Anna University Chennai 2003 B.Tech Electrical and Electronics Engineering Thermodynamics - Question Paper

B.E / B.Tech. DEGREE EXAMINATION, NOVEMEBER/DECEMBER 2003.

Third Semester

Electrical and Electronics Engineering

ME 251- THERMODYNAMICS
Time : 3 hours Maximum : 100 marks

ans ALL ques..

Use of Steam tables, Mollier chart and HMT data book permitted.

PART A- (10 X two = 20 marks)

1. Define 1st legal regulations 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 discuss its principles of operation.
6. How heat exchangers are classified?
7 Compare the parallel and counter flow heat exchangers and also state which 1 is having higher efficiencies
And why?
8 Write the theory and formula for convective heat transfer as per PRANDTL’S mixing length concept.
9 What is the principle of operation of simple jet propulsion system?.
10. describe overall heat transfer coefficient.

PART B- (5 X 16 = 80 MARKS)

11. Air undergoes a cyclic process in a cylinder and piston arrangement. 1st the atmosphere a air at one bar 27oC
Is compressed adiabatically to 10 bar, then expended isothermally up to initial pressure, then brought to initial conditions under constant pressure, obtain out.

a. Change in internal energy
b. Change in enthalpy
c. Heat transfer
d. Work transfer for every process and also for the cycle.

12 (a) The engines are to operate on Otto and diesel cycles with the subsequent data. Maximum temperature =
1400 K. Exhaust temperature = 700 K. Air is taken in at one bar pressure and 300 K temperature. obtain
Compression ratios, maximum pressures, air standard efficiencies and rates of work output of the respective cycles for one kg/min of air supply.

Or

(b) Describe with neat sketches the working of two stroke cycle petrol engine. Draw the indicator and valve ti-
ming diagrams for these engines.

13 (a) define a system sketches the working of two 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 one bar. If the nozzle is needed to supply two kg/sec of steam to the
Turbine, then compute
(i) the velocities at throat and exit.
(ii) Areas at throat and exit.
presume 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 seven bars. The clearance quantity is 5% of the stroke quantity and legal regulations 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 ranging from 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 two kg/min and efficiency of compressor is 0.85. Determine
(i) Capacity of the plant is tons of refrigeration
(ii) Power needed 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 ranging from the 2 is filled with crushed diatomite brick (K2= 0.13 W/m-oC).
The thickness of fireclay, diatomite and red brick are 12 cm, five cm and 25 cm respectively. What should
Be thickness of the red brick layer if the brickwork is to be laid without diatomite filling ranging from the 2
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 two 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. compute the heat exchanger area.

Earning:   Approval pending.