Water sorption in wood and modified wood at high values of relative humidity. Part I: Results for untreated, acetylated, and furfurylated Norway spruce

Holzforschung ◽  
2010 ◽  
Vol 64 (3) ◽  
Author(s):  
Lisbeth G. Thygesen ◽  
Emil Tang Engelund ◽  
Preben Hoffmeyer
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Norway Spruce ◽  
Water Sorption ◽  
Capillary Condensation ◽  
Theoretical Contribution ◽  
Low Field ◽  
Condensed Water ◽  
Relaxation Curves ◽  
Curve Form

Abstract Desorption isotherms at 20°C for untreated, acetylated, and furfurylated Norway spruce [Picea abies (L.) Karst.] sapwood were established in the 91.9–99.9% relative humidity (RH) range. Three methods were employed to secure various constant RH levels: saturated salt solutions, climate chambers, and the pressure plate technique. The curve form for the untreated samples did not show an upward bend, except perhaps above 99.5% RH, indicating that – contrary to what has hitherto been assumed – capillary condensation does not play a significant role for water sorption in wood below fiber saturation. Three additional results corroborate this conclusion: (1) calculation of the theoretical contribution of capillary condensation to the moisture content (MC) in wood based on idealized microstructural geometries by means of the Kelvin and Laplace equations resulted in very small contributions to the equilibrium moisture content (EMC), i.e., below 0.35% moisture at 99.9% RH. (2) The ratio between the EMC of acetylated and untreated samples did not show an increasing trend for increasing RH, as would have been the case if capillary condensation had taken place in both untreated and acetylated wood. (3) Low field time domain nuclear magnetic resonance results showed that only the relaxation curves from the furfurylated samples were affected systematically by freezing, indicating that neither untreated nor acetylated wood contained significant amounts of capillary condensed water.

Water sorption in wood and modified wood at high values of relative humidity. Part 2: Appendix. Theoretical assessment of the amount of capillary water in wood microvoids

Holzforschung ◽  
2010 ◽  
Vol 64 (3) ◽  
Author(s):  
Emil Tang Engelund ◽  
Lisbeth G. Thygesen ◽  
Preben Hoffmeyer
Keyword(s):  
Relative Humidity ◽  
Theoretical Study ◽  
Capillary Condensation ◽  
Small Contribution ◽  
Structural Elements ◽  
Capillary Water ◽  
Bordered Pits ◽  
Condensed Water ◽  
Theoretical Assessment ◽  
Theoretical Amount

Abstract A theoretical study of the amount of moisture held in wood as capillary condensed water in the relative humidity (RH) range of 90–99.9% is carried out. The study is based on idealized geometries of the softwood structure related to micrographs. It is confined to structural elements such as bordered pits and the pointed ends of tracheids. The theoretical amount of water in these elements is found by employing the Kelvin equation. An equal amount of earlywood and latewood cells with different geometries and with different amounts of pits is assumed. The effect of pit aspiration is considered, and different degrees of pit aspiration are assigned to earlywood and latewood. We suggest based on the results that capillary condensation makes only a very small contribution to the equilibrium moisture content. At 99.9% RH the contribution amounts to less than 0.0035 kg water per kg dry wood. This is in line with the experimental results presented in Part 1 of this study.

scholarly journals Equilibrium moisture content (EMC) in Norway spruce during the first and second desorptions

Holzforschung ◽  
2011 ◽  
Vol 65 (6) ◽  
pp. 875-882 ◽  
Author(s):  
Preben Hoffmeyer ◽  
Emil Tang Engelund ◽  
Lisbeth G. Thygesen
Keyword(s):  
Moisture Content ◽  
Norway Spruce ◽  
Equilibrium Moisture Content ◽  
Initial Conditions ◽  
Boundary Curve ◽  
Significant Loss ◽  
Desorption Isotherm ◽  
Oven Drying ◽  
Low Field ◽  
Drying And Rewetting

Abstract It is a commonly accepted notion that the equilibrium moisture content (EMC) of wood at a given relative humidity (RH) is highest during initial desorption of green wood due to an irreversible loss of hygroscopicity during the 1st desorption. The basis for this notion is investigated by assessing how drying and saturation procedures influence the differences between the 1st and the 2nd desorption curves for Norway spruce (Picea abies (L.) Karst.) sapwood. The study establishes 1st and 2nd desorption isotherms for a variety of initial conditions and it covers the RH range from 60.1% to 99.9%. The state of the water is not affected by oven-drying and rewetting as demonstrated by time domain low field NMR relaxometry. The results challenge the conclusions of earlier studies and indicate that in these studies the 2nd desorption was initiated at much too low EMC and therefore fails to describe a boundary desorption isotherm. Instead, it becomes an intermediate desorption isotherm starting at the adsorption boundary curve and crossing over to eventually meet the desorption boundary curve. The results also show that vacuum drying at room temperature only gives a modest loss of hygroscopicity compared to the green state. Conversely, oven-drying at 103°C results in a more significant loss of hygroscopicity, except for RH above 96% where an increase in EMC surprisingly is seen.

