MCCHANICAL CNGINCCAING

Answer any three of the folloWlng­
(a)With the help of Maxwell's relation of thermo dynamics, prove that Joule-Thomson coefficient, mewJ of a gas is given by the following, expressiOn: <img src='./qimages/1135-1a.jpg'>

08 kg metal bar kept initia11y at 1500°C is removed suddenly 110m an oven and quenched by immersing it initia11y a closed tank containing 12 kg of water kept initia11y at 400°C. The metal and water can be modeled as incompressible and the specific heat of water and metal are 4.18kJ/kg-K and 05 kJ/kg-K respectively The heat transfer from the tank may be neglected Work out the folloWIng
(i)Draw the system and system boundary and list assumptions made
The final temperature of metal bar and water
The entropy produced

(c)Draw the characteristic curves between the following parameters for an SI engine
air standard efficiency vs Compression ratio
(ii)Relative efficiency vs air-fuel ratio
Brake thermal efficiency vs Load
(iv)Volumetric efficiency vs Engine speed
(v)Peak-cycle temperature vs Equivalence ratio

Discuss Significant points in each case in the light of deSign parameters.

rectangular cooper plate 10cm x50cm, having a mass of 1 kg and at a temperature of 100°C, is suspended vertically in still air at 20°C so that 50 cm Side is vertical. Neglecting radiation effect, find heat transfer coefficient due to natural convection and initial rate of cooling of the plate m °C/minute Take Cp for copper= 383 J/kg-K The properties of air at mean temperature 60°C are
1.06 kg/m3, 18.97 x 10 power-6 m2/s
Pr=0.696, Cp 1.005 kJ/kg-K
k=28.96xl0 power
mew=20.1x 10 power-6 N-s/m2

You may use the following correlation
Nu=0.1 (CrPr)1/3
Will the result change if 10cm Side is vertical? Why?

2.(a)A counter flow heat exchanger acting as a recuperator, of gas turbine receives compressed air operating at steady state at 650K, 12 bars and exits at850K, 11.6 bars. Hot combustion from the exhaust of gas turbine enters as a separate stream at 1000 1.1 bars and comes out at 1 bar. The mass flow rate of each stream is 200 kg/s. The heat transfer from the outer surface of the heat exchanger to surroundings may be neglected The changes in kinetic and potential energy are negligible. Take To 228K and P0 1 bar. Assume ideal gas model for combustion gas. Work out the following:

(i)Draw the system and show the temperature distribution for each stream
(ii)The exit temperature of combustion gas
The net change in the flow energy rate from inlet to outlet for each stream
The energy distribution rate
(v)Comment on the results

During summer to cool water for drinking purpose, 2 kg of ice at in an insulated container which is subjected to atmospheric pressure of 1 bar. Assume specific heat of ice is 2.093 kJ/kg-K and 1atent heat of ice as 335 kJ/kg Work out the following
(i)Draw the system and show the process on T-Q for both ice and water.
(ii)The temperature of the miXture
The change of entropy for instantaneous process.

3.(a)Derive an expression for air-fuel ratio delivered by a Simple carburetor, neglecting the effect of compressibility Discuss the limitations of Simple carburetor. What are the modifications incorporated for its use in automotive vehicles?

four-stroke petrol engine develops 30 kW at 2600 r.p.m. The compression ratio of the engine is 8 and its fuel consumption is 84 kg/h with calorific value of 44 MJ/kg. The air consumption of the engine as measured by means of a sharp edge orifice is 2m3 per mm. If the piston displacement volume is 2 liters, calculate
Volumetric efficiency
(ii)Air-fuel ratio
(iii)Brake mean effective pressure
Brake thermal efficiency
(v)Relative efficiency

