# Thermal Field¶

## Basic Concepts¶

Thermal fields, which are an extension of the scalar field, are used to describe the time-evolution of a temperature field across the flow domain. When evoking the thermal field, users specify the initial temperature of the fluid, the thermal diffusivity, the specific heat and, if desired, the fluid expansion coefficient and viscosity activation energy. The thermal diffusivity and specific heat influence the rate of thermal transport through the fluid, and temperature increase associated with thermal viscous dissipation. The fluid expansion coefficient, which informs natural convection, describes the link between temperature and density. The viscosity activation energy links the local viscosity to the local temperature field.

Tank walls can be either insulating or assume a constant surface temperature. Likewise, tank internals can be either insulating or assume a constant surface temperature. The temperature at each inlet can likewise be specified independently. The time-evolution of the fluid temperature is recorded in the output file thermodynamics.dat.

For tank internals defined with a constant surface temperature, the time-evolution of the surface heat flux into the fluid is printed to the internalsN.dat file. From this heat flux data, users can predict convective heat transfer coefficients using a representative temperature difference and the surface area. The average temperature across each inlet and outlet is recorded in the inletOutletDataN.dat files. With the temperature field activated, the solver automatically accounts for the effects of viscous dissipation on temperature rise, thereby satisfying the first law of thermodynamics.

## Properties¶

- Minimum Temperature
Minimum allowable temperature in the system [K]

- Maximum Temperature
Maximum allowable temperature in the system [K]

- Global Heating
Adds a global volumetric heating rate to the thermal field. [W/m^3]. May be an expression as function of time ‘t’

- Dissipation Heating
Enable or disable heating from EDR

- Limiter
Flux limiter for convective term

- Advection Algorithm Option
Lattice: Use LBM algorithm to solve thermal field

Finite Volume: Use conventional finite volume method to propogate thermal field

- Initial Temperature
Fluid Initial Temperature (K)

- Input Option
Change thermal properties

Constant: Use this whenever possible. Thermal properties are all constant

CPU MuParser: Thermal properties may be function of temperature ‘T’. Enables MuParser expression inputs for each property.

GPU CUDA Code: Thermal properties may be function of temperature ‘T’. Enables CUDA code inputs for each property.

- Specific Heat
Specific heat of the base fluid (J/kg-K)

- Conductivity
Thermal conductivity (W/(m*K))

- Expansion Coefficient
Fluid Thermal Expansion (1/K)

- Boundary Conditions
This section lists out all available boundary conditions that can be configured with the thermal field Each boundary may be configured with a boundary condition type

Constant Temperature: Holds temperature of surface constant at specified temperature [K]

Adiabatic: Enforces a zero gradient boundary condition on the surface

Heat Flux: Specify the heat flux at a boundary condition with a constant, CPU, or GPU code.