In autumn and spring a reversed air flow of smoke may occur in very long chimneys of apartment buildings. This is undesirable. Therefore the goal was to propose changes in the design to guarantee that no reversal of air flow in the chimney could happen. Computational Fluid Dynamics (CFD) were used for time dependent simulations.
FEM simulations flow in chimney
Several possible causes were written down after conversations with the technical and maintenance departments. Blueprints of the chimney were used for the simulation of the smoke exhaust. The smoke pipe of the boiler was added for every apartment of the building and a dynamic air flow was simulated. During the use of the chimney it can happen that the warm gases don’t have enough upward force so a reversed flow occurs. This happens for example when starting up the boiler. To prevent this from happening several dynamic flow analyses were carried out to map the geometry and temperature at start-up.
CFD Flow reversal
The thermal flow analyses provided insight into the upward forces of flue gas, which depend in part on the diameter of the chimney. The improved chimney did not show any reversal of flow, and its proper functioning can be guaranteed now in spring and autumn. Several adjustments were proposed for the start-up cycle of the boilers, which all contribute to its performance. This resulted in savings on maintenance and most of all less error messages.