FLUE GAS MOVEMENT IN A FURNACE

The movement of the flue gases in the furnace and in the chimney is due to the temperature difference: hot gases as much lighter rise up, and the colder as heavier they fall down.

Self-moving, based on this principle, we call gravity motion.

Oven malfunction, or a chimney, often referred to as "bad thrust". It would follow from the definition, that it is about the phenomenon of "gas drawing". Meanwhile, it is in fact the lack of a proper one, the necessary differential pressure, as found in the ducts and ducts of the furnace. From what we said above, that the colder as heavier gases fall down, and the hot ones rise to the top as lighter ones, results, that the hot gases can exert pressure by their upward draft, which displaces the colder gases from the stove or chimney to the outside.

Of course, in the movement of gases, the physical obstacles in their path are of great importance.

The cause of the air draft in the ducts of the furnace and in the chimney is the difference in air weight depending on the temperature.

Weight 1 m3 of air at different temperatures is presented below:

temperature weight 1 m3 of air

0°C 1,29 kG

273°C 0,645 kG

546°,C 0,430 kG

819°C 0,332 kG

1365°C 0,258 kG

1638°C 0,215 kG

The gas temperature at the chimney inlet must not be too high, because the thermal efficiency of the furnace is then reduced due to the escape of hot gases into the chimney. However, this temperature must not be lower than 100 ° C, because at lower temperatures we can get too little draft, not sufficient to overcome the resistance to the flow of gases through the furnace channels and the chimney flue.

Gases can flow through the channels of the furnace in two ways: creating vortices and recurrences due to uneven and rough canal walls or their sharp bends, and calmly and gently with speed 2,5 m / sec. The first way of flow is called turbulent movement, the other is the laminar movement of gases. In laminar motion, gas particles flow through the channel in a layered motion, i.e.. they flow in almost parallel layers, while turbulent motion creates vortices and strong swirls of gas particles.

In a rationally constructed furnace, the movement of gases should be laminar. There is less heat flow in laminar motion, but the drag due to friction of the gas particles against the channel walls is also lower, hence the losses of thermal energy are lower. Accordingly, changes in cross-sections in the construction of the furnace channels are undesirable, and the kinks of the channels should be gentle.