Difference Between Conduction Convection and Radiation

What's the Difference Between Conduction, Convection and Radiation

We know that heat is the form of energy that creates molecular movement. Molecules with a lot of heat move quicker, and molecules with less heat move slower. We also know that as molecules heat up and move quicker, they unfold apart and objects expand (get bigger). This is called thermal expansion.

Heat transfer is that the physical act of thermal energy being changed between 2 systems by dissipating heat. Temperature and also the flow of heat (thermal energy in terms of Physics) are the essential principles of heat transfer. The amount of thermal energy that can be obtained is set by the temperature, and also the heat flow represents the movement of thermal energy.
On a microscopic scale, the Kinetic Energy of molecules is that the direct reference to thermal energy. With the rise in temperature, the thermal agitation within the molecules increases. Energy is transferred from the zone with higher kinetic energy to that of lower kinetic energy. Simply put, heat transfer may be classified into 3 broad categories: physical phenomenon, convection, and radiation. (Fig 1)

                        Figure 1


Conduction transfers heat via direct molecular collision. An area of larger mechanical energy can transfer thermal energy to a region with lower mechanical energy. Higher-speed particles will collide with slower speed particles. The slower-speed particles can increase in mechanical energy as a result. Conduction is that the most typical sort of heat transfer and happens via physical contact Example: A cooking pan on flame or oven gets heated due to conduction (Fig 2).

                    Figure 2
 The process of this physical phenomenon depends on the subsequent factors: gradient, cross-sectional of the solid body, length of the path, and physical material properties. The gradient is the physical amount that describes the direction and rate of heat transmission. Temperature flow can continually occur from hottest to coldest or, as declared before, higher to lower kinetic energy. Once there's an equilibrium between the 2 temperature variations, the thermal transfer stops.

Cross-section and path of travel each play a very important half in this physical phenomenon. The larger the dimensions and length of an object, more amount of energy will be required to heat it. And the larger the extent that’s exposed, more heat is lost. Smaller objects with little cross-sections have borderline heat loss.

Some materials are better conductors than others. Metals are great conductors. That’s why metal objects get hot so easily.
Plastic and wood are poor conductors. They will still get hot, however, it takes longer time for them to pass the thermal energy from molecule to molecule. Likewise, the conductivity in solid is way far more than fluids. This is because the solids have molecules that are very tightly packed, therefore it’s abundant easier for the molecules to pass the energy on. The molecules in liquids and gases are loosely packed so that they aren't touching the maximum amount. Thus, fluid takes longer time compared to solid to conduct heat. Conduction is larger in solids as a result of the network of comparatively shut mounted spatial relationships between atoms helps to transfer energy between them by vibration. 

On a microscopic scale, conduction occurs within a body considered as being stationary; this means that the kinetic and potential energies of the bulk motion of the body are separately accounted for. Internal energy diffuses as vibratory atoms and molecules act with near particles, transferring a number of their microscopic kinetic and potential energies. The collision of adjacent atoms or molecules causes transfer of heat through conduction. The forward and backward movements of multiple electrons from an atom to the other in an unorganized manner stop the generation of a macroscopic current, or as photons collide and scatter.

Thermal contact conductance is the study of conduction of thermal energy between solid bodies in contact with each other. A temperature drop is commonly ascertained at the interface between the 2 surfaces in contact. This development is the results of a thermal contact resistance existing between the contacting surfaces. This thermal resistance varies from contact resistance, as it is even found at atomically perfect interfaces. The study of thermal properties is all about understanding the thermal resistance at the interface of two bodies. The thermal resistance is different from the contact resistance. 


When a fluid, such as air or a liquid, is heated and then it travels away from the source, it carries the thermal energy along. This type of heat transfer is called convection. The fluid on top of a hot surface expands, becomes less dense, and rises.
The introduction of thermal energy causes the expansion of molecules. As the temperature of the given fluid mass will increase, the amount of the fluid should increase by the same issue. This effect on the fluid causes displacement. As the immediate hot air rises, it pushes denser, colder air down(Fig 3).

       Figure 3

 Convection will not take place in most solids as a result of neither bulk current flows nor important diffusion of matter can happen in solid. Diffusion of thermal energy takes place in rigid solids, however, that's referred to as heat conductivity. Convection may be observed in soft solid though as the molecules are less densely packed.

Thermal convection may be observed by inserting a heat supply (e.g. a burner) at the side of a glass filled with a liquid and observing the changes in temperature in the glass caused by the warmer fluid circulating into cooler areas.

Convection is a common phenomenon in atmospheres, planetary mantles, oceans and it is responsible for the mechanism of heat transfer for a large part of the heat movement in the galaxy. Fluid movement throughout convection is also invisibly slow, or it may be obvious and rapid, as in a hurricane. On astronomical levels, it has been found that convection of gas and dust occurs in the accretion disks of black holes, at a rate which may closely approach that of light.


Both conductivity and convection need a medium for the transfer of the heat. Radiation could be a methodology of heat transfer that doesn't rely on any contact between the warmth supply and therefore the heated object. For example, we have a tendency to feel the heat from the sun even if we have a tendency to aren't touching it. Heat may be transmitted through an empty area by thermal radiation. Thermal radiation (often referred to as infrared radiation) could be a kind nonparticulate radiation (or light). Radiation could be a variety of energy transport consisting of magnetism waves traveling at the speed of sunshine. No mass is changed and no medium is needed. Ultraviolet rays reach the planet by means of radiation. (Fig 4) 

Figure 4
Objects emit radiation once very high energy electrons in an exceedingly higher atomic level crumple to lower energy levels. The energy lost is emitted as light-weight or nonparticulate radiation. The energy that's absorbed by associate degree atom causes its electrons to "jump" up to higher energy levels. All objects absorb and emit radiation. To keep the temperature of the object constant, the absorption of energy should balance the emission of energy. If the absorption of energy is bigger than the emission of energy, the temperature of an object rises. If the absorption of energy is a smaller amount than the emission of energy, the temperature of an object falls.

All materials radiate thermal energy supported their temperature. The hotter associate degree object, the more it will radiate. The sun could be a clear example of heat radiation that transfers heat across the galaxy by means of radiation. At traditional space temperatures, objects radiate as infrared waves. The temperature of the thing affects the wavelength and frequency of the radiated waves. As temperature will increase, the wavelengths inside the spectra of the emitted radiation decrease and emit shorter wavelengths with higher-frequency radiation.

Emissivity for a perfect radiator includes a worth of one. Common materials have lower emissivity values.

Emissivity is outlined as associate degree object's effectiveness in emitting energy as thermal radiation. It is the quantitative relation, at a given temperature, of the thermal radiation from a surface to the radiation from a perfectly black surface as determined by the Stefan-Boltzmann law.

Basic definition Conduction is a procedure by means of which heat transfer occurs between objects that are in direct contact.Convection can be defined as the form of heat transfer where energy is transferred within liquid or gas.Radiation involves the mechanism where heat is transmitted between objects that are devoid of any physical contact.
RepresentationHow heat traverses between the bodies in direct contact.How heat gets diffused through fluids.How heat passes through the vacuum.
Cause of occurrenceThe temperature difference or the difference in kinetic energy results conduction. The difference in density of the fluid results in convection.Any object at a temperature greater than 0K can radiate.
Medium of OccurrenceTakes place preferably in solids, due to molecular collisions.The actual flow of matter in fluid results in convection.Without heating the intervening surface, it heats the medium at a distance.
Transfer of heatHeated solid bodies Through intermediate substance.In the form of electromagnetic waves.