Download Flow Rate - Thermofluids - Exam and more Exams Physics Fundamentals in PDF only on Docsity!
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2009/
Module Title: Thermofluids 3
Module Code: INTR 7009
School: Mechanical and Process Engineering
Programme Title: Bachelor of Engineering in Mechanical Engineering
Programme Code: EMECH_7_Y
External Examiner(s): Mr. Alan Bateman, Dr Eamonn Ahearne Internal Examiner(s): Dr Keith McMullan, Mr. Michael P. O’Mahony
Instructions: Answer question 1 and three other questions
Duration: 2 Hours
Sitting: Autumn 2010
Requirements for this examination: Steam tables Log book
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you are attempting the correct examination. If in doubt please contact an Invigilator.
(1) Sketch an ideal vapour compression refrigeration cycle on Pv, Ts and Ph diagrams. Indicate how a real cycle would differ from the ideal. (8 marks)
Why is the compressor/motor assembly usually housed in a hermetically sealed housing? (2 marks)
Discuss how a refrigerant is selected and the importance of a low ODP. (8 marks)
An ideal vapour compression freezing plant has an evaporating temperature of -40degC and a condensing temperature of 30degC. The plant uses R12 and freezes 1.6 tonnes of fish per hour. The reduction in specific enthalpy of the fish is 420 kJ/kg
Determine (a) the COPref of the cycle (b) the power input to the plant (c) the mass flow rate of the refrigerant (22 marks)
(2) Discuss the significance of the emissivity of a material, and how this might impact on equipment design. (4 marks)
A furnace wall consists of 250 mm firebrick, 125 mm insulating brick and 250 mm building brick. The inside wall is at 600°C and atmospheric temperature is 20°C. Calculate the heat transfer rate per unit area and the outside wall surface temperature. For the outside surface of the wall, h = 10 W/m²K and for the firebrick, insulating brick and building brick k = 1.4, 0. and 0.7 W/mK respectively. (16 marks)
(3) Exhaust gases flowing through a tubular heat exchanger at 0.3 kg/s are cooled from 400degC to 120degC by water (Cp = 4.186 kJ/kgK) entering at 10°C. The specific heat capacity of the gases is 1.13 kJ/kgK. The overall heat transfer coefficient is 140 W/m²K. Calculate the surface area required for a water flow rate of 0.4 kg/s under conditions of:-
(a) parallel flow (b) counter flow (20 marks)
(4) Briefly explain how the operation of the boiler in a power station can be monitored by examining the composition of the flue gas. (4 marks)
A fuel for a petrol engine consists of 86% carbon (C) and 14% hydrogen (H 2 ) by mass. Calculate the stoichiometric air-fuel ratio by mass. (16 marks)
(5) Describe three different methods of measuring the flow of liquid in a pipe; highlight the advantages and disadvantages of each method (8 marks)
In an engine test, 0.04kg/s of air flows through a 50mm diameter pipe, into which is fitted a 40mm diameter orifice plate. The density of the air is 1.2kg/m^3 and the coefficient of discharge of the orifice is 0.63. The pressure-drop across the orifice is measured by a U-tube manometer filled with water.
Calculate the manometer reading. (12 marks)