The ambient temperature of air can be taken as 27oc, R for air as 287 J/kg-K and y 14.
The barometer reads 755 mm of mercury
4.(a)A counterfoil, concentric tubes heat exchanger is designed to heat water from 20 0c to 80°c using hot oil flowing through the annulus. The oil temperature gets reduced from 160 0c to 140°C. The nominal diameter of the inner tube is 20 mm and the corresponding overall heat transfer coefficient is 500 W/m2-K. The heat transfer rate from the oil is 3000 watts Determine the length of the exchanger. Because of fouling after some days the outlet temperature of water reduced to 65°C for the same flow rates and same inlet conditions. Determine the outlet temperature of oil, the fouling factor and the new heat transfer rate. Sketch the heat exchanger arrangement and the temperature profiles
(b)The temperature of a gas flowing through a pipe was measured by a mercury-in-glass thermometer, dipped in an oil-filled steel tube welded radially to the pipeline. The thermometer indicates a temperature lower than the gas temperature. How large is the error in the temperature measurement If the thermometer reads 85°C and the temperature of the pipe wall is 40°C? The steel tube lS 125 mm long and has a 15 mm thick wall. The thermal conductivity of this tube materials 56W/m-K and the local heat transfer co efficient between the gas and the tube is 23-5W/m2-K In what way the thermometric error can be reduced?
SElmON B
Write any three of the following­
5.(a)For flow through a compressor cascade, show that lift and drag coefficients are given by the following expressions <img src='./qimages/1135-5a.jpg'>
ammonia ice plant operates on Simple saturation cycle at the following/temperatures Condensing temperature =40°C Evaporation temperature -15°C It produces 10 tonnes of ice per day at from water at 30°C. If the COP of the system is determine:
(i)Capacity of the refrigeration plant in tones of refrigeration
(ii)Mass flow rate 0f the refrigerant, kg/mm
(iii)Isentropic discharge enthalpy kJ/kg
take:
Cp 4.187 kJ/kg-K for water 2000 kJ/kg-K for ice
Latent heat of fusion of ice 335 kJ/kg
Sensible enthalpy at 40°C 600 kJ/kg
Enthalpy of sat vapour at -15°C 1675 kJ/kg

(c)Explain the concept of effective temperature used in air-conditioning practice Discuss the parameters on which it depends
superheater is to be designed using metallic coils (heat flux 150 kW/m2) of inside diameter 50 mm and wall thickness 5 mm. The steam leaving the superheater coils is at 60 bars, 500°C and flows at a velocity of 10 m/s. if the steam mass flow rate is 90 find the number and length of coils For steam at 60 bars, take the following values-dry saturated steam h 2784.3 kJ/kg, at 500°C superheated steam temperature 3422.2 kJ/kg and specific volume Vsup 0.05665 m3/kg. The steam enters the super heater as city and saturated.
AVCC refrigerating machine using R-12 refrigerant produces 10 tonnes of refrigeration at 10°C when the ambient is at 35°C. A temperature difference of minimum 5°C is required at the evaporator and condenser for spontaneous heat transfer The refrigerant is dry saturated at the outlet and to the inlet of compressor The adiabatic efficiency of the compressor is 90%. The enthalpy at the end of isentropic compression is estimated to be 370 kJ/kg Determine:
(i)COP
(ii)Power of the compressor
Capacity of the condenser
Represent the cycle on hand drawn T-S plane and show the refrigerating effect, compressor work and condenser capacity on the same. Properties of R-12 are
<img src='./qimages/1135-6a.jpg'>

(b)Explain the procedure for cooling load estimation for comfort air-conditioning in the summer.
Also explain the concept of different Sensible Heat Factors (SHFs) and importance in designing an air-conditioning system.

7.(a)Explain the concept of types of Similarities between model and prototype What do you mean by distorted model? What are its advantages? it is proposed to design a ship The proposed ship (prototype) is having a length of 150 m and a wetted surface area of 2000 m2 with a speed of 40 km/h. A model of 1:20 is to be tested in the laboratory at a velocity corresponding to the wave resistance The total drag of the model is 50 N. Determine the following:
(i)Wave resistance drag of the model
(ii)Wave resistance drag of the prototype
(iii)Friction drag of the prototype
Give,
Fnction drag,Rf=1/2CD row AV2
where
A Wetted surface area
CD Average friction drag coefficient
<img src='./qimages/1135-7a.jpg'>

define Rayleigh flow give one example of rayleigh flow show that the mach numbers at the maximum enthalpy and maximum entropy points on the rayleigh line are 1/root V and 1.0 respectively.
8.(a)An axial flow compresses the air up to overall stagnation pressure 10 bars with overall stagnation isentropic efficiency 0f 88%. The inlet stagnation pressure and temperature are 1 bar and 300 K. The mean blade speed lS 200 m/s. The degree of reaction is 0.5 at the mean radius with air angles of 30° and 10° at rotor inlet and outlet with axial direction respectively. The work done factor is 088. The hub-tip ratio is 0.4 The mass flow rate is 50 kg/s Work out the following:

(i)Draw the inlet and outlet velocity triangles and show the compression process on T-S diagram
(ii)The stagnation polytrophic efficiency
(iii)The number of stages
(iv)The blade height in first stage of the compressor
A nuclear power plantlS set up With a generating capacity of 10 MW, the capital cost being Ks 80,000 per kW. It meets the following demands:
(i)Service sector: Total load 400 kW at 30% load factor
(ii)Cottage industries: Total load 36 MW at 50% load factor
Household: Total loads 6 MW at 20% load factor. The operative cost of the plant is Rs.30,00,000 per annum and annual rate of interest and depreciation is 10%. If as per promotion policy of government, a flat rate is to be charged from all categories of consumers calculate the overall production cost. If the power is sold at the rate of production cost estimate the loss/gain each sector consumer will get per kWh for power consumed.