Issues regarding the formula for calculating the natural ventilation force of chimneys in HG 20680-2011
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Page 37 of HG 20680-2011 provides the formula for the natural ventilation force of chimneys: δP=8*h*（ρ_air-ρ_smoke）*g/10. The notes indicate that ρ_air and ρ_smoke refer to the densities of air and smoke under standard conditions respectively. This formula is different from those in other reference books; from a design perspective, it is advisable to follow the standards. However, after analysis, it seems that the formulas in reference books are easier to understand. I would appreciate guidance from experts on how to interpret this formula. First: Under standard conditions, the densities of air and flue gas in typical calculations are 1.293 and 1.34 respectively; if these values are used, the result will be negative, which is definitely incorrect. Second: Usually, when calculating the natural ventilation force (draw force), temperature corrections are applied to the air density and the smoke density; in high-altitude areas, pressure corrections are also necessary. This formula does not include such corrections, which seems incorrect ； Third: the coefficients outside are 8 and 10, and they don’t have a clear meaning; I’m not sure what they represent. If there are experts from Ningbo Engineering Company or other companies, please help to clarify this. Thank you.
This post was last edited by snakegqw on 2019-9-11 21:24. The guidelines state that you should use r0 empty = 1.293 and r0 smoke = 1.34 to perform temperature corrections in order to calculate density. When the flue gas temperature is high, its density is less than that of air. Note: The corrected unit remains kg/NM3. Do not mistake it for the standard condition at 0°C and 1 atmosphere.