Chimney flow

With very long chimneys in apartment buildings, flow reversal of the flue gas can occur in autumn and spring. This is an undesirable situation. The assignment was to make a time-dependent simulation using CFD (Computational Fluid Dynamics) flow calculations and to come up with proposals to adjust the design so that the flue gas discharge can be guaranteed without flow reversal.


Flow in Chimney
Flow detail

Flow reversal,

Based on discussions with the technical and maintenance departments, some possible causes were listed. Construction drawings served as a starting point for the simulation of the flue gas discharge. A dynamic air flow was simulated, and several flue gas channels from the central heating boilers per apartment in the flat were connected to the chimney. When using the chimneys, it may happen that the warm gases cannot exert sufficient upward forces in the chimney, so that when starting up central heating boilers, for example, the flue gases backfire. To prevent this, some dynamic flow analyzes were carried out to map the influence of geometry and temperature on the start-up behavior.

Chimney simulation

The thermal flow analyzes provided insight into the upward forces of the flue gases, which also depend on the diameter of the chimney. The improved chimney no longer shows backfire, and operation can now be guaranteed in autumn and spring. Some adjustments were also proposed in the start-up cycle of the central heating boilers, all of which contribute to improved functionality. This represents a significant saving on maintenance costs, and especially on malfunction reports.