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Discussion :: Heat and Mass Transfer

  1. A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

    2. A.

     k₁ k₂
    B.

     (k₁ + k₂)
    C.

     (k₁ + k₂)/ k₁ k₂
    D.

     2 k₁ k₂/ (k₁ + k₂)

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    Answer : Option D

    Explanation :

    conductance = k * (A/l) where A = slab area, l = slab thickness, k = conductivity. The equation for series conductance is : cond(total) = (cond1 * cond2)/(cond1 + cond2) Because the geometry of the slabs is the same: k(total) = 2(k1 * k2)/(k1 + k2)

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