Experiments on The Effect of Ultrasonic Energy on The Absorption of Preservatives By Wood

The effect of ultrasonic energy on the absorption of CCA by spruce, Douglas-fir, and ponderosa pine, as well as the absorption of pentachlorophenol and creosote by the latter species was investigated at atmospheric pressure and 20 C temperature. The results showed an increase in the percentage uptake due to the effect of the ultrasound for all species and preservatives, with the only exception being creosote at immersion times below 30 minutes. The effect of ultrasound was more pronounced in more permeable species

Wood Sorption Fractality in The Hygroscopic Range. Part I. Evaluation of A Modified Classic Bet Model

A new model for determining the fractal dimension (D) of the internal cell-wall surfaces of klinki pine by using sorption isotherms at a relative vapor pressure range from 0.0 to 0.96 is derived and evaluated. The new model was derived from the classic BET theory based on the assumption that the wood internal surfaces are geometrically complex, rather than flat. The results showed that within cell walls, the wood surface profiles and the sorbed water molecules organization changed under different moisture contents and temperatures. for both desorption and adsorption at all four temperatures, namely, 10, 25, 40, and 55°C, there were at least two distinct fractal dimensions (D 2) to characterize fractality of internal wood surfaces. Fractal dimensions were larger in adsorption than in desorption for all temperatures, except 10°C, from 13% to 20% moisture content range

Predicting Wood Thermal Conductivity Using Artificial Neural Networks

An artificial neural network model that estimates wood thermal conductivity under a wide range of conditions of moisture content, temperature and apparent density was developed and tested with literature-obtained experimental data. The optimal network was determined to consist of an input layer, three hidden layers, and one output layer following the feed forward network structure and more specifically the back-propagation algorithm. Each of the three hidden layers of the ANN consisted of eleven neurons. The Neuralworks software package was used for the determination of the network structure and architecture, and for the training and testing phase. The evaluation produced an R2 value equal to 0.9994 and a RMS Error equal to 0.0123, thus proving that the developed ANN model is a reliable approach with powerful predictive capacity towards the estimation of thermal conductivity and it can be used by researchers under a wide range of conditions

Wood Sorption Fractality in the Hygroscopic Range. Part II. New Model Development and Validation

The sorption isotherms of mature sapwood and heartwood from two softwood species were obtained experimentally. The data were used for the determination of how their fractal values change with an increase in moisture content using the Hao-Avramidis model developed in the past, and for the substantiation of a new fractal polynomial sorption equation based mainly on the fractal parameter D, assuming D being the dominant control parameter of sorption at higher sorption regions. The new sorption theory considered both the molecular layering stage at low humidities and the non-layering or fractal sorption stages at high humidities. Its good curve-fitting behavior justified the assumption that the state dynamics of the sorbed water were stepwise or locative instead of smooth, and three or four steps were identified

Simulated Comparative Analysis of Sorting Strategies for RFV Drying

In this work, a numerical stochastic model is used to compare three possible sorting strategies in radio frequency vacuum (RFV) drying of thick timbers, namely, moisture content based pre-sorting (MCPS), batch dry/sort/redrying (b-DSRD) and continuous or retro-feed dry/sort/redry (c-DSRD). The model parameters were calibrated with experimental data of western hemlock dried in a commercial RFV dryer, and the results of the simulations were compared to a single pass base case (SPBC). The numerical results clearly demonstrated the differences among these strategies. The MCPS showed no significant improvement in final timber quality as defined by average timber moisture content, but there is an evident improvement in both b-DSRD and c-DSRD. The comparison was based on the increment of the percent of the on-grade wood (within moisture content range) and the reduction of overdried and underdried (wets) percentages. Furthermore, it was also shown that the effective drying time is roughly independent of the drying strategy

The Surface Emission Coefficient of Wood

Considerable research has been undertaken to measure and characterize the mass convective surface resistance of wood, with particular emphasis on conditions below the fiber saturation point. While the effects of air velocity and wood moisture content have been demonstrated, the influence of other critical factors such as wood specific gravity, surface condition, and specimen size have not been evaluated. Results obtained by several investigators indicate little agreement between them with a wide range of coellicients whose values are a small fraction of those calculated from the classical equations that have been successfully applied to drying from moist surfaces. The low coefficients in the hygroscopic range indicate that surface resistance can add significantly to the energy consumption during drying. Therefore, a better understanding of the convection losses of dry hygroscopic materials such as wood may offer the opportunity of more effective optimisation of drying conditions

Effect of Ultrasonic Vibration on Convective Heat Transfer Between Water and Wood Cylinders

A study has been conducted to examine the effect of ultrasonic vibration on convective heat transfer of wooden cylinders. Forty fully saturated and air-dried cylindrical wood specimens were partially submerged in a heated water bath of 59.8 C (with and without ultrasound). The temperature versus time relationship at the center of the cylinders was monitored. Results indicate that ultrasound significantly influenced the heat transfer to wooden cylinders

Determination Of Parallam® Macroporosity by Two Optical Techniques

The macroporosity of Parallam®, a structural wood-based product based on parallel strand lumber technology, was investigated using two imaging techniques. A video camera and a line scan camera were used to capture the images of thin Parallam® squares viewed in transmitted light. Quantification of macro-void areas in the images recorded was performed using an image analysis system. Total macro-void areas determined for fifty Parallam® squares ranged from 2.90% to 3.90% as determined using the video camera and from 1.29% to 2.24% as determined using the line scan camera. The relative merits of the two imaging systems are discussed

Experiments in Nonisothermal Diffusion of Moisture in Wood. Part II.

This paper is the second in a series of papers reporting on experiments in nonisothermal diffusion of moisture in wood. Additional experimental steps to those series previously reported and one more series are included here. A reversal of flux direction was observed in all three series of experiments as the relative humidity of the warm side was increased.The results were analyzed using the general sorption data presented in the USDA Wood Handbook using two equations. The first of each is based on a gradient of activated moisture content, and the second is based on a gradient of chemical potential which contains an additional term to account for the effect of the temperature gradient. Both equations predicted reversal of flux direction, but the second equation (chemical potential) generally provided the best fit to the experimental results

Experiments in Nonisothermal Diffusion of Moisture in Wood

A series of nine experiments was performed with one surface of the wood specimen maintained at approximately 70 C and the other at 29C. The warm surface was exposed to relative humidities between 10% and 50%. One series of four experiments was conducted with the cool surfaces exposed to relative humidities between 34% and 42%, while those of the other series of five were exposed at 52% to 53%. In both series, a reversal of flux direction was observed as the relative humidity of the warm surface was increased. The results were analyzed using the general sorption data presented in the USDA Wood Handbook using two equations, the first of which is based on a gradient of activated moisture content and the second on a gradient of chemical potential that contains an additional term to account for the effect of the temperature gradient. Both equations predicted the observed reversal of flux direction, but the chemical potential equation generally provided the better fit to the experimental results