JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II HEAT AND MASS TRANSFER Previous Question Paper (December – 2017 - R13)

A mild steel tank of wall thickness 10 mm contains water at 90°C. The thermal conductivity of mild steel is 50 W/m°C, and the heat transfer coefficient for inside and outside of the tank area are 2800 and 11 W/m²°C, respectively. If the atmospheric temperature is 20°C, calculate a) the rate of heat loss per m² of the tank surface area. b) The temperature of the outside surface tank.

Air at 25°C flows past a flat plate at 2.5 m/s. the plate measures 600 mm × 300 mm and is maintained at a uniform temperature at 95°C. Calculate the heat loss from the plate, if the air flows parallel to the 600 mm side. How this heat loss would be affected if the flow of air is made parallel to the 300 mm side.

The sun emits maximum radiation at λ = 0.52 μ. Assuming the sun to be a blackbody, calculate the surface temperature of the sun. Also calculate the monochromatic emissive power of the sun’s surface.

A 70 mm thick metal plate with a circular hole of 35 mm diameter along the thickness is maintained at a uniform temperature 250°C. Find the loss of energy to the surroundings at 27°C, assuming the two ends of the hole to be as parallel discs and the metallic surfaces and surroundings have black body characteristics.

Hot chemical products (Cph = 2.5 kJ/kg K) at 600°C and at a flow rate of 30 kg/s are used to heat cold chemical products (Cp = 4.2 kJ/kg K) at 200°C and at a flow rate 20 kg/s in a parallel flow heat exchanger. The total heat transfer is 50 m² and the overall heat transfer coefficient may be taken as 1500 W/m² K. calculate the outlet temperatures of the hot and cold chemical products.

Estimate the diffusion rate of water from the bottom of a tube of 10 mm diameter and 15 cm long into dry air 25°C. Take the diffusion coefficient of water through air as 0.235 × 10^-4 m²/s.