FEN241: ENGINEERING THERMODYNAMICS
FEN241: ENGINEERING THERMODYNAMICS
(FUO 1ST SEMESTER EXAM, 2018/2019 SESSION)
INSTRUCTION: ANSWER ALL QUESTIONS IN SECTION A AND ANY OTHER FOUR IN SECTION B)
SECTION A
1. 1. The zeroth law of thermodynamics defines.
A. Temperature B. Internal energy C. Enthalpy D. all of the above.
2. 2. A control volume refer to.
A. A fixed region in space B. A closed system C. An isolated system D. none.
3. 3. In an irreversible process there is a
A. gain of heat B. loss of heat C. no loss of heat D. no gain of heat
4. 4. Which of the following is an intensive property of a thermodynamic system?
A. temperature B. volume C. mass D. energy
5. 5. A series of operations, which take place in a certain order and restore the initial condition, is known as.
A. thermodynamic cycle B. irreversible cycle C. reversible cycle D. none of the above.
6. 6. The processes occurring in open system which permit the transfer of mass to and from the system, are known as
A. flow process B. non-flow process C. adiabatic processes D. none of the above
7. 7. An Isentropic process is always
A. reversible and adiabatic B. irreversible and adiabatic C. reversible and isothermal D. frictionless and irreversible
8. 8. In an reversible adiabatic kudos process, the ratio (T1/T2) is equal to
A. (v1/v2)r-1/r B. (v1v2)r-1/2r C. (p2/p1)r D. (p1/p2)r-1/r
9. 9. In the polytropic process equation pvn = constant, if n = 0 the process is termed
A. constant pressure B. constant temperature C. constant volume D. adiabatic
10.10. The processes or systems that do not involve heat are called.
A. steady processes B. adiabatic processes C. thermal processes D. isothermal processes
11. The internal energy of a perfect gas depends on
A. temperature only B. temperature, specific heats and pressure C. temperature, specific heat and enthalpy D. temperature, specific heat and entropy
12. The internal energy of 1kg of perfect gas can be computed with the following equations except
A. Cv(T2 – T1) B. Cp/r(T2 – T1) C. (Cp – R)(T2 – T1) D. Cp(T2 – T1)
13. At triple point
A. ice on heating becomes super-heated vapor B. liquid water, dry saturated steam co-exist C. ice occupies maximum specific volume D. solid, liquid and vapor co-exist.
14. The state of a substance whose evaporation from its liquid state is complete, is known as
A. steam B. perfect gas C. vapor D. air
15. In an isentropic process
A. W = 2(u2 – u1) B. W = u2 – u1 C. W = (u2 – u1)2 D. none of the above
16. A process, in which the temperature of the working substance remains constant during its expansion or compression, is called
A. isothermal process B. hyperbolic process C. adiabatic process D. polytropic process
17. A closed system undergoes a process 1 -2 for which the value of W1-2 and Q1-2 are 50kJ and +20kJ respectively. If the system is returned to state 1 and the Q1-2 is -10kJ, the work W1-2 is?
A. -40kJ B. -40 C. +40kJ D. +40
18. Which of the following is a point function as in thermodynamics
A. Work B. Gas C. heat D. Pressure
19. Dryness fraction of steam is defined as
A. mass of dry steam/mass of water vapor in suspension B. mass of dry steam/(mass of dry steam + mass of water vapor in suspension) C. mass of water vapor in suspension/mass of dry steam D. mass of dry steam/(mass of dry steam + mass of water vapor in suspension).
