*63 9 Figure 18-49 shows (in cross section) a wall consisting of four layers, with thermal conductivities k = 0.060 W/m -K, kz = 0.040 W/m - K, and k4 = 0.12 W/m - K (k, is not known). The layer thicknesses are L = 1.5 cm, L3 = 2.8 cm, and L4 = 3.5 cm (L2 is not known). The known temperatures are T1 = 30°C, T12 = 25°C, and T, = -10°C. Energy transfer through the wall is steady. What is interface temperature Ty? T- T12 Tys -4-

An iron bar is held between a fire at fixed temperature, T1 = 444 C and the other end is embedded into a block of ice of mass m = 0.478 kg at 0 C. The latent heat of fusion of ice is 334 kJ/kg. The thermal conductivity of metallic iron is 80 W/m-K. The length of the bar is /= 2.2 m and it has a width of w = 0.203 m and height of h = 0.119 m. The density of iron is 7.874 kg/m^3. The specific heat capacity of iron is 0.44 kJ/kg-K and the specific heat capacity of water is 4.182 kJ/kg-K. a) At t=0, what is the power (J/s) of heat transfer across the bar? b) If T1 is held constant, how long does it take to melt the entire block of ice? c) Suppose now that as soon as all of the ice has melted the water is put into an insulating container. The iron bar is now heated completely to T1 and dropped, cheerfully and with reckless abandon, into the container. What is the final temperature of the system?

A) Estimate the total solar heating absorbed by the Earth every second. Assume 36% of the incoming solar radiation is reflected by clouds and lost. You can assume that the Earth intercepts sunlight with an effective area of πr2 where r is Earth’s radius. B) Estimate the total heat lost by the Earth as infrared radiation every second. Assume Earth has an  effective temperature of 252 K (-21 C).

What is the change in length of a 3.4-cm-long column of mercury if its temperature changes from 35 ºC to 35.3 ºC, assuming the mercury is unconstrained? The thermal coefficient of expansion of mercury is 6×10-5 /oC.