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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2011/
Module Title: Thermofluids 3
Module Code: INTR
School: Mechanical & Process Engineering
Programme Title: Bachelor of Engineering (Honours) in Sustainable Energy
Programme Code: ESENT_8_Y
External Examiner(s): Mr. Paul Kenny, Mr. Conor Buckley Internal Examiner(s): Michael P O’Mahony
Instructions: Answer Question ONE and THREE other Questions
Duration: 2 hours
Sitting: Winter 2011/
Requirements for this examination: Steam tables Log book
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Q1.
(a) In the context of a refrigerant, explain the meaning of ODP and GWP (4 Marks)
(b) It is proposed to use a heat pump working on the ideal vapour-compression cycle for the purpose of heating the air supply to a building. The supply of heat is taken from a river at 7oC. Air is required to be delivered into the building at 1.013 bar and 32oC at a rate of 0.5 m^3 /s. The air is heated at constant pressure from 10oC as it passes over the condenser coils of the heat pump. The refrigerant is R 134a which is dry saturated leaving the evaporator; there is no undercooling in the condenser. A temperature difference of 17 K is necessary for the transfer of heat from the river to the refrigerant in the evaporator. The delivery pressure of the compressor is 11. bar. (i) Draw the P-h and T-s diagrams for this process (6 Marks) Calculate: (ii) the COPhp (18 Marks) (iii) The mass flow of Refrigerant (8 Marks) (iv) The motor power required to drive the compressor if the mechanical efficiency is 87% (4 Marks) Take Specific heat capacity of air(constant pressure) 1.01kJ/kgK, density of air 1.2kg/m^3
Q
(a) When selecting a pump for a given application, it is important to know the “Pump curve” and “system Curve”. Explain these terms and why it is important to know. (10 Marks)
(b) Determine the head loss due to friction when water flows through 300m of 150mm diameter galvanised steel pipe at 50 litres/s.
For water take = 1.14 x 10-3^ Pa.s =1000kg/m^3 (10 Marks)
Q
(a) In Heat Exchanger analysis when is LMTD method suitable and when is the Effectiveness/NTU method suitable (8 marks)
(b) After a long time in service, a counterflow oil cooler is checked to ascertain if its performance has deteriorated due to fouling. In a test, SAE50 oil flowing at 2.0kg/s is cooled from 420K to 380K by a water supply of 1.0kg/s at 300K. If the heat transfer surface is 3.33m^2 and the system design value of the overall heat transfer coefficient is 930W/m^2 K, how much has it been reduced by fouling? (12 Marks) Specific Heat capacity of oil 2.33kJ/kgK, water 4.18kJ/kgK
103 2 4 104 2 4 105 2 4 106 2 4 107 2 4 108
Reynolds Number
ud
Re (logarithmic scale)
Friction Factor
(^) f (logarithmic scale)
Relative roughness
(^) k / d
Fully developed turbulence - rough pipes
Smooth pipes
critical region
Material k Glass, Brass, Copper, Lead smooth Steel, wrought iron 46 m Ashphalted cast iron 120 m Galvanized iron (^150) m Cast iron (^260) m Concrete 3 mm Riveted steel 9 mm
f (^) Re ^16
Laminar flow
unstable transition
region
