TUTORIAL 1

1. Consider a 1.2 m high and 2 m wide double-pane window consisting of two 3 mm thick layers of glass (k=0.78 W/m.oC) separated by a 12 mm wide stagnant air space (k=0.026 W/m.oC). Determine the steady rate of heat transfer through this double-pane window and the temperature of its inner surface for a day during which the room is maintained at 24oC while the temperature of the outdoors is -5oC. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to be h1=10 W/m2.oC and h2=25 W/m2.oC, and disregard any heat transfer by radiation.Ans: 114 W, 19.2oC

2. A cylindrical resistor element on a circuit board dissipates of 0.15 W of power in an environment at 40oC. The resistor is 1.2 cm long and has a diameter of 0.3 cm. Assuming heat to be transferred uniformly from all surfaces, determine (a) the amount of heat this resistor dissipates during a 24h period; (b) the heat flux on the surface of the resistor, in W/m2; and (c) the surface temperature of the resistor for a combined convection and radiation heat transfer coefficient of 9 W/m2.oC. Ans: (a) 3.6 Wh; (b) 1179 W/m2; (c) 171oC

3. A 1 mm thick copper plate (k=386 W/m.oC) is sandwiched between two 5 mm thick epoxy boards (k=0.26 W/m.oC) that are 15 cm x 20 cm in size. If the thermal contact conductance on both sides of the copper plate is estimated to be 6000 W/m.oC, determine the error involved in the total thermal resistance of the plate if the thermal contact conductances are ignored.Ans: 0.88%