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Resistance-type wood moisture meters are not reliable at moisture contents above the fibre saturation point. The aim of this study was to develop an alternative polarization-type wood moisture meter and to analyse the different calibration methods of this moisture meter in comparison with the traditional resistance-type wood moisture meter calibration method. A significant decrease (up to 3.5% of moisture content) in the tolerance interval of a single measurement was attained by introducing and integrating the original electrical wood charging number into the calibration model of the novel wood moisture meter with electric polarization effect for a high wood moisture content (MC) above 100%. The tolerance interval convergence was analysed using the traditional method of increasing the number of measurements and averaging the results and was compared to the novel method of compensating for random deviations, as used in this study. To calibrate the wood moisture meter, the wood’s electrical resistance and electrical capacitance timelines during the electrical charging cycle were registered in real time (online) with a preselected measuring speed and saved to the microcomputer memory. When the measurements were completed, the measurement data was processed by the device’s microcomputer. This novel polarization-type moisture meter allows for the moisture content of specific tree species to be predicted by selecting a suitable calibration model from a set of eight. The novel wood moisture meter can be used to monitor wood drying and to determine seasonal variations in the moisture content of growing trees.

This research aimed to evaluate the profile of temperature and moisture content in Pinus oocarpa wood being dried with heating oven and microwave oven. The size of samples were (25x70x120) mm3. The temperature profiles in heating oven and microwave oven drying were taken every 10 minutes and 0.5 minutes, respectively. The moisture profiles in heating oven and microwave oven drying were made in every 24 hours and 10 minutes, respectively. The heating oven was set at 60 °C, while microwave oven was set for 2 minutes intermittently with 5 minutes break. In microwave drying, the temperature inside the boards increased faster and higher compared to that in the heating oven, which resulted in a faster moisture movement to the board’s surface. The drying rate of pine increased 48-72 times in microwave compared to that in heating oven. The moisture content in the centre of boards being dried in heating oven was much higher than that of in the outer parts. On the other hand, the moisture profile in the woods being dried in microwave oven distributed more evenly.

Predicting kiln-drying schedules for a given wood species is not yet possible, despite many research efforts. This is mainly due to insufficiently considering important spatio-temporal variables such as moisture and temperature gradients, and wood anatomical features during drying in the predictive modelling framework. To understand the influence of aforementioned variables, an experimental measurement set-up was developed consisting of heat-resistant load cells mounted in an oven to record the weight of the wood specimens dried at 100 °C. A camera was mounted outside the oven to acquire images of the end grain through the transparent door of the oven, as such enabling to monitor the occurrence of cracks. Furthermore, custom-made electrodes were inserted as well at different depths in the specimen to measure the electrical resistance, which relates to the moisture content. Specimens were also equipped with thermistors to record the temperature in the specimens at different depths from the surface. Heat-resistant wires from load cells, electrodes and thermistors were connected with data loggers outside the oven. Three specimens of basralocus (Dicorynia guianensis) were selected, measuring 50 mm wide, 50 mm thick and 120 mm long. The results show that it is possible to real-time monitor average moisture loss, local moisture content gradient represented by the electrical resistance gradient and wood temperature gradient as a function of time. These temporally resolved gradients can be related to the occurrence of cracks. This methodology enables to unveil interrelationships between the measured variables and changes of the wood anatomical structure, of utmost importance for the fine-tuning of kiln-drying schedules.

