What factors affect thermal conductivity? At the macroscopic level, thermal conductivity largely depends on three main factors:
operating temperature, moisture content, and density
[33,37,42]. Other factors are a thickness, pressure, air surface velocity, and aging.
What affects conductivity?
Factors affecting conductivity
There are three main factors that affect the conductivity of a solution:
the concentrations of ions, the type of ions, and the temperature of the solution
.
How is thermal conductivity affected by temperature?
In pure metals the electrical conductivity decreases with increasing temperature and thus the product of the two, the thermal conductivity, stays approximately constant. However,
as temperatures approach absolute zero, the thermal conductivity decreases sharply
.
Does thermal conductivity increases with temperature?
The thermal conductivity of liquids decreases with increasing temperature
as the liquid expands and the molecules moves apart. While in solids, the thermal conductivity decreases at higher temperatures due to the anharmonic scattering which is inversely proportional to the temperatures changes.
How does density affect thermal conductivity?
An increase in the bulk density will decrease the “heat transfer average distance,” and therefore
decrease the thermal conductivity
. Counteracting this effect is the increased mass within the same volume, which will increase the solid conduction.
Hence, the thermal conductivity of a rod depends on
length, area of cross-section and material of rod
.
As the concentration of ions increases, the conductivity increases
. This is because conductivity increases as water dissolves more ionic compounds due to the ions transporting an electrical current in the solution.
The electrical conductivity of a metal (or its reciprocal, electrical resistivity) is determined by
the ease of movement of electrons past the atoms under the influence of an electric field
.
In metals, conductivity is due to movement of free electrons. When temperature increases,
the vibration of metal ions increases
. This results in increase in resistance of metal and hence, decrease in conductivity.
With the increasing thickness, the average grain size increases and the grain boundary decreases, which means less electrons and phonons can be scattered, thus increasing the thermal conductivity
.
2, it appears that
thermal resistance increases linearly with density
and that an increase in thickness augments the effect, as shown by the change in slope as thickness increases.
Thermal conductivity is not only affected by changes in thickness and orientation
;temperature also has an effect on the overall magnitude. Because of the material temperature increase, the internal particle velocity increases and so does thermal conductivity.
Gases transfer heat by the collision of molecules. As the temperature increases,
the kinetic energy of molecules of gases also increases and eventually collision between molecules also increases
which increases the thermal conductivity of gases. ∴ As temperature increases the thermal conductivity of gases increases.
A material’s thermal conductivity is a fundamental property. Those materials with high thermal conductivity will
transfer heat rapidly, either by receiving heat from a hotter material or by giving heat to a colder material
.
In short,
molar conductivity does not depend on the volume of the solution
.
Answer: Specific Conductivity decreases with a decrease in concentration. Since
the number of ions per unit volume that carry current in a solution decrease on dilution
. Hence, concentration and conductivity are directly proportional to each other.
Thermal conductivity can be defined as
the rate at which heat is transferred by conduction through a unit cross-section area of a material, when a temperature gradient exits perpendicular to the area
.
For all liquids
the coefficient of thermal conductivity increases with increasing pressure
. Upon compression molecules draw together, their mutual attraction grows, therefore, viscosity and thermal conductivity increase.
An increase in the bulk density will decrease the “heat transfer average distance,” and therefore
decrease the thermal conductivity
. Counteracting this effect is the increased mass within the same volume, which will increase the solid conduction.
