8/15/2019 Tutorial Sheet for practice of heat transfer problems

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Tutorial Sheet for MEC 301

Sheet 2

Problem 1 : Consider a 3-m-high, 5-m-wide, and 0.3-m-thick wall whose thermal

conductivity is K = 0.9 W/m · °C. On a certain day, the temperatures of the inner and theouter surfaces of the wall are measured to be16°C and 2°C, respectively. Determine the rateof heat loss through the wall on that day.

Problem 2 : Consider a 0.8-m-high and 1.5-m-wide glass window with a thickness of 8 mmand a thermal conductivity of k = 0.78 W/m · °C. Determine the steady rate of heat transferthrough this glass window and the temperature of its inner surface for a day during which theroom is maintained at 20°C while the temperature of the outdoors is 10°C. Take the heattransfer coefficients on the inner and outer surfaces of the window to be h 1 = 10 W/m

2 °C andh2 = 40 W/m 2°C, which includes the effects of radiation.

Problem 3 : Consider a 0.8-m-high and 1.5-m-wide double-pane window consisting of two 4mm thick layers of glass (k = 0.78 W/m °C) separated by a 10 mm wide stagnant air space (k= 0.026 W/m °C). Determine the steady rate of heat transfer through this double-panewindow and the temperature of its inner surface for a day during which the room ismaintained at 20°C while the temperature of the outdoors is -10°C. Take the convection heattransfer coefficients on the inner and outer surfaces of the window to be h 1 = 10 W/m

2 °C andh2 = 40 W/m

2 °C, which includes the effects of radiation.

Problem 4 : Steam at T a1 = 320°C flows in a cast iron pipe (k = 80 W/m · °C) whose innerand outer diameters are D 1 = 5 cm and D 2 = 5.5 cm, respectively. The pipe is covered with 3-cm thick glass wool insulation with k = 0.05 W/m · °C. Heat is lost to the surroundings at T a2 = 5°C by natural convection and radiation, with a combined heat transfer coefficient of h 2 =18 W/m 2 °C. Taking the heat transfer coefficient inside the pipe to be h 1 = 60 W/m 2 °C,determine the rate of heat loss from the steam per unit length of the pipe. Also determine thetemperature drops across the pipe shell and the insulation.