Reg. No. :

SCAD GROUP OF INSTITUTIONSB.E.,/ B.Tech., DEGREE EXAMINATION, COMMON INTERNAL ASSESSMENT TEST – III

Fifth Semester

Mechanical Engineering ME6502/HEAT AND MASS TRANSFER

(Regulation 2013)

Time: 3 Hours Maximum marks: 100 marksAnswer All The Questions

PART –A ( 10 x 2 =20)

1 Write the Poisson’s equation for heat conduction?2 What do you understand by free and forced convection?3 Define Radiation?4 What is meant by transmissivity?5 State Planck’s distribution law.6 Discuss the radiation characteristics of carbon dioxide and water vapour.7 What is mass transfer?8 Give the examples of mass transfer.9 What are the modes of mass transfer?10 State Fick’s law of diffusion.

PART –B ( 5 x 16 =80)

11 A i A furnace wall consists of three layers. The inner layer of 10cm thickness is made of fire brick (k=1.04W/mK). The intermediate layer of 25cm thickness is made of masonry brick (k=0.69W/mK) followed by a 5cm thick concrete wall (k=1.37W/mK). When the furnace is in continuous operation the inner surface of the furnace is at 800ºC while the outer concrete surface is at 50ºC. Calculate the rate of heat loss per unit area of the wall, the temperature at the interface of the firebrick and masonry brick and the temperature at the interface of the masonry brick and concrete

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OrB i An aluminum pan of 15cm diameter is used to boil water and the water depth at the

time of boiling is 2.5cm.The pan is placed on an electric stove and the heating element raises the temperature of the pan to 110ºC.calculate the power input for boiling and the rate of evaporation. Take Csf=0.0132.

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12 A i Calculate the following for an industrial furnace in the form of a black body and emitting radiation at 2500ºC (1) Monochromatic emissive power at 1.2µm length(2) Wavelength at which the emissive is maximum(3) Maximum emissive power(4) Total emissive power

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OrB i Two parallel plates of size 1 m × 1 m are spaced 0.5 m apart are located in a very large

room , the walls of which are maintained at a temperature of 27ºC .one plate is maintained at a temperature of 900ºC and the other at 400ºC their emissivity are 0.2 and 0.5 respectively . If the plates exchange heat between themselves and surroundings, find the net heat transfer to each plate and to the room. Consider only the plate surfaces facing each other.

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13 A i Determine the view factor (f14) for the figure shown below

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OrB i Calculate the net radiant heat exchange per m2 area for two large parallel plates at

temperature of 427ºC and 27ºC respectively є( hot plate) =0.9 and є( cold plate) =0.6.If the polished aluminum shield is placed between them, find the percentage of reduction in the heat transfer’s (shield) =0.04

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14 A i A gas mixture contains 20% CO2 and 10% H2O by volume. The total pressure is 2atm.The temperature of the gas is 927ºC.The means beam length is 0.3m.Calculate the emissivity of the mixture.

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OrB i A vessel contains a binary mixture of O2 and N2 with partial pressures in the ratio 0.21

and 0.79 at 20ºC.If the total pressure of the mixture is 1.1bar.calculate the followingi) Molar concentrationsii) Mass densitiesiii) Mass fractionsiv) Molar fractions of each species

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15 A i Hydrogen gases at 3bar and 1bar are separated by a plastic membrane having thickness 0.25mm.The binary diffusion co-efficient of hydrogen in the plastic is 9.1 ×10-8m2/s. The solubility of hydrogen in the memberane is 2.1×10-3kg-mole/m3bar.An uniform temperature condition of 20ºC is assumed. Calculate the following

i) Molar concentration of hydrogen on both sidesii) Molar flux of hydrogeniii) Mass flux of hydrogen

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OrB i Ammonia and air are in equimolar counter diffusion in a cylindrical tube of 2.5mm

diameter and 15m length. The total pressure is 1atmosphere and the temperature is 25ºC.One end of the tube is connected to a large reservoir of ammonia and the other end of the tube is open to atmosphere. If the mass diffusivity for the mixture is 0.28 ×10-4m2/sCalculate the following

a) Mass rate of ammonia in kg/hb) Mass rate of air in kg/h

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