Applied Thermodynamics - Dec 2013
Mechanical Engg (Semester 4)
TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.
Answer any one question from Q1 and Q2
1 (a) State and prove the equivalency of Kelvin Planck and Clausius statement.(6 marks)
1 (b) Prove: S2-S1=Cvlm(T2/T1)+R ln(V2/V1).(6 marks)
1 (c) State the limitations of First law of thermodynamics. How does the second law of thermodynamic overcome these limitations.(4 marks)
10 (a) Discuss the factors those influence the volumetric efficiency of a reciprocating air compressor.(6 marks)
10 (b) A two stage single acting reciprocating compressor takes in air at the rate of 0.2 m3/s. The intake pressure and temperature of air are at 0.1 Mpa and 16°C. The air compressed to a final pressure of 0.7 Mpa. The intermediate pressure is ideal and inter-cooling is perfect. The compression index in both the stages is 1.25 and the compressor runs at 600 RPM. Neglecting clearance, determine:
i) The intermediate pressure
ii) The total volume of each cylinder
iii) The power required to drive the compressor
iv) The rate of heat rejection in the intercooler.
Cp=1.005 kJ/kgK and R=0.287 kJ/kgK.(10 marks)
Answer any one question from Q11 and Q12
11 (a) Differentiate between mountings and accessories of the boiler. Give at least two examples of each.(8 marks)
11 (b) In a boiler test 1250 kg of coal are consumed in 24 hours. The mass of water evaporated is 13000 kg and mean effective pressure is 7 bar. The feed water temperature was 40°C, heating value of coal is 30000 kJ/kg. The enthalpy of 1 kg of steam at 7 bar is 2570 kJ. Determine:
i) Equivalent evaporation per kg of coal
ii) Efficiency of the boiler.(10 marks) 12 (a) Explain the following terms:
i) Boiler efficiency
ii) Equivalent evaporation.(8 marks) 12 (b) A boiler produces 200 kg of dry saturated steam per hour at 10 bar and feed water is heated by an economizer to a temperature of 100°C. 225 kg of coal of a calorific value 30100 kJ/kg are fired per hour. If 10% of coal remains unburnt, find the thermal efficiency of the boiler and the boiler grate combined.(10 marks) 2 (a) State and prove the Clausius Inequality.(8 marks) 2 (b) 5 kg of air is expanded at a constant pressure to four times its initial volume. The initial temperature of air is 400°C. It is then brought to its original temp, by a constant volume change. Calculate the entropy change.(8 marks)
Answer any one question from Q3 and Q4
3 (a) Explain the following:
i) Available and unavailable energy
ii) Principal reasons for irreversibility
iii) Helmholtz and Gibbs function.(9 marks) 3 (b) Calculate the decrease in available energy when 20kg of water at 90°C mixes with 30 kg of water at 30°C, the pressure being taken as constant and the temperature of surrounding is 10°C (Cp for water 4.18 kJ/kgK).(7 marks) 4 (a) Derive an expression for work transfer in reversible adiabatic process.(7 marks) 4 (b) 1 kg of air at pressure of 8 bars and temp. of 100°C undergoes a reversible polytropic process following the law pv1.2=C. If the final pressure is 1.8 bars, determine:
i) Final specific volume, temperature and increase of entropy.
ii) The work done and heat transfer.
Assume R=0.287 kJ/kgK.(9 marks)
Answer any one question from Q5 and Q6
5 (a) With the help of T-S diagram, explain the effect of the following parameters on the performance of Rankine cycle:
i) Effect of superheat
ii) Condenser pressure.(8 marks) 5 (b) A steam turbine receives superheated steam at a pressure of 17 bar and having degree of superheat of 110°C. The exhaust pressure is 0.07 bar and expansion of steam takes place isentropically.
i) The heat supplied and heat rejected
ii) Network output
iii) Thermal efficiency
iv) Specific steam consumption.
Neglect pump work.(10 marks) 6 (a) Explain the following terms:
i) Critical point
ii) Dryness fraction.(4 marks) 6 (b) With the help of a neat sketch explain the working of separating and throttling calorimeter.(6 marks) 6 (c) Steam at 7 bar and 250°C has a volume of 0.5046 m3. In a frictionless constant volume process the pressure changes to 3.5 bars. Find the final temperature and heat transfer. Also determine the change in entropy.(8 marks)
Answer any one question from Q7 and Q8
7 (a) Write a short note on calorific value of a fuel.(5 marks) 7 (b) A coal sample gave the following analysis by weight, Carbon 85%, Hydrogen 6%, Oxygen 6%, the remainder being incombustible. Determine minimum weight of air required per kg of coal for chemically correct composition.(6 marks) 7 (c) Explain NDIR method of gas analysis in brief.(5 marks) 8 (a) Write a note on theoretical and excess air.(5 marks) 8 (b) The following particulars refer to an experimental determination of the calorific value of a sample of coal containing 88% C and 4.2% H2. Weight of coal =0.848 gm, weight of fuse wire 0.027 gm, of calorific value 6700 J/gm, weight of water in the calorimeter=1950 gm, water equivalent of calorimeter=380 gm, observed temperature rise=3.06°C, cooling correction = +0.017°C. Find the higher and lower calorific values of the coal.(6 marks) 8 (c) With the help of neat sketch discuss the method of determining calorific value of gaseous fuel.(5 marks)
Answer any one question from Q9 and Q10
9 (a) What are the advantages and disadvantages of multistage reciprocating air compressor?(6 marks) 9 (b) A single stage reciprocating compressor takes 1 m3 of air per minute at 1.013 bar and 157deg;C and delivers it at 7 bar. Assuming that the law of compression is pV1.35=constant, and the clearance is negligible, calculate the indicate power.(10 marks)