## What are boundary conditions in mechanics?

In FEM boundary conditions are used to describe the state between the associated parts of a body model. The mechanical boundary conditions include the load boundary condition and the displacement condition.

## What is heat transfer boundary condition?

Surface-based heat transfer boundary conditions represent either a known physical state, such as temperature, or an amount of heat entering or leaving the device, such as a heat flux. Temperature is the only condition that can be applied to openings and wall surfaces. You should apply the others only to wall surfaces.

**What is the formula for calculating diffusion?**

Diffusion coefficient is the proportionality factor D in Fick’s law (see Diffusion) by which the mass of a substance dM diffusing in time dt through the surface dF normal to the diffusion direction is proportional to the concentration gradient grad c of this substance: dM = −D grad c dF dt.

### What is the difference between diffusion and convection?

Diffusion occurs via the random motion of molecules; movement is from high to low concentration and depends upon the size of the molecule. Convection is the transport of a substance by bulk flow, where bulk flow is often the movement of fluid down a pressure gradient.

### Is convection diffusion equation parabolic?

Common simplifications. In this form, the convection–diffusion equation combines both parabolic and hyperbolic partial differential equations.

**What do you mean by diffusion equation?**

The diffusion equation is a parabolic partial differential equation. In physics, it describes the macroscopic behavior of many micro-particles in Brownian motion, resulting from the random movements and collisions of the particles (see Fick’s laws of diffusion).

#### What is Fick’s second law of diffusion?

Fick’s 2nd law of diffusion describes the rate of accumulation (or depletion) of concentration within the volume as proportional to the local curvature of the concentration gradient.