What is the Difference Between Convection and Diffusion

The key difference between convection and diffusion is that convection is the large movement of a large mass of particles in the same direction through the fluid, whereas diffusion is the movement of single particles and transfer of particle’s momentum and energy to other particles in the fluid.

Convection and diffusion are two physical processes we can describe chemically through the movement of particles.

1. Overview and Key Difference
2. What is Convection
3. What is Diffusion
4. Convection vs Diffusion in Tabular Form
5. Summary – Convection vs Diffusion

What is Convection?

Convection is the process of heat transfer through the bulk movement of molecules within fluids. The fluid can be either a gas or a liquid. Initially, the heat transfer between the fluid and an object occurs through conduction; however, the bulk heat transfer occurs due to the motion of the fluid. We can simply say convection is the heat transfer process in fluids through the actual motion of matter. This process can occur as a natural or a forced process.

Concerning the process of convection, heating a fluid causes thermal expansion, and the layers which are closest to the heating source gets hotter and become less dense. Thus, followed by this is the rising up of the hotter part of the fluid according to buoyancy where the colder fluid layers tend to replace the rising hot fluid layers. This process repeats, and it is the process of convection where heat transfer occurs.

There are two forms of convection as natural convection and forced convection. Natural convection occurs due to the buoyant force, and forced convection occurs due to an external source such as wind from a fan or a pump.

What is Diffusion?

Diffusion is the movement of molecules from a region of high concentration to a low concentration via a concentration gradient. These movements occur in the same solution. The factors that affect the concentration gradient affects diffusion as well.

In diffusion, this motion is terminated when the concentrations of the two regions become equal at every point. This means this motion occurs until the concentration gradient disappears. Then the molecules spread everywhere inside the solution.

The rate of the movement of the molecules through diffusion is a function of temperature, the viscosity of the gas (or fluid) and particle size. Usually, molecular diffusion describes the net flux of molecules from a region of high concentration to a low concentration. When considering the two systems, A1 and A2, which are at the same temperature and are capable of exchanging molecules between them, a change in the potential energy in either of these systems can create an energy flow from one system to the other (from A1 to A2 or vice versa). This is because any system naturally prefers low energy and high entropy states. This creates a state of molecular diffusion.

What is the Difference Between Convection and Diffusion?

Convection and diffusion are physical processes we can describe chemically through the movement of particles. The key difference between convection and diffusion is that convection is the large movement of a large mass of particles in the same direction through the fluid, whereas diffusion is the movement of single particles and transfer of particle’s momentum and energy to other particles in the fluid.

The following infographic lists the differences between convection and diffusion in tabular form for side by side comparison.

Summary – Convection vs Diffusion

Convection is the process of heat transfer through the bulk movement of molecules within fluids. Diffusion is the movement of molecules from a region of high concentration to a low concentration via a concentration gradient. Therefore, the key difference between convection and diffusion is that convection is the large movement of a large mass of particles in the same direction through the fluid, whereas diffusion is the movement of single particles and transfer of particle’s momentum and energy to other particles in the fluid.

Reference:

1. “What Is Convection? – Definition, Types, Examples.” BYJUS, 8 Sept. 2020.

Image Courtesy:

1. “Convection cells” By Convection_cells.png: theresa knott (original), Joanjoc version without textderivative work: McSush – This file was derived from: Convection cells.png: (CC BY-SA 3.0) via Commons Wikimedia
2. “Blausen 0315 Diffusion” By BruceBlaus – Own work (CC BY 3.0) via Commons Wikimedia