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GATE Prev Year : Heat-Transfer Test-6
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Question 1
Biot number signifies the ratio of
Question 2
If a foam insulation is added to a 4cm outer diameter pipe as shown in the figure, the critical radius of insulation (in cm) is __________ .
Question 3
A brick wall (k =0.9
) of thickness 0.18 m separates the warm air in a room from the cold ambient air.On a particular winter day the outside air temperature is -5 °C and the room needs to be maintained at 27 °C. The heat transfer coefficient associated with outside air is 
Neglecting the convective resistance of the air inside the room, the heat loss, in
, is
) of thickness 0.18 m separates the warm air in a room from the cold ambient air.On a particular winter day the outside air temperature is -5 °C and the room needs to be maintained at 27 °C. The heat transfer coefficient associated with outside air is Neglecting the convective resistance of the air inside the room, the heat loss, in, isQuestion 4
A hemispherical furnace of 1 m radius has the inner surface (ϵ =1) of its roof maintained at 800 K, while its floor (ϵ = 0.5)is kept at 600 K. Stefan-Boltzmann constant is 5.668×10-8W/m2K4. The net radiative heat transfer (in kW) from the roof to the floor is
Question 5
In a counter flow heat exchanger, for the hot fluid the heat capacity = 2kJ/kg K, mass flow rate = 5 kg/s, inlet temperature = 150 °C, outlet temperature = 100 °C. for the cold fluid, heat capacity = 4 kJ/kg K, mass flow rate = 10 kg/s, inlet temperature = 20 °C. Neglecting heat transfer to the surroundings, the outlet temperature of the cold fluid in °C is
Question 6
A spherical thermocouple junction of diameter 0.706 mm is to be used for the measurement of temperature of a gas stream. The convective heat transfer co-efficient on the bead surface is 400 W/m2 K. Thermo physical properties of thermocouple material are k = 20 W/mK, C = 400 J/kg K and 
=8500kg /m3 . If the thermocouple initially at 30oC is placed in a hot stream of 3000C, the time taken by the bead to reach 2980C, is
=8500kg /m3 . If the thermocouple initially at 30oC is placed in a hot stream of 3000C, the time taken by the bead to reach 2980C, is - 1807 attempts
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