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Thermodynamics Question Paper - Dec 17 - Mechanical Engineering (Semester 3) - Pune University (PU)
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Thermodynamics - Dec 17
Mechanical Engineering (Semester 3)
Total marks: 80
Total time: 3 Hours
INSTRUCTIONS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Draw neat diagrams wherever necessary.
1.a.
Define and explain on P-v diagram:
( 6marks)
00
(i)Thermodynamics state
(ii)Thermodynamics Process
(iii)Thermodynamics Cycle.
1.b
Experimental data of Specific heat capacity measurement of air at constant Pressure are as follows:
(6 marks)
00
1.Mass of air = 0.05 kg
2.Air heated from 287 K to 347 K for 300 seconds using a heater with input Power-10.04 W.
3.Adiabatic index = 1.4.
Determine: 1. Specific heat of air at constant pressure.
Characteristics gas constant of Air (R)
Density of air at 273 K and 1 bar.
2.a
Draw any three of the following processes:
(6 marks)
00
(i) Constant Pressure and Isobaric process on P-v diagram
(ii) Constant volume or Isochoric process on P-v diagram
(iii) Constant temperature or Isothermal Process on T-s diagram.
(iv) Reversible Adiabatic or Isentropic Process on T-s diagram.
2.b
The COP of the Carrot refrigerator is 6, when it maintains the temperature of 270 K in the evaporator. Determine the condenser temperature and Refrigerating effect if the power required to run the refrigerator is 7.5 kW.
(6 marks)
00
3.a
Define and explain any six of the following terms with neat sketch showing piston, cylinder arrangement for air standard cycle:
(6 marks)
00
(i) Clearance volume
(ii) Swept volume
(iii) Total volume
(iv) TDC
(v) BDC
(vi) Compression ratio
(vii) Air standard efficiency.
3.b
A throttling calorimeter is used to determine the dryness fraction of the steam using steam at 10 bar. The condition of steam after throttling is 1.2 bar, 118°C. Calculate the dryness fraction of the steam assuming Cp=2.1 kJ/kg
(6 marks)
00
4.a
State and explain different components of Rankine cycle on flow diagram and draw the Thermodynamics cycle on T-s diagram .
(6 marks)
00
4.b
A refrigerating system operates on reversed Carnot cycle. The higher temperature of the refrigerant in the system is 308 K and the lower temperature is 258 K. Refrigerating effect of the refrigerator is 42.2 kW.
(6 marks)
00
Determine: (i) COP and (ii) heat rejected from the system.
5.a
Give the function and location of any three of the following:
(6 marks)
00
(i)Super heater
(ii) Air pre heater
(iii) Fusible plug
(iv)Water level indicator
(v)Spring loaded from the system.
5.b
The following results were obtained in a boiler trial:
(6 marks)
00
(i) Feed water per hour = 700 kg at 27°C
(ii) Steam produced at 8 bar and 0.97 dry.
(iii) Fusible plug
(iv) Water level indicator
(v) Spring loaded safety valve.
5.b
The following results were obtained in a boiler trial:
(7 marks)
00
(i) Feed water per hour = 700 kg at 27°C
(ii) Steam produced at 8 bar and 0.97 dry.
(iii) Coal used = 100 kg/hr having CV of coal = 25000 kJ/kg
(iv) Ash and Unburnt coal collected = 7.5 kg/hr having CV = 2000 kJ/kg
(v) Mass of flue gases produced per kg of fuel burnt = 17.3 kg
(vi) Flue gas temperature = 327°C
(vii) Room temperature = 16°C
(viii)Specific heat of flue gases = 1.025 kJ/kgK
Draw the energy balance on minute basis.
Or
6.a
Derive the formula for:
(6 marks)
00
(i) Equivalent evaporation and
(ii) Boiler efficiency.
6.b
How much air is used per kg of coal burnt in a boiler having chimney of 32.3 height to create the draught of 19 mm of water column when the temperature of the flue gases in the chimney is 370°C and the temperature of the boiler house is 29.5°C.
(7 marks)
00
7.a
Define Human comfort condition and discuss the factors affecting human comfort.
(6 marks)
00
7.b
Atmospheric air at 30°C DBT and 18°C WBT is cooled to 20°C. DBT without changing its moisture content. Find:
(7 marks)
00
(i) Initial enthalpy and specific humidity of air.
(ii) Final relative humidity of air and WBT.
(iii) Sensible heat removed per kg of air.
Or
8.a
Define the following terms :
(6 marks)
00
DBT
Specific humidity
WBT
Relative humidity
Degree of saturation
DPT
8.b
Moist air enters a steam heating coil at 10°C, 50% RH which is heated sensibly and leaves the coil at 30°C The mass flow rate of the moist air is 50 kg/s.
(7 marks)
00
Find:
(i) Sensible heat gained by air.
(ii) Mass flow of the steam in the coil if the steam enters the coil as saturated steam and the condensate leaves the coil at 85°C at atmosphere pressure.
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