MECHANICAL ENGINEERING

PAPER II
SECTION A
1 . Answer any lout pans
A salesman reports that he has a steam turbine available that delivers 3MW. The steam
enters the turbine in a pressure of 6 bar and leaves at 0.15 bar and the required rate of steam
consumption is 12000 kg/hour.
(i)How do you evaluate his claim?
(ii)Next he changed his statement and said that the required steam flow was 20,000
kg/hour,how do you evaluate his claim now?

(b)Derive Clausius-Clapeyron equation and calculate the change in freezing temperature per bar
change in pressure for water Given that specific volume of water at 0 degC is l0power-3 m3/kg and
that of ice is 1.09x10power-3 m3/kg Latent heat of ice= 335kJ/kg

Using the Maxwell relation, derive the following equation dh
<img src='./qimages/1510-1c.jpg'>
Discuss the various fuels used in compression ignition engines and spark ignition engines
What are the desirable properties of fuels used in these two types or engines? How are the
fuels used in C.I. and S.I engines rated?
steam pipe 75 mm OD and 30m long conveys 1000 kg of steam/hour at a pressure of 2 MN/m2
The steam enters the pipe with a dryness fraction of 0.98 and is to leave the other
end of the pipe with a minimum dryness fraction of 0.96. This is to be accomplished by
suitable insulating the pipe,the thermal conductivity of insulating material being 0.19 W/m
K. Neglecting the temperature drop along the stem pipe, determine the minimum thickness of
insulation required to meet the necessary conditions, Take the temperature of outside surface
of insulation as 27°C. For steam at 2 MN/m2, t=212.4°C and hrg=1888.6 kJ/kg.

In a parallel flow heat exchanger water enters at 90°C and leaves at 110 degc. while oil of
specific gravity 0.8 enters the exchanger at 280 degC and leaves at 200 degC. The specific heat of
oil is 2kJ/kg-K Determine the loss in availability of the system for 1 kg/s or oil now rate.
Environment is at 300 K.

a closed system, dry saturated steam at 100 bar expands isothermally and reversibly to a
pressure of 10 bar Calculate the heat supplied and work done per kg of steam during the
process

3.(a)The following observations were made during a 30-minute trial of a single-cylinder, four stroke
gas engine having cylinder diameter of 18cm and stroke 24cm, running at 300 rpm
Indicated mean effective pressure 5 bar,total number of explosions 4425, total gas
consumption 2.4m3
calorific value of gas= 19000 kJ/m3
density of gas 1.275 kg/m3, air consumption=32.l m3,density of air 1.29kg/m3, temperature of
exhaust gas 350 degC
specific heat of gases 1.0 kJ/kg-k. mass of cooling water circulated 120 kg. rise in
temperature of cooling water=30 degC. Net load on the brake drum is 38kg and the effective
diameter of the brake drum is lm.
assuming room temperature of27 degC. calculate
(i)Indicated power.
(ii)Brake power.
(iii)indicated thermal efficiency,
mechanical efficiency, and
Brake thermal efficiency,
Also draw up a heat balance sheet on per minute basis as well as percentage basis

(b)the venturi of a simple carburettor has a throat diameter of 20 mm and the fuel orifice has a
diameter of l.12mm. the petrol surface in the float chamber is 6mm below the throat of
venturi Coefficient of discharge for venturi and fuel orifice are 0.85 and 0.78 respectively.
Density of petrol is 750 kg/m3 calculate

(i)the air-fuel ratio for a pressure drop of 0.08 bar.
(ii)the minimum air velocity at which petrol starts flowing into venturi throat. and
(iii)Petrol consumption in kg/hr.
Intake air condition is l bar and 17deg C. For air take C 1.005 kJ/kg-k and C 0.718 kJkg-K.

4.(a)What is the main difference in the construction in the two-stroke and four-stroke engines?
What is scavenging in two stroke engines and how is it carried out? Explain with neat
sketches various methods of scavenging in two-stroke engines. Give also their comparative
merits and demerits.

A 1 meter long 6m diameter cylinder placed in an atmosphere of 30deg C provided with 10
longitudinal straight fins (thermal conductivity k 150 W/m K). the fins are 0.80mm thick
and extend 25cm from the cylinder surface. the heat transfer coefficient between the
cylinder and the atmospheric air is 25W/m2K.the surface temperature of the cylinder is
160 deg C. Calculate
(i)the rate of heat transfer from cylinder to air.
(ii)the percentage increase in heat transfer by providing fins in comparison to cylinder
without fins.
(iii)the temperature at end of fins. and
(iv)the efficiency of tins.

SECTION · 8
5. Answer any four port.
The air condition l7°C and relative humidity 60% is passed over a cooling coil at the rate
of 0.5m3/sec. The temperature of cooling coil is 6 deg C. Calculate the rate of water vapour
condensed assume that the barometric pressure is 1.01325 bar and the air leaving the coil is
at 9 degC and 90% relative humidity. Determine also its by-pass factor.
(b)Explain the phenomena of equimolar counter diffusion. Derive on expression of equimolar
counter diffusion between two gases.

