Development of a Convective Mass Transfer Coefficient Conversion Method

Because of the difficulty of determining wood surface moisture concentration nondestructively and continuously in unsteady-state drying conditions, theoretically calculated convective mass transfer coefficients have not been well proved by experimental results. The convective mass transfer coefficient conversion method developed using surface moisture data in this study has proven that boundary layer theory is useful for evaluating external resistance during wood drying. Because of this proof, the external resistance for wooden surfaces can be theoretically described in dynamic drying situations

Determination of Surface Moisture Content of Wood Utilizing a Colorimetric Technique

Optical properties of cobalt chloride (CoCl2) hydrate, whose color changes with surrounding humidity, were used to develop a colorimetric technique for determining surface moisture content of wood nondestructively. The colorimetric CoCl2 treated wood technique for determining surface moisture content through color degree change in CIE L*a*b* color space has been experimentally verified

Development of a Method to Predict the Bending Strength of Lumber Without Regard to Species Using X-Ray Images

Several models have been developed for predicting bending strength of lumber using X-rays, but most require species-specific classifications. However, the classification is very difficult because logs or cants can arrive without leaves or bark. This study was carried out to develop an alternative bending strength prediction model that does not lose precision when the species is unknown. The study proposes an Equivalent Density Model (EDM), in which a cross-section is quantified as equivalent density. Because the relationship between density and strength of small clear specimens is not affected by species, the EDM was expected to correlate to strength regardless of species. This model predicted the modulus of rupture in two species with R2 = 0.73, although the two were mixed. Therefore, it may be possible to predict bending strength using X-rays without classifying lumber by species

Improvement of Wood CT Images by Consideration of the Skewing of Ultrasound Caused by Growth Ring Angle

For the purpose of removing distortions in ultrasonic computerized tomographic (CT) images of wood, this study proposes a technique for taking into account the skewing effect in reconstructing the image. First, it was experimentally confirmed that an ultrasonic wave is refracted because of the anisotropic characteristics of wood. Transmission paths of an ultrasonic wave through a cross-section of wood were predicted by considering the change in wave velocity based on the annual ring angle and the presence of juvenile wood. Then, the methodology of the application of the predicted paths to CT image reconstruction was proposed and verified. The accuracy of defect detection in wood was significantly improved by the proposed technique

Moisture Content Prediction Below and Above Fiber Saturation Point by Partial Least Squares Regression Analysis on Near Infrared Absorption Spectra of Korean Pine

This study was performed to predict the surface moisture content of Korean pine (Pinus koraiensis) with low moisture content (approximately 0%) and high moisture content above the FSP using near IR spectroscopy. Near IR absorbance spectra of circular specimens were acquired at various moisture contents at 25°C. To enhance the precision of the regression model, mathematical preprocessing was performed by determining the three-point moving average and Norris second derivatives. After preprocessing, partial least squares regression was carried out to establish the surface moisture content prediction model. We divided the specimens into two groups based on their moisture contents. For the first group, which possessed moisture contents less than 30%, the R2 values and root mean squared error of prediction (RMSEP) of the model were 0.96 and 1.48, respectively. For the second group, which possessed moisture contents greater than 30%, the R2 values and RMSEP of the model were 0.94 and 4.88, respectively. For all moisture contents, the R2 and RMSEP were 0.96 and 5.15, respectively. As the range of moisture contents included in the prediction model was expanded, the error of the model increased. In addition, the peak positions of the water absorption band (1440 and 1930 nm) shifted to longer wavelengths at higher moisture contents

Feature importance measures from random forest regressor using near-infrared spectra for predicting carbonization characteristics of kraft lignin-derived hydrochar

This study investigated the feature importance of near-infrared spectra from random forest regression models constructed to predict the carbonization characteristics of hydrochars produced by hydrothermal carbonization of kraft lignin. The model achieved high coefficients of determination of 0.989, 0.988, and 0.985 with root mean square errors of 0.254, 0.003, and 0.008 when predicting the carbon content, atomic O/C ratio, and H/C ratio, respectively. The random forest models outperformed the multilayer perceptron models for all predictions. In the feature importance analysis, the spectral regions at 1600–1800 nm, the first overtone of C–H stretching vibrations, and 2000–2300 nm, the combination bands, were highly important for predicting the carbon content and O/C predictions, whereas the region at 1250–1711 nm contributed to predicting H/C. The random forest models trained with the high-importance regions achieved better prediction performances than those trained with the entire spectral range, demonstrating the usefulness of the feature importance yielded by the random forest and the feasibility of selective application of the spectral data.This study was supported by the Korea Forestry Promotion Institute through the R&D Program for Forest Science Technology funded by the Korea Forest Service (Project No. 2020215D10-2122-AC01)

