, Mass Transfer Unit Operation, Fundamentals of chemical engineering, •