# Fluid Flow in Nanosilver-Impregnated Heat-Treated Beech Wood in Different Mediums
## 1 Introduction  
Wood, a valuable and precious raw material helped mankind establish civilization in the past and present. It is however susceptible to bio-deteriorating agents [1; 2; 3; 4]. Heat treatment is a commercially-advance modification process which is recognized as a potentially useful method to improve both decay resistance and dimensional stability of wood [5; 6]. The chemistry of thermal modification and heat transfer within the wood is affected by the presence of water, liquid, or vapor. Under dry treatment conditions, it is reported that wood is dried before the application of heat treatment, or the water is removed by the use of a re-circulating system equipped with a condenser or an open system. In closed systems, on the other hand, water evaporated from the wood remains as high-pressure steam during the process. Steam may also be injected into the reactor, and acts as a heat-transfer medium, or as an inert blanket to limit oxidative processes. Such a steam treatment process is referred as hygothermal treatment. When wood is heated in water, the process is referred as hydrothermal [5]. Heat treatment mediums affects the physicochemical properties; it is reported that wood that was hygthermally treated showed lower mass loss and dimensional stability and higher bending properties compared to hydrothermally treated at the same temperature. Reduction of swelling values with increased temperature was often attributed to degradation of cell-wall polymers,mostly hemicellulose. Furthermore, chemical changes of lignin and various structural modifications are also involved in the process [7]. In addition, the potential reduction in hygroscopicity is not attributed solely to mass loss but it may be related to irreversible hydrogen bonding in the course of water molecules movements within the micropore in the wood cell wall.  
In this connection, permeability on the microstructure of the wood cell wall, and therefore potential alterations, caused by the above mentioned degradation of cell-wall polymers, may have a significant affect on permeability [8; 9]. Even after wood is formed by trees, its porosity may be changed due to biological deterioration or due to thermal modification in different mediums [1; 10]. However, few studies have so far been focused on the effect of heat treatments in different mediums on the fluid flow in wood. Therefore, the aim of this study was to find possible effects of heat treatment in three mediums of air, water (hydrothermal), and water steam (hygrothermal) on specific gas permeability in beech wood and its correlation with liquid permeability; potential improvement in permeability can be beneficial to many industries. It is to be noted that permeability is an important property of solid wood that affects many of the processes prior to its final applications in different industries, like cabinet making industry, wooden structures, and traverse for railroads. The processes in these industries may involve impregnation with different preservatives and fire-retardants, and drying in kiln and open air as well.  
In addition to the chemical and structural effects of heat treatment under different mediums on wood, and their effects on preparation processes and final applications of wood, it is to be noted that thermal conductivity of wood is low [11; 12]; therefore, separate sets of specimens were first impregnated with nanosilver suspension to find out if an improved thermal conductivity can have any effects on permeability of heat-treated beech wood under different mediums.