Date: 02/11/2015
THE
INSTITUTION OF ENGINEERS, BANGLADESH AMIE SECTION "A" EXAMINATION,
OCTOBER 2015
Sub : Thermal
Engineering
Full Marks : 100 Time
: 3 Hours
The figures in the margin indicate full marks.
There are SEVEN
questions in this paper. Answer any FIVE.
The necessary property tables are provided. Assume any reasonable data,
if necessary.
1. (a) What is the difference between intensive and extensive
properties? (4)
(b) State and explain
the Zeroth law of thermodynamics. (6)
(c) 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. (10)
2. (a) Define turbine efficiency, generator efficiency, and
combined turbine-generator efficiency.
(6)
(b) Define and explain briefly an adiabatic process. (4)
(c) An 80-L vessel contains 4 kg of Refrigerant-134a at a
pressure of 160 kPa. Determine . (10)
(i) the temperature (ii) the quality (iii) the enthalpy of
the refrigerant, and (iv) the volume occupied by the vapor phase.
3. (a) What are the differences between mass and molar mass?
How are these two related? (4)
(b) Define the compressibility factor. What is the principle
of corresponding states? (6)
(c) A rigid tank is divided into two equal parts by a
partition. Initially, one side of the tank contains 5 kg of water at 200 kPa
and 25°C, and the other side is evacuated. The partition is then removed, and
the water expands into the entire tank. The water is allowed to exchange heat
with its surroundings until the temperature in the tank returns to the initial
value of 25°C. (i) the volume of the tank, and (ii) the final pressure.
4. (a) Define the specific heat ratio. Show that for an ideal
gas C, = Cy + Ru. (8)
(b) A piston-cylinder
device, whose piston is resting on a set of stops, initially contains 3 kg of
air at 200 kPa and 27°C. The mass of the piston is such that a pressure of 400
kPa is required to move it. Heat is now transferred to the air until its volume
doubles. Determine (i) the work done by the air, and (ii) the total heat
transferred to the air during this process. (iii) Also show the process on a
p-v diagram. (12)
5. (a) Define mass and volume flow rates. How are they
related to each other? (6)
(b) Air enters an
adiabatic nozzle steady at 300 kPa, 200°C, and 30 m/s and leaves at 100 kPa and
180 m/s. The inlet area of the nozzle is 80 cm2. Determine (i) the mass flow rate
through the nozzle, (ii) the exit temperature of the air, and (iii) the exit
area of the nozzle. (14)
6. (a) What is the Kelvin-Planck expression of the second law
of thermodynamics? (5)
(b) What are the four processes that make up the Carnot
cycle? Explain briefly. (8)
(c) A heat pump is used to maintain a house at a constant
temperature of 23°C. The house is losing heat to the outside air through the
walls and the windows at a rate of 60,000 kJ/11 while the energy generated
within the house from people, light, and appliances amounts to 4000 kJfh. For a
COP of 2.5, determine the required power input to the heat pump. (7)
7. (a) What is the difference between spark-ignition and
compression-ignition engines? (4)
(b) What is the difference between the specific humidity and
the relative humidity? (4)
(c) An ideal Otto cycle has a compression ratio of 8. At the
beginning of the compression process, -air is at 95 kPa and 27°C, and 750 kJ/kg
of heat is transferred to air during the constant volume heat-addition process.
Taking into account the variation of specific-heats with temperature, determine
(i) the pressure at the end of the heat addition process, (ii) the net work
output, and (iii) the thermal efficiency.
(12)
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