A wall is composed of two materials. Material 1 has a thickness of 4.81 cm and a

Question

A wall is composed of two materials.  Material 1 has a thickness of 4.81 cm and a thermal conductivity of 0.1 while material 2 has a thickness of 5.13 cm and a conductivity of 1.  If the temperature difference inside to outside is 25 Co and the wall has an area of 10 m2, what is the energy loss per second to the nearest watt?

In the previous problem, if the energy loss is 553 watts, the material 2 has a thickness of 5.87 cm and the inside temperature is 25.8 oC, what is the temperature of the interface to the nearest tenth of a degree Celsius?

I did the first problem, but I can't figure out the second. The answer should be 4, not sure how to get there. Thank you.

A wall is composed of two materials. Material 1 has a thickness of 4.81 cm and a thermal conductivity of 0.1 while material 2 has a thickness of 5.13 cm and a conductivity of 1. If the temperature difference inside to outside is 25 Co and the wall has an area of 10 m2, what is the energy loss per second to the nearest watt? In the previous problem, if the energy loss is 553 watts, the material 2 has a thickness of 5.87 cm and the inside temperature is 25.8 degree C, what is the temperature of the interface to the nearest tenth of a degree Celsius? I did the first problem, but I can't figure out the second. The answer should be 4, not sure how to get there.

Explanation / Answer

thermal resistacne = (0.0481 / (0.1 * 10 ) ) + (0.0513 / ( 1 * 10 ) ) = 0.05323

temp difference = 25

so.. heat loss = 25 / 0.05323 = 469.659966 W = 470 W ( approx )

b) Let the temperture at teh interface be T ...
so.. thermal resistance of material 1 = (0.0481 / (0.1 * 10 ) ) = 0.0481

so... 553 = ( 25.8 - T ) / 0.0481
so.. T = -0.7993 C

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