number of question 1a 1b 2a 2b 3a 3b 4 mark total 30 ... 1432-1433h_solution.pdftime: 2 hr. group:...

of 9 Examiner: Dr. Walid Aniss.

KING ABDULAZIZ UNIVERSITY.

Faculty of Engineering, Rabigh Branch. Student Name:

Mechanical Engineering Department. Student Number:

Subject: Thermodynamics (I) MEP261. Time: 2 hr. Group: ZA.

Fall 1432/1433 H. Final Exam. Property Tables are allowed.

Number of Question 1a 1b 2a 2b 3a 3b 4

30 Mark

Total

Answer the following questions:

Question (1) (8 Marks)

1a)Water is being heated in a closed pan on top of

a range while being stirred by a paddle wheel.

During the process, 30 kJ of heat is transferred to

the water, and 5 kJ of heat is lost to the

surrounding air. The paddle-wheel work amounts

to 500 N · m. Determine the final energy of the

system if its initial energy is 10 kJ. (2 Marks)

Sol.







1b) Complete these data for H2O: ( 6 Marks)

T, °C p, kPa u, kJ/kg v, m3/kg Phase description x

400 1450

220 Saturated vapor

190 2500

4000 3040

Sol.

Question (2) ( 7 Marks)

2.a) A frictionless piston–cylinder device contains 2 kg of

nitrogen at 100 kPa and 300 K. Nitrogen is now compressed

slowly according to the relation Pv1.4

= constant until it reaches

a final temperature of 360 K. Calculate the work

input during this process. (3 Marks)

Solution


2.b) Refrigerant-134a enters a 28-cm diameter pipe steadily at

200 kPa and 20°C with a velocity of 5 m/s. The refrigerant gains

heat as it flows and leaves the pipe at 180 kPa and 40°C.

Determine (a) the volume flow rate of the refrigerant at the

inlet, (b) the mass flow rate of the refrigerant, and (c) the

velocity and volume flow rate at the exit. (4 Marks)

Solution

Solution







Question (3) ( 9 Mark)

3.a) An air conditioner removes heat steadily from a house at a

rate of 750 kJ/min while drawing electric power at a rate of 6

kW. Determine (a) the COP of this air conditioner and (b) the

rate of heat transfer to the outside air.

Answers: (a) 2.08, (b) 1110 kJ/min

.

Solution

)sMark 3(


3.b) A piston–cylinder device contains 5 kg of steam at 100°C with a

quality of 50 percent. This steam undergoes two processes as follows:

1-2 Heat is transferred to the steam in a reversible manner while the

temperature is held constant until the steam exists as a saturated vapor.

2-3 The steam expands in an adiabatic, reversible process until the

pressure is 15 kPa.

(a) Sketch these processes with respect to the saturation lines on a single

T-s diagram.

(b) Determine the heat added to the steam in process 1-2, in kJ.

(c) Determine the work done by the steam in process 2-3, in kJ. (6 Marks)

Sol.

Solution







Question (4) (6 Marks)

Air enters the compressor of a gas-turbine engine at 300 K and 100 kPa,

where it is compressed to 700 kPa and 580 K. Heat is transferred to air in

the amount of 950 kJ/kg before it enters the turbine. For a turbine

efficiency of 86 percent, determine (a) the fraction of the turbine work

output used to drive the compressor and (b) the thermal efficiency.

Assume variable specific heats for air. .

Sol.


Solution

number of question 1a 1b 2a 2b 3a 3b 4 mark total 30 ... 1432-1433h_solution.pdftime: 2 hr. group:...

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