Why spirals are provided at the Idustrial Boiler Chimney

Chimney:-

Chimney, as we know, is used to reject the flue gases to the atmosphere, coming from the Steam Boiler during operation. Also, it is a megastructure in Steam Boiler assembly and any discrepancy in its structural and foundation work can cause extremely serious damages, may even lead to casualties or plant shut off till its re-erection. The designer must consider all the factors while designing chimneys and one of the major factors amongst them is the wind factor. Blowing wind tries to overcome its static inertia but fails, if spirals are provided on the surface of the chimney.

BUT THE QUESTION IS HOW?????

Consider a chimneys (without spiral wings), when the blowing wind comes in contact with its upstream surface, stagnation point (zero velocity) is achieved at that point i.e. pressure generated is high at that point and at the downstream end a vacuum is created as the wind coming in contact with the chimneys, gets deflected and meets after some point (wake region) downstream of the chimney. Longer is this joining point of two wind streams, greater is the vacuum created by them. So, we have high pressure on the upside and vacuum on the downside. This pressure difference tries to push the chimney in the direction of the wind. It can be avoided by spiraling the top outer surface of the chimney. After their fit-up, now when the wind comes in contact with the surface, again the stagnation point is achieved at the upstream side but the wind instead of getting deflected, gets aligned (wrapped up) to the surface because of spiral wings and both the deflected portions of the wind, gets attached to themselves on the downside of the chimney, quite early thereby narrowing down the vacuum region. The pressure difference between the up and the downside gets largely reduced. And due to this reduction, the force trying to fall the chimney becomes inadequate to affect the robustness of Chimneys.

We, at Thermodyne, supply chimneys designed as per IS-6533 (part 1 & 2) with spirals fitted at our workshops, to enhance the safety of the complete Steam Boiler assembly.