Conduction Vs Convection: Critical Facts

The physical process of transport of heat involves many processes. In this post, we are going to know the difference between Conduction Vs Convection.

Conduction is a method of transferring heat molecules between two objects in direct contact with each other. But in convection, the mode of transport of heat molecules is within the fluid matter is due to differences in density regions. Both methods occur in different states of matter.

Now let us learn about Conduction Vs Convection in depth.

Conduction Vs Convection cooling

Both conduction and convection also help in the process of cooling specific devices.

Conduction Cooling

  • It is generally defined as the transport of heat from the hotter component to the cooler part.
  • Example: Conduction is the essentially used mode of heat transfer because, in all the power supplies, the heat sinks are used to transfer the heat away from the boiling appliances.

Convection Cooling

  • It is defined as the transfer of energy between two systems of objects which involves the movement of the massive bulk of the fluid.
  • Example: The fans’ built-in ovens and many other devices provide convection cooling. Even the air present in our surroundings provides cooling naturally.
  • Some heavy power applications contain heat sinks that depend on cooling through convection; it helps transport heat far from the appliances to cooler air.

These are some differences between Conduction Vs Convection cooling.

Heat transfer rate Conduction Vs Convection

The heat transfer rate between conduction and convection differs like matter.

  • The heat transfer rate of conduction depends on the thermal difference between two systems of substance where the transfer is due to direct contact. It usually transfers at a lower rate than convection.
  • The rate of flow of heat molecules also depends on the nature of matter. Since the two processes happen in different matters, i.e., solids (conduction) and fluids (Convection).
  • Conduction is mainly due to collision, affecting heat transfer and convection due to area, temperature, density, etc.

There is a change in the rate of transfer of heat of conduction and convection.

Conduction Vs Convection vape

The method of heat transfer is in use to vaporize certain products, and the primary difference is as given below;

  • The convection mode of heat transfer is always superior in comparison to conduction.
  • If we take the example of terpenes, there is a high exposure of heat in conduction, which leads to a lot of waste products; direct heat exposure destroys the materials. While in convection, it helps to revert all the materials of terpenes.
  • Conduction uses the direct mode of heat transfer to vaporize the substances, passing over the surface to remove the vapors from objects, say a herb. In contrast, the convection process is used in vaporizers that concentrate with hot air on a surface, not directly removing vapors.

Both conduction and convection vaporizers are in use to remove vapors from many appliances.

Conduction Vs Convection

The primary difference between conduction and convection is given in the below table,

        COMPARISON         CONDUCTION           CONVECTION
             DefinitionIt is a heat transfer process between two objects in direct contact and occurs due to free electrons present in the system.It refers to the mode of heat transfer that occurs in fluid in which energy is transmitted from one region to another.
DirectionIt is through direct contactHorizontal path
Nature of processPhysical processPhysical process
Mode of heat transferSolid objectsIntermediate systems
SpeedSlow processFast process
EffectOccur because of temperature difference.Occur because of the difference in mass density.
             AppearanceThrough the collision of molecules.Due to transport of matter.
LawsBoth reflection and refraction laws are absent.Both reflection and refraction laws are absent.
ExampleHand and cup of hot
tea
Steam of hot beverage.

Therefore, conduction and convection are two essential methods of heat transfer.

Read about: Examples of convection

Conduction: How does it work

Conduction is one of the methods of transport of heat molecules in heated solid materials.

  • Conduction happens between the two substances or objects that are directly in contact with one other.
  • It generally happens when temperature increases; due to this, the heat molecules start to vibrate; these vibrating molecules collide with neighbor molecules and make them vibrate; heat is transferred from the hotter region to the cooler area.
  • The main consequence for conduction to take place is due to the variation in temperature between the two substances that are together.
  • It is mainly seen in solid substances.
  • The collision of molecules occurs in a straight path.

It is how a conduction process occurs in the matter.