Aim of study: The adsorption properties of the samples of full-dry Eastern Spruce (ES) [Picea orientalis (L). Link.] with 12.5 mm, 25 mm, 37.5 mm and 50 mm thick is to determine under the climate conditions with 42%, 65% and % 78 of relative humidity and at a constant temperature of 20 °C.Material and method: The wood samples used in this study were the Eastern Spruce woods which were obtained from Forestry Process Management in the city of Trabzon/Turkey. With regard to mathematical modeling used to determine the wood moisture content (MC), the equation constants in case of adsorption was determined. Experiments were conducted at three different equilibrium moisture content (EMC); 8%, 12% and 16%.Main results: Cross section had no crucial effect on the rate of accessibility to the final MC. However, EMC and thickness have been effective.Research highlights: In practice, since dried wood is kept at outside weather conditions for a certain time before operation, an increase can be observed in the wood MC. It is practically important that under the influence of climate conditions until its utilization, the tendency of water adsorption of wood is determined as a function of time., Çalışmanın amacı: Tam kuru Doğu ladini [Picea orientalis (L). Link.] örneklerinin 12.5 mm, 25 mm, 37.5 mm ve 50 mm kalınlıkta, 20 ° C sabit bir sıcaklıkta ve % 42 ,% 65 ve %78 farklı bağıl nem koşullarında adsorpsiyon özelliklerini belirlemektir.Materyal ve yöntem: Bu çalışmada Maçka Orman İşletme Müdürlüğü’nden alınan Doğu Ladini örnekleri kullanılmıştır. Odun rutubet içeriğini belirlemek için kullanılan matematik modelleme ile adsorpsiyon durumunda denklem sabitleri belirlenmiştir. Deneyler, % 8, % 12 ve % 16 olmak üzere üç lif doygunluk noktası için gerçekleştirilmiştir.Sonuçlar: Kesitin, denge rutubetine erişilebilirlik oranı üzerinde önemli bir etkisinin olmadığı, bununla birlikte denge rutubet miktarı ve kalınlığın etkili olduğu belirlenmiştir.Araştırma vurguları: Kurutulmuş odunun, kullanım öncesinde belirli bir süre dış hava şartlarında tutulduğunda rutubet içeriğinde bir artış gözlemlenebilir. Kullanıma kadar iklim koşullarının etkisi altında, odunun rutubet alma eğiliminin zamanın bir fonksiyonu olarak belirlenmesi pratik olarak önemlidir.

In the present study, a mathematical model with a moving evaporation interface was constructed to quantitatively assess the mechanisms of moisture and heat transfer during superheated steam wood dr...

Wood drying is a compulsory technological process in the production of lumber, furniture billets, building components, etc. Various aspects of the problems discussed in the article are of interest to forestry enterprises specialists. The main forms of moisture communication with wood (adsorption, capillary condensation and capillary bond of free moisture in cell cavities) are known to depend on the temperature and relative humidity of the drying agent. This means that wood being a material of plant origin behaves in a peculiar way, depending on the temperature and humidity fields. The problem of wood drying includes the issue of heat and moisture (mass) transfer, both in the middle of the body and in the boundary layer at the interface of the phases "body (object of drying) -" environment ". We should note that the intensity of drying is of maximum value when the possibility of heat and mass transfer in the boundary layer corresponds to the possibilities of moisture and heat movement inside the object of drying. Furthermore, the characteristics of wood as a natural polymer possessing specific elastic viscous properties are described. The mechanism of moisture (mass) transfer from the central layers of drying objects to their surfaces is identified. The phenomenon of drying, both complete and in three structural directions, is highlighted in theoretical studies. Moreover, drying is noted to be a complicated heat and mass transfer process, which is characterized by the molecular nature and mechanism of the phenomena determining the kinetics of their flow. In the course of the study we have revealed that the solution of the corresponding equations of molar and molecular heat and mass (moisture) transfer under the corresponding boundary conditions enables describing the fields, i.e. the distribution of the transfer potential – temperature and moisture content in the object of drying at any moment of drying time. Therefore, the drying curves (in the coordinates of the "drying rate – material humidity") and the temperature curves (in the coordinates "the temperature of the drying object – the humidity of the drying object ") reflect the nature of the drying process.

The article presents the results of the experimental studies of the processes of removing moisture from fairly typical and widespread forest combustible materials, and woodworking waste under conditions of their thermal preparation for combustion. Based on the results of the experiments, the main regularities of the drying processes of woody biomass under conditions of radiation-convective heating have been established. The integral characteristics (characteristic times) of the drying process of forest biomass under typical (for this technology) heating conditions have been determined. The experiments were carried out on equipment that provides a low level of error (less than 3.3%) for determining the main characteristics of the biomass dehydration process. The values of the mass rates of moisture removal (Weva) of four promising (for modern and future power engineering) and fairly common types of biomass have been established in the ambient temperature range from 333 to 393 K, which corresponds to the operating modes of the drying equipment of power plants. According to the results of the experiments, it was shown that at relatively moderate ambient temperatures (333≤ Tg ≤ 353 K), the type of wood has a rather significant effect on the characteristics and conditions of the dehumidification process. At the same time, the process of drying wood chips is much faster compared to other types of biomass. As the ambient temperature rises (at 373≤Tg ≤ 393 K), the influence of the type of biomass decreases. As a result of