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03000ME302052002

and 0.5 respectively. If a radiation shield of emissivity 0.3 is placed in between
them, calculate the percentage reduction in heat transfer.

State the law governing mass diffusion and name it. Explain all the terms
involved with units.

Gaseous hydrogen is stored at elevated pressure in a steel container of 16 mm wall
thickness. The molar concentration of hydrogen in steel at the inner surface is 1.2
kg mol/m*, while the concentration of hydrogen in steel at the outer surface is
zero. The binary diffusion coefficient for hydrogen in steel is 0.25 x 10 7 m’/s.
What is the mass flux of hydrogen through the steel?

Define equimolar counter diffusion. In a binary diffusion process of components
A and 8, show that Dag = Dga for an equimolar counter diffusion.

Discuss Reynolds analogy for heat transfer and mass transfer.

Explain Lewis number and Schmidt number. How are they related to Prandtl
number?

Air at 20°C flows through a pipe of 25 mm diameter with a velocity of 5 m/s. The
inner surface of the tube is constantly wetted with water so as to maintain a thin
water film on the surface. The mass diffusivity of water vapour in air is 0.25 x 10”
m’/s. Calculate the mass transfer coefficient of water vapour in air. Use properties

of dry air at 20°C.

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