Thermal CAT 2012

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Subject Code & Title: &THERMAL ENGINEERING


Unit-1

CAT-1

PART-A (3X2=6)

ANSWER ALL THE QUESTIONS

1.What is mean effective pressure?

2.In an engine working on an ideal Otto cycle, the temperatures at the beginningat the end of compression are 27C and 327C respectively. Find the compression ratio and

air standard efficiency of the engine.3.Which RF standard cycle (Otto / Diesel / Dual) is more efficient for the same heat input? justify.

PART-B (2x12=24)

1.A four stroke, four cylinder petrol engine of 250 mm bore and 375 ram stroke works on

Otto Cycle. The clearan ce volume is 0.01052 m3. The initial pressure and temperature are

1 bar and 47C. If the maximum pressure is limited to 25 bar, find the (i) the air

standa rd e fficie ncy of the cycle (ii) mean effecti v e pressure. Take Cp = 1.005 kJ/kgkandy =1.4.

2.For air standard diesel cycle the following data isvailableCompression ratio =16

Heat added/kg =2500 kJ/kg

Lowest temperature in the cycle = 300 K

Lowest pressure in the cycle = 1 bar

Calculate:

1.Pressure and temperature at each point in the cycle

2.Thermal efficiency

3.Mean effective pressure if air flow rate of 0.25 kg/ sec

Assume Cp =1 kJ/kg K and Cv = 0.714 kJ/kg K.

CAT-2

PART-A

ANSWER ALL THE QUESTIONS (3X2=6)

1. List out any two assumptions for the analysis of thermodynamic air cycles.

2. Explain the effect of pressure ratio on the net output and efficiency of a Brayton cycle.

3. Define air standard efficiency of Dual cycle.

PART-B (2x12=24)

1. In an air standard dual cycle, the pressure and temperature at the beginning of compression are

1 bar and 57C, respectively. The heat supplied in the cycle is 1250 kJ, kg, two third of thisbeing added at constant volume and rest at constant pressure. If the compression ratio is 16

determine the maximum pressure, temperature in the cycle, thermal efficiency and mean

effective pressure.2. A gas turbine works on an air standard Brayton cycle. The initialcondition of the air is 25C and 1 bar.The maximum pressure and temperature are limited to 3

bar and 650C. Determine the following :

(i) Cycle efficiency(ii) Heat supplied and heat rejected/kg of air

(iii) Work output/kg of air (iv) Exhaust temperature.

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Unit-2

CAT-3

PART-A


1.Mention any four applications of Two Stroke Engine and Four Stroke Engine.

2.state the merits of a Diesel engine over a petrol engine.

3. What is scavenging in two stroke engine?

PART-B (2x12=24)

1. Explain the working principle of a four stroke petrol engine.

2. Sketch the typical valve timing diagram of a high speed 4 stroke petrol engine.

CAT-4

PART-A


1.What are the limitations of battery ignition system?

2.List out the major pollutants from a petrol engine.

3. What do you understand by Cetane Number?

PART-B (2x12=24)

1. Give the classification of bridges based on superstructure.

2. What is the objective of plastering? List and comment any five defects in plastering.

Unit-3

CAT-5

PART-A


1.Define Nozzle efficiency.

2.What is supersaturated flow in a nozzle?

3. What are the effects of super saturation in a nozzle?

PART-B (2x12=24)

1. Steam enters a convergent-divergent nozzle at 2 MPa and 400C with a negligible velocity and

mass flow rate of 2.5 kg/s and it exits at a pressure of 300 kpa. The flow is isentropic between

the nozzle entrance and throat and overall nozzle efficiency is 93 percent. Determine (i) throat

area and (ii) exit area.

2. Derive an expression for maximum mass flow rate through convergent divergent nozzle for

steam.

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CAT-6

PART-A


1.What is the principle of Impulse and Reaction turbines?

2.State the necessity for governing of steam turbines.

3. How is the speed of the steam turbine regulated?

PART-B (2x12=24)1.The nozzle of a de-Laval turbine deliver 1.5 kg/s of steam of 800 m/s to a ring of owing blades having a

speed of 200 m/s. The exit angle of the nozzle is 18. If the blade velocity coefficient is 0.75 and the exit

angle of the moving blades is 25, calculate (i) Inlet angle of moving and fixed blades (ii) diagram

efficiency (iii) energy lost in blades per second (iv) power developed and (v) axial thrust on the turbine

rotor.

