摘要:

A new laboratory kiln was developed and built to perform over a very wide range of drying conditions. For example, the dry bulb temperature can vary from 30°C to 150°C and the dew point can be adjusted between 20°C and 130°C. Obviously, with such a high level of dew point, pressures over atmospheric pressure may be induced inside the chamber. For this reason, the kiln has been designed to withstand pressure of up to 3 bars. This kiln can also perform vacuum drying.

ISSN:0737-3937    

DOI:10.1080/07373930008917814

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A one-dimensional mathematical model is evaluated for flow through a timber-drying kiln. This model is used to develop recommendations for the design of the plenum chambers on either side of the timber stack. The variation of the vertical air velocity was explored for a sticker spacing of 20 mm and a board thickness of 50 mm. When the width of the plenum chambers is at least equal to the sum of the thickness of the stickers, flow maldistribution is substantially reduced in single-track kilns. The width of the plenum chambers of double-track kilns may be reduced to three-quarters of the sum of the thickness of the stickers, because the increase in timber-stack resistance to airflow mitigates the effect of pressure variations down the length of the plenum chambers.

ISSN:0737-3937    

DOI:10.1080/07373930008917815

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The crook instability of lumber at moisture contents below the fiber saturation point was studied using both experiments and mathematical modeling. The changes in overall length and in crook that were observed with environmental humidity cycling at ambient temperature suggest that crook instability at such conditions is determined largely by elastic phenomena. Consequently, a simplified mathematical model of crook instability based on only elastie paramelers was created and verified using property data and crook measurements from selected boards. Results indicate that the elastic model accurately describes crook instability in the hygroscopic moisture content range near ambient temperatures. Experimental observations also show that board-to-board differences in crook instability can be quite complex. A better fundamental understanding of wood shrinkage behavior would help to explain these differences.

ISSN:0737-3937    

DOI:10.1080/07373930008917816

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In timber exposed to moisture variations, drying distortions is a serious problem that might result into sawn timber and other wood products unsuitable for construction purposes. Two characteristics of wood are that its behaviour is strongly orthotropic and that it is very sensitive to variations in moisture content. In addition, wood is characterised by variation in its properties from pith to bark. A further important property of wood, which affects its behaviour, is its spiral grain. For timber containing much compression wood the drying distortions are also highly dependent upon where the compression wood is located in the sawn boards. The present study concerns an experimental investigation of density, grain angles, shrinkage parameters and longitudinal elastic modulus in a number of spruce boards containing much compression wood. On the basis of the data obtained, numerical simulations have been carried out in order to determine the deformations that developed in the boards during changes in moisture content.

ISSN:0737-3937    

DOI:10.1080/07373930008917817

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In vacuum-press drying of softwood species, wood lemperaiure exhibited a low temperature gradient, and plateau temperature of core lasied during all stages of drying. The drying curves were close to “linear”. The drying rates of the short lumbers were higher for red pine and western hemlock, lower for white pine and similar for larch lumber compared to the long ones. Transverse and longitudinal moisture gradients were small for western hemlock and red pine, and great for larch and white pine lumber. Energy consumption curves were split into three sections: increasing moderately, fairly constant and increasing rapidly. Casehardening stress of dried lumber occurred very slightly. Dried lumbers exhibited strong tendency for fine end checking, slight surface checking and no internal checking. Shrinkage appeared to be low.

ISSN:0737-3937    

DOI:10.1080/07373930008917818

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0737-3937    

DOI:10.1080/07373930008917819

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0737-3937    

DOI:10.1080/07373930008917820

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0737-3937    

DOI:10.1080/07373930008917821

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor