In the figure below, it is known that the thermal conductivity of k1 = 0.06 W/mK, k3 = 0.04 W/mK, and k4 = 0.12 W/mK. The thickness of the layers is L1 = 1.50 cm, L3 = 2.8 cm, and L4 = 3.50 cm. Known temperatures T1 = 30°C, T12 = 25°C, and T4 = -10°C. Energy transfer through walls is constant. How much is T34?

A brass plug is to be placed in a ring made of iron. At 20°C, the diameter of the plug is 8.755 cm and that of the inside of the ring is 8.741 cm. They must both be brought to what common temperature in order to fit?  Given : Required : Illustration:  Solution:  final answer:

3-52 A 4-m-high and 6-m-wide wall consists of a long 18-cm X 30-cm cross section of horizontal bricks (k = 0.72 W/m . °C) separated by 3-cm-thick plaster layers (k = 0.22 W/m . °C). There are also 2-cm-thick plaster layers on each side of the wall, and a 2-cm-thick rigid foam (k = 0.026 W/m - °C) on the inner side of the wall. The indoor and the outdoor temperatures are 22°C and −4°C, and the convec- tion heat transfer coefficients on the inner and the outer sides are h₁ = 10 W/m² . °℃ and h₂ = 20 W/m². °C, respectively. Assuming one-dimensional heat transfer and disregarding radi- ation, determine the rate of heat transfer through the wall. Foam Plaster Brick 1+₂+18 2 FIGURE P3-52 18 cm N 1.5 cm 30 cm 1.5 cm