Download AKTU B-Tech 4th Sem 2015-16 NBT 402 Heat Mass Transfer Question Paper

Attempt any three questions from this section. (10×3 = 30)

1. (a) Write briefly the use of Humid Heat. What methods of external heat transfer can increase the intensity of convection cooling.
   (b) Derive the Frendulich's adsoption isotherm. Discuss the various limitations under which it is valid.
   

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   (c) Explain thermal boundary layer concept. Give it's significance.
   (d) Calculate the boundary layer thickness at a distance of 40 cm from the leading edge of a flat plate maintained at 27°C which is exposed to a stream of air at 20°C at a velocity of 20 m/sec.
   Given: Kinematic viscosity for air at the given conditions is 15×10^-6 m²/sec.
   (e) Air at 27°C flows over a flat plate at a velocity of 2 m/s. What length of the plate would be turbulent?
   Take the critical Reynolds number for turbulence as 5×10⁵.

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2. (a) Differentiate between a distillation for one to all components. Write the uses.
   (b) Deduce equation Mass transfer coefficient km, by the dimensional analysis. Explain the significance of various dimensionless groups involved in the equation. (3)
   (c) In an open pan, water is evaporated at 25°C into air flowing (cross-ventilation) parallel to the surface. The distance moved by the air is 3meter, completely une-saturated.

Section-C

Attempt any one question from this section. (20×1 = 20)

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1. (a) Differentiate between molecular diffusion and eddy diffusion. Molecular diffusion is a result of random movement of individual molecules, but eddy diffusion is caused by the turbulent motion of large groups of molecules.
   (b) Air at 30°C (DB=0.257 cm²/s) is blown over the top of a water filled vertical tube. The distance from the water surface to the top is 15cm. Determine the rate of evaporation if the diameter of the tube is 1.5 cm. and total pressure is 1 standard atmosphere. The saturation pressure of the water at 30°C is 31.82mm.
2. What is HETP? Derive the relation between HETP and Murphee plate efficiency? (2)

Section-D

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