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Posted By: Jose Mathew Member Level: Platinum Posted Date: 15 Aug 2007
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2003 Anna University B.Tech Electrical and Electronics Engineering Thermodynamics Question paper
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B.E / B.Tech. DEGREE EXAMINATION, NOVEMEBER/DECEMBER 2003.
Third Semester
Electrical and Electronics Engineering
ME 251- THERMODYNAMICS
Time : Three hours Maximum : 100 marks
Answer ALL questions.
Use of Steam tables, Mollier chart and HMT data book permitted.
PART A- (10 X 2 = 20 marks)
1. Define first law of thermodynamics.
2. Write down the expression for air standard efficiency of Diesel cycle.
3. Explain why nozzles are made convergent and divergent.
4. What do you mean by “Calusius inequality”?
5. Draw the layout of vapour compression refrigeration cycle and explain its principles of operation.
6. How heat exchangers are classified?
7 Compare the parallel and counter flow heat exchangers and also state which one is having higher efficiencies
And why?
8 Write the theory and equation for convective heat transfer as per PRANDTL’S mixing length concept.
9 What is the principle of operation of simple jet propulsion system?.
10. Define overall heat transfer coefficient.
PART B- (5 X 16 = 80 MARKS)
11. Air undergoes a cyclic process in a cylinder and piston arrangement. First the atmosphere a air at 1 bar 27oC
Is compressed adiabatically to 10 bar, then expended isothermally up to initial pressure, then brought to initial conditions under constant pressure, find out.
a. Change in internal energy
b. Change in enthalpy
c. Heat transfer
d. Work transfer for each process and also for the cycle.
12 (a) The engines are to operate on Otto and diesel cycles with the following data. Maximum temperature =
1400 K. Exhaust temperature = 700 K. Air is taken in at 1 bar pressure and 300 K temperature. Find
Compression ratios, maximum pressures, air standard efficiencies and rates of work output of the respective cycles for 1 kg/min of air supply.
Or
(b) Describe with neat sketches the working of 2 stroke cycle petrol engine. Draw the indicator and valve ti-
ming diagrams for these engines.
13 (a) Describe a system sketches the working of 2 stroke cycle petrol engine Draw the indicator and valve
timing diagrams for these engines.
Or
(b) Steam at a pressure of 15 bar with 500 C of superheat is allowed to expend through a convergent-
Divergent nozzle. The exit pressure is 1 bar. If the nozzle is required to supply 2 kg/sec of steam to the
Turbine, then calculate
(i) the velocities at throat and exit.
(ii) Areas at throat and exit.
Assume 10% frictional loss in divergent part only and percentage taken as % of total heat drop.
14. (a) The free air delivery of a single cylinder single stage reciprocating air compressor is 2.5 m3/min. The
ambient air is at STP conditions and delivery pressure is 7 bars. The clearance volume is 5% of the stroke volume and law of compression and expansion is pV1.25= C. If L= 1.2 D and the compressor runs at 150 rpm, determine the size of the cylinders.
Or
(b) A refrigeration machine using F 12 as works between the temperatures 18oCand 37oC. The enthalpy of liquid at 37oC is 455 kJ/kg. the enthalpies of F12 entering and leaving the compressor are 563.15 kJ/kg and 595.4 kJ/kg respectively. The rate of circulation of refrigerant is 2 kg/min and efficiency of compressor is 0.85. Determine
(i) Capacity of the plant is tons of refrigeration
(ii) Power required to run the plant
(iii) COP of the plant.
15. (a) A brickwork of a furnace is built-up of layers laid of fire clay (K1= 0.93 W/m-oC). And red brick(K3 = 0.7
W/m-oC) and the space between the two is filled with crushed diatomite brick (K2= 0.13 W/m-oC).
The thickness of fireclay, diatomite and red brick are 12 cm, 5 cm and 25 cm respectively. What should
Be thickness of the red brick layer if the brickwork is to be laid without diatomite filling between the two
Layers, so that the heat flow through the brick work reminds constant?
Or
(b) Water at the rate of 70 kg/min is heated from 35oC. To 75oC by oil having a specific heat of 2 kJ/Kg-oC.
The fluids are used in a counter flow double pipe heat exchanger and oil enters the heat exchanger at 110oC. and leaves at 75oC. the overall heat transfer coefficient is 320 W/m2-oC. Calculate the heat exchanger area.
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