(a)
We have to calculate the rate of heat loss
through a glass window of area
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Solution: Click For PDF Version (a) Inside
temperature is
Outside
temperature is
Thermal
conductivity of glass is
Area of the
glass window is
Thickness of
glass is
Therefore, the rate of heat loss through the glass window can be calculated from the heat conduction equation
Substituting the numerical values from the data above, we get
(b) We will compute the rate of heat loss from inside of the room to the outside when a storm window of thickness 3 mm but with an air gap of 7.5 cm between the two windows has been installed.
Thermal
conductivity of air is
We will use
the result that the rate of heat transfer through a compound slab
consisting of materials having thicknesses
Substituting the data, we find
We notice that the heat flow is determined essentially by the air gap, as air has very low heat conductivity in comparison to that of glass.
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and thickness 3.0 mm if
the outside temperature is
and the inside temperature is
.
(b) A storm window is installed having the
same thickness of glass but with an air gap of
7.5 cm between the two windows. We have to
calculate the corresponding rate of heat loss presuming that
conduction is the only important heat-loss mechanism.
,
,
and thermal conductivities
,
,
is
given by the generalisation of the heat conduction given equation
