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Total Energy Systems Question Paper
Total Energy Systems
Course:Master Of Science
Institution: Kenyatta University question papers
Exam Year:2007
KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2007/2008
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF MASTER OF SCIENCE
SAT: TOTAL ENERGY SYSTEMS
DATE: Monday 3rd December 2007 TIME: 2.00pm - 4.OOpm
=========================================================================
INSTRUCTIONS
Answer any THREE (3) questions
All questions carry equal marks
Answer books, h-s chart, steam tables provided
Q1. (a) Steam is supplied dry saturated at 40 bar to a turbine and the condenser is
0.035 bar. If the plant operates on the Rankine cycle, calculate per kg of
steam
(i) The Rankine efficiency
•(ii) Specific steam consumption
(iii) The heat supplied to the condenser cooling water and the amount
of cooling water required through the condenser if the temperature
rise of the water is assumed to be 5.5k.
(b) In a regenerative steam cycle employing two closed feed heaters, the
steam is supplied to the turbine at 40 bar and 500°C and is exhausted to
the condenser at 0.035 bar. The intermediate bleed pressures are obtained
such that the saturation temperature intervals are approximately equal,
giving pressures of 10 and 1.1 bar.
Determine
(i) The amount of steam bled at each stage
(ii) The work output ofthe plant in kj/kg of boiler steam and
(iii) The thermal efficiency of the plant.
Assume ideal processes where required.
(sketch the schematic and T-s or h-s diagrams)
Q2.(a) For the Joule cycle, show that the ideal air standard efficiency is
7J = 1- (~Jy - 1 and the work ratio:
rp 7J
TI y-l
r =1-r
W T p -2 7J where rp = P2 / = P3 / is the pressure ratio. 7PI 7P4)
[6 marks]
(b) An ideal dual combustion cycle has a volume ratio of the adiabatic
compression of 15:1. At the beginning of the adiabatic compression the
pressure, volume and temperature of the gas are 97kn1m2
, O.084m2 and 280C respectively. The maximum pressure and temperature ofthe cycle
are 6.2mn1m2 and 1320°C, respectively. For the cycle determine:-
(i) the pressure, volume and temperature at the cycle process change points.
(ii) the net work done
(iii) the thermal efficiency
(iv) the heat received
(v) the work ratio
(vi) the mean effective pressure
(vii) the carnot efficiency within the cycle temperature limits
Take C, = l.005KJ/kgK, C, = O.717KJ/kgK. [14 marks]
Q.3 Saturated vapour enters the first stage compressor at a pressure of 1.2 bar while
saturated vapour at a pressure of 4.3 enters the second stage compressor and
leaves at a pressure of 15.54 bar and a temperature of 75°C. This vapour then
enters the condenser. Assuming there are no pressure losses in the condenser and
evaporator and that the compressor processes are reversible and may be
represented as straight lines on the T-s diagrams.
(a) Determine the COP of the plant
(b) Compare this value of COP with that of a reversed camot for the same
condenser and evaporator temperatures.
(c) Discuss, briefly, why the values differ.
Q4. The cycle of operations in a compression ignition engine may be represented
approximately as follows:-
(i) Compression according to py1.3 = constant, through a volume
compression ratio of 14:1 from an initial pressure of 1 bar,
(ii) Constant volume combustion to a maximum pressure of 50 bar
(iii) Constant pressure combustion during which the volume increase by 50%
(iv) Expansion, according to py1.3=constant, to the original volume,
(v) Reduction of pressure at constant volume to the original pressure of 1 bar.
(a) Sketch a P-Y diagram showing these operations [3 marks]
(b) Calculate the mean effective pressure [9 marks]
(d) The cylinder bore and stroke of such an engine operating on the four
stroke cycle for a brake power of 100kW at 3000rev/min ifthere are 4
cylinders and the piston is equal to 1.25 x cylinder bore diameter. Assume
that the mechanical efficiency is 80%. [8 marks]
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