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Transport equations for moist air at elevated wet bulb temperatures

Berg, C G A; Kemp, I C; Stenström, Stig LU and Wimmerstedt, Roland LU (2004) In Drying Technology 22(1-2). p.201-224
Abstract
In meteorological applications psychrometers are used both as a humidity transfer standard and as a measurement instrument. Unfortunately wet bulb temperature, t(wb), is not a thermodynamic property and consequently, in equation linking vapor pressure and temperature, the psychrometer constant, from now on called the psychrometer coefficient, a, must be experimentally evaluated. Both theoretical formulations and experimental results show that the psychrometer coefficient, a, depends on a number of parameters. In this work a thermodynamic model of the coupled heat and mass transfer formulation of an adiabatic drying process is derived to state the adiabatic saturation temperature, t(as). Derived equations are also used in a couple of... (More)
In meteorological applications psychrometers are used both as a humidity transfer standard and as a measurement instrument. Unfortunately wet bulb temperature, t(wb), is not a thermodynamic property and consequently, in equation linking vapor pressure and temperature, the psychrometer constant, from now on called the psychrometer coefficient, a, must be experimentally evaluated. Both theoretical formulations and experimental results show that the psychrometer coefficient, a, depends on a number of parameters. In this work a thermodynamic model of the coupled heat and mass transfer formulation of an adiabatic drying process is derived to state the adiabatic saturation temperature, t(as). Derived equations are also used in a couple of calculated examples to show to the reader why some psychrometric relations tend to be less usable at high wet bulb temperatures. The authors have found, based on the calculations, that the past conclusions of experimental studies of adiabatic evaporation from a water surface in humid air may verify both an assumption that the apparent heat transfer coefficient, is greater than the apparent mass transfer coefficient, alpha'(tot), (i.e., alpha(tot) > alpha'(tot) and t(wb) > t(as)) as well as an assumption that the apparent heat transfer coefficient is smaller than the apparent mass transfer coefficient (i.e., alpha(tot) < alpha'(tot) and t(wb) < t(as)) although pure analogy considerations propose that the apparent heat transfer coefficient is smaller than the apparent mass transfer coefficient (i.e., alpha(tot) < alpha'(tot) and t(wb) < t(as)). (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Drying Technology
volume
22
issue
1-2
pages
201 - 224
publisher
TAPPI
external identifiers
  • wos:000220456500015
  • scopus:16544367858
ISSN
1532-2300
DOI
10.1081/DRT-120028229
language
English
LU publication?
yes
id
3d13b83e-6c0f-49e4-b875-63c04e12ab9f (old id 138885)
date added to LUP
2007-06-25 10:26:22
date last changed
2017-01-01 04:39:26
@article{3d13b83e-6c0f-49e4-b875-63c04e12ab9f,
  abstract     = {In meteorological applications psychrometers are used both as a humidity transfer standard and as a measurement instrument. Unfortunately wet bulb temperature, t(wb), is not a thermodynamic property and consequently, in equation linking vapor pressure and temperature, the psychrometer constant, from now on called the psychrometer coefficient, a, must be experimentally evaluated. Both theoretical formulations and experimental results show that the psychrometer coefficient, a, depends on a number of parameters. In this work a thermodynamic model of the coupled heat and mass transfer formulation of an adiabatic drying process is derived to state the adiabatic saturation temperature, t(as). Derived equations are also used in a couple of calculated examples to show to the reader why some psychrometric relations tend to be less usable at high wet bulb temperatures. The authors have found, based on the calculations, that the past conclusions of experimental studies of adiabatic evaporation from a water surface in humid air may verify both an assumption that the apparent heat transfer coefficient, is greater than the apparent mass transfer coefficient, alpha'(tot), (i.e., alpha(tot) &gt; alpha'(tot) and t(wb) &gt; t(as)) as well as an assumption that the apparent heat transfer coefficient is smaller than the apparent mass transfer coefficient (i.e., alpha(tot) &lt; alpha'(tot) and t(wb) &lt; t(as)) although pure analogy considerations propose that the apparent heat transfer coefficient is smaller than the apparent mass transfer coefficient (i.e., alpha(tot) &lt; alpha'(tot) and t(wb) &lt; t(as)).},
  author       = {Berg, C G A and Kemp, I C and Stenström, Stig and Wimmerstedt, Roland},
  issn         = {1532-2300},
  language     = {eng},
  number       = {1-2},
  pages        = {201--224},
  publisher    = {TAPPI},
  series       = {Drying Technology},
  title        = {Transport equations for moist air at elevated wet bulb temperatures},
  url          = {http://dx.doi.org/10.1081/DRT-120028229},
  volume       = {22},
  year         = {2004},
}