Factors affecting conduction and convection heat transfer

The factors which affect the conduction mode of heat transfer are as follows,

  • Area of the cross-section.
  • Time is required for the process to complete.
  • Heat molecules travel the length of distance.
  • Temperature.
  • Nature of matter.

They are some of the critical factors which affect heat transport.

Peclet number

Peclet is a number used to indicate the thermal transfer of heat within a matter.

Peclet is a dimensionless number used to denote the ratio of flow of matter, especially by thermal conduction. It is also obtained by multiplying Reynolds and Schmidt numbers. The formula to calculate Peclet number is as follows,

c7

Where,

u = fluid velocity,

L = characteristic dimension

k = thermal diffusivity of the fluid.

Re = Reynolds Number and

Pr = Prandtl Number

c5 1
Image: Graph of Peclet number of heat transfer of liquid matter for three different stages of transfer.

Peclet number is different for all the modes of heat transfer.

Rayleigh number of convection

The convection number, which is also known as Rayleigh-Benard Convection, is a vital phenomenon discovered.

It is a type of natural convection. The convection number is dimensionless, obtained when there is a flow of heat in a horizontal path. The convection appears due to the factors of gravity and buoyancy. The formula is as given below.

c8

Where,

Tu = temperature of the upper plate

Tb = temperature of the lower plate

L = height of the container

g = Acceleration due to gravity

ν = kinetic of viscous fluid

α = Thermal diffusivity

β = Thermal expansion coefficient

It is a significant number to calculate the rate of convection in a material.

Examples of conduction and Convection

Several examples happen in daily routines in which we experience conduction and convection.

While frying some ingredients in the pan, heat transfer from stove flame to the bottom of pan and then to the elements. It is an example of conduction.

Conduction Vs Convection
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Pixabay free images

But in the case of convection, when you take any liquid in the pan and heat it at the bottom, the molecules of fluid will be able to move freely, and interchange occurs between hot and cold molecules.

Conduction Vs Convection
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Pixabay free images

We observe that when we heat one end of the rod, the other end would automatically heat up because of the convection process of transport of hot molecules from one end to the other end. In the case of conduction, the molecules of matter transfer heat directly to neighboring molecules, and the movement of heat occurs.

When you take any hot beverages, you feel warmth, and it is because of conduction. In the same hot drinks, the steam observed is due to convection.

These are some essential daily routine examples of conduction and convection.

Frequently Asked Questions on conduction and convection| FAQs

Do conduction and convection need matter to transfer heat?

The mode of heat transfer conduction and convection require matter for the process to occur.

If there are two systems that are in contact with each other and if there is a variation in temperature difference between the systems, then the transport of heat happens between the two temperature regions.

Can conduction and convection processes happen together?

The conduction and convection process of heat transfer cannot happen simultaneously.

When heat transfer takes place in a fluid, it is by anyone mode, i.e., convection or conduction. It always depends on the quantity of fluid present. Hence, it is possible to say that the two ways of transfer of heat cannot happen together.

What state of matter can undergo conduction and convection heat transfer?

Conduction and convection depend on the nature of matter to transfer heat.

Conduction usually occurs in solids, but there is no chance of convection due to their molecular structure. Hence, convection can happen only in fluids (gases and liquids) and conduction in solids.

Can the conduction and convection process happen in a vacuum?

Vacuum is different compared to gases or air.

A vacuum is known as a space where matter cannot be seen. Both heat transfer conduction and convection cannot happen in a vacuum due to the absence of states of matter. The heat transfer method that can be seen in a vacuum is the radiation mode of transfer.

State Fourier law of conduction?

The critical law of heat conduction which Fourier states, is given as follows,

The law states as follows, “The rate of flow of heat transport through an object is directly proportional to the region of negative gradient of temperature and area, measures at normal to the gradient, through which heat transports.”

                                                                   Q = -kAdT / dx

where,

The Q= time interval during which the amount of heat 

A= cross-sectional surface area.

dt= the temperature difference between the ends.

dx= the distance between the ends.

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