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A New Method of Determining Moisture Flow Coefficients for both Isothermal and Non-isothermal Conditions

Burke, Stephen LU ; Claesson, Johan LU and Arfvidsson, Jesper LU (2008) 8th Symposium on Building Physics in the Nordic Countries, 2008 In Proceedings of the 8th Symposium on Building Physics in the Nordic Countries 2. p.975-982
Abstract
The calculation of isothermal moisture transport requires a moisture flow coefficient, Dφ(φ,T), for isothermal flow with φ as the moisture state variable. In the non-isothermal case, a second flow coefficient, DTφ(φ,T), is required to account for the temperature gradient. This means that a number of isothermal measurements are required for a few different temperature levels. It also means that a corresponding second set of measurements with temperature gradients are required.

This paper presents a new method of determining these flow coefficients for a set of moisture states and temperature levels. This is accomplished by measuring the change in mass over time as the sample absorbs or desorbs moisture. The sample is sealed and... (More)
The calculation of isothermal moisture transport requires a moisture flow coefficient, Dφ(φ,T), for isothermal flow with φ as the moisture state variable. In the non-isothermal case, a second flow coefficient, DTφ(φ,T), is required to account for the temperature gradient. This means that a number of isothermal measurements are required for a few different temperature levels. It also means that a corresponding second set of measurements with temperature gradients are required.

This paper presents a new method of determining these flow coefficients for a set of moisture states and temperature levels. This is accomplished by measuring the change in mass over time as the sample absorbs or desorbs moisture. The sample is sealed and thermally insulated on all but one side with a heating pad at the top of the sample (within the insulation). This assembly is hung from a balance in a climate box that has a controlled temperature and relative humidity. The sample is exposed to a step-wise change in relative humidity and the change in mass over time is recorded. Care is taken to ensure that the sample is either absorbing or desorbing moisture in order to avoid complications with hysteresis. In the isothermal case, the sample is kept at a constant temperature during the measurements. In the non-isothermal case the sample has a known temperature gradient set by the temperature of the heating pad and the temperature of the climate box. The moisture flow coefficients are obtained from an analysis of the transient changes in mass.

The method and the ideas upon which it is based are presented. A few preliminary results, and technical difficulties encountered during the experimental development, are reported. (Less)
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author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
moisture transport, isothermal, phenomenological, experimental, non-isothermal
in
Proceedings of the 8th Symposium on Building Physics in the Nordic Countries
editor
Rode, Carsten
volume
2
pages
8 pages
publisher
Department of Civil Engineering, Technical University of Denmark
conference name
8th Symposium on Building Physics in the Nordic Countries, 2008
ISBN
978-87-7877-265-7
language
English
LU publication?
yes
id
fd680576-56bf-476d-a7d4-f2c3a6fa0632 (old id 1164023)
date added to LUP
2008-08-29 08:27:08
date last changed
2016-07-01 13:44:30
@inproceedings{fd680576-56bf-476d-a7d4-f2c3a6fa0632,
  abstract     = {The calculation of isothermal moisture transport requires a moisture flow coefficient, Dφ(φ,T), for isothermal flow with φ as the moisture state variable. In the non-isothermal case, a second flow coefficient, DTφ(φ,T), is required to account for the temperature gradient. This means that a number of isothermal measurements are required for a few different temperature levels. It also means that a corresponding second set of measurements with temperature gradients are required. <br/><br>
This paper presents a new method of determining these flow coefficients for a set of moisture states and temperature levels. This is accomplished by measuring the change in mass over time as the sample absorbs or desorbs moisture. The sample is sealed and thermally insulated on all but one side with a heating pad at the top of the sample (within the insulation). This assembly is hung from a balance in a climate box that has a controlled temperature and relative humidity. The sample is exposed to a step-wise change in relative humidity and the change in mass over time is recorded. Care is taken to ensure that the sample is either absorbing or desorbing moisture in order to avoid complications with hysteresis. In the isothermal case, the sample is kept at a constant temperature during the measurements. In the non-isothermal case the sample has a known temperature gradient set by the temperature of the heating pad and the temperature of the climate box. The moisture flow coefficients are obtained from an analysis of the transient changes in mass.<br/><br>
The method and the ideas upon which it is based are presented. A few preliminary results, and technical difficulties encountered during the experimental development, are reported.},
  author       = {Burke, Stephen and Claesson, Johan and Arfvidsson, Jesper},
  booktitle    = {Proceedings of the 8th Symposium on Building Physics in the Nordic Countries},
  editor       = {Rode, Carsten},
  isbn         = {978-87-7877-265-7},
  keyword      = {moisture transport,isothermal,phenomenological,experimental,non-isothermal},
  language     = {eng},
  pages        = {975--982},
  publisher    = {Department of Civil Engineering, Technical University of Denmark},
  title        = {A New Method of Determining Moisture Flow Coefficients for both Isothermal and Non-isothermal Conditions},
  volume       = {2},
  year         = {2008},
}