Transport equations for moist air at elevated wet bulb temperatures
(2004) In Drying Technology 22(12). p.201224 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:
http://lup.lub.lu.se/record/138885
 author
 Berg, C G A; Kemp, I C; Stenström, Stig ^{LU} and Wimmerstedt, Roland ^{LU}
 organization
 publishing date
 2004
 type
 Contribution to journal
 publication status
 published
 subject
 in
 Drying Technology
 volume
 22
 issue
 12
 pages
 201  224
 publisher
 TAPPI
 external identifiers

 wos:000220456500015
 scopus:16544367858
 ISSN
 15322300
 DOI
 10.1081/DRT120028229
 language
 English
 LU publication?
 yes
 id
 3d13b83e6c0f49e4b87563c04e12ab9f (old id 138885)
 date added to LUP
 20070625 10:26:22
 date last changed
 20190220 03:59:03
@article{3d13b83e6c0f49e4b87563c04e12ab9f, 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) > 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)).}, author = {Berg, C G A and Kemp, I C and Stenström, Stig and Wimmerstedt, Roland}, issn = {15322300}, language = {eng}, number = {12}, pages = {201224}, publisher = {TAPPI}, series = {Drying Technology}, title = {Transport equations for moist air at elevated wet bulb temperatures}, url = {http://dx.doi.org/10.1081/DRT120028229}, volume = {22}, year = {2004}, }