9. A hollow aluminum sphere, with an electrical heater in the center, is used in tests to determine the thermal conductivity of insulating materials. The inner and outer radii of the sphere are o.18 and o.21 m, respectively, and testing is done under steady-state conditions with the inner surface of the aluminum maintained at 250°C. In a particular test, a spherical shell of insulation is cast on the outer surface of the sphere to a thickness of o.15 m. The system is in a room for which the air temperature is 20°C and the convection coefficient at the outer surface of the insulation is 30 W/m2. K. If 80 W are dissipated by the heater under steady-state conditions, what is the thermal conductivity of the insulation?
9. A hollow aluminum sphere, with an electrical heater in the center, is used in tests to determine the thermal conductivity of insulating materials. The inner and outer radii of the sphere are o.18 and o.21 m, respectively, and testing is done under steady-state conditions with the inner surface of the aluminum maintained at 250°C. In a particular test, a spherical shell of insulation is cast on the outer surface of the sphere to a thickness of o.15 m. The system is in a room for which the air temperature is 20°C and the convection coefficient at the outer surface of the insulation is 30 W/m2. K. If 80 W are dissipated by the heater under steady-state conditions, what is the thermal conductivity of the insulation?
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
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Transcribed Image Text:9. A hollow aluminum sphere, with an electrical heater in the center, is used in tests to
determine the thermal conductivity of insulating materials. The inner and outer radii of
the sphere are o.18 and o.21 m, respectively, and testing is done under steady-state
conditions with the inner surface of the aluminum maintained at 250°C. In a particular
test, a spherical shell of insulation is cast on the outer surface of the sphere to a
thickness of o.15 m. The system is in a room for which the air temperature is 20°C and
the convection coefficient at the outer surface of the insulation is 30 W/m2. K. If 80 W
are dissipated by the heater under steady-state conditions, what is the thermal
conductivity of the insulation?
w w
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