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IES Full Length Mock Test Online 2014

BRANCH: Mechanical EngineeringPAPER 1

(Conventional)

INSTRUCTIONS

Please read each of the following instructions carefully beforeattempting questions:

Candidates should attempt FIVE questions in all.

Question No.1 is compulsory. Out of the remaining SIXquestions attempt any FOUR.

All questions carry equal marks. The number of marks carriedby a part of a question is indicated against it.

Time Allowed: Three Hours Maximum Marks : 200

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Answers must be written in ENGLISH only.

Assume suitable data, if necessary and indicate the same

clearly. For air R = 0.287 kJ/kg K CP = 1.005 kJ/kg K, = 1.4,M = 28.966 kg/kg mole

Unless otherwise mentioned, symbols and notations have theirusual standard meanings.

Assume suitable data, if necessary and indicate the sameclearly.

Neat sketches may be drawn, wherever required.

All parts and sub-parts of a question are to be attemptedtogether in the answer book.

Any pages left blank in the answer book must be clearly struckout.

01.

(a) Compare the phenomenon of detonation in spark ignitionengine with that of knocking in compression ignitionengines. (4 M)

(b) Explain why PMMK-I and PMMK-II devices are notpracticable. (PMMK - Perpetual Motion Machine Kind)

(4 M)

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(c) Define the following terms:(i) WBT (ii) DPT (iii) Relative humidity(iv)Sensible heat factor (v) Comfort zone.

(5 M)

(d) What is meant by boundary layer thickness, displacementthickness and energy thickness? (6 M)

(e) Explain stable, unstable & neutral equilibrium with respectto floating bodies when partially submerged and fullysubmerged in liquid. (4 M)

(f) Define and give physical significance of Froude number,Eulers number? (4 M)

(g) How does filmwise condensation differ from dropwisecondensation? (4 M)

(h) Experimental results indicate that the local heat transfer co-efficient hx for flow over a flat plate with an extremelyrough surface is approximated by the relation:

hx = a x0.12

Where a is a constant coefficient and x is distance fromthe leading edge of the plate. Set up a relation between thislocal heat transfer coefficient and the average heat transfercoefficient h for a plate of length x. (5 M)

(i) Define Degree of reaction and derive an expression? (4 M)

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02(a) A reversible Heat engine A absorbs energy from a

reservoir at temperature T1 and rejects energy to a reservoirat temperature T2. A second engine B absorbs the sameamount of energy as rejected by the engine A from thereservoir at temperature T2 and rejects energy to a reservoirat temperature T3. What is the relation between T1, T2 andT3 if:(i) The efficiencies of both the engines A and B are the

same and(ii) The work delivered by both the engines are the same

(10 M)

(b) Distinguish between Octane and Cetane rating of fuel.Explain how they are determined. What is the Cetanerating of diesel oil marketed in India (10 M)

(c) A turbojet aircraft flies with a velocity of 300 m/s at analtitude where the air is at 0.35 bar and 40C. Thecompressor has a pressure ratio of 10, and the temperatureof the gases at the turbine inlet is 1100C. Air enters thecompressor at a rate of 50 kg/s. Estimate (a) thetemperature and pressure of the gases at the turbine exit,(b) the velocity of gases at the nozzle exit, and (c) thepropulsive efficiency of the cycle. (20 M)

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03.(a) Calculate the (i) COP (ii) Power requirement and (iii)

cooling capacity of a CO2 compressor working between22.68 bar and 64.32 bar pressures. The liquid in thecondenser gets cooled, by another system, to 15C beforeentering the expansion valve. The system is assumed towork on wet-compression with x = 0.9. The compressordata: stroke volume = 500 c.c.; r.p.m. = 500 and vol =0.85. Property values are: sp. heat of CO2 vapour = 2.4kJ/kgC and

P(bar)

Enthalpy(kJ/kg)Liq. Vap.

v(m3/kg)Liq. Vap.

s (kJ/kgC)Liq. Vap.

t(C)

22.6850.9264.32

49.62127.75164.17

322.86308.08283.63

0.001010.001300.00147

0.01660.00660.0042

0.19760.46970.5903

1.25671.09590.9912

151525

(20 M)(b) The following are the data given of a change in diameter

effected in laying a water supply pipe. The change indiameter is gradual from 20 cm at A to 50 cm at B.Pressures at A and B are7.848 N/cm 2 and5.886N/cm 2 respectively with the end B being 3 m higherthan A. If the flow in the pipe line is 200 litre/s,

Find: ( i ) direction of flow, (ii) the head lost in frictionbetween A and B. (10 M)

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(c) From the fundamentals, derive the expression for hydrodynamic boundary layer thickness if velocity profile is

given by the relation:

y2

sinu

u (10 M)

04.

(a) What is the significance of a draft tube? Why it is requiredonly with reaction turbines? (6 M)

(b) A Pelton wheel is to be selected to drive a generator at 600rpm. The water jet is 75 mm in diameter and has a velocityof 100 m/sec with the blade deflection angle is 1700. Theratio of vane speed to inlet jet speed is 0.49 and neglectingthe losses, determine

(i) Diameter of wheel to center line of bucket?(ii) Power developed by the runner?(iii) Kinetic energy per Newton remaining in the fluid?

(12 M)

(c) A steam power plant of large capacity a shell and tube heatexchanger having 30,000 thin wall tubes of 25 mmdiameter condenses on the surface of these tubes withconvection coefficient 10 kW/m2 deg. Water serves as thecoolant entering the tubes at 200C at mass flow rate of30103 kg/s. If the condenser (heat exchanger)arrangement involves one shell pass and two passes and theheat transfer rate is 200 MW.

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Determine

(i) Temperature of cooling water at exit from condenser

(ii) Over all heat transfer coefficient

(iii) Heat transfer area and length of tube /pass (Ifcorrection factor is 0.9) (12 M)

(d) How does the PWR differ BWR? Give examples of each.What is a breeder reactor? (10 M)

05.(a) A four stroke single cylinder oil engine has a bore of 300

mm and stroke 460 mm and runs at 200 rpm. The fuel oilhas a composition by mass of 87% Carbon and 13%Hydrogen. It is consumed at the rate of 6.75 kg/hr. Thevolumetric composition of dry exhaust gases is 7 % CO2,10.5% O2 and 82.5% N2. Atmospheric temperature andpressure are 17C and 100 kN/m2 respectively.Determine:(i) the actual quantity of air supplied/kg of fuel and(ii) volumetric efficiency of the engine.

Take R for air as 0.287 kJ/kg K. (10 M)

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(b) The following data are obtained from a test on a singlecylinder 4-stroke oil engine:Cylinder bore = 15 cm, Stroke = 25 cm, area of indicatordiagram = 450 sq. mm, Length of indicator diagram = 50mm, Indicator spring rating 1.2 mm for a pressure of 9.81N/cm2. Engine speed = 40 rpm, Brake torque = 22.5 Nm,Fuel consumption = 3 kg/hr, Calorific value of fuel =44,200 kJ/kg. Cooling water flow rate = 4 kg/min. Coolingwater temperature rise = 42C, Specific heat of coolingwater = 4.187 kJ/kg-K.Determine:(i) the mechanical efficiency(ii) brake thermal efficiency(iii) Specific fuel consumption and(iv) draw heat balance in kW. (20 M)

(c) A single-acting reciprocating pump has piston diameter 15cm and stroke length 30cm. The centre of the pump is 5mabove the water level in the sump. The diameter and lengthof the suction pipe are 10cm and 8m respectively. Theseparation occurs if the absolute pressure head in thecylinder during suction stroke falls below 2.5m of water.Calculate the maximum speed at which the pump can runwithout separation. Take atmospheric pressure head =10.3m of water. (10 M)

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06.(a) An elastic balloon submerged in water is attached to a base

of a tank. Estimate the changing tension (%) if the pressureof air increases from 100 kPa to 1.6 MPa by assuming theinitial diameter of balloon as 30 cm and varying withpressure as P=CD-2. Where C= Constant D=Diameter ofthe balloon (8 M)

(b) Derive an expression for the drag on a submergedtorpedo, 22D VLFrRe,fF The parameters : size of the torpedo L, the velocity of thetorpedo V, the viscosity of the water , the density ofwater and acceleration due to gravity g by usingdimensional analysis ? (12 M)

(c) The following refer to a stationary gas turbine:Compressor inlet temperature = 311 KCompressor pressure ratio = 8Combustion chamber pressure drop = 5 % of inlet pressureTurbine inlet temperature = 1367 KTurbine exit and compressor inlet pressures areatmospheric.There exists a facility to take air from the compressor exitfor use in cooling the turbine. Find the percentage of airthat may be taken from the compressor for this purpose sothat the overall cycle efficiency drops by 5% from that ofthe case of no usage of compressed air for cooling ofturbine. For simplicity, assume the following;

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(i) Take properties of gas through the turbine as those ofair,

(ii) Addition of cooling air to the turbine and addition offuel to the combustion chamber do not affect theturbine power and

(iii)Compressor and turbine efficiencies are 0.87 and 0.90respectively. (10 M)

(d) A Blimp is designed to move in air at 200 C at 7 m/sec if a1:20 scale model is tested in water 200 C what should bethe water velocity ? If the measured drag on the model is309 kN, calculate the drag on the prototype blimp and thepower required to propel it? (Take air = 1.2 kg/m3, water =998kg/m3 water = 1.0210 3 Pa-sec and air = 1.81105Pa-sec. (10 M)

07.

(a) The temperature on the two sides of a plane wall are T1 andT2, and thermal conductivity of the wall material is givenby relation K = K0 e-(x/), where K0 is constant and is thewall thickness. Derive expression for temperaturedistribution & heat transfer in the wall? (8 M)

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(b) Pressurized water is to be carried through a pipe whosetemperature is to be maintained at 120C. At what depth isthe pipe to be buried in the ground such that water doesnot freeze, if out side temperature is 300C ?

Consider following data

= 1.24 107m2/sec, = 30 days, (T0)soil = 170C erf()

0.40.50.60.70.80.91.0

0.42840.52050.63090.67780.74210.79700.8427

(10 M)(c) An electric heating system is installed in the ceiling of a

room that measures 300 300cm with a height of 4m.Thetemperature of ceiling is maintained at 320K where as thewall is at 300 K as shown in figure.

3m

3m

4m Wall

1

ceiling2

1

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Determine net radiant heat interchange between the wall &ceiling if emissivities are 0.6 & 0.7 respectively.

[F12 = 0.18] (8 M)(d) For an air flow over a flat plate assuming shear stress

varies linearly in laminar boundary layer such that

y10 . Calculate the displacement and momentum

thickness in terms of ? (8 M)

(e) The (NPSHmin ) for a pump given by the manufacturer. Apump is being used to pump water from a reservoir at rateof 0.2832 m3/sec. The water level in the reservoir is 1.28 mbelow the pump. Atmosphere pressure is 98.62 kN/m2 andatmosphere temperature is 200 C. Assume total head loss inthe suction pipe is 1.158 m of water. Determine whether ornot it safe from cavitation effect. (Vapour pressure of wateris 23.128 m).

(6 M)

END OF THE PAPER

Air

Water

P1=100kPa