JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year THERMAL ENGINEERING - II Previous Question Paper (January/February - 2023 - R18)

B. Tech | III Year | I Semester | R18 | January/February - 2023

Answer PaperPaper Code: 155DGMaximum Marks: 75Time: 3 Hours

Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.

Part A

125 marks

Explain different methods to improve the efficiency of Rankine cycle.

2 marks

Answer

Increasing boiler pressure: Raises the mean temperature of heat addition, thereby increasing thermal efficiency.
Superheating steam: Increases the average temperature at which heat is added and reduces moisture content at the turbine exhaust.
Reducing condenser pressure: Lowers the temperature of heat rejection, increasing the cycle work output.
Reheating steam: Allows for higher expansion without excessive moisture at the turbine exit.
Regenerative feed heating: Preheats the feedwater using steam extracted from the turbine, reducing the heat required from the boiler.

Explain significance of boiler mountings and accessories.

3 marks

Answer

Boiler Mountings: These are essential safety devices required for the safe operation of the boiler (e.g., safety valves, water level indicators, pressure gauges). Without these, the boiler cannot operate safely.
Boiler Accessories: These are auxiliary components used to improve the overall efficiency and performance of the boiler plant (e.g., economizers, air preheaters, superheaters, feed pumps). They are not mandatory for operation but are critical for economic output.

Draw different nozzle cross sections and explain them.

2 marks

Answer

What is the condition for maximum discharge through nozzle?

3 marks

Answer

Draw velocity triangle at exit for impulse turbine.

2 marks

Answer

Explain the effect of friction on the blade diagram efficiency in steam turbines.

3 marks

Answer

What is the purpose of regeneration in the gas turbine?

2 marks

Answer

Draw line diagram and explain the working of Evaporative Condenser.

3 marks

Answer

List out the factors which are to be considered for the comparison of different types of rockets.

2 marks

Answer

Explain thrust power and propulsion efficiency of jet propulsion.

3 marks

Answer

Part B

210 marks

Explain the effect of operating variables on Rankine cycle performance.

5 marks

Answer

A steam power plant operates on ideal Rankine cycle. The steam enters the turbine at 3 MPa, 350C and is condensed in the condenser at 75 kPa, calculate thermal efficiency, back work ratio and work ratio of this cycle.

5 marks

Answer

310 marks

What is meant by super critical boiler and explain one such boiler?

5 marks

Answer

Draw the line diagram and explain the working principle of economizer and discuss the precautions to be made in usage.

5 marks

Answer

410 marks

Explain the effects of irreversibilities on the performance of nozzle.

5 marks

Answer

Calculate the throat and exit diameters of a convergent- divergent nozzle, which will discharge 820 kg of steam per hour at a pressure of 8 bar superheated to 220C into a chamber having a pressure of 1.5 bar. The friction loss in the divergent portion of the nozzle may be taken as 0.15 of the isentropic enthalpy drop.

5 marks

Answer

510 marks

Derive the equation for critical pressure ratio of nozzle for different conditions.

5 marks

Answer

In a convergent-divergent nozzle, the steam enters at 15 bar and 300C and leaves at 2 bar. The inlet velocity to the nozzle is 150 m/s. Find the required throat and exit areas for a mass flow rate of 1 kg/s. Assume nozzle efficiency to be 90% and Cps = 2.4 kJ/kg K.

5 marks

Answer

610 marks

Derive the equation optimum work out put in impulse turbine.

5 marks

Answer

The reaction turbine runs at 300 rpm and the steam consumption is 20000 kg/h. The pressure of steam at a certain pair is 2 bar, its dryness fraction is 0.93 and the power developed by the pair is 50 kW. The discharge blade angle is 20 for both the fixed and moving blades and the axial velocity of flow is 0.72 times the blade velocity. Find the drum diameter and the blade height. Take the tip leakage steam as 8%. Neglect the blade thickness.

5 marks

Answer

710 marks

Derive the condition for maximum efficiency and blade height of reaction turbine.

5 marks

Answer

In a Parson reaction turbine, the angles of receiving tips are 35 and of discharging tips, 20. The blade speed is 100 m/s. Calculate the tangential force, power developed, diagram efficiency and axial thrust of the turbine, if its steam consumption is 1 kg/min.

5 marks

Answer

810 marks

Explain with neat line diagram the working of evaporative steam condenser.

5 marks

Answer

The following data refers to a test of the surface condenser of a steam turbine. Absolute pressure of the steam entering the condenser = 5.628 kPa, Temperature of condensate leaving the condenser = 32C, Inlet temperature of cooling water = 15C, Outlet temperature of cooling water = 30C, Mass of cooling water per kg of steam = 32 kg. Assuming that all the heat lost by the exhaust steam is taken up by the circulating water; determine the dryness fraction of the steam as it enters the condenser.

5 marks

Answer

910 marks

Explain the deviation of actual gas turbine cycle from ideal Brayton cycle.

5 marks

Answer

A gas turbine takes in air at 27C and 1 bar. The pressure ratio is 4. The maximum temperature of the cycle is 560C. The efficiency of the compressor and turbine is 0.83 and 0.85 respectively. Find the overall efficiency, if the regenerator effectiveness is 0.75.

5 marks

Answer

1010 marks

Explain the working of turboprop engine and its advantages.

5 marks

Answer

A jet propelled engine having two jets and working on turbojet has a velocity of 210 m/s, when flying at an altitude of 12000 m. The density of air at this altitude is 0.172 kg/m3. The resistance or drag of the plane is 6670.8 N and propulsive efficiency of the jet is 50%. The overall efficiency of the unit is 18%. Calorific value of the fuel is 4.895 × 10^4 kJ/kg. Calculate i) Absolute velocity of jet, ii) Quantity of air compressed per minute, iii) Diameter of jet, iv) Net power output of the plant v) Thrust specific fuel consumption, vi) Air-fuel ratio.

5 marks

Answer

1110 marks

What are the desirable properties of a liquid propellant for a rocket engine?

5 marks

Answer

For a rocket engine, jet velocity is 1600 m/s, flight to jet speed ratio is 0.7. Oxidizer flow rate is 4 kg/s. Fuel flow rate is 1 kg/s. Heat of reaction per kg of exhaust gas is 2500 kJ/kg. Calculate the Thrust, specific impulse, propulsive efficiency, thermal and overall efficiency of rocket engine.

5 marks

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year THERMAL ENGINEERING - II Previous Question Paper (January/February - 2023 - R18)

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Part B

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