Section A
Q1.
(a) A 4 m × 5 m × 7 m room is heated by the radiator of steam heating system. The steam radiator transfers heat at a rate of 10,000 kJ/h and a 100 W fan is used to distribute the warm air in the room. The heat losses from the room are estimated to be at the rate of 5,000 kJ/h. If the initial temperature of the room air is 10°C, determine how long it will take for the air temperature to rise to 20°C. Assuming constant specific heat of air [cp = 1.007 \text kJ/kg K] and take the value of R = 0.287 kPa m3/kg K for air. Further assume room pressure = 100 kPa.
(b) Using pressure vs crank angle diagrams compare the detonation observed in SI engines with knock of CI engines. Also show that factors which favour knock in SI engines are desirable in CI engines.
(c)
Define the following non-dimensionless numbers and explain their physical significance :
(i) Nusselt number
(ii) Grashof number
(iii) Stanton number
(iv) Prandtl number
(d) On a cold winter night, with an outside ambient temperature of 5°C, a wall of the house loses 30 kJ per minute steadily. If the inner and outer surface temperatures of the wall are maintained at 25°C and 9°C respectively, what would be the energy destruction rate (in Watts) within the wall?
(e) A furnace is shaped like a long equilateral triangular duct where the width of each side is 2 m. Heat is supplied from the base surface, whose emissivity is \varepsilon1 = 0.8, at a rate of 800 W/m2, while the side surfaces, whose emissivities are 0.5, are maintained at 500 K. Neglecting the end effects, determine the temperature of the base surface. Can you treat this geometry as a two surface encloser? Take σ = 5.67 × 10-8 W/m2 K4 and area of base surface = 1 m2 and total area of other side surfaces = 2 m2.
