Thermal Conductivity

Thermal conductivity is a measure of a material's ability to conduct heat.

Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity.

Preface

Thermal conductivity (often denoted by k, λ, or κ) refers to the intrinsic ability of a material to transfer or conduct heat.

It is one of the three methods of heat transfer, the other two being convection and radiation.

Heat transfer processes can be quantified in terms of appropriate rate equations.

According to wikipedia…

The thermal conductivity of a material is a measure of its ability to conduct heat. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. For instance, metals typically have high thermal conductivity and are very efficient at conducting heat, while the opposite is true for insulating materials.

Table of contents

You can expect this article to cover:

  • What does thermal conductivity mean
  • Thermal conductivity uses
  • How to reduce thermal conductivity
  • How is thermal conductivity measured
  • Can thermal conductivity be negative
  • Thermal conductivity vs specific heat
  • Thermal conductivity vs electrical conductivity
  • Thermal conductivity vs heat transfer coefficient
  • Thermal conductivity vs temperature
  • Thermal conductivity vs diffusivity
  • Thermal conductivity vs heat capacity
  • Thermal conductivity vs thermal resistance
  • How does thermal conductivity change with temperature
  • Does thermal conductivity change with thickness
  • How can thermal conductivity of a liquid be obtained
  • How thermal conductivity detector works
  • How to convert thermal conductivity units
  • How to calculate thermal conductivity
  • Thermal conductivity equation
  • What is thermal conductivity coefficient
  • How to calculate heat transfer coefficient from thermal conductivity
  • How to calculate thermal resistance from thermal conductivity
  • Which material has the highest thermal conductivity

What does Thermal Conductivity Mean

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.

Thermal conductivity uses

Heat sink applications.

If a metal has high thermal conductivity, then it is used in heat sink applications.

On the other hand, if the metal has low thermal conductivity, then it is used in thermal insulation applications.

Can Thermal Conductivity Be Negative

The thermal conductivity cannot be negative.

Thermal conductivity vs specific heat

Thermal conductivity is the ability to transfer heat while the specific heat is the ability to hold a particular amount of heat.

Thermal conductivity vs electrical conductivity

By definition, electrical conductivity is a measure of how well electrical current (charge in motion) can pass through a material under the influence of an applied voltage/electric field.

Thermal conductivity measures how well heat (thermal energy in motion) can pass through a material under a temperature differential.

Thermal conductivity vs heat transfer coefficient

The thermal conductivity of the fluid is related to the spatial molecular diffusion of heat throughout the fluid.

The convective heat transfer coefficient is related to transport of heat due to the bulk motion of the fluid above or around a solid.

Thermal conductivity vs temperature

Temperature on thermal conductivity is different for metals and nonmetals.

The effect of temperature on thermal conductivity is different for metals and nonmetals.

In metals, heat conductivity is primarily due to free electrons.

In alloys the change in electrical conductivity is usually smaller and thus thermal conductivity increases with temperature, often proportionally to temperature.

Thermal conductivity vs diffusivity

The key difference between thermal conductivity and diffusivity is that thermal conductivity refers to the ability of a material to conduct heat whereas thermal diffusivity refers to the measurement of the rate of transfer of heat of a material from its hot end to the cold end.

Thermal conductivity vs heat capacity

Thermal conductivity describes the ability of a material to conduct heat, and the specific heat capacity tells how much heat energy is absorbed or released depending on the temperature difference and mass "1".

Thermal conductivity vs thermal resistance

Thermal conductivity is a material property and describes the ability of the given material to conduct heat.

Thermal resistance is another inherent thermal property of a material, and is the measure of how a material of a specific thickness resists the flow of heat.

How does Thermal Conductivity Change With Temperature

IN GENERAL, the thermal conductivity of gases increases with temperature.

Kinetic theory of gases explains why.

Thermal conductivity of liquids decreases with increasing temperature as the liquid expands and the molecules move apart.

Does Thermal Conductivity Change With Thickness

Does not change.

Thermal transmission in a certain material depends upon the thermal property (in this case the thermal conductivity) and the thickness of that material.

How can Thermal Conductivity Of A Liquid Be Obtained

Thermal conductivity can be calculated by dividing the heat flux applied to internal tube to the temperature distribution within the fluid flowing inside the tube.

Therefore by using thermocouples you measure the radial temperatures in the fluid, and so calculate thermal conductivity.

How thermal conductivity detector works

By having two parallel tubes both containing gas and heating coils.

Thermal conductivity detectors work on the principle of heat transfer by convection (gas cooling).

The temperature change of a heated RTD or thermistor caused by exposure to a gas mixture with changing specific heat value indicates when a new sample species exits the chromatograph column.

Thermal conductivity equation

K = (QL)/(AΔT).

Every substance has its own capacity to conduct heat.

The thermal conductivity of a material is described by the following formula: K = (QL)/(AΔT), where K is the thermal conductivity in W/m.

What is Thermal Conductivity Coefficient

Coefficient of thermal conductivity : The coefficient of thermal conductivity of a material is defined as the quantity of heat that conducts per unit time through a unit cube of the material when its opposite faces are kept at a temperature difference of one degree.

How to Calculate Heat Transfer Coefficient From Thermal Conductivity

K/Δx.

The most common way of doing this is by dividing the thermal conductivity of the convection fluid by a length scale.

It is also common to calculate the coefficient with the Nusselt number (one of a number of dimensionless groups used in fluid dynamics).

How to Calculate Thermal Resistance From Thermal Conductivity

R = e / λ.

The thermal resistance R (in m2.K / W) depends on the insulation thickness (e expressed in meters) and the thermal conductivity (λ) of the material: R = e / λ.

Which Material Has The Highest Thermal Conductivity

Diamond

Diamond is the leading thermally conductive material and has conductivity values measured 5x's higher than copper.

Diamond atoms are composed of a simple carbon backbone that is an ideal molecular structure for effective heat transfer.

Video: What is Thermal Conductivity? | Physics...

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