2. A single row impulse turbine develops 132.4 kW at a blade speed of 175 m/s, using 2 kg of steam per

sec. Steam leaves the nozzle at 400 m/s. Velocity coefficient of the blades is 0.9. Steam leaves the turbine

blades axially. Determine nozzle angle, blade angles at entry and exit, assuming no shock.

Unit-4

CAT-7

PART-A


1.Define Free Ain Delivered with regard to a compressor.

2.State the effect of clearance on work done in a recprocating compressor.

3.Why clearance is necessary in reciprocating compressors?

PART-B (2x10=20)

1.ASingle stage, single acting reciprocating air compressor has a bore of 20 cm and a stroke of 30 cm.

The compressor runs at 600 rpm. The clearance volume is 4% of the swept volume and index if expansion

and compression is 1.3.Thesuction conditions are 0.97 bar and 27C and delivery pressure is 5.6 bar. The

atmospheric conditions are at 1.01 bar and 17C. Determine (i) the free air delivered inm3/min (ii) the

volumetric efficiency referred to the free air conditions (iii) the indicated power.

2.A single stage double acting air compressor delivers 15 m3/min of air measured at 1.013 bar, 27C. The

air is delivered at 7 bar. The conditions at the end of suction stroke are pressure 0.98 bar and temperature35C. The clearance volume is 4% of stroke volume, the L/D ratio is 1.3 and the compressor runs at 300

rpm. Calculate the volumetric efficiency, cylinder: dimensions and isothermal efficiency of the

compressor. Take index of expansion and compression as 1.3 and R = 0.287 kJ/kg.K

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CAT-8

PART-A


1.What are the advantages of multistage compression over single stage compression?2.Why clearance is necessary in reciprocating compressors?

3.Differentiate positive and non positive displacement compressors.PART-B (2x10=20)

1.2 kg/s of air enter the LP cylinder of a two stage, reciprocating air compressor. The overall pressure

ratio is 9.The air at inlet to compressor is at 100 kPa and 35C.The index of compression in each cylinder

is 1.3.Find the intercooler pressure for perfect inter cooling . Also , find the minimum power required for

compression,and percentage saving over single stage compression.Take R = 0.287la/kgK and C =1

kJ/kgK 2. Describe the principle parts of Babcock Wilcox boiler with neat sketch.

2.The free air delivery of a single stage reciprocating air compressor is 2.5 m3/min. The ambient air is at

N.T.P condition and the delivery pressure is 7 bar. The clearance volume is 5% of stroke volume and law

of compression and expansion is pv1.25 = C. If L = 1.2 D and the compressor runs at 150 rpm, determine

the dimensions of the cylinder.

Unit-5

CAT-9

PART-A


1.Sketch the T-s and p-h diagrams for the vapour compression cycle when the vapour

after compression is dry saturated.

2.What is the effect of sub-cooling a refrigerant in a vapour compression cycle?

3.How does the sub cooling influence the refrigerating effect of a vapour compression

refrigerator?

PART-B (2x10=20)1. A vapour compression refrigerator works between the pressure limits of 60 bar and25

bar.Theworkingfluidisjustdryattheend of ompression and there is no under cooling of the liquid before the

expansion valve. Determine (i) COP of the cycle and (ii) capacity of the refrigerator if the fluid is at the

rate of 5 kg/mm.

ressure Saturationtemperature Enthalpy (kJ/kg)

_

Entropy(kJ/kgK)

(bar) (K) Liquid Vapour Liquid Vapour

6 295 151.96 93.29 0.554 1.0332

25 261 156.32 22.58 0.226 1.2464

2. Explain the working principle of vapour absorption refrigeration system and compare it with vapour

compression refrigeration system.

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CAT-10

PART-A


1.Define Bypass factor of a heating coil.

2.What are the components used in winter air conditioning system?

3.Which thermodynamic cycle is used in air conditioning of airplanes using air as a

refrigerant?

PART-B (2x10=20)1. The air enters a duct at 10C and 80% RH at the rate of 150 m3/min and is heated to 30C without

adding or removing any moisture. The pressure remains constant at 1 atm. Determine the RH of air at exit

from the duct and the rate of heat transfer.

2. Saturated air at 2C is required to be supplied to a room where the temperature must be held at 20C

with a relative humidity of 50%. The air is heated and then water at 10C is sprayed to give the requiredhumidity. Determine the temperature to which the air must be heated and the mass of spray water required

per m3 of air room conditions. Assume that the total pressure is constant at 1.013 bar and neglect fan

power.

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Thermal CAT 2012