The energy equation, that is solved along the equation of continuity and the momentum equation, can be formulated by two different approaches, either by using internal energy, or enthalpy. Both internal energy end enthalpy may or may not include heat of formation. When heat of formation is included, the quantity is called absolute, when not, it is called sensible. This results in four possibilities and there are four classes to represent the corresponding possibility:

• sensibleEnthalpy
• sensibleInternalEnergy
• absoluteEnthalpy
• absoluteInternalEnergy

In our case without any chemistry, including heat of formation does not make any sense, so sensible variant is chosen, so the class sensibleInternalEnergy is used and the energy equation will be solved in internal energy. Source code for all classes representing type of energy can be found found in

$FOAM_SRC/thermophysicalModels/specie/thermo

in subdirectories named after respective type of energy, eg.

sensibleInternalEnergy/sensibleInternalEnergy.H