An electric kitchen range has a total wall area of 1.40 m2 and is insulated with

Question

An electric kitchen range has a total wall area of 1.40 m2 and is insulated with a layer of fiberglass 4.0 cm thick. The inside surface of the fiberglass has a temperature of 175 C and its outside surface is at 35 C. The fiberglass has a thermal conductivity of 0.040 W/(mK).

Part A

What is the heat current through the insulation, assuming it may be treated as a flat slab with an area of 1.40 m2?

Express your answer using two significant figures.

Part B

What electric-power input to the heating element is required to maintain this temperature?

Express your answer using two significant figures.

Explanation / Answer

Using the thermal conduction equation .. H/t = k.A.{d/dL}

H/t = (0.04 W/mºC)(1.40 m²){(175 - 35 ºC) / 0.04 m} .. .. H/t = 196.0 W (through insulation)

To maintain the temperature inside the heating element must replace the conduction loss
ie heater power = 196.0 W (assuming no other losses ie infrared radiation and ventilation)

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