06 ME 43 USN IV Sem B E Examination
APPLIED THERMODYNAMICS [ Common to ME / IP / IM / AU / MA ] MODEL QUESTION PAPER Time: 3 Hrs.]
[Max. Marks: 100
Note : Answer any five full Questions, choosing at least 2 Questions from each part. PART A 1.
a) b)
With a neat sketch, Explain analysis of Exhaust gases by Orsat apparatus. Octane (C8H18) is burnt in the air and an Orsat analysis of the product of combustion yielding the following results CO2 – 10.5%, CO – 1.8%, O2 – 5.3% and N2 = 82.4% Determine (i) (ii) (iii) (iv)
2.
a) b)
3.
4.
5.
a) b)
a) b)
a)
10
actual air fuel ratio on mole. Basis actual air fuel ratio on mass basis Percent excess air Dew point temperature of the products
Represent Otto, diesel and dual cycle on P-V diagram and T-S diagram. When heat supplied on each cycle is same. Compare them. An air-std diesel cycle has a compression ratio of 16. The temperature before compression is 27oC and temperature after expansion 627oC. Determine (i) The Net Work output per unit mass of fuel (ii) Specific air consumption in kg/kWh
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12
What are the different methods of improving Thermal ? of gas turbine. Explain. A Simple GT plant operating on Brayton cycle has air entering the compressor 100 kPa and 27oC. The pressure ratio is 9 and maximum cycle temperature = 727oC. What will be the percentage change in the cycle efficiency ? and net work output if expansion in the turbine is divided into 2-stages. Each of pressure ratio is 3, with intermediate reheating to 727oC? Assume compression and expansion are ideal isentropic.
08
Explain with T-S diagrams, reheat and regenerative rankine cycles. A steam power plant operates between boiler pressure of 42 bar and a condenser pressure of 0.035 bar. Calculate for these limits, the cycle efficiency, the work ratio and the specific heat consumption. (i) For a carnot cycle using wet steam (ii) For a Rankine cycle with dry saturated steam of entry to the turbine (iii) For the Rankine cycle when the expansion process has an isentropic efficiency of 80%.
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For
an
N
Stage
P Nn P1V1 N +1 P1 n −1 b)
10
n −1 Nn
compressor
PART B with perfect
intercooling
S.T.
work
done
12
10
=
− 1
A Multistage air compressor compresses air from 1 bar to 40 bar. The maximum temperature of
10
10
air is not to exceed 400 k in any stage. If the law of compression PV1.3 = C, find the number of stages for minimum power input. Also find actual intermediate pressures and temperatures. What will be the minimum power input in KW required to compress and deliver 10 kg/min of air and rate of heat rejection in each intercooler? Assume ambient temperature 27oC and perfect intercooling in between stages. 6.
7.
a) b)
a)
b)
8.
a)
b)
With a neat sketch explain practical vapour absorption cycle. An air refrigerant plant is to be designed to the following specifications. Pressure of air at compressor inlet = 101 kPa Pressure of air at compressor exit = 404 kPa Pressure loss in the inter cooler = 12 kPa Pressure loss in the cold chamber = 3 kPa Temperature of air at compressor inlet = -6oC Temperature of air at turbine inlet = 27oC Isentropic efficiency of compressor = 85% Isentropic efficiency of turbine = 85% Determine (i) COP of the cycle (ii) Power required to produce 1 ton of refrigeration (iii) Air circulation rate per ton of refrigeration With the help of schematic Psychrometric chart diagram, explain (i) Cooling and Dehumidification (ii) Chemical Dehumidification (iii) Adiabatic Saturation An air conditioning system is designed under following conditions: Outdoor conditions : 30oC DBT, 75% RH Required indoor conditions : 22oC DBT, 70% RH Amount of free air circulated 3.33 m3/sec Coil dew point temperature (DPT) = 14oC The required condition is achieved first by cooling and dehumidification and by heating. Estimate (i) The capacity of the cooling coil in tones of refrigeration (ii) The capacity of heating coil in kW (iii) The amount of water vapour removed in kg/hr Explain briefly, the following frictional power determination method (i) Willian’s line method (ii) Morse test method During a test ib a single cylinder 4 stroke cycle oil engine, the following observations were made: Bore = 30 cm, Stroke = 45 cm, Duration of trail = 1 hr, Total fuel consumption = 7.6 kg, Calorific value of fuel = 45000 KJ/kg, Total revolutions made = 12000, Mean effective pressure = 6 bar, Net brake load = 1.47 KN, Brake drum diameter = 1.8 cm, Rope diameter = 3 cm, Mass of jacket cooling water circulated = 550 kg, Water enters at = 15 deg cent, Water leaves at = 60 deg cent, Total air consumption = 360 kg, Room temperature = 20 deg cent, Exhaust gas temperature = 300 deg cent. Calculate, (i) Indicated and brake power (ii) Indicated thermal efficiency (iii) Mechanical efficiency (iv) Draw the heat balance sheet on minute basis
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12
08
12
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12
06 ME 43 USN IV Sem B E Examination
APPLIED THERMODYNAMICS [ Common to ME / IP / IM / AU / MA ] MODEL QUESTION PAPER Time: 3 Hrs.]
