Re-creating Hottel’s emissivity charts for water vapor and extending them to 40 bar pressure using HITEMP-2010 data base

Hottel’s water vapor emissivity chart and the pressure correction chart have been re-created using the most recent HITEMP-2010 data base to provide more accurate values. Hottel’s standard emissivity has been redefined in order to produce smooth and accurate graphs and correlations. The new charts allow for calculating the water vapor emissivities at homogeneous pathways up to 200 bar equivalent pressure, in the 450–3000 K temperature range and in the 0.01–3000 bar cm pressure path length range; a departure from the original Hottel’s emissivity values can be larger than 300% at high pressures. Departures from Leckner’s (1972) correlations are typically in the ± 40% range. Besides the new paper graphs, showing the standard emissivity as well as the pressure correction factor at different temperatures, the calculated emissivities have been tabulated (see Supplementary material) at equivalent pressures ranging from 0.05 bar up to 250 bar. Using appropriate interpolation techniques, these charts can be used as look-up tables to calculate accurate total emissivity values without using pressure correction factors. To this end, linear interpolation for temperature scaling and logarithmic interpolation for pressure and pressure path length scaling are included in the Supplementary material.