How to calculate the water vapor diffusion coefficient

This is an important data required for smoke condensation calculations. In the absence of detailed experimental data, the flue gas from natural gas is treated as moist air. D=2.56*(10^-5)*^1.5*c. t is the temperature in °C, c is the proportion of water vapor, and D is the diffusion coefficient of water vapor, with units of m²/s. The meaning of this formula is that the diffusion coefficient D is proportional to the 1.5th power of the flue gas temperature T, and it is also proportional to the concentration.

Where can I find the origin of this formula? Also, is C the volume fraction?

In the edition of Chemical Engineering Principles by Chen Minheng, there is a method for calculating the diffusion coefficient: D = D. *(T/T. )^1.81*(P/P. ) This is the diffusion rate of water in air. In the formula you provided above, should the percentage value for C be included with a percent sign? For example, if C=13%, should 0.13 or 13 be used? Where did you get your formula from?

It seems you know a lot about this area. When smoke is condensed and heat exchange occurs between the smoke and water, how is the temperature difference for heat exchange determined? It’s not the logarithmic mean temperature difference, right?

c represents the proportion of water vapor; I have seen values of 0.13 raised to the power of 1.5 as well as 1.81. Different reference articles use different exponents, and I’m not sure which one to use. I calculated it using 1.5 to the power of something. The heat exchange due to flue gas condensation must be calculated separately, that is, the heat exchange resulting from temperature differences and the heat exchange resulting from concentration differences; of course, logarithmic averages are used for both temperature differences and concentration differences.

However, the formulas for 1.5 and 1.81 powers are not just related to differences in exponents; the 1.81 power value does not take into account the percentage volume of water vapor, and is only related to pressure and temperature. By calculating the temperature differences separately, it means that the heat exchange areas are calculated independently – one area for sensible heat and another for latent heat. Is the total heat exchange area then the sum of these two areas? I saw an example before, but in that case it was pure steam; the flue gas temperature was 180 degrees at the inlet and 50 degrees at the outlet, with the dew point of water vapor being 51.5 degrees. How is the temperature difference determined in such cases? Thank you

Let’s answer that one last time. 1. When the air excess factor for natural gas flue gas is 1.15, the dew point temperature is 57°C. 2. Heat transfer and mass transfer are calculated separately because their driving forces are different. For example, when the water temperature reaches 53°C, no condensate water is generated on the flue gas side; therefore, only heat transfer occurs, with no mass transfer. When the water temperature is below 53°C, heat and mass transfer occur simultaneously on the flue gas side, but since the driving forces are different, different formulas are used; therefore, they are calculated separately. For mass transfer calculations, the temperature difference is not used instead, the concentration difference is employed. I am preparing to submit an article to the journal “Industrial Boilers” on several issues related to the thermal calculations of condensing boilers. But even if it’s hired, it will have to be published next year. \"Discussion on the Calculation Method of the Reverse Balance Efficiency of Condensing Boilers\" was published in the 5th issue of \"Industrial Boilers\" in 2015, which contains several formulas specifically designed for calculating condensing boilers.

You’ve misunderstood what I meant. When calculating the heat transfer coefficient, the latent heat is taken into account based on the concentration difference; whereas when determining the heat transfer area, it is the overall heat transfer temperature difference that is used. It is this heat transfer temperature difference that determines how to calculate the condensation of flue gas. Also, why is the dew point temperature of your natural gas flue gas so high? When I calculated an excess air coefficient of 1.5, the dew point temperature was 51.5. The dew point temperature should be related to the composition of the natural gas as well as the volume fraction of water vapor