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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2010/
Module Title: Introductory Thermofluids
Module Code: MECH
School: School of Mechanical & Process Engineering
Programme Title: Bachelor of Engineering (Honours) in Mechanical Engineering Bachelor of Engineering (Honours) in Biomedical Engineering
Programme Code: EMECH_8_Y EBIOM_8_Y EOMNI_8_Y
External Examiner(s): Mr. John J. Hayes, Prof. R. Clarke Internal Examiner(s): Mr. W.M. Corr
Instructions: Answer any THREE questions. All Questions carry equal marks.
Duration: 2 Hours Sitting: Autumn 2011
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination. If in doubt please contact an Invigilator.
Q1. (a) Starting from the steady flow energy equation, show that the exit velocity from a nozzle can be approximated by cex it 2 h where h is the change in specific enthalpy across the nozzle. (5 marks) List and justify all assumptions. (5 marks) (b) Steam at 50 bars, 350C, 12.5 kg/s enters a horizontal nozzle with negligible velocity; and leaves at 2 bars, 150C. Calculate: (i) The exit velocity. (5 marks) (ii) The exit cross-sectional area. (5 marks)
Q2. (a) Define the terms: polytropic adiabatic isothermal when applied to an ideal gas process. (6 marks)
(b) A quantity of gas occupies a volume of 0.4m^3 at a pressure of 100 kN/m^2 and a temperature of 20C. The gas is compressed isothermally to a pressure of 450 kN/m^2 and then expanded adiabatically to its initial volume. Sketch the processes on a p-v diagram and determine, for this quantity of gas: (4 marks) (i) The heat transferred during the compression. (6 marks) (ii) The change of internal energy during the expansion (4 marks) Assume for this gas that = 1.4 and cp = 1.0 kJ/kg K.
Q5. (a) Explain the term Centre of Pressure of a submerged surface. (5 marks)
(b) Oil, of relative density 0.820 is held in a tank with an overflow safety mechanism consisting of a rectangular door 2 m high x 1.8m wide, hinged at its base and held in place at the top by a spring force of 180 kN, acting horizontally. At what level of oil, above the top of the door, will the door open? (15 marks)
