F5 Physics Temperature

2012-05-05 5:18 am

The walls of a container used for keeping objects cool consist of two thickness of wood 0.5cm thick separated by a space 1 cm wide packed with a poorly conducting material. Calculate the rate of flow of heat per unit area into the container if the temperature difference between the internal and external surfaces is 20°C.
(Given that thermal conductivity of wood = 0.24Wm^-1K^-1 and
thermal conductivity of poorly conducting material = 0.024Wm^-1K^-1)

Give a me a guide. Thank you.

回答 (1)

天同

2012-05-05 6:38 am

✔ 最佳答案

Thermal resistivity of wood = 1/0.24 m.K/w = 4.167 m.K/w
Thermal resistivity of poorly conducting material = 1/0.024 m.K/w = 41.67 m.K/w

Hence, thermal resistance per unit area of wood = 4.167 x 0.01 K/w = 0.4167 K/w
Thermal resistance per unit area of poorly conducting material
= 4.167 x 0.01 K/w = 0.04167 m/w
Total resistance per unit area = (0.4167 + 0.04167 ) K/w = 0.4584 K/w
Total conductance per unit area = 1/0.4584 w/K = 2.182 w/K
Therefore, heat flow rate per unit area = 2.182 x 20 w = 43.6 w

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