Conduction of heat or heat flow depends on the temperature difference, cross section, separation, and a constant of the material according to

The units of H are energy per time or Joule/sec which is a watt. The thermal conductivity, k, has units of W/m-K.

17-10 Calculate the heat flow through a wooden door of area 2.0 cm² and thickness 5.0 cm when the temperature difference is20 K. The k for wood is0.10 W/m-K.

Solution: The heat flow is

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17-11 Two rods with cross sections of4.0 cm², one copper of 1.2 m length, and the other steel of 1.0 m length, are connected together with their opposite ends held at 100^o C and 0^o C as shown. What is the heat flow and the temperature of the junction at equilibrium? (k_cu = 380 W/m-C^o and k_st = 50 W/m-C^o .

Solution: The key to this problem is that the heat flow in the two rods must be the same. If the heat flow in the copper is greater than the heat flow in the steel then the joint will get hot. This does not happen so the heat flow must be the same.

Take the temperature of the junction as T_j, and set the heat flows equal

Putting in the numbers

The heat flow is from either formula