scholarly journals The Thermodynamics of Tobacco-Water Interactions

1999 ◽  
Vol 18 (5) ◽  
pp. 189-204
Author(s):  
JL Banyasz
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Binding Sites ◽  
Water Sorption ◽  
Water System ◽  
Free Water ◽  
Water Binding ◽  
Sorption Data ◽  
General Role ◽  
Water Sorption Isotherm

AbstractAn equation to describe the water sorption isotherm of tobacco is developed based on a model of the tobacco-water system as a mixture or solid solution comprised of water and water binding sites of many different kinds. It is assumed that free water has an activity coefficient of one. The result is an equation that predicts moisture content as a function of relative humidity given the numbers of each of the different kinds of sites and the associated water binding equilibrium constants. It is shown that this multi-site equation reduces to a one site equation if the different kinds of water binding sites are symmetrically distributed with regard to their affinity for water. The result is a two parameter, average site equation that fits water sorption data for tobacco over the range of 10-80% relative humidity. The average site equation is identical to the equation derived by BRUNAUER, EMMETT and TELLER for binding to surface sites (1). The two models start from very different points of view but come to the same conclusion because they are ultimately based on thermodynamics which is indifferent as to the physical nature of the sites. Inferences as to the microscopic nature of water binding sites cannot be made from thermodynamic isotherm equations. In order to describe the effects of water on the physical properties of tobacco the solution analogy is extended further. If tobacco is a mixture or solution of unhydrated sites, hydrated sites and free water, then the value of a physical property should be a function of the concentrations of those species and the associated partial molar values of the property. As the total moisture content changes the distribution of species will change and, in turn, change the properties. Applications of this rationale are presented for heat capacity, thermal diffusivity and the kinetics of the Browning reaction. The results demonstrate that the parameters derived from water sorption data play a more general role in the thermodynamics of the tobacco-water system.

scholarly journals Humidity-dependence of the hydroxyl accessibility in Norway spruce wood

Cellulose ◽  
2020 ◽  
Author(s):  
Michael Altgen ◽  
Lauri Rautkari
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Norway Spruce ◽  
Deuterium Oxide ◽  
Dry Mass ◽  
Thin Sections ◽  
Dependent Change ◽  
The Fourier Transform ◽  
Humidity Dependence

Abstract This study aimed at a better understanding of the wood-water interaction, in particular the role of the hydroxyl accessibility during the humidity-dependent change in moisture content. Thin sections (80 µm) of never-dried Norway spruce sapwood that contained early- and latewood were used for the experiments. Sorption isotherm measurements confirmed the humidity-dependent moisture content changes and the effect of the first drying of the wood sections. Changes in hydroxyl accessibility were then determined by deuteration of the sections using deuterium oxide, followed by their re-protonation in water (H2O) vapor at different relative humidity: 15, 55 or 95%. The deuteration and re-protonation of the wood sections were quantified by dry mass changes as well as by changes in the OH and OD stretching vibrations in the Fourier transform infrared spectra. The results showed that the deuterated sections could be almost completely re-protonated in H2O vapor, nearly irrespective of the applied relative humidity. Therefore, changes in hydroxyl accessibility were not the driving force for the humidity-dependent changes in moisture content. However, a slow re-protonation rate at low relative humidity had to be considered. Nonetheless, a small quantity of OD groups persisted the re-protonation in H2O vapor and liquid H2O, which was not related to the drying of the wood. Graphic abstract

scholarly journals Moisture Performance of Façade Elements Made of Thermally Modified Norway Spruce Wood

Forests ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 348 ◽  
Author(s):  
Miha Humar ◽  
Boštjan Lesar ◽  
Davor Kržišnik
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Norway Spruce ◽  
Spruce Wood ◽  
Moisture Performance ◽  
Average Relative Humidity ◽  
Thermally Modified Wood ◽  
Moisture Content Measurement ◽  
Modified Wood

Wooden façades are gaining in importance. Thermally modified wood is becoming one of the preferred materials for claddings. In spite of the fact that façades made of thermally modified wood have been in use for more than two decades, reports about long-term monitoring have been sparse. The results of three-year monitoring of a façade made of thermally modified wood in Ljubljana are reported. Moisture content measurements of thermally modified façades were taken at 22 locations and compared to the moisture content of untreated Norway spruce wood. Temperature and relative humidity were recorded in parallel. The moisture content of the wood was compared to the average relative humidity before the measurements. The results confirm the lower moisture content of thermally modified wood in comparison to reference Norway spruce. The moisture content of the wooden façade could be best correlated with the average relative humidity and temperature 48 h before the wood moisture content measurement was taken.

