Thermal properties
There are basically three types of thermal
properties.
Heat capacity
C= ∆Q/∆T
Heat capacity shows the ability of material to
absorb thermal energy.
We can say that heat capacity is defined as the
ratio of heat, added or removed from the system, to the change in temperature.
Unit = J/^{0}C
Specific heat c, C= mc
Heat capacity can be calculated in two conditions,
Heat capacity at Constant pressure, C_{P} =
(∆Q/∆T)_{ P}
Heat capacity at Constant volume, C_{V} =
(∆Q/∆T)_{ v}
Thermal expansion
If materials are heated then there will be expansion
and if materials are cooled then there will be contraction.
∆L/L_{i} = a ∆T,
Where,
L_{i} is original length of bar
∆T change in temperature (T_{f }T_{i)}
a is linear coefficient of thermal
expansion. a= ∆L/ (L_{i }∆T)
Thermal stress
When materials are heated or cooled, there will be
some changes in dimension of materials and a stress will be produced which is
known as thermal stress because it is produced due to thermal action.
For example,
For a rod the thermal stress is б=E a ∆T, where E is young modulus
The coefficient of linear expansion
Let us take a rod of length Li at temperature Ti.
Let us think that it is heated up to a temperature of T_{f} and therefore
final length of bar after heating will be L_{f}.
∆L = L_{f} – Li and ∆T = T_{f }–
Ti
a= ∆L/ (L_{i }∆T)
So, we may say that the coefficient of linear
expansion is defined as the change in length of unit length of bar due to
change in temperature by unit degree.
Unit = ^{0}C^{1} or K^{1}
The coefficient of thermal conductivity
According to Fourier law we have, q =  λ (dT/dX)
Where q is amount of heat flow per unit area per
unit time
dT/dX is temperature gradient. If we
think dT/dX = 1 then, q =  λ
Coefficient of thermal conductivity is defined as
amount of heat flow per unit area per unit time with unit temperature gradient.
Construction materials

Coefficient of thermal expansion

Coefficient of thermal conductivity
(k  W/(m. K))

Concrete

10^{6 0}C^{1}

0.1 To 1.7

Timber

3 to 5 x10^{6 }K^{1}

0.048

Steel

13 x 10^{6} ^{0}C^{1}

54

Let us see
"Mechanical
properties of materials"
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