Heat Transfer – Conduction, Convection, Radiation
Every substance or quantity that exists in and around us is comprised of molecules and atoms. All the atoms have distinguished motion types, which in turn are responsible for the generation of heat in the said substance. Moreover, the process of transfer of heat from a high-temperature body to a low-temperature body is referred to as Heat Transfer. Besides, there are multiple types are Heat Transfers, such as Conduction, Radiation, and Convection, which we are going to talk about in a much more detailed way, in the following columns.
Let us first understand heat transfer and its basic definition which will lead us to understanding the different ways of heat transfer.
What is Heat Transfer?
Heat Transfer is defined as the movement of heat across the same body, or from one body to another, mainly because of the temperature difference between surroundings and system. And the process of Heat Transfer is differentiated in multiple types, also discussed as distinct mechanisms.
In the study of heat transfer, the difference in the temperature is referred to as potential that is responsible for heat transfer from one point to the other.
Types of Heat Transfer
Types of Heat Transfer are,
- Radiation
- Conduction
- Convection
What is Radiation?
Radiation is one of the most commonly observed and experienced mechanisms of heat transfer in our daily lives. The thermal radiations we observe regularly are radiant heats.
When the heat generated in the body results in emissions of electromagnetic waves, then it is said to be because of the direct result of Thermal Radiation. Moreover, electromagnetic waves will allow energy to be released by the body. Besides, the radiation does not have any kind of medium restrictions, as it can be seen actively in both vacuum and transparent mediums. And the main reason for the generation of radiation in a body is due to the random movement of charged protons and electrons in the said body.
Thermal Radiation is mathematically expressed through the Stefan-Boltzmann Law,
\(P=e. \sigma .A. ( T_{r} – T_{c} )^{4} \)
Where A = Area of Radiation
\(T_{c}\) = Surrounding Temperature
E = emissivity
\(T_{r}\) = Radiator Temperature
P = Power of Radiation
Radiation Examples
Let us look at some of the examples of heat radiation heat transfer:
- The ultraviolet rays or UV rays emitting from the sun represent radiation
- Microwave radiation
- The X-rays are also classified under radiation
- Gamma rays from radioactive elements
- Our mobile phones and computers too emit radiation
The major kinds of radiation are:
Alpha, beta, neutrons, and electromagnetic waves
What is Convection?
Convection, another mode of heat transfer, is only applicable for fluids, as it is described as the process of molecules in higher-temperature regions moving to lower-temperature regions. Moreover, when the temperature of the liquid rises, it causes an increase in the volume of the liquid, which is generally called displacement. In simple terms, when the temperature of the liquid rises, the volume of the liquid also is bound to increase, by the same factor. This reaction or development is referred to as displacement. In convection, generally, the movement of the heated fluid happens rapidly.
In order to calculate the rate of the convection,
\(Q= h_{e}.A.( T_{s} – T_{f})\)
Where Q = Heat Transfer per Unit Time
A = Area of Heat Transfer
\(T_{s}\) = Surface Temperature
\(H_{c}\) = Coefficient of Convective Heat Transfer
\(T_{f}\)= Fluid Temperature
Convection Examples
Let us check certain examples in the convection type of heat transfer:
- One of the most classic examples of convection kind of heat transfer is the blood circulation in human beings, mammals or those generally referred as warm-blooded species. This circulation of blood happens through convection mode, where the temperature of the body is invariable regulated.
- Water boiling also happens as part of convection heat transfer where denser molecules collect at the bottom, while those with lesser density float upwards, thus causing their circular motion due to which the water heats.
- Another important example is the warm water around the equator that travels towards the poles, whereas the cooler water at poles are tempted to move closer to the equator.
What is Conduction?
Another commonly observed or discussed heat transfer modes is conduction. This type of heat transfer is observed only when the two bodies or the mediums are in direct contact with each other. Conduction is generally described as the process of transmission of energy from one body to another when both are in contact. Moreover, specifically, in this process, the area that has the higher kinetic energy will transfer its thermal energy to the lower kinetic energy region through contact. Conduction heat transfer is also referred to as heat induction or thermal induction. Usually, heat transfer under conduction is a slower process.
\(Q= \frac{[K.A.( T_{hot} – T_{cold} )]}{d}\)
Q = Transfer of Heat per Unit Time
D = thickness of the body
K = Thermal Conductivity of Body
\(T_{hot}\)= Temperature of Hot Region
\(T_{cold}\)= Temperature of Cold Region
A = Area of Heat Transfer
Conduction Examples
A few examples of conduction heat transfer:
- Have you ever noticed how heat is transferred from hands to ice cubes or pieces, leading to their melting in hands? This is a simple example of conduction heat transfer
- Clothes that are ironed clearly depict the conduction of heat from iron to clothes
- Sands on beaches are great conductors of heat
Difference Between Conduction, Convection, Radiation
As we have covered all the detailed information about what is Conduction, Convection, and Radiation? Let us talk about the differences between types of heat transfers in much more detailed way.
| Conduction | Convection | Radiation |
| Heat Transfer between objects that are in direct contact. | Heat Transfer occurs only between the fluids. | Heat Transfers occur through electromagnetic waves regardless of the mediums or substances involved. |
| Conduction is a slow process | Convection is a fast process | Radiation is a very fast process. |
| Conduction usually takes place due to differences in temperature. | Convection takes place because of the difference in density between two mediums. | Radiation occurs in all types of bodies, with a temperature higher than 0K. |
| It is observed only in heated solid objects. | It is observed in intermediate mediums like air and water. | It is observed in electromagnetic waves. |
| Does not obey laws of reflection and refraction. | Does not obey laws of reflection and refraction. | It obeys the laws of reflection and refraction. |
Conclusion
The above article has covered all about Conduction, Convection, and Radiation, and how they are different from each other. And in physics subject, you will many more complex topics like this all the time, which can be hard to understand or memorize. Thus, it is better to join the online interactive classes offered by Tutoroot, as they come with various amazing benefits, such as cost-effective prices, expert staff guidance, best study materials access, and a lot more.
Frequently Asked Questions
What are the modes of heat transfer?
As you know, there are different modes of heat transfer such as Conduction, Convection, and Radiation.
What is Radiation Formula?
Radiation is mathematically expressed through the Stefan-Boltzmann Law,
\(P=e. \sigma .A. ( T_{r} – T_{c} )^{4} \)
Where A = Area of Radiation
Tc = Surrounding Temperature
E = emissivity
Tr = Radiator Temperature
P = Power of Radiation
What is an example of conduction
A few examples:
- Heat s transferred from hands to ice cubes or pieces, leading to their melting in hands is an example of conduction heat transfer
- Clothes that are ironed clearly depict conduction of heat from iron to clothes
- Sands on beaches are great conductors of heat
How does heat flow
Heat is transferred from one object to the other, through three ways – conduction, convection, and radiation
What is Conduction Formula?
\(Q= \frac{[K.A.( T_{hot} – T_{cold} )]}{d}\)
- Q = Transfer of Heat per Unit Time
- D = thickness of the body
- K = Thermal Conductivity of Body
- Thot= Temperature of Hot Region
- Tcold= Temperature of Cold Region
- A = Area of Heat Transfer
What is Convection Formula?
\(Q= h_{e}.A.( T_{s} – T_{f})\)
Where Q = Heat Transfer per Unit Time
- A = Area of Heat Transfer
- Ts = Surface Temperature
- Hc = Coefficient of Convective Heat Transfer
- Tf= Fluid Temperature