Cork insulation; a complete illustrated textbook on cork insulation ...

96
CORK INSULATION
and the temperature difference,—may be expressed in symbols,
thus:
H=K A (ti—t.)
in which H is the total heat transfer in B.t.u. per hour, K is
the total heat transfer coefficient in B.t.u. per hour per degree
temperature difference F., A is the area of the heat trans-
mitting surface in square feet, and (t^—U) is the temperature
difference in degrees Fahrenheit between the regions of high-
est and lowest levels.
It is evident, therefore, that if the heat transmitting area
and the temperature levels are held constant, the heat transfer
depends entirely upon conduction, convection and radiation.
FIG 34.—TRANSFER OF HEAT BY CONDUCTION.
65.—Conduction.—Heat transfer by conduction is accom-
plished in a body of material by the vibration or impact of
the molecules or particles of matter that compose the body
itself, such molecular disturbance being produced by an unbal-
anced thermal condition within the mass. Thus heat may be
interchanged between different parts of the same body, or
between two separate bodies in actual contact, by conduction
but due to friction and adhesion between the molecules of a
body, the vibration or impact of the particles of matter will
become slower as the heat energy passes from one molecule to
the other, and consequently the amount of heat that will be
transmitted through the body will be something less than
that applied to it. The amount of heat that will be transmitted
through a given material, due to a given temperature
difference, depends on the characteristic internal thermal con-
; ;
J