CATFISH DRYING (Clarias Batraclus) USING ‘TEKO BERSAYAP’ SOLAR DRYER

2012 ◽  
Vol 2 (1) ◽  
pp. 14-20
Author(s):  
Yuwana Yuwana
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Ambient Temperature ◽  
Drying Rate ◽  
Drying Process ◽  
Drying Time ◽  
Ambient Relative Humidity ◽  
Solar Dryer

Experiment on catfish drying employing ‘Teko Bersayap’ solar dryer was conducted. The result of the experiment indicated that the dryer was able to increase ambient temperature up to 44% and decrease ambient relative humidity up to 103%. Fish drying process followed equations : KAu = 74,94 e-0,03t for unsplitted fish and KAb = 79,25 e-0,09t for splitted fish, where KAu = moisture content of unsplitted fish (%), KAb = moisture content of splitted fish (%), t = drying time. Drying of unsplitted fish finished in 43.995 hours while drying of split fish completed in 15.29 hours. Splitting the fish increased 2,877 times drying rate.

Inorganic salt hydrates and zeolites composites studies for thermochemical heat storage

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ata Ur Rehman ◽  
Muhammad Zahir Shah ◽  
Shehla Rasheed ◽  
Wasim Afzal ◽  
Muhammad Arsalan ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Water Sorption ◽  
Inorganic Salt ◽  
Heat Storage ◽  
Water Molecules ◽  
Thermochemical Heat Storage ◽  
Dehydration Enthalpy ◽  
Salt Hydrates ◽  
Heat Storage Materials ◽  
Pure Salt

Abstract Salt hydrates (MgSO4 and ZnSO4) impregnated in zeolites, offer a variety of improvements, mostly providing a large surface area for salt hydrates and water molecules. A composite of 5 and 10% of salt contents were prepared as heat storage materials. The study’s finding showed that dehydration enthalpy of MgSO4 (1817 J g−1) and ZnSO4 (1586 J g−1) were 10 and 15% improved than pure salt hydrates by making composites. During the hydration process of composites, the water sorption is 30–37% improved and further the increasing of salt contents in composites enhances more 10% increase in the water resorption. The cyclicability of MgSO4/zeolite and ZnSO4/zeolite were 45 and 51% improved than their corresponding pure salt hydrates. The effect of humidity on the water sorption result reveals that composites of MgSO4/zeolite and ZnSO4/zeolite at 75% relative humidity (RH), the mass of water are 51 and 40% increase than 55% RH.

scholarly journals Study on the Moisture Absorption and Thermal Properties of Hygroscopic Exothermic Fibers and Related Interactions with Water Molecules

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 98 ◽  
Author(s):  
Yi Cui ◽  
Shuyi Gao ◽  
Ruiyun Zhang ◽  
Longdi Cheng ◽  
Jianyong Yu
Keyword(s):  
Moisture Content ◽  
Thermal Performance ◽  
Water Sorption ◽  
Moisture Absorption ◽  
Bound Water ◽  
Absorption Process ◽  
Heating Performance ◽  
Hygroscopic Behavior ◽  
Water Sorption Capacity ◽  
Main Factor

The aim of this paper is to study the hygroscopic behavior of hygroscopic exothermic fiber-based materials and to obtain a better understanding of the thermal performance of these fibers during the moisture absorption process. The temperature distribution of different kinds of hygroscopic exothermic fibers in the process of moisture absorption, observed by infrared camera, demonstrated two types of heating performance of these fibers, which might be related to its hygroscopic behavior. Based on the sorption isotherms, a Guggenheim-Anderson-de Boer (GAB) multi-layer adsorption model was selected as the optimal moisture absorption fitting model to describe the moisture absorption process of these fibers, which illustrated that water sorption capacity and the water–fiber/water–water interaction had a significant influence on its heating performance. The net isosteric heats of sorption decreased with an increase of moisture content, which further explained the main factor affecting the heat dissipation of fibers under different moisture contents. The state of adsorbed water and water vapor interaction on the fiber surface were studied by simultaneous thermal analysis (TGA-DSC) measurement. The percentage of bound and unbound water formation at low and high humidity had a profound effect on the thermal performance of fibers. It can therefore be concluded that the content of tightly bound water a strong water–fiber interaction was the main factor affecting the heating performance of fibers at low moisture content, and the content of loosely bound water reflected that water sorption capacity was the main factor affecting the heating performance of fibers at high moisture content. This was further proven by the heat of desorption.

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