20. In the polytropic process equation pvn = constant, if n is infinitely large, the process is termed as
A. constant temperature B. adiabatic C. constant pressure D. constant volume
21. The gas constant (R) is equal to the
A. sum of two specific heats B. difference of two specific heats C. ratio of two specific heat D. product of two specific heats
22. The followings are true of isothermal process except
A. dT = 0, du = 0 B. Q = mRTln(T2/T1) C. du = 0, Q = W D. P2V2 = P1V1
23. Characteristic gas constant of a gas is equal to
A. cv/cp B. cp + cv C. cp/cv D. cp - cv
24. The heating and expanding of a gas is known as
A. thermodynamic process B. thermodynamic system C. thermodynamic law D. thermodynamic cycle
25. In an extensive property of a thermodynamic system
A. extensive heat is transferred B. extensive work is done C. extensive energy is utilized D. none
26. The amount of heat required to raise the temperature of the unit mass of gas through one degree at constant volume, is called
A. Cv B. Cp C. kilo Joule D. none of these
27. Which of the following is a path function as in thermodynamics?
A. Heat B. Pressure C. Temperature D. Volume
28. In Isothermal process
A. volume remains constant B. change in internal energy is zero C. enthalpy change is maximum D. pressure remains constant
29. The efficiency of an Ideal Carnot engine depends on
A. the temperature of the source only B. the temperature of both the source and the sink C. the working fluid D. the temperature of the sink only
30. Volume of wet steam (per kg) with dryness fraction x Is given by
A. xvg B. xvg C. x2(vg – vf) D. x2vg
31. An adiabatic process is one in which
A. no heat enters or leaves the gas B. the pressure of the gas changes C. the change in internal energy is equal to the mechanical heat transfer D. none.
SECTION B
1. QUESTION ONE
a. What is the Zeroth law of Thermodynamics?
b. Consider that a gas power cycle operating on an isobaric combustion process with the following data; Minimum pressure = 98.5kPa, Peak Pressure = 268kPa, Initial Temperature = 60°C, Compression Ratio = 15.3, Expansion Ratio = 7.5 (ϒ = 1.4, Cp = 1.003kJ/kg°K)
i. Identify and draw p – V diagram of the cycle.
ii. What is the maximum temperature attainable during the cycle
iii. Calculate the thermal efficiency of the cycle
2. QUESTION TWO
a. Would it be possible that water would boil at higher temperatures at higher pressures? Explain.
b. A fluid system undergoes a non-flow frictionless process following the pressure-volume relation as p = 6V + 2.5 where ρ is in bar and V is in m3. During the process the volume changes from 0.35m3 to 0.25m3 and the system rejects 35kJ of heat. Determine:
i. Change in internal energy
ii. Change in enthalpy
3. QUESTION THREE
a. What is a pure substance?
b. A fluid undergoes the following processes:
i. Heated reversibly at a constant pressure of 2.15bar until it has a specific volume of 0.3m3/kg
ii. It is then compressed reversibly according to a law pv = constant to a pressure of 6.2bar
iii. It is then allowed to expand reversibly according to a law pv1.3 = constant
iv. Finally it is heated at constant volume back to initial conditions. The work done in the constant pressure process is 755Nm and the mass of fluid present is 0.25kg. Calculate the net work done on or by the fluid in the cycle and sketch the cycle on a p-v diagram.
4. QUESTION FOUR
a. Most of the heat energy generated in the engine of a car is rejected at the radiator to the atmosphere through the circulating water (hence the name “water-cooled engine”). Should the radiator be analyzed as a closed system or as an open system? Explain.
b. In a system, executing a non-flow process, the work and heat per degree change of temperature are given by dW/dT = 4000W-s/°C and dQ/dT = 3160J/°C. What will be the change of internal energy of the system when its temperature changes from T1 = 95°C to T2 = 135°C?
5. QUESTION FIVE
a. The power developed by a turbine in a certain steam plant is 2400kW. The heat supplied to the boiler is 4560kJ/kg, the heat rejected by the system to cooling water in the condenser is 3540kJ/kg and the feed pump work required to pump the condensate back into the boiler is 12kW. Calculate the steam flow in the cycle in kg/s.
b. A cylinder contains 10kg of a certain fluid at an initial pressure of 40bar. The fluid is allowed to expand reversibly behind a piston according to a law pV2 = constant until the volume is doubled. The fluid is then cooled reversibly at constant pressure until the piston regains its original position; heat is then supplied reversibly with the piston firmly locked in position until the pressure rises to the original value of 40bar. Calculate the net work done by the fluid, for an initial volume of 0.05m3
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