JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III THERMAL ENGINEERING - II Previous Question Paper (September - 2021 - R18)
Answer any five questions
All questions carry equal marks
Main
Explain the Regenerative cycle in detail with a neat sketch.
Answer
The Regenerative cycle improves the thermal efficiency of a steam power plant by extracting a portion of steam from the turbine at intermediate stages to heat the feedwater before it enters the boiler. This process reduces the amount of external heat required to raise the feedwater temperature to the saturation temperature, thereby increasing the mean temperature of heat addition.
In a typical regenerative cycle, steam is bled from the turbine and mixed with the cold condensate in a feedwater heater (regenerator). This process minimizes the irreversibility associated with the large temperature difference between the combustion gases and the feedwater. The cycle is represented on a T-s diagram by a series of heat addition processes that follow the saturation curve more closely than the basic Rankine cycle, effectively raising the efficiency toward that of a Carnot cycle.
In a Rankine cycle, the steam at inlet to turbine is saturated at pressure of 30 bar and exhaust pressure is 0.25 bar. Determine (i) The pump work (ii) Turbine work (iii) Rankine efficiency (iv) Condenser heat flow (v) dryness at the end of expansion. Assume flow rate of 10 kg/s.
Answer
Given: P1 = 30 bar, P2 = 0.25 bar, m = 10 kg/s. From steam tables:
At 30 bar (saturated): h1 = hg = 2802.3 kJ/kg, s1 = sg = 6.1856 kJ/kgK, vf = 0.001216 m^3/kg.
At 0.25 bar: hf = 271.9 kJ/kg, hfg = 2346.3 kJ/kg, sf = 0.8932 kJ/kgK, sfg = 6.937 kJ/kgK.
1. Dryness fraction (x2): s1 = sf + x2(sfg) => 6.1856 = 0.8932 + x2(6.937) => x2 = 0.7629.
2. Enthalpy at turbine exit (h2): h2 = hf + x2(hfg) = 271.9 + 0.7629(2346.3) = 2062.2 kJ/kg.
3. Pump work (Wp): Wp = vf(P1 - P2) = 0.001216(3000 - 25) = 3.61 kJ/kg. Total Wp = 10 * 3.61 = 36.1 kW.
4. Turbine work (Wt): Wt = h1 - h2 = 2802.3 - 2062.2 = 740.1 kJ/kg. Total Wt = 10 * 740.1 = 7401 kW.
5. Condenser heat flow (Qc): Qc = m(h2 - hf) = 10(2062.2 - 271.9) = 17903 kW.
6. Rankine efficiency (η): Net work = Wt - Wp = 740.1 - 3.61 = 736.49 kJ/kg. Heat supplied (Qs) = h1 - (hf + Wp) = 2802.3 - (271.9 + 3.61) = 2526.79 kJ/kg. Efficiency = 736.49 / 2526.79 = 29.15%.
Sketch and describe the operation of Babcock and Wilcox boiler and explain its limitations.
Answer
Sign in to view the complete answer paper.
Derive an expression for maximum discharge rate of gases through the chimney for a given height of the chimney.
Answer
Sign in to view the complete answer paper.
During a test on steam nozzle steam impinges a stationary flat plate which is perpendicular to the direction of flow and the force on the plate is measured. The force is found to be 350 N when dry saturated steam at 8 bar is expanded to 1 bar. Throat cross-section area is 5 cm2 and exit area is such that the complete expansion is achieved under these conditions. Determine the discharge at throat.
Answer
Sign in to view the complete answer paper.
What do you understand by nozzle? Discuss different types of nozzles.
Answer
Sign in to view the complete answer paper.
A convergent-divergent nozzle is required to discharge 2 kg of steam per second. The nozzle is supplied with steam of 10 bar and 200°C and discharge takes place against a back pressure of 0.34 bar. Estimate the throat and exit areas. Assume isentropic flow and take the index n = 1.3. If the nozzle efficiency is assumed to be 85%, determine the exit area.
Answer
Sign in to view the complete answer paper.
Why compounding is necessary in the impulse turbines? What are the types and explain any one type of compounding with neat sketch.
Answer
Sign in to view the complete answer paper.
Sketch the velocity diagram of a single stage impulse turbine and determine the expression for the force, work done, diagram efficiency and axial thrust.
Answer
Sign in to view the complete answer paper.
A Parson’s reaction turbine has mean diameter of blades as 1.6 m and rotor moving at 1500 rpm. The inlet and outlet angles are 80° and 20° respectively. Turbine receives steam at 12 bars, 200°C and has isentropic heat drop of 26 kJ/kg. 5% of steam supplied is lost through leakage. Determine the following considering horse power developed in stage to be 600 hp.
The stage efficiency
Answer
Sign in to view the complete answer paper.
The blade height.
Answer
Sign in to view the complete answer paper.
Explain working principle of Surface Condenser with neat sketch.
Answer
Sign in to view the complete answer paper.
A surface condenser is designed to handle 10000 kg of steam per hour. The steam enters at 0.08 bar abs. and 0.9 dryness and the condensate leaves at the corresponding saturation temperature. The pressure is constant throughout the condenser. Estimate the cooling water flow per hour, if the cooling water temperature rise is limited to 10°C.
Answer
Sign in to view the complete answer paper.
Derive the expressions of thrust and thrust power for jet engine.
Answer
Sign in to view the complete answer paper.
A gas turbine unit receives air at 100kPa and 300K and compresses it adiabatically to 620kPa with efficiency of the compressor 88%. The fuel has a heating value of 44,180kJ/kg and the fuel/air ratio is 0.017kg fuel/kg air. The turbine internal efficiency is 90%. Calculate the compressor work, turbine work and thermal efficiency.
Answer
Sign in to view the complete answer paper.