RGPV Mechanical Engineering (Semester 4)
Thermal Engg and gas dynamics
December 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary


1(a) Define super critical boiler.
2 M
1(b) What are different between forces circulation and natural circulation?
2 M
1(c) What are the advantages of High pressure Boiler?
3 M
Solve any one question from Q.1(d) & Q.1(e)
1(d) The following reading were obtained during a boiler trail of 5 hours duration.
Mean steam pressure =15 bar
Mean of steam generated =50,000kg
Mean dryness traction =0.85
Mean water temperature=30°C
Coal used=4000kg, Calorific value of coal=33400kJ/kg
Calculate:
i) Factor of equivalent evaporation
ii) Equivalent evaporation from and at 100°:C
iii) Efficiency of boiler
7 M
1(e) i) How much air used 1 kg of coal burnt in a boiler having Chimney height 50m to create a draught of 30.2 mm of water column when the temperature of the gases in the Chimney is 370°C and the temperature of boiler house is 25°C.
ii) What are advantages of artificial draught over natural draught.
7 M

2(a) What are limitations of Carnot cycle?
2 M
2(b) How can we increase the efficiency of Rankine cycle?
2 M
2(c) Derive an expression of thermal efficiency for regenerative cycle.
3 M
Solve any one question from Q.2(d) & Q.2(e)
2(d) In a Rankine cycle, the steam at inlet to turbine in saturated at pressure of 30 bar and the exhaust pressure is 0.25 bar.
Determine:
i) Pump work
ii) Turbine work
iii) Rankine efficiency
iv) Condenser heat flow
v) Dryness at the end of expansion
vi) Work ratio
Assume mass flow rate = 10 kg/sec
7 M
2(e) i) Explain the binary vapour cycle with neat line diagram.
ii) Explain the modified Rankine cycle and show the modification by P-V and T-S curve.
7 M

3(a) How can we find the stagnation state? Write the equation for stagnation properly in insentropic flow.
2 M
3(b) What is Mach number? How is it useful for calculation of gas-flow?
2 M
3(c) Derive the equation
\[\dfrac{dA}{A}=\dfrac{dV}{V}(m^{2}-1)\]
Where A=area of cross section of duct
V=velocity of gas through duct
3 M
Solve any one question from Q.3(d) & Q.3(e)
3(d) Define the critical pressure ratio, for the nozzle of steam turbine and derive the equation for maximum flow rate at throat in-terms of critical pressure ratio
7 M
3(e) i) Explain meta stable flow of steam in nozzle
ii) Derive the expression for nozzle efficiency.
7 M

4(a) What are effect of clearance on the performance of reciprocating compressors.
2 M
4(b) Why is multistage essential for high compression ratio?
2 M
4(c) Classify the rotary compressor and write comparison of rotary and reciprocating compressor.
3 M
Solve any one question from Q.4(d) & Q.4(e)
4(d) An air compressor takes in air at 1 bar and 27°C and delivers it after compression at 5 bar. Find the :
  1. Work done
  2. Heat transfer
  3. Change in internal energy when compression process are
    1. Isothermal
    2. Reversible adiabatic
7 M
4(e) Derive the equation for minimum work done in-terms of intermediate pressure of multistage compressor.
7 M

5(a) Explain the term vacuum and how it is measured?
2 M
5(b) How air leakage effects the performance of condenser?
2 M
5(c) What is fouling factor? What is difference between counter flow and parallel flow condenser.
3 M
Solve any one question from Q.5(d) & Q.5(e)
5(d) A steam condenser in equipped in a steam power plant which handles 1500kg/hr of steam and develops 2.5MW power. The initial condition of steam 27 bar, 300°C, the exhaust after condenser maintained at 72cm of Hg. Temperature at circulating water increases from 20°C to 28°C. While condensate removed at a temperature of 27°C, workout followings:
i) 7.5 diagram
ii) Dryness fraction of steam entering the condenser
iii) Mass rate of circulating water and cooling ratio
iv) Degree of under cooling.
7 M
5(e) Explain various types of cooling tower and its design construction.
7 M



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