Thermal boundary layer

from Wikipedia, the free encyclopedia
Thermal boundary layers
when heat passes through a solid wall

Thermal boundary layer is the area of ​​a fluid that is influenced by a heat flow out of or into a wall when the wall has a different temperature than the fluid. Instead of a wall, another fluid can also create a thermal boundary layer.

It is not necessary for the fluid to flow; As a rule, a flow will form in the boundary layer area as a result of free convection . If the fluid has an inflow velocity , the heat flow is called "forced convection".

The thermal boundary layer is limited on the one hand by the wall, on the other hand by an imaginary surface on which the temperature no longer changes in the direction of the interior of the fluid.

The thickness of the thermal boundary layer increases in the direction of the flow because, depending on the wall temperature, heat is added to or withdrawn from the fluid. If the fluid flows in a pipe or a channel, the thermal boundary layers on both sides can grow together after a certain distance in the middle. From then on, the area-related heat transfer capacity decreases, as the temperature difference between the wall and the core flow also decreases. The heat transfer capacity cannot be increased at will by lengthening the flow path.