2.5 cm-thick sheet of plastic initially at 21°C is placed between two heated steel plates that are maintained at 138°C. The plastic is to be heated just long enough for its midplane temperature to reach 132°C. If the thermal conductivity of the plastic is 1.1 × 10-3 W/(m K), the thermal diffusivity is 2.7 × 10-6 m2 /s, and the thermal resistance at the interface between the plates and the plastic is negligible, calculate: (a) the required heating time, (b) the temperature at a plane 0.6 cm from the steel plate at the moment the heating is discontinued,

Troom = 25°C Problem-4: An 8-m-internal-diameter spherical tank made of 1.5-cm-thick stainless steel (k = 15 W/m-K) is used to store iced water at 0°C. The tank is located in a room whose temperature is 25°C. The walls of the room are also at 25°C. The outer surface of the tank is black (emissivity = 1), and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. The convection heat transfer coefficients at the inner and the outer surfaces of the tank are 80 W/m²-K and 10 W/m².K, respectively. Determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at 0°C that melts during a 24-h period. The heat of the fusion of water at atmospheric pressure is hf5 333.7 kJ/kg. Iced water D D₁= 8 m Tin = 0°C 1.5 cm

A cast iron pipe (k = 80 W/m - oC) whose inner and outer diameters are 5 cm and 5.5 cm respectively is coverd with a 3 cm thick glass wool insulation (k = 0.05 W/m - oC) The temperature at the inner surface of the pipe is 320 oC and the interface temperature between the pipe and insulation is 300 oC. Determine the surface temperature of the insulation.

A wall receives sunlight from 7:30 am to 6:30 pm. The amount of energy it receives is 420 W/m2 and 15% is emitted as radiation into the surrounding air. The inside of the wall has a temperature of 48°C. If the wall is 7 m long and 6 m high and 30 cm thick, what is the temperature when x=20 cm?