Moisture content gradient in a softwood board during drying: simulation from a 2-D model and measurement

1996 ◽  
Vol 30 (3) ◽  
Author(s):  
Shusheng Pang
Keyword(s):  
Moisture Content ◽  
D Model ◽  
Moisture Content Gradient

scholarly journals Quality Assessment of Air-dried Teakwood Boards Using Moisture Content Gradients

2016 ◽  
Vol 24 (0) ◽  
Author(s):  
Djeison Cesar Batista ◽  
José Tarcísio da Silva Oliveira ◽  
Rená Porto Pizetta ◽  
Vinicius Munaldi Lube
Keyword(s):  
Moisture Content ◽  
Average Moisture Content ◽  
Drying Process ◽  
Air Drying ◽  
Kiln Drying ◽  
Moisture Meter ◽  
Environment Control ◽  
Moisture Content Gradient

ABSTRACT The determination of moisture content gradients is one of the most important steps for assessing the quality of wood drying. The general aim of this work was to study the quality of air-dried teakwood boards according to the gradients of moisture content in thickness and length. Six representative boards (40 × 180 × 2,300 mm) were sampled from a stack air-dried under shelter, divided into 30 equal parts in length and measured with a resistance moisture meter, resulting in four treatments: two depths (1/4 and 1/2 thickness) and two surfaces (inner and outer) of measurement. As main results, we can conclude that the air-drying quality can be considered good, mainly for two reasons: i) the average moisture content gradients in thickness were comparable to those reported in literature for kiln-drying of less thick boards; ii) the range of average moisture content among boards (2.5 p.p.) was satisfactory for a drying process carried out without environment control. Length moisture content gradient was completely different from that reported in literature, in which no board tops had smaller moisture content than the parts comprehended in between the tops.

Dynamic Bending of an Oak Board Due to a Moisture Content Gradient

2017 ◽  
Author(s):  
T. Arends ◽  
L. Pel ◽  
H. P. Huinink ◽  
H. L. Schellen ◽  
D. M. J. Smeulders
Keyword(s):  
Moisture Content ◽  
Dynamic Bending ◽  
Moisture Content Gradient

OBSERVATIONS ON THE PERMEABILITY OF HYGROSCOPIC MATERIALS TO WATER VAPOUR: I. OBSERVATIONS AT RELATIVE HUMIDITIES LESS THAN 75%

1940 ◽  
Vol 18a (6) ◽  
pp. 105-121 ◽  
Author(s):  
J. D. Babbitt
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Vapour Pressure ◽  
Fick’S Law ◽  
Moisture Movement ◽  
Fick's Law ◽  
Vapour Pressure Difference ◽  
Moisture Content Gradient ◽  
Vapour Pressure Gradient

It is pointed out that experimental work has shown that for the transpiration of moisture through hygroscopic materials two distinct regions of relative humidity can be distinguished: (i) A region below some value between 70 and 80% where the moisture movement is proportional to the vapour pressure difference, and (ii) a region of high relative humidity where the moisture movement is not directly proportional to the vapour pressure. A theory is advanced that these two regions correspond to the two conditions in which water may be present in a hygroscopic material: (i) the water may be molecularly adsorbed, that is to say, the water is bound by the affinity of the molecules of water for those of the solid on which it is adsorbed; (ii) the water may be held in small fissures in the sub-microscopic structure of the sorbing material by capillary forces. The mechanism by which the moisture will move through the material would be different in the two cases and would result in the distinction between regions of high and of low relative humidity.A short discussion is given of Fick's law showing the form in which it might be expected to apply in the two cases. Measurements are given for fibreboards showing that below 75% relative humidity the resistance of the board to moisture transpiration is proportional to the thickness. The moisture content gradients through fibreboard samples have been determined. The diffusance through a board in which the moisture content gradient is opposed to the vapour pressure gradient shows that the latter is the important factor, and the determination of the moisture content gradient indicates that at these low humidities Fick's law is applicable.

scholarly journals Application of the Response Surface Methodology for Designing Oscillation Drying of Beech Timber

Forests ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 541
Author(s):  
Jerzy Majka ◽  
Wiesław Olek
Keyword(s):  
Response Surface Methodology ◽  
Moisture Content ◽  
Response Surface ◽  
Maximum Rate ◽  
Early Stage ◽  
Phase 1 ◽  
Initial Moisture Content ◽  
Drying Time ◽  
Flux Change ◽  
Moisture Content Gradient

Oscillation drying is one of the possible approaches for reducing drying time and limiting drying defects of hardwood timber. This study aimed to design oscillation-drying schedules for beech (Fagus sylvatica L.) timber using the response surface methodology (RSM) and to develop an empirical model describing relationships between drying time, drying rate, moisture content gradient after drying, and the parameters of oscillation drying, i.e., dry-bulb temperature increase, equilibrium moisture content (EMC) decrease, and the duration of phase #1 in the drying schedule. The design employed 8 unique drying schedules for which early stage of drying was studied. The Gompertz model was used to describe the change in moisture flux as a function of moisture content, with estimated parameters of the model used to determine relations between the maximum flux at the initial moisture content, the maximum rate of flux change, and the critical moisture content for the maximum rate of flux change for each oscillation-drying schedule. Analysis of variance (ANOVA) revealed that the decrease in EMC was the only factor significantly influencing oscillation drying. For the most intense oscillation-drying schedule, maximum moisture flow was ca. 75% higher compared with the control drying schedule. Drying processes that accounted for a decrease of EMC from 15% to 12% were characterized by significantly shorter drying time (by 35.8%), 52.6% higher drying intensity, and ca. two times larger moisture content gradient. These results confirm theoretical findings relating the increase of oscillation-drying intensity with the difference in wet-bulb temperature between phases of the drying processes.

The effect of the through-thickness moisture content gradient on the moisture accelerated creep of paperboard: Hygro-viscoelastic modeling approach

2018 ◽  
Vol 33 (1) ◽  
pp. 122-132 ◽  
Author(s):  
Joonas Sorvari ◽  
Teemu Leppänen ◽  
Jukka Silvennoinen
Keyword(s):  
Finite Element Method ◽  
Moisture Content ◽  
Constitutive Law ◽  
Time Dependent ◽  
The Finite Element Method ◽  
Dependent Behavior ◽  
Accelerated Creep ◽  
Moisture Accelerated Creep ◽  
Viscoelastic Modeling ◽  
Moisture Content Gradient

Abstract Paper-based materials are viscous materials, the time-dependent behavior of which depends strongly on moisture content. Particularly the creep of paperboard containers under compressive forces is greatly affected by changes in the relative humidity. In the present paper, we examine the creep behavior of paperboard under cyclic humidity conditions using the finite element method. Especially the shape and rate of the through-thickness moisture content gradient on moisture accelerated creep are studied. An isotropic hygro-viscoelastic constitutive law is used for paperboard. The results of the simulations are compared with experiments. It is concluded that the through-thickness moisture gradients have a great impact on the moisture accelerated creep of paperboard. Furthermore, the results show that depending on the direction of external load the through-thickness moisture content gradient may increase or decrease creep rate.

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