Hi,

Is there a way to model water vapor's absorption of a continuous spectrum?

Water vapor has various vibrational and rotational modes which together contribute to the myriad number of spectroscopy lines as shown in the Hitran spectrum:

If the incident (on the vapor) light is monochromic, it is would be easy to use Beer's law to calculate the absorbance/transmittance. However if radiation is coming from a black-body like object whose spectrum is continuous, like sun or incandescent lamp, then how should the calculation be done?

Can we simply do an integration using the Hitran graph data (txt data obtainable) with the radiation spectrum? I doubt the validity of this approach since if the incident radiation is not monochromatic, it is unknown which spectrum will dominate, hence if we do a simple integration(summation) we would ignore the weighing factor (dominant ones, less-important ones, etc.).

Given the number of water vapor absorbance lines and the continuous nature of the blackbody nature, this appears to be a hard problem and might require some intense computation. Has this problem been studied before? And is there any analytic formula to model it? Does Solidworks Flow Simulation support it?

Jerry

Update:

Should use the table in:

H. C. Hottel. “Radiant Heat Transmission.” In Heat Transmission, ed. W. H. McAdams. 3rd ed. New York: McGraw-Hill, 1954.

cited both by Lienhard A Heat Transfer Textbook, 4/e, pdf.page.584, and by Cengel - Heat Transfer: A Practical Approach in Chapter 12 Radiation Heat Transfer, as the experimental data basis to do the calculation? I guess perhaps the intrinsic complicacy of the problem make it only amanable by direct experimental measurement, rather than calculation/simulation?

The Hottel graph as shown in Lienhard book is attached for reference:

Jerry