An electric resistance space heater is designed such that it resembles a rectangular box 50 cm high, 80 cm long, and 15 cm wide filled with 45 kg of oil. The heater is to be placed against a wall, and thus heat transfer from its back surface is negligible. The surface temperature of the heater is not to exceed 75°C in a room at 25°C for safety considerations. Disregarding heat transfer from the bottom and top surfaces of the heater in anticipation that the top surface will be used as a shelf, determine the power rating of the heater in W. Take the emissivity of the outer surface of the heater to be 0.8 and the average temperature of the ceiling and wall surfaces to be the same as the room air temperature. Also, determine how long it will take for the heater to reach steady operation when it is first turned on (i.e., for the oil temperature to rise from 25°C to 75°C). State your assumptions in the calculations.
An electric resistance space heater is designed such
that it resembles a rectangular box 50 cm high, 80 cm long,
and 15 cm wide filled with 45 kg of oil. The heater is to be
placed against a wall, and thus heat transfer from its back
surface is negligible. The surface temperature of the heater
is not to exceed 75°C in a room at 25°C for safety considerations.
Disregarding heat transfer from the bottom and
top surfaces of the heater in anticipation that the top surface
will be used as a shelf, determine the power rating of the
heater in W. Take the emissivity of the outer surface of the
heater to be 0.8 and the average temperature of the ceiling
and wall surfaces to be the same as the room air temperature.
Also, determine how long it will take for the heater to
reach steady operation when it is first turned on (i.e., for
the oil temperature to rise from 25°C to 75°C). State your
assumptions in the calculations.
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