Thermodynamics - Dec 2012

Mechanical Engineering (Semester 3)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks.

Answer any five of the following -

1 (a) Differentiate between point function and path function.(4 marks) 1 (b) Show that entropy is property of system.(4 marks) 1 (c) Define thermodynamic cycle, process, intensive properties and extensive properties.(4 marks) 1 (d) What are the assumptions of air standard cycle?(4 marks) 1 (e) State the zeroth law of thermodynamics. What is it's significance?(4 marks) 1 (f) What do you mean by Available and unavailable energy ?(4 marks) 1 (g) Define heat engine refrigerator and heat pump.(4 marks) 2 (a) Derive an expression for heat absorbed or rejected during polytropic process for ideal gas.(6 marks) 2 (b) What is Joule-Thomson coefficient? What conclusion can be drawn from a given value of this coefficient ? Explain in brief.(6 marks) 2 (c) 0.18 m³ of air at a pressure of 1000 kPa and 300°C is expanded polytropically following the law PV^1.5=C and finally compressed back to initial state isothermally calculate (i) Heat received (ii) Heat rejected (iii) efficiency of the cycle.(8 marks) 3 (a) Write the statement of second law of thermodynamics.(4 marks) 3 (b) State and prove clausius in equalily for an irreversible cycle.(6 marks) 3 (c) A reversible heat engine operated between two reservoirs at temperature of 600°C and 60°C the engine drives the refrigerator which operates between the reservoirs at temperature of 60°C and -30°C. The heat transfer to the engine is 3 MJ and the net work output of the combined engine and refrigerator plant is 380 kJ. Find heat transfer to the refrigerant and the ner heat transfer to the reservoir at 60°C.(10 marks) 4 (a) Explain steady flow energy equation. Apply to nozzle, turbine.(8 marks) 4 (b) In a steady flow system fluid flow at the rate of 5 kg/s. it enters at a pressure of 620 kPa a velocity of 300 m/s internal energy 2100 kJ/kg and specific volⁿ 0.37 m³/kg it leaves the system at a pressure of 130 kPa a velocity of 150 m/s internal energy 1500 kJ/kg and specific volⁿ 1.2 m³/kg. During it's flow through system there is a heat loss of 30 kJ/kg. determine the power capacity of the system in kW. state wheather it is from or to the system. Neglect change in P.E.(12 marks) 5 (a) Define -
(i) wet steam
(ii) Superheated steam
(iii) Dryness fraction
(iv) Saturation temperature.(6 marks) 5 (b) Steam turbine working on Rankine cycle is supplied with dry saturated steam at 20 bar and the exhaust take place at 0.3 bar. For a steam flow rate of 10 kg/s determine (i) quality of steam at end of expansion (ii) turbine shaft work
(iii) power required to drive the pump (iv) work ratio (v) Rankine efficiency (iv) heat flow in the condensor.(14 marks) 6 (a) Prove the thermal efficiency of dual cycle.(8 marks) 6 (b) In an air standard diesel cycle the stroke is 30 cm and dia is 25 cms. Pressure and temperature at the start of compression is 100 kPa and 27°C. The cut off takes place at 6% of the stroke and the compression ratio is 14. find pressure and temperature at all points - (i) heat added, heat rejected and net work done (ii) mean effective pressure.(12 marks) 7 (a) Define -
(i) Mach no
(ii) Stagnation temp
(iii) Stagnation pressure
(iv) Sonic velocity (4 marks) 7 (b) Explain the effect of variation in back pressure on C-D nozzel performance.(6 marks) 7 (c) Derive with usual notations the relations for one dimensional isentropic flow of gas
$$ \dfrac {dA}{A} =\dfrac {dV}{V} (1-M^2)$$
Explain the significance of the above relationship.(8 marks)