We have often heard about thermal conductivity while studying temperature and materials. Heat transfer in a material takes place through three processes: convection, conduction and radiation.
In the convection method, heat transfer takes place by the bulk movement of molecules within fluids such as liquids and gases. In thermal radiation methods, heat is generated by the emission of EM waves. These waves carry energy from one body to another. In the method of conduction, heat flows from objects with a higher temperature to objects with lower temperature.
In the process of heat conduction in a material, conduction is affected by two phenomena, namely:
- Thermal conductivity
- Thermal diffusivity
Thermal conductivity is a well-known concept that refers to the ability of a given material to transfer or conduct heat.
In this article, let us learn about Thermal diffusivity.
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What Is Thermal Diffusivity?
Thermal diffusivity is one of the important concepts in the heat transfer process. Thermal diffusivity is defined as the rate of temperature spread through a material. It is the measurement of heat transfer in a medium. It measures the heat transfer from the hot material to the cold.
Thermal diffusivity is denoted by the letter D or α (alpha).
SI unit of thermal diffusivity is m²/s.
The thermal diffusivity of a material is given by the thermal conductivity divided by the product of its density and specific heat capacity where the pressure is held constant.
Where,
k is the thermal conductivity
cp is the specific heat capacity
ρ is density
ρcp is the volumetric heat capacity
Thermal diffusivity can be defined as the ratio of heat that is let pass through the material to the heat per unit volume that is stored in the material.
Laser flash analysis or laser flash method, infrared thermography, and thermal wave interferometry are used to measure the thermal diffusivity of various materials.
Laser flash analysis involves heating a strip or cylindrical sample with a short energy pulse at one end and analyzing the temperature change at another end of the sample. The laser flash technique for the measurement of thermal diffusivity was first explained in the year 1960 by Parker et al. of the U.S. Navy Radiological Defense Laboratory.
The thermal wave interferometry technique is used for thermal diffusivity measurements of coatings and thin slabs.
Thermal Diffusivity of Various Materials
Thermal diffusivity of different materials is given in the table below.
| Material | Thermal diffusivity (mm²/s) |
| Gold | 127 |
| Silver | 165.63 |
| Aluminium | 97 |
| tin | 40 |
| iron | 23 |
| Quartz | 1.4 |
| Ice at zero degrees | 1.02 |
| Brick | 0.52 |
| Glass | 0.34 |
We can observe that, material like silver has a high thermal diffusivity, while material like glass has a low thermal diffusivity. This means silver is a better diffuser of thermal energy than glass.
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Frequently Asked Questions on Thermal Diffusivity
What is meant by thermal conductivity?
The ability of the material to transfer or conduct heat is known as thermal conductivity.
Name the three processes of heat transfer in a material.
Convection, Conduction and Radiation.
Name the factors on which heat conduction in a material depends.
- Thermal conductivity
- Thermal diffusivity
What is the SI unit of thermal diffusivity?
SI unit of thermal diffusivity is m²/s.
What is the thermal diffusivity of tin?
40 mm²/s.
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