Help The figure shows (in cross section) a wall that consists of four layers. Th

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The figure shows (in cross section) a wall that consists of four layers. The thermal conductivities are k1 = 0.060 W/m = K, k3 = 0.050 W/m = K and k4 = 0.100 W/m = K (k2 is not known). The layer thicknesses are L1 = 1.8 cm, L3 = 1.6 cm and L4 = 1.2 cm. The hottest temperature on the extreme left is 30 degree C while the coldest is on the extreme right at -10 degree C. If we number the temperatures at the interfaces between different materials as 12, 23, 34, then T12 = 25 degree C. What is T34? (deg) Tries 2/7 Previous Tries What is T23? Tries 0/7 That is the ratio of k2 to L2? (enter no units) Tries 0/7

Explanation / Answer

Heat flux is constant throughout.

For constant flux, kA(T2-T1)/ALshould be constant. Since A is constant, k(T2-T1)/L should be constant.

1)Flux in L1=0.06*5/0.018=16.67

Matching flux in L4,

0.1*(T34+10)/0.012=16.67

T34=-8C

2)Similarly in L3,

0.05*(T23+8)/0.016=16.67

T23=-2.67C

3)k2/L2*(25+2.67)=60.24

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