Determine the conduction heat transfer through an air layer held between two 10 mm × 10 mm parallel aluminum plates. The plates are at temperatures Ts,1 = 305 K and   Ts, 2 = 295 K, respectively, and the air is at atmospheric pressure. Determine the conduction heat rate for plate spacings of L = 0.8 mm, L = 1.2 μm, and L = 20 nm. Assume a thermal accommodation coefficient of αt = 0.92. For air, the molecular weight is 28.97 kg/kmol and the molecular diameter is 0.372 nm. Determine the conduction heat rate for L= 0.8 mm, in W. q1, Determine the conduction heat rate for L= 1.2 μm, in W q2, and Determine the conduction heat rate for L= 20 nm, in W q3.

Respuesta :

Answer:

A) 0.0325 W

B)21.667 W

C)1300 W

Explanation:

A)

THERMAL CONDUCTIVITY OF AIR IS K 0.026 w/m-k

Thermal resistance is given as

[tex]Rth = \frac{L}{KA}[/tex]

and [tex]\Delta T = Q_1 \times Rth[/tex]

therefore  we have

[tex]305 - 295 = q_1 \times \frac{0.8\times 10^{-3}}{0.026\times 10\times 10 \times 10^{-6}}[/tex]

[tex]q_1 = 0.0325 w[/tex]

B) WHEN [tex]L = 1.2 \mu m[/tex]

therefore we have

[tex]305 - 295 = q_2 \times \frac{1.2\times 10^{-6}}{0.026\times 10\times 10 \times 10^{-6}}[/tex]

[tex]q_2 = 21.667 w[/tex]

C) When L is 20 nm

therefore we have[tex]305 - 295 = q_1 \times \frac{20\times 10^{-9}}{0.026\times 10\times 10 \times 10^{-6}}[/tex]

[tex]q_1 = 1300 w[/tex]

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