Thermal Conductivity Unit

All the materials we see in the world have their ways and heat-producing rates. People can see the best example of thermal conductivity in winters. In Winter, many materials get chilled within microseconds. For example, the carpet and marbles (or tiles) are present in the same room in winters. The marbles or tiles are colder as compared to the carpets (or mats). 

This is due to the fact that carpets can’t release heat faster than marbles or tiles. The heat releasing rates of stone are high. Therefore, the stone would get cold within a few seconds in the winters. Many factors affect the heat conduction of any material. The thermal conductivity can be calculated with the help of all these factors.

What is the meaning of Thermal Conductivity?

In simple terms, thermal conductivity refers to the heat transferring process of objects. Thermal conductivity has its origins in Fourier’s law of heat conduction. The heat travels from an object with high temperature to another object with low temperature. The heat travels along a temperature gradient till the actual thermal equilibrium is obtained. 

The heat transfer rates depend on various natures and characteristics of materials. The magnitude of the temperature gradient influences the heat transfer rate. 

Unit of Thermal Conductivity

There is a specific unit of thermal conductivity. The SI unit of thermal conductivity is given as watts per metre-kelvin.

What is the equation of thermal conductivity?

The heat conduction depends on four factors. These four factors are important for the calculations of thermal conductivity.

The formula for the thermal conductivity equation is,

Q/t= kAΔT/d

where,

Q stands for representing the amount of heat transferred

t sands for representing the time taken for the amount of heat transfer

A stands for the cross-sectional area of any material.

ΔT stands for the difference in temperature of both sides of the material.

d stands for the thickness of the heat-producing material.

Always make sure the value of thermal conductivity is given with the unit of thermal conductivity.

Does temperature influence the thermal conductivity of the material?

The temperature influences the thermal conductivity of the material. The whole concept of thermal conductivity depends on the movement of molecules. Therefore, the role of temperature in the calculation of thermal conductivity is huge. The molecule’s movement increases under a high-temperature area. Faster molecular movement means heat transfer will get speedier. Now, it is concluded that the thermal conductivity of the material will fluctuate according to the nature of the temperature.

You must have observed that metal can produce heat into a material. On the other hand, metals take away heat from the materials.

For example, in summers, the metals get hot and cold in winters. For example, when someone touches a cold metal, the heat present in the person’s hands gets transferred by the metal. This causes your hands to feel cold, and hence the metals seem to be chilled. 

Similarly, when someone touches hot metals, the heat energy gets transferred to the hands or skin of a person. This makes the person feel the heat present in the metal or hot metals. This is the reason why the stones feel extremely hot in the summer, as they can transfer heat from the human’s skins or hands. 

How to measure thermal conductivity?

Measuring thermal conductivity is vital for people to understand the material nature and characteristics properly. The thermal conductivity helps comprehend better understanding how two objects work together and build relationships. The thermal conductivity helps the material to perform best in various aspects. Thermal conductivity testing or measurement is critical. The testing or measurement methods for thermal conductivity either last for a very short time or are constant (steady). 

The testing process for both transient and steady methods is different. For performing the steady testing or measurement for thermal conductivity, all the required samples should be in their thermal equilibrium state. If any single reference piece required for the thermal conductivity test is not in a thermal equilibrium state, then the test could not get conducted. 

For performing a transient thermal conductivity test, all the sample or reference pieces need not be in their thermal equilibrium state.

Relation Between Thermal Conductivity and Structure

The structure plays a vital role in determining the thermal conductivity of the materials. The thermal conductivity of any material is directly proportional to the material’s structure. There are many materials whose thermal conductivity depends on the heat travel direction of materials. Such materials are known as anisotropic materials. In anisotropic materials, the heat travels in one particular direction as it depends on the structure of the materials. 

The materials can be of three types of thermal conductivity. These are metallic solids, gases, and nonmetallic solids. All these materials differ in their structure and movement of molecules. Hence, the heat travels would vary for all three types of materials. The thermal conductivity of gases is lower than solids. 

The main reason behind the low thermal conductivity of gases is that gases have loosely packed molecules. The thermal conductivity of metallic and nonmetallic solids is higher than gases. The arrangement of molecules inside the solids is more uniform and higher than the gases. Therefore, the thermal conductivity of metal solid is more than nonmetallic solid. 

The main reason is that the molecules present in metal are very closely packed, which increases thermal conductivity in metal solids. According to Wiedemann-Franz Law, the increase in temperature will increase the thermal conductivity of materials. The electrical conductivity of materials increases with the thermal conductivity, but there are some exceptional cases. 

If the temperatures come in such cases, then the electrical conductivity would shrink, but the thermal conductivity would increase.

Conclusion

Thermal conductivity has a direct relationship with the temperature and structure of materials. All the materials have thermal conductivities. The materials with proper molecule arrangements would have higher thermal conductivities. People can find out the value of thermal conductivity with the help of mathematical formulas by giving exact values of variables.