Distinguish with the help of simple sketches the difference between natural circulation and
forced circulation steam generators. State advantages and disadvantages of each. Also
compare them with on be through boilers.

With the help of a neat sketch. explain the working of an absorption refrigeration system
based on solar heating Give the function of each component.
what is the maximum possible thermal coefficient of performance of an absorption
refrigeration if heat is supplied at 90°C. heat rejection is at 40 deg C and refrigeration
effect is to be obtained at

a hydroelectric generating plant there are four similar turbines of total output 200MW.
Each turbine is 90% efficient and runs at 100rpm under a heat of 60m.it is proposed to test
the model of the above turbines in the laboratory where the water available is 400 lit/sec
under a head of 5m. Calculate (i)the scale ratio and the power and speed of the model.
Take efficiency of model
Give also the specific speed of turbines and specify the type of turbine runner.

A hemispherical cavity of 60cm radius is covered by a plate with a hole of 20cm diameter
drilled in its centre. The inner surface of the plate is maintained at 250°C by a heater
embedded in the surface. The surfaces may be assumed to be blank and the hemispheric is
well insulated. Assuming that the energy entering the hole from outside is negligible,
Calculate the temperature of the surface of the hemisphere and the power input to the heater.

(b)explain the effect of area change in subsonic and supersonic flows.
A stream of air flows in a duct of 100 mm diameter at the rate of 60 kg/mm. the stagnation
temperature is 47deg C. At one section of the duct the static pressure is 40 kpa. Calculate the
mach number. velocity and stagnation pressure at its section. Take=1.4 and R=0.287
kJ/kg-k

7.(a)A vapour compression system uses R-22 as a refrigerant and works between in condenser
pressure and evaporator pressure corresponding to saturation temperatures of 44°C and
20 degC respectively. it uses a single acting reciprocating compressor having bore equal to 10
cm and stroke equal to l2cm Speed of the compressor is 2800rpm. the clearance factor for
compressor is 0.04. assume the process of compression to be isentropic. Refrigerant vapour
at the outlet of the evaporator is dry and saturated and liquid at the outlet of the condenser is
sub cooled to a temperature of 35 degC.Assume the behaviour of the superheated vapour to be
that of an ideal gas at constant pressure.
(i)temperature of the superheated vapour atthe exit of compressor.
(ii)volumetric efficiency of the compressor.
(iii)mass flow rate of the refrigerant,
(iv)cooling capacity of refrigeration system in Ions of refrigeration,
power needed to drive the compressor,
(vi)COP of the system,
(vii)Draw the cycle on and p-h diagram.
Use following properties of
<img src='./qimages/1510-7a.jpg'>
Assume average specific heat of superheated vapour and subcooled liquid at 16:885 bar to be
equal to 0.05 and 1.30kj/kg deg C respectively.

(b)Dry bulb temperature td and wet bulb temperature, tw of moist air measured by a sling type
psychrometer are 40 degC and 26 degC respectively. Total pressure p of moist air is 1.02 bar.
for a sling type psychrometer
<img src='./qimages/1510-7b.jpg'>
Assume gas constant for water vapour 461 J/kg-k
determine using only steam tables and properties of dry air
spedfic humidity.
relative humidity,
dew point temperature
specific enthalpy.
degree of saturation
specific volume. and
define thermodynamic wet bulb temperature and discuss the procedure for
determining the thermodynamic wet bulb temperature in the present case.

A centrifugal compressor running at 10.000 rpm delivers 800 m3/mm of free air.The air is
compressed from 100 kpa and 17 degC to a compression ratio of 4 with an isentropic efficiency
of 82%. Impeller has radial blades at outlet and flow velocity of 60m/sec may be assumed
constant throughout, The outer radius of impeller is twice the inner The slip factor is 0.9 At
inlet blade area coefficient is 0.85 Calculate
final temperature of air,
theoretical power required.
diameler of impeller at inlet and
blade angle of impeller at inlet,and
blade angle of diffuser at inlet,outlet,
breadth of impeller at inlet.
Take for air
Cp 1.005
Cy 0.718 KJ/kg-K.
(b)The load has annual duration characteristics as tinder
<img src='./qimages/1510-8b.jpg'>

Two plants a steam turbine plant and a diesel engine plant are being considered. For the
steam plant, coal at Rs.4000 per ton with a calorific value of 25,00 kJ/kg is available
whereas for the diesel plant. oil at Rs.8000 per ton with a calorific value of 40,000 kJ/kg is
available
The performance characteristics of the two plants are
Stream:I 2.5xl0 power4 +0.10 L2)
Diesel 2.5X10 power 4 +0.50 L2)
Where I is input in kJ/hour and L is load in MW The steam plant would require more men at
a total salary of Rs.4,00,000 per annum for operation than the diesel plant Which plant
would be selected if the steam plant cost is Rs.4000 per kW and diesel plant cost is Rs.6000
per kW and no reserve capacity is required? The fixed charges are 12% of each plant.