# Tech by CQkc23E

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B.E./B.Tech. DEGREE EXAMINATION, APRIL/MAY 2003.

Third Semester

Aeronautical Engineering

AT 231 — ENGINEERING THERMODYNAMICS

(Common to Automobile and Production Engineering)

Time : Three hours                                              Maximum : 100 marks

Use of Thermodynamics Data Books and Table permitted.

PART A — (10  2 = 20 marks)

1.    What is the difference between work transfer and heat–transfer?

2.    Give the Clausius statement of the Second Law.

3.    State the four processes of the Diesel Cycle.

4.    Define volumetric efficiency and free air delivery of a compressor.

5.    Define pure substance.

6.    Differentiate between jet propulsion and rocket propulsion.

7.    Show the single vapour compression cycle on a p–h chart.

8.    What are the properties of an ideal refrigerant?

9.    What is the overall heat transfer coefficient?

10.   Classify the heat exchangers according to the flow directions of fluid and give
few examples of each in actual field of application.
PART B — (5  16 = 80 marks)

11.   Calculate the power required to compress air in a steady state, steady flow
process at a rate of 2.0 kg/s from 0.101 MPa, 40C, 10 m/s to 0.3 MPa, 50C,
125 m/s. During this process, the enthalpy of air increases by 40.15 kJ/kg while
7.0 kJ/s of heat is lost to the environment. Neglect the changes in potential
energy.                                                                       (16)

12.   (a)   An engine working on the Otto cycle is supplied with air at 0.1 MPa,
35C. The compression ratio is 8. Heat supplied is 2100 kJ/kg. Calculate
the maximum pressure and temperature of the cycle, the cycle efficiency,
and the mean effective pressure. (For air, cp = 1.005 kJ/kg K,
cv = 0.718 kJ/kg K and R = 0.287 kJ/kg K).                              (16)

Or

(16)

13.   (a)   A steam power plant operates between a boiler pressure of 4 MPa and
300C and a condenser pressure of 50 kPa. Determine the thermal
efficiency of a simple ideal Rankine cycle and the specific steam flow rate.
(16)

Or

(b)   Air is discharged from a reservoir at P0 = 6.91 bar and T0 = 325C
through a nozzle to an exit pressure of 0.98 bar. If the flow rate is
3600 kg/hr, determine for isentropic flow

(i)    throat area, pressure and velocity                               (12)

(ii)   exit area, Mach number.                                           (4)

14.   (a)   Discuss the merits and demerits of a vapour compression system.         (16)

Or

(b)   Explain with neat sketches the principle of operation of a simple vapour
absorption system.                                                      (16)

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15.   (a)   A cold storage room has walls made of 0.23 m of brick on the outside,
0.08 m of plastic foam, and finally 1.5 cm of wood on the inside. The
outside and inside air temperatures are 22C and –2C respectively. If
the inside and outside heat transfer coefficients are respectively 29 and
12 W/m2 K, and the thermal conductivities of brick, foam and wood are
0.98, 0.02 and 0.17 W/mK respectively, determine (i) the rate of heat
transfer if the total wall area is 90 m2 and (ii) the temperature of the
inside surface of the brick.                                      (8 + 8 = 16)

Or

(b)   A tubular heat exchanger cools 25 kg/min of exhaust gas passing through
it from 400C to 130C by water initially at 10C.

The specific heat of gases may be taken as 1.13 kJ/kg K and overall heat
transfer coefficient as 140 W/m2K. Find the surface area required if the
water flows at the rate of 30 kg/min. for (i) parallel and (ii) counter flow.
(8 + 8 = 16)

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