1 / 20

Moist adiabatic processes on a thermodynamic chart.

Moist adiabatic processes on a thermodynamic chart. Atms Sc 4310 / 7310 Lab 3 Anthony R. Lupo. Moist adiabatic processes on a thermodynamic chart. Last time we examined dry adiabatic processes  Now examine moist processes (saturation!)

xenon
Télécharger la présentation

Moist adiabatic processes on a thermodynamic chart.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Moist adiabatic processes on a thermodynamic chart. Atms Sc 4310 / 7310 Lab 3 Anthony R. Lupo

  2. Moist adiabatic processes on a thermodynamic chart. • Last time we examined dry adiabatic processes •  Now examine moist processes (saturation!) •  moist adiabats are lines of moist potential temperature, read; Bluestein, pp 201 – 211..

  3. Moist adiabatic processes on a thermodynamic chart. • Mixing ratio: Mv (mass of vapor) _______________ Md (masss of dry air) • Thermodynamics of dry air  air without any form of water. • Moist air  dry air + water vapor.

  4. Moist adiabatic processes on a thermodynamic chart. • Let: Md = mass of dry air (N2, O2 etc.) • Then: Mv (is the mass of water vapor) • Note: you may see Ml (liquid) or Mi (ice) in this class or in other classes.c

  5. Moist adiabatic processes on a thermodynamic chart. • The mixing ratio (m) (r)  general definition: • m = Mass of trace substance / mass of fluid • so, using water vapor  m, • but ml or mi can also be defined

  6. Moist adiabatic processes on a thermodynamic chart. • The specific humidity • (q) = Mv / Md + Mv • Recall “fun fact” from Atms. 50 •  Water vapor constitutes near 0 to up to 4%, water vapor (usually about 1%)

  7. Moist adiabatic processes on a thermodynamic chart. • Thus, for most situations: “m” roughly equals “q” • Mixing ratio (m)  of air is the actual mixing ratio (and is associated with the dewpoint) • Saturated mixing ratio (ms)  mixing ratio the air would have at the ambient temperature if it was saturated.

  8. Moist adiabatic processes on a thermodynamic chart. • Vapor pressure  partial pressure of water (Dalton’s Law) • Thus the ideal gas law for dry air is • P – e = rd Rd T

  9. Moist adiabatic processes on a thermodynamic chart. • Relate mixing ratio (m) to vapor pressure (e) ! • Relative humidity:

  10. Moist adiabatic processes on a thermodynamic chart. • Equivalent Potential Temperaure: Moist adiabats • Let’s derive!  • 1st law:

  11. Moist adiabatic processes on a thermodynamic chart. • What to do? Let’s • 1. substitute in pa = RT • 2. “parameterize” the Latent Heat Release:

  12. Moist adiabatic processes on a thermodynamic chart. • This becomes equation (1) • OK, let’s leave this alone and look at:

  13. Moist adiabatic processes on a thermodynamic chart. • Take natural log: • Take the derivative of this, and “a little” algebra to get equation (2):

  14. Moist adiabatic processes on a thermodynamic chart. • Hmm…. The RHS of eq. (1) and (2) are the same, so: • Then apply “the snake”

  15. Moist adiabatic processes on a thermodynamic chart. • After integrating, a bit o’ algebra, and assuming: • 1) ws / T  0 • 2) qo = qe • we get moist potential temperature!

  16. Moist adiabatic processes on a thermodynamic chart. • Virtual temperature • When air is inherently moist, if we could take into account the effect of moisture and get a temperature the air would have if it were dry: • p = rd Rd T + rv Rv T • p = r R T = r Rd Tv •  where Tv is the Virtual temperature.

  17. Moist adiabatic processes on a thermodynamic chart. • We can calculate using “brute force” • Tv = (1 + 0.609m)T • where T = Kelvins and m is kg / kg or a unitless number!!

  18. Moist adiabatic processes on a thermodynamic chart. • Or, the shortcut (graphical) method: • Tv = T + (ws / 6) • where T is degrees C and ws is g/kg

  19. Moist adiabatic processes on a thermodynamic chart. • Questions? • Comments? • Criticisms?

  20. Moist adiabatic processes on a thermodynamic chart. • The end!

More Related