A New Method of Determining Moisture Flow Coefficients for both Isothermal and Non-isothermal Conditions
Author
Editor
- Carsten Rode
Summary, in English
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.
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.
Publishing year
2008
Language
English
Pages
975-982
Publication/Series
Proceedings of the 8th Symposium on Building Physics in the Nordic Countries
Volume
2
Document type
Conference paper
Publisher
Department of Civil Engineering, Technical University of Denmark
Topic
- Building Technologies
Keywords
- moisture transport
- isothermal
- phenomenological
- experimental
- non-isothermal
Conference name
8th Symposium on Building Physics in the Nordic Countries, 2008
Conference date
2008-06-16 - 2008-06-18
Conference place
Copenhagen, Denmark
Status
Published
ISBN/ISSN/Other
- ISBN: 978-87-7877-265-7