Control of Interior Darkening in Hard Maple

Industrial experience and research have shown that hard maple lumber color changes are very often affected by the temperature and relative humidity conditions the wood is exposed to during drying. For this reason, appropriate kiln schedules should be selected and properly used to control not only surface, but entire board color. In this research study, a technique was developed that successfully demonstrated occurrence of interior darkening of hard maple at particular drying temperature and moisture content conditions. Results show that the critical temperature causing this interior darkening is 110°F, and it particularly develops with elevated temperatures while the MC is at and above the FSP. There appears to be minimal color change when drying below the FSP

Mass Transfer in Wood Evaluated with a Colorimetric Technique and Numerical Analysis

A colorimetric CoCl2-treated wood technique was used for determining surface moisture content of wood nondestructively and continuously during unsteady state desorption conditions. Utilizing these surface moisture data, diffusion and surface emission coefficients have been determined simultaneously and continuously during drying. The conversion method, which has been developed to facilitate making comparison between mass transfer coefficients in this study, has proven that the boundary layer theory is useful for evaluating the external moisture resistance during wood drying. The moisture profiles simulated by the finite difference method were quite comparable to the actual moisture profiles in real dried wood, which substantiates the high credibility of using the colorimetric technique for determining surface moisture content and mathematical procedure for determining the diffusion and surface emission coefficient

Determination of Internal Moisture Transport and Surface Emission Coefficients for Eastern White Pine

Moisture movement in eastern white pine wood specimens was evaluated during drying at specific temperature and RH conditions. The objective of this work was to build an appropriate numeric analysis model for predicting moisture profile changes in wood and apply this to the kiln-drying of large cross-section eastern white pine timbers. The internal moisture transport coefficients were dependent on the temperature and average moisture content, and the surface emission coefficients on the water vapor pressure in air adjacent to the surface. The internal moisture transport coefficients decreased with decreasing temperature and internal moisture content. Surface emission coefficients increased with increasing temperature and decreasing surface moisture content

Some considerations in heterogeneous nonisothermal transport models for wood: a numerical study

This study compares a number of coupled heat and mass transfer models and presents numerical comparisons of phenomenological coefficients between the four models (Stanish, Perre, Pang, and Avramidis) that are most frequently used in the literature to describe wood-drying processes. The USDA sorption isotherm, the Hailwood-Horrobin model, was adopted to calculate the relations between moisture content in wood and water vapor pressure at any temperature. Due to different assumptions about the driving forces of heat and mass transfer, coefficients in each model represent different values for moisture content and temperature and are closely related to each other. In the case of isothermal mass transfer, the moisture diffusion coefficient in the transverse directions from the Stanish and Pang models increased with decreasing moisture content. This contradicts the Avramidis and Perre models and numerous experimental results. Thermal diffusion effects on the drying process may not be predominant because the nonisothermal state is relatively short. Therefore, the Perre model, which does not consider the thermal diffusion effect, has been used successfully in the drying simulation. However, it may be erroneous in certain cases when the nonisothermal state prevails over the system, such as building physics. The Pang model cannot explain the phenomena of thermal diffusion and moisture thermodiffusion. It might be reasonable to modify the thermal diffusion of the Avramidis model, which is lower than that of the Stanish model. The apparent heat diffusivity was higher than the true heat diffusivity.OAIID:oai:osos.snu.ac.kr:snu2008-01/102/0000039153/1SEQ:1PERF_CD:SNU2008-01EVAL_ITEM_CD:102USER_ID:0000039153ADJUST_YN:YEMP_ID:A076734DEPT_CD:524CITE_RATE:.696FILENAME:JWRS 2008 54 (267-277) - Heterogeneous Nonisothermal.pdfDEPT_NM:산림과학부EMAIL:[email protected]: