MECHANICAL ENGINEERING Paper-II-2011


TIme Allowed: Three Hours )[Maximum Marks
INSTRUCTIONS
Each question is printed both in Hindi a d in English. Answers must be written i h meai
specified in the Admission er ific e issued
to you, which must be st ed. ea Y (In. the
cover ofthe answer-book i the s I provided
for the purpose. No marks will e giv n for the answers written' amediu ot er than that specified in A21mission ertificate. Candidates sho d ttemp!' Question Nos. 1 and 5 which are compulsory, and any t/tree ofthe rema; ing questi9ns selecting at least ques rom each Section.
The n mber oJmarks carried by each question
'cated at the end ofthe question. is considered insufficient, assume value. Psychrometric chart is ed with this question paper. Wher ver required, neat sketches/diagrams e drawn on the answer-book itself.
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SECTION-A

. Answer the following

It is desired to maintain a room at temperature of 20°C when outside temperature is 30(degrees)C. The volume of this room is 300 m3. The pressure in the room and outside is 1 bar.

The air in the room is renewed completely in 1 hour. Calculate the mass of air that the air conditioning system pumps into the room.
Compute maximum possible C.O.P. of this A/C system.
When this A/C system is switched-off, the temperature inside the room reaches 21°C in 20 minutes. Calculate the amount of heat transferred from the surroundings to the room.
calculate power required by this system.

Air is contained in a piston-cylinder arrangement mitially at 1.2 bar and 300 K with a volume of m3. Energy as heat of 11.82 Joule is transferred to the air in a quasi-equilibrium constant pressure process to yield a final temperature of 370.2 K. The piston moves without friction. Taking 1.005 kJ/kg K and C 0.72 kJ/kg determine the availability change for the process. reference environment is at 298 K and 1.0135 bar.

Sunlight of 1 kW/m2 falls directly on a window which is a vertical sheet of plain glass. Sun is in southwest and 30° above horizon. Window points towards the south. Estimate the amount of solar energy that,
enters the building through the window
is reflected by the window.

Given black body emisivity power table
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Draw rotor and stator blades and velocity diagrams or an axial flow compressor stage and derive the expression for energy transfer in terms of blade speed axial velocity Ca and blade angles. Discuss the effect of variation of axial velocity along blade height on energy transfer. How the influence is taken into account? .

2. An engine using 10 moles of diatomic ideal gas works 0on the reversible cycle having the fo1lowing processes
Adiabatic compression from 1 bar pressure and 300 K temperature to pressure of 9 times the initial value,
the initial value,
Constant pressure transformation temperature upto temperature of 1000
Adiabatic expansion upto 3 bars,
Constant pressure transformation such that temperature of 1000
Adiabatic expansion,
Constant pressure transformation upto the original state.
For this engine,
Represent the cycle on a p-v diagram.
Calculate pressure, temperature and volume at salient
points.
Calculate the efficiency of the engine summarizing results in a tabular form.
Compare the efficiency of the engine operating on Carnot cycle between the same extreme temperatures. Give comments.


Steam enters a nozzle operating at steady state at 40 bars, and 400°C and 10 m/s. Steam flows through this nozzle with negligible heat transfer and change in potential energy. Steam exits at 15 bars and 665 m/s. Mass flow rate is 2 kg/so.Compute exit area of the nozzle.
Given data for steam at 15 bar
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and Enthalpy of steam at inlet 3214.5 jk/kg.

What do you understand by governing of steam turbine? Explain the principle and working of throttle governing with the aid of a neat sketch. Compare the throttle governing with nozzle control governing with following aspects losses, use.
Sketch the efficiency against load with throttle governing.

3.
Water enters a tube of dia D and length L. Inlet and outlet temperatures are T1 and T2 respectively and temperature is T0. Convective heat transfer is h.

Derive the following expression for heat transfer:
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What is the significance of the logarithmic term in part above?
State assumptions. used in part 20

Air is supplied to a convergent-divergent nozzle with a static temperature of 300 static pressure of 5 bar and a velocity of 150 m/s. The inlet area of the nozzle is 10 cm2. A normal shock at a section of the nozzle where flow is 2. The flow Mach number downstream of shock corresponding to Mach number 2 is O.77. The flow Mach number at the exit of the nozzle is 0.4. Considering isentropic flow before and after shock and using isentropic flow relation for and Mach number provided below, find:
throat area of the nozzle
area of the nozzle where shock occurs
exit area of the nozzle
loss of stagnation pressure across shock. Sketch the variation of pressure and Mach number along the length of the nozzle

M 2 0·577 0·4
1·688 1·22 1·59

30
State the factors affecting the amount of draught produced in the boiler and discuss merits and demerits of induced draught system with reference boiler efficiency, fan maintenance,
power to drive the fan, leakages. 10


4.
A steam power plant runs on an ideal reheat ­regenerative. Rankine cycle. Details are given in Figure. Steam at turbine inlet is at 150 bars apd 600°C. Condensor pressure is 0.10 bar. Steam exiting the HPT is at 40 bars. This steam is split in two parts, y and x. Part x is reheated at the same pres,sure to 600°C and sent to LPT. Part y is condensed completely in CFWH and it is pumped to 150 bars before. it mixes with the flow at same pressure. A fraction of steam, is extracted from LPT at 5 bars. Assume steam output of boiler as 1 kg/s for ease of computations. Determine

fraction y
fraction z
thermal efficiency of the cycle.
Given data is
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Air flow is entering to a frictionless duct of 0.3 m diameter at a velocity of 580 m/s and a Mach number of 2. A 100 kJ/kg of heat is added to the flow and Mach number of 1.2 is attained.. Determine change in enthalpy of flow, change in kinetic energy of the f1ow,
change in static pressure in terms of inlet pressure. Comment on result and show the process on diagram.


Mention the unique features of modern high pressure boiler and describe the operation of Lamont boiler with a sketch.

Presentation on diagram, explain supersaturated expansion of steam in a nozzle. Indicate Wilson line on diagram and state effects of supersaturated. 10



5. Answer the fi .. iog:
A thermostatic expansion valve using R-134a in
the power assembly is designed to produce 10°C superheat at an evaporator temperature of O°C. What will be the superheat that it will maintain when the evaporator temperature is -30°C given for R-134a, the saturation pressure temperature data
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Cold water bottles kept in a room often start condensing atmospheric moisture. What is the minimum temperature to which water bottle. can be cooled without any dripping of moisture from its surface when kept in a room at 25°C DBT and 60% RH If it is desired that a water bottle at 10°C should also not condense moisture on its surface what should be the RH in the room,
keeping the DBT the same 15
A Rankine cycle based power plant is designed with superheat and reheat.

Sketch T-s diagram.
Explain the effect of lowering/raising condenser pressure.
Explain the effect of lowering/raising boiler pressure 15

A taxicab is equipped with a flexible four cylinder
S.l, engine running on a mixture of methanol and gasoline at an equivalence ratio of 0.95. How must the air-fuel ratio change as the fuel flow to the engine shifts from 10% methanol to 85% methanol 15
What are the main pollutants emitted by petrol and diesel engine? Discuss their effect on human and biological life.

What do you understand by catalytic converter Explain the principle and the working of 3-way catalytic converter.
Why do some thermostatic expansion valves have an 'external equalizer'? How does it improve its performance?



Explain the phenomena of knocking in S.I. engine. Discuss the effects of following factors on the knocking tendency of S.I.engine:
Compression ratio
Spark timing
Engine speed
Air-Fuel Ratio.

What are the functions of an additive Discuss different type of additives and their effect on the properties of lubricating oil. How the lubricating oils are graded as per SAE?

What are the important points that should be borne in mind when considering the new combustion chamber design What are the different types of combustion chamber used in C.l. engine? Discuss them in detail with specific advantages and disadvantages and dp/d9 for different combustion

In a winter-heating "air-conditioning system 1 kg/s of ambientair at 7°C DBT, 80% RH is sensibly heated, then adiabatically saturated to a high humidity of RH 90% and then further sensibly heated to the desired outlet state of 25°C and 50% RH.
Determine the temperature of air at various state points and show all the processes on a psychrometric chart. Also determine the amount of moisture added per hour in he adiabatic saturator.
30

8.
The following data relate to a boiler using induced draught system:
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Assuming that a 45(degrees) bend equal one-half of 90(degrees) bend and that the resistance offered by square duct is 20% greater than a similar round duct,determine:

Draft to be produced due to friction in square cross section duct in mm of water.
Draft due to velocity head of flue gases in mm of water.
Total draft for the boiler.
Draft to be produced by induced fan.
Power required to drive fan. 30

During a trail of a single cylinder, 4 stroke diesel engine the following observations were recorded:

Bore 340 mm
Stroke 440 mm
rpm 400
Area of indicator diagram= 465 mm2
Length of diagram 60 mm
Spring constant 0.6 bar/mm
Load on hydraulic dynamometer= 950 N
Dynamometer constant 7460
Fuel used 10.6 kg/h
Calorific value of fuel 49500 kj/kg
Cooling water circulated 25 kg/mindRise in temp. of cooling water 25(degrees)CFWHMass analysis of fuel:
Carbon 84%
Hydrogen 15%
Incombustible
Volume analysis of exhaust gas:
Carbon dioxide
Oxygen 10%
Temp. of Exhaust gases 400%
Sp. heat of exhaust gas 1.05 kj/kg (degrees)C
Partial pressure of steam in exhaust gas= 0.030 bar
Sp. heat of superheated steam 2.1 kj/kg(degrees)C
Saturation temp. of steam at 0.030 bar 24.1(deg)C
Draw up heat balance sheet on minute basis.
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