,.BCHANICAL INGINB.IUNG



·11


SECnONA
Answer any three of the following parts (Answer 10 each p<rt should not exceed 200 words) 20x3=60
Using the concept of Second Law of Thermo dynamics show that it iS impossible to reach absolute zero temperature.
(b)Using Maxwell's reLtions, show that for a pure substance, <img src='./qimages/1131-1b.jpg'> where beta is the coefficient of cubical expansion, K is coefficent of compressibility and Cp, Cv are specific heats at constant pressure and constant volume respectively.

(c)Justify in brief the following statements advancing the spark timing, the possibility to knock in a S.I engine increases,
(ii)Willans line method for estimating frictional power can be used only in case of unthrottled engines.
(iii)Exhaust hydro carbon emissions increase with increase in surface to volume ratio of an engine. (iv)Carbon monoxide emissions are low for fuel lean miXtures

An I.C engine fuel has the following composition: C H2 o2= and rest N2. Determine the chemically correct air-fuel ratio. If 40% excess air is supplied, find the percentage of dry products of combustion by volume.
A reversible heat engine operating between thermal reversible reservoir at 800 0C and 30 0C drives a reversible refrigerator which refrigerates a space at -15OC and delivers heat to a thermal reservoir at 30 OC. The heat input to the heat engine is 1900 kJ and there is a net work output from the combined plant (heat engine and refrigerator) of 290 kJ Determine the heat transfer to the 30 0C thermal reservoir 30

kg 0f air at 600 K and 5.0 bar is enclosed in a closed system
(i)Determine the availability of the system if the surrounding pressure and temperature are 10bar and 300 K.
If the air is cooled at constant pressure to the atmospheric condition, determine the availability and effectiveness For air take, Cp 1005 kJ/kg Cv 0.718 kJ/kg K and R 0287 kJ/kg K.

A six-cylinder, 4-stroke petrol engine has a swept volume of 30 liters with a compressiOn ratio of 95 Brake output torque is 205 N-m at 3600 r.p.m Air enters at 85 N/m2 and 60 0C. The mechanical efficiency of the engine iS 85% and air-fuel ratio is 15:1 The heating value of fuel is 44,000 kJ/kg and the combustion efficiency is 97% Calculate:
Rate of fuel flow
Brake thermal efficiency
Indicated thermal efficiency
Volumetric efficiency
rake specific fuel consumption

Explain the various stages of combustion in a diesel engine. Discuss the effect of volatility 0f gasoline on engine starting, acceleration and vapour lock.
A 4-stroke petrol engine has a swept volume of 20 liters and is running at 4000 r.p.m The volumetric efficiency at this speed is 0.75 and the air-fuel ratio is 14:1 The venturi throat diameter of the carburettor fitted to the engine is 30 mm. Estimate the air velocity at the throat If the discharge coefficient for air is 0.9 The ambient conditions are pressure 10 bar, temperature 20 0C Calculate the diameter of the fuel Jet If the fuel density is 760 kg/m3 For air C 1005 kJ/kg K and R287l/kg K. Assume Cdf= 1.0

(b)Explain the necessary modifications that have to be made to convert a bus running on diesel fuel to Compressed natural Gas (CNG).
(c)Discuss the advantages of using multi-point fuel injection system in place of conventional carburettor.


SElmON B
Answer any three of the following 20x3=60

5.(a)illustrate, with neat sketches, the temperature profile for hot and cold fluids as a function of the distance along the path for (i)parallel f1ow heat exchangers,
(ii)counter flow heat exchangers, condenser and gas-heated boiler
(iv)Show that the COP of a cascade refrigeration system is
<img src='./qimages/1131-5b.jpg'> where COP1 and COP2 and COP's of low temperature and high temperature Side respectively.

air compressor has eight stages of equal pressure ratio 1.35 The flow rate through the compressor and its overall efficiency are 50kg/s and 82 percent respectively. If the condition of air at entry are l.0 bar and 40 OC, determine the state of air at the compressor exit, (ii)polytropic or small stage efficiency, efficiency of each stage, (iv)power required to drive the compressor assuming overall efficiency of the drive as 90% TakeCp=1.005kJ/kg K and gaama =1.4
central power station has annual factors as follows Load factor 0.6, Capacity factor 0.4 and Use factor 0.45. The power station on has a maximum demand of 15 MW. Determine:
(i)Annual energy production (ii)Reserve capacity over and above peak load (iii)Hours per year the plant is not in service

Two large parallel plates at T1 1000 K and =750 K have emissivities epsilon1 0.5 and epsilon2=0.8 respectively. A radiation shield haVing an emissivity of epsilon3 0.12 on one Side and an emissivity of epsilon3,2 0.08 on the other side is placed between the plates. Calculate the heat transfer rate by radiation per square meter with and without radiation shield
Take sigma= 5.67K x 10power-8W/m2 K4.
With usual notations, develop an expression for the efficiency of a fin of uniform cross­section when the heat loss from the tip lS considered negligible.

7.(a)An air conditioning plant is designed to maintain a room at a condition of 20° C dry bulb temperature and specific humidity 0.0079 kg/kg dry air when the outside condition is 30° C dry bulb temperature and 40% saturation. The corresponding heat gains are 18000W (sensible) and 3600W (latent). The supply air contains one-third outside air by mass and the supply temperature is to be 15° C dry bulb temperature. The plant consists of mixing chamber for fresh and recalculated air, an air washer with chilled spray water with an efficiency of an after heater battery and a supply fan. Neglecting temperature changes in fan and ducting, Calculate
the mass flow rate of supply air necessary;
(ii)the specific humidity of the supply air;
the cooling load on the washer;
the heating load on the after heater.

Explain the working principle of Electrostatic Precipitator (ESP). Discuss the factors which affect its efficiency.
A small compressor has the following data Air flow rate 1.5778 kg/s
pressure 16
Rotational speed 54,000 rpm
Efficiency 85%
State of air at entry, Po1 1.008 bar; To1 300 K
Cp for air 1009 kJ/kg K

(i)Calculate the power required to drive this compressor.
geometrically similar compressor of three times the Size is constructed Determine, for this compressor
I mass flow rate,
II Pressure ratio,
III speed and
IV the power required

Assume same entry conditions and efficiency for the two compressors and also assume kinematics and dynamic Similarities between the two machines.
Explain clearly what do you understand by Fanno flow. Show its plot on h diagram and give its characteristics. Air flows in an insulated duct with a Mach number of 0.2. The initial temperature and pressure are 290 K and 20 bar respectively.
Determine:
(i)the pressure and temperature at a section of the duct where the Mach number is 0.8.
(ii)the distance between these two points if the duct diameter is 10cm and friction factor
is 0.004
what will be the maximum length of the duct to avoid choking?
Use the following table
<img src='./qimages/1131-8b3.jpg'>