[Max. Marks: 100
Note : Answer any five full Questions, choosing at least 2 Questions from each part. 1
a)
b) c)
2
a) b)
3
a) b)
4
a) b)
5
6
PART A Explain the following i) Stoichiometric air ii) Enthalpy of formation iii) Adiabatic Flame Temperature iv) Combustion Efficiency Calculate the theoretical air fuel ratio for the combustion of octane (C8 H18) The percentage composition by mass of fuel is given as follows C=90%, H2 =3.3 %, O2 =3%, N2 =1.1 % S=0.9% and reminder is incombustible. Find i) The mass of air required /kg of fuel for complete combustion ii) If 60% excess air supplied. Find the % of exhaust gas by volume. Define MEP. Derive an expression for MEP of Diesel cycle in terms of compression ratio and cut –off ratio. Air standard dual cycle uses 1 kg of air and has comp. ratio of 14. The pressure and temperature at the beginning of adiabatic compression are 1 bar at 300C respectively. The temperature at the end of the constant volume and constant pressure heat addition are 12000C & 15000C respectively. Calculate i) Heat supplied ii) Heat rejected iii) Net work done iv) Air standard efficiency. With neat sketches explain Turbo Jet and Ram Jet Propulsions A simple gas turbine draws air at 1 bar & 150C and compresses with a pressure ratio if 5:1. The temperature of the gas entering the turbine is 7400C. The isentropic efficiencies of the compressor and the turbine are 85% and 80% respectively. There is a loss of pressure in compression system which is equal to 0.7 bar. Calculate i) Thermal efficiency of the plant ii) Mass of air and gasses if out put of the plant is 1616 kW Explain briefly Mean temperature of heat addition in a Rankine cycle and obtain the expression for the same. Steam at 20 bar and 3600C is expanded in a turbine to 8 kPa. Then it is condensed to saturated liquid. Pump feeds back the condensate in to boiler. i) Assuming Ideal process estimate the cycle efficiency. ii) What would be the cycle efficiency if the pump and turbine efficiencies are 80% each
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5 7
10
8
12
10
PART B Define the following with respect to a reciprocating air compressor: a) i) Iso thermal efficiency ii) Adiabatic efficiency iii) Mechanical efficiency and iv) Volumetric efficiency b) In a single acting two stage reciprocating compressor, 4.5 kg of air per minute are compressed from 1.013 bar and 150 C through a pressure of 9:1. Both the stages have the same pressure ratio and the law of compression and expansion in both the stages is PV1.3 = C, if inter cooling is complete, calculate the indicated power and the cylinder swept volume required. Assume 5% clearance volume for both stages of their respective swept volume compressor runs at 300 rev/min.
a) b)
Derive an expression for COP of a Bell Coleman Cycle A water cooler using F-12 as refragment works between 26o C to 8 o C respectively. The vapour
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(12)
(8) (12)
leaves the evaporator dry and saturated. The output of cold water is 100 kg/hr cooled from 260 C to 60 C. Taking ηmech = 85% & motor efficiency = 95% & assuming 20% of the useful cooling effect is lost in cooling water. Determine 1) Motor power 2) Vol. Displacement of cylinder 7
8
a)
Define and obtain expression for the following terms (i) Specific humidity (ii) Degree of saturation (iii) Relative humidity (iv) Enthalpy of moist air.
b)
30 m3 of air at 150 C DBT & 13o C WBT is mixed with 12 m3 of air at 250 C DBT & 180 C WBT. Calculate DBT, Specific humidity and enthalpy of a mixture. Take Patm as 760 mm of Hg
a)
Define the following w.r.t. IC engines. i) Brake specific fuel consumption ii) Relative efficiency iii) Cubic capacity iv) Brake mean efficiency The following observations were made during a trial of a single cylinder four stroke cycle gas engine having cylinder diameter of 18 cm and stroke of 24 cm Duration of trial = 30 min Total number of revolution = 9000 Total number of explosion = 4450 Indicated mean effective pressure = 5 bar Net load on the brake wheel = 390 N Effective diameter of the brake =1m Calorific value of gaseous fuel at NTP = 19 MJ/m3 Total fuel used at NTP = 2.4 m3 Total air used = 36 m3 Pressure of air = 720 mm of mercury Density of air at NTP = 1.29 kg/m3 Temperature of air = 170 C Temperature of exhaust gas = 3500 C Specific head of exhaust gas = 1.0 KJ/kg-k Room temperature = 170 C Cooling water circulated = 80 kg Rise in temperature of cooling water = 300 C
b)
Draw up a heat balance sheet and estimate the Mechanical and indicated thermal efficiencies of the engine. Take R = 287 KJ/kg-k
(10) (10) (6)
(14)
