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Mechanical Engineering Exam: Thermofluids - Bachelor of Engineering CIT, Exams of Mechanical Engineering

University of KeralaMechanical Engineering

A past exam from the mechanical technology - thermofluids module of the bachelor of engineering program at cork institute of technology. The exam covers various topics related to thermodynamics and fluid mechanics, including p-v and t-s diagrams, compressible air, rankine cycle, indicator diagrams, stochiometric air-fuel ratio, and energy forms in liquids. Students are required to answer questions related to these topics, including calculations and diagrams.

Typology: Exams

2012/2013

Uploaded on 03/28/2013

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Cork Institute of Technology
Bachelor of Engineering in Mechanical Engineering - Stage 2
(EMECH_7_Y2)
Summer 2008
Mechanical Technology - Thermofluids
(Time: 3 Hours)
INSTRUCTIONS
Answer 5 questions, at least two questions
from Section A and two from Section B plus
one other. Tick off which questions you
attempt on the front of the script.
Examiners: Ms. M. Kavanagh
Mr. A. Bateman
Dr. P. Delassus
SECTION A
Q1. (a) A cycle consists of the following processes in order:
(1) adiabatic expansion
(2) constant volume heating
(3) isothermal compression to its original condition.
Sketch the cycle on a P-V diagram (5 marks)
(b) 1m3 of air at a pressure and temperature of 110kN/m2 and 16oC,respectively, is
compressed according to the law PV1.32=C in a cylinder to a final volume of 0.175m3.
Determine:
(i) the pressure and temperature of the air at the end of the compression (5 marks)
(ii) the work done in compressing the air (5 marks)
(iii) the change of internal energy (5 marks)
For air, take R=287J/kgK, cv=717 J/kgK.
pf3
pf4

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Cork Institute of Technology

Bachelor of Engineering in Mechanical Engineering - Stage 2

( EMECH_7_Y2 )

Summer 2008

Mechanical Technology - Thermofluids

(Time: 3 Hours)

INSTRUCTIONS Answer 5 questions, at least two questions from Section A and two from Section B plus one other. Tick off which questions you attempt on the front of the script.

Examiners: Ms. M. Kavanagh Mr. A. Bateman Dr. P. Delassus

SECTION A

Q1. (a) A cycle consists of the following processes in order: (1) adiabatic expansion (2) constant volume heating (3) isothermal compression to its original condition. Sketch the cycle on a P-V diagram (5 marks) (b) 1m^3 of air at a pressure and temperature of 110kN/m^2 and 16 o^ C,respectively, is compressed according to the law PV1.32^ =C in a cylinder to a final volume of 0.175m^3. Determine: (i) the pressure and temperature of the air at the end of the compression (5 marks) (ii) the work done in compressing the air (5 marks) (iii) the change of internal energy (5 marks) For air, take R=287J/kgK, c (^) v =717 J/kgK.

Q2. Draw the Rankine cycle on the T-S diagram. Label each process and indicate the flows of heat to and from the substance and of work on and by the substance. (4 marks) Dry saturated steam at a pressure of 30 bar is fed to a steam turbine. Steam from the turbine exhausts into a condenser at a pressure of 1 bar. Determine; (i) the specific enthalpy of the steam entering the turbine (3 marks) (ii) the specific enthalpy of the condensate leaving the condenser (3 marks) (iii) the dryness fraction of the steam entering the condenser (4 marks) (iv) the specific enthalpy of steam entering the condenser (3 marks) (v) the Rankine efficiency of the plant (3 marks)

Q3. Sketch a typical indicator diagram for a four stroke cycle petrol engine and label each process. (4 marks) A four cylinder, four-stroke cycle engine has cylinders of diameter 75mm and a piston stroke 100mm. When the engine speed is 2000rpm it uses 0.24kg of fuel per minute. The indicated mean effective pressure is 2.5MN/m^2 and the mechanical efficiency is 85%. The calorific value of the fuel is 43MJ/kg. Determine: (a) The indicated power. (4 marks) (b) The brake power. (3 marks) (c)The indicated thermal efficiency. (5 marks) (d) If 30% of the total energy supplied in the fuel is accounted for by friction, exhaust gases and losses to the surroundings, estimate the heat given off to the cooling water. (4 marks)

Q4. Define stiochiometric air to fuel ratio and discuss briefly the need to supply excess air in combustion systems. (4 marks)

Propane (C 3 H 8 ) is burned with 10% excess air. For the combustion of 1kg of the gas; (a) Determine the stoichiometric mass of air. (8 marks) (b) Determine the actual mass of air. (3 marks) (c) Determine the products of combustion by mass and as a percentage. (5 marks) Composition of air by mass: 77% Nitrogen 23% Oxygen Atomic mass: Carbon(C) 12 Hydrogen(H) 1 Oxygen(O) 16