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Engineering Thermodynamics Ii Question Paper

Engineering Thermodynamics Ii

Course:Bachelor Of Science In Manufacturing Engineering And Technology

Institution: Kenyatta University question papers

Exam Year:2009

KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2009/2010
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF
SCIENCE IN MANUFACTURING ENGINEERING

SET 307:
ENGINEERING THERMODYNAMICS II

DATE: Wednesday, 30th December, 2009
TIME: 2.00 p.m. – 4.00 p.m.
------------------------------------------------------------------------------------------------------------
INSTRUCTIONS:
Attempt any THREE of the following five questions.
Question 1
a)
State the second law of thermodynamics

(3 marks)
b)
Explain the meaning of the terms:
a)
Reversibility

(2 marks)
b)
Irreversibility
(2
marks)
c)
A heat engine operates on the Carnot Cycle and receives 528 KJ from a
reservoir at 535oC and rejects heat at 27oC.
i)
Show the cycle on a T – S diagram considering the working fluid
as gas

ii)
Calculate the work done by the cycle

(3 marks)

iii)
Calculate the efficiency of the cycle

(3 marks)

iv)
Calculate the change in Entropy of the high-temperature and low
temperature
reservoirs
(3
marks)

d)
If the engine operates on the Carnot Cycle above, but the temperature of
the high – temperature reservoir is increased to 815oC (Heat is then
transferred from the reservoir at 815oC to the working fluid at 528oC).
The low temperature reservoir remains at 27oC. Determine the Entropy
change
for
each
reservoir.
(5
marks)

Question 2
a)
Describe briefly with reference to a P-V diagram, the constant volume cycle

(4 marks)
b)
Prove that the air-standard efficiency of the cycle is given by
1

? =? -
where ? = compression ratio
.....
?

? = the adiabatic index

Page 1 of 3

(10 marks)
c)
Calculate, the air standard efficiency of an engine working on the Otto cycle if the
pressure at the beginning and the end of compression are ? bar and 8 bar
respectively. (Assume ?
=
1.4)
(5
marks)

Question 3
a)
Explain the meaning of the terms:-

i)
dryness fraction

(1 mark)
ii)
Super
heated
steam
(1
mark)
iii)
Dry
saturated
steam
(1
mark)

iv)
Wet Steam

(1 mark)
b)
A vessel having a volume of 1 m3 contains 1.35 kg of liquid water and vapour
mixture in equilibrium at a pressure of 7 bar.
Calculate:-
i)
the volume and mass of the liquid

(2 marks)
ii)
the volume and mass of the vapour

(2 marks)
(4 marks)
c)
A 0.2 kg of steam at initial temperature of 165oC, with an initial dryness
fraction of 0.7, expands reversibly at constant pressure of 7 bar till the
volume is doubled
Calculate
i)
Work
done
(4
marks)
ii)
Heat
transferred (4
marks)

Question 4
a)
Define the terms
i)
Calorific value of a fuel

(1 mark)
ii)
Specific fuel consumption of an engine

(2 marks)
iii)
Indicated
power (1
mark)

b)
An oil engine developing indicated power (P2) of 37.5 KW used 9.0 kg of
oil of calorific value 45 MJ/kg. 8.5 KW are used in overcoming friction
in the engine itself.
Calculate:-
i)
Brake
power

(1
mark)
ii)
Specific fuel consumption in Kg/Kh (brake basis) (1 mark)
iii)
Mechanical
Efficiency (1
mark)
iv)
Indicated Thermal Efficiency of the engine
(1 mark)

c)
A sample of coal has the following analysis by weight. Carbon 86%,
Hydrogen 6%, Oxygen 5%, the remainder being incombustible mars.
i)
Calculate the theoretical mass of air required per Kg of coal for
chemically correct combustion

(6 marks)

ii)
If 60% excess air is supplied, determine the dry flue gases analysis
by
weight.
(6
marks)

Question 5
a)
Make a fully labeled schematic diagram of a combined separating and throttling
calorimeter.
(6
marks)
b)
The Rankine cycle is using steam between pressures of 30 and 0.04 bars.
Calculate:

Page 2 of 3

i)
the
cycle
efficiency
(2
marks)
iii)
work
done
(2
marks)
iv)
steam
consumption
(2
marks)
c)
Steam at 11 bar and 204oC is delivered to the throttle of an engine. The steam
expands to 2.1 bar where release occurs. Exahust is at 1.05 bar.
A test on the engine showed a specific steam consumption of 13.265 Kg/Kw - Hr
and a mechanical efficiency of 85%.
Find:-
i)
the ideal work and ideal thermal efficiency

(4 marks)
ii)
the brake and indicated work
(4
marks)

Page 3 of 3

Engineering Thermodynamics Ii Question Paper

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