If the outer air temperature in Problem 1.11 is –2°C, calculate the convection heat transfer coefficient between the outer surface of the window and the air assuming radiation is negligible.
GIVEN
• Window: 1 m by 3 m
• Thickness (L) = 7 mm = 0.007 m
• Surface temperatures
? Inner (Ti) = 20°C
? outer (To) = 17°C
• The rate of heat loss = 1040 W (from the solution to Problem 1.11)
• The outside air temperature = –2°C
FIND
• The convective heat transfer coefficient at the outer surface of the window ( h c)
ASSUMPTIONS
• The system is in steady state and radiative loss through the window is negligible
SKETCH
For steady state the rate of heat transfer by convection from the outer surface must
be the same as the rate of heat transfer by conduction through the glass
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