Important Questions in **Engineering Thermodynamics ****113301 **

subject for NOV/DEC 2011 AUT ANNA UNIVERSITY OF TECHNOLOGY EXAMINATIONS FOR SECOND YEAR 3RD semester MECH Students

**113301 - Engineering Thermodynamics**

**UNIT I**

1. A reciprocating air compressor takes in 2 m3/min air at 0.11 MPa, 293 K which it delivers at 1.5 MPa, 384 K to an after cooler where the air is cooled at constant pressure to 298 K. The power absorbed by the compressor is 4.15 kW. Determine the heat transfer in (i) the compressor (ii) the cooler. State your assumptions.

2. A certain quantity of gas is head at constant pressure from 35 °0 to 185°c. Estimate the amount of hem transferred, ideal work done, change in internal energy, when the initial volume of the gas is 0.6 m3.

3. 2kg of gas at a pressure of 1.5 bar. Occupies a volume of 2.5 m3. If this gas compresses isothermally to 1/3 times the initial volume. Find initial. Final temperature, work done, heat transfer.

4. Explain and derive Isobaric process.

5. The velocity and enthalpy of fluid at the inlet of a certain nozzle ate 50 m/sec and 2800 kJ/kg respectively. The enthalpy at the exit of nozzle is 2600 kJ/kg. The nozzle is horizontal and insulated so that no heat transfer takes place from it' Find

(1) Velocity of the fluid at exit of the nozzle

2) Mass flow rate, if the area at inlet of nozzle is 0.09 m2

(3) Exit area of the nozzle, if the specific volume at the exit of the nozzle is 0.495 m3/hg.

UNIT II

1. The interior lighting of refrigerators is provided by incandescent lamps whose switches are actuated by the opening of the refrigerator door. Consider a refrigerator whose 40W light bulb remains on continuously as a result of a malfunction of the switch. If the refrigerator has a coefficient of performance of 1.3 and the cost of electricity is Rs. 8 per kWh, determine the increase in the energy consumption of the refrigerator and its cost per year if the switch is not fixed.

2. One kg of air is contained in a piston cylinder assembly at 10 bar pressure and 500 K temperature. The piston moves outwards and the air expands to 2 bar pressure and 350 K temperature. Determine the maximum work obtainable. Assume the environmental conditions to be 1 bar and 290 K.Also make calculations for the availability in the initial and final states.

3. Establish the inequality of Clausius

4. Explain Carnot engine cycle and its efficiency.

UNIT III

1. Explain P-V diagram and P-V-T surface.

2. explain the regenerative Rankine cycle with an open feedwater heater

3. Consider a steam power plant operating on the ideal reheat Rankine cycle. Steam enters the high-pressure turbine at 15 MPa and 873 K and is condensed in the condenser at a pressure of 10 kPa. If the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 10.4 percent, determine (i) the pressure at which the steam should be reheated and (ii) the thermal efficiency of the cycle. Assume the steam is reheated to the inlet temperature of the high-pressure turbine.

4. Determine the change of internal energy, enthalpy and entropy when the gas obeys van der Waal’s equation.

5. In an ideai reheat cycle, the steam enters the turbine at 30 bar and 500.c. After expansion to 5 bar, the steam is reheated to 500'c and then expanded to the condenser plessure of 0.1 bar. Determine the cycle thermal efficiency, mass flow rate of steam. Take power output as 100 MW

UNIT IV

1. Derive the Clapeyron equation.

2. A certain quantity of air initially at a pressure of 8 bar and 280°C has a volume of 0.035 m3. It undergoes a cycle consisting of the following processes:

(1) Expands at constant pressure to 0.1 m3.

(2) Follows polytropic process with *n *= 1.4 and

(3) A constant temperature process which completes the cycle.

Evaluate the heat received and rejected in the cycle and cycle efficiency.

3. Using the cyclic relation and the first Maxwell relation, derive the other three Maxwell relations

4. Consider a room that contains air at 1 atm, 308 K. and 40 percent relative humidity. Using the psychrometric chart, determine: the specific humidity, the enthalpy, the wet-bulb temperature, the dew-point temperature and the specific volume of the air.

5. Derive vandar Waals equation.

UNIT V

1. Explain sensible heating process, sensible cooling, and humidification process.

2. Dry bulb and wet temperatures of 1 atmospheric air stream are 40°0 and 30°c

respectively. Determine

(a)Humidity (b) Relative humidity (c) Specific humidity

3. Explain with an example evaporative cooling.

4. Explain the process of cooling and dehumidification.

not even one 16 mark came.

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