1. Thermo-physical properties 2. Radiation properties - nptel - Indian ...

Mechanical Measurements Prof S.P.Venkatesan
Indian Institute of Technology Madras
Thermal conductivity may be measured by either steady state methods or
unsteady (transient) methods.
(i) Steady state methods
o Guarded hot plate method
Solid, Liquid
o Radial heat flow apparatus
Liquid, Gas
o Thermal conductivity comparator
Solid
Steady state methods normally involve very large measurement times since the
system should come to the steady state, possibly starting from initial room
temperature of all the components that make up the apparatus. Also maintaining
the steady state requires expensive controllers and uninterrupted power and
water supplies.
(ii) Unsteady method
o Laser flash apparatus
Solid
Even though the unsteady methods may be expensive because of stringent
instrumentation requirements the heat losses that plague the steady sate
methods are not present in these. The entire measurement times may be from a
few milliseconds to seconds or at the most a few minutes.
Thermal conductivity is defined through Fourier law of conduction. In the case of
one-dimensional heat conduction the appropriate relation that defines the thermal
conductivity is