JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II HEAT AND MASS TRANSFER Previous Question Paper (December - 2018 - R13)

What are the conditions for better heat transfer? Explain.

How does the thermal conductivity vary with temperature?

Discuss the reflectivity and transimissivity of radiation.

Write the equation for thermal resistivity of composite wall.

How to take into the account of negligible resistance for transient heat conduction.

Differentiate between black body and grey body radiation.

What are different non dimensional numbers involved for free convection? Explain.

Explain the importance of LMTD of heat exchanger.

State and explain Fick’s law of mass transfer.

Explain the importance of mass transfer process.

What do you understand from the thermal resistance? On what parameters does this resistance depend?

A thin metallic plate is insulated at the back surface and is exposed to the sun at the front surface. The front surface absorbs the solar radiation at 900 W/m² and dissipates it mainly by convection to the ambient air at 30^oC. If the heat transfer coefficient between the plate and the air is 15 W/m²K, then what is the temperature of the plate?

Distinguish the heat transfer by conduction and convection.

Hot gases at 980^oC flow past the upper surface on the blade of a gas turbine the lower surface is cooled by air bled off the compressor. The convective heat transfer coefficients at the upper and lower surface are estimated to be 2830 and 1415 W/m² K respectively. The blade material has a thermal conductivity of 11.6 W/mK. If the temperature of blade is limited to 870^oC, work out the temperature of the cooling air. Consider the blade as a flat plate 0.115 cm thick and presume that steady state conditions have been reached.

Define emissivity of a surface. Explain spectral, directional, hemispherical and total emissivity.

In a vertical cylindrical furnace 0.6 m in diameter and 1 m high, the upper surface with emissivity of 0.8 is maintained at 1000 K and the lower surface is 0.7 is maintained at 700 K. Assuming the cylindrical wall as a refractory no flux surface, estimate the net radiative energy transfer between the upper and lower surfaces.

What is the shape factor with respect to itself if the surface is concave, convex or flat?

A room measuring 3m×4m×2m high has the ceiling covered with heating panels. Under steady state conditions, the ceiling is at a temperature of 50^oC and the walls and floor at a temperature of 20^oC. Assuming all the surfaces have an absorptivity of unity, calculate the net radiant heat transfer from the ceiling.

Annular aluminum (k = 200 W/m-K) fins are attached to a tube of OD 5 cm with a thickness of 2 mm. The fins have a thickness of 2 mm and a radial length of 15 mm. The base surface temperature is maintained at 200^oC. The temperature and the heat transfer coefficient of the adjoining fluid are 30^oC and 50 W/m²-K respectively. Find the fin efficiency, the heat loss per metre length of the tube and the effectiveness of the fin.

Differentiate between free and forced convection heat transfer.

How to consider lumped mass for the transient heat transfer? Explain its significance.

An aluminium plate with thermal conductivity 160 W/mK, density 2790 kg/m³, specific heat 0.88 kJ/kg K of thickness 30 mm and at a uniform temperature of 225^oC is suddenly quenched at time t = 0 in a well stirred fluid at a constant temperature of 25^oC. The heat transfer coefficient between the plate and the fluid is 320 W/m²K. Then determine the time required for the centre of the plate to reach 50^oC.

What do you mean by thermal boundary layer? How does the ratio δ/δ_t vary with the Prandtle Number.

Atmospheric air at 300 K flows with a velocity of 5 m/s along a flat plate 1 m long. The plate has width of 0.5 m and the total drag force on the plate is 0.0018 N. Estimate the average heat transfer coefficient for flow of air over the plate.

How to consider the fouling factors for the parallel flow and counter flow heat exchangers? Explain.

The flow rates of hot and cold water streams running through a parallel flow heat exchanger are 0.2 kg/sec and 0.5 kg/sec respectively. The inlet temperatures on the hot and cold side are 75^oC and 20^oC respectively. The exit temperature of hot water is 45^oC. If the individual heat transfer coefficients on both sides are 650 W/m²K, calculate area of heat exchanger.

Explain the law of diffusion to consider the mass transfer process and derive the corresponding equation.

Discuss the importance of Reynolds analogy for studying the mass transfer coefficient.

What are the nondimensional terms involved during the mass transfer process? Explain their significance.

What is the anology between heat transfer and mass transfer? Explain along with the practical applications.