# OpenFOAM Thermophysical Models¶

When the Boussinesq approximation is ‘ON’ the fluid is considered to be incompressible. In that case the the density change is calculated based on the Boussinesq approximation. The fluid properties necessary for this approximation can be specified while selecting the material.

## 1. Viscosity model¶

Viscosity model describes relation between viscosity and strain rate. Different viscosity models are available along with the most widely used Newtonian model.

## 2. Thermal expansion coefficient¶

The Thermal expansion coefficient is the ratio a material expands with respect to change in its temperature.

## 3. Reference temperature¶

The temperature at which the kinematic viscosity is calculated.

## 4. Laminar Prandtl number¶

Prandtl number is the dimensionless parameter defined as the ratio of momentum diffusivity to thermal diffusivity.

$Pr = \frac{\nu }{\alpha }= \frac{c_{p}\mu }{k }$
$$\nu$$ is momentum diffusivity
$$\alpha$$ is thermal diffusivity
$$c_{p}$$ is specific heat
$$\mu$$ is dynamic viscosity
$$k$$ is thermal conductivity

## 5. Turbulent Prandtl number¶

Turbulent Prantl number is the ratio of eddy momentum diffusivity to thermal eddy diffusivity.

$Pr_{t} =\frac{\varepsilon _{M}}{\varepsilon _{H}}$

Where $$\varepsilon _{M}$$ is the eddy momentum diffusivity and $$\varepsilon _{H}$$ is eddy thermal diffusivity.

## 6. Specific heat¶

Specific heat (Cp) is the amount of heat required to increase the temperature of a unit mass by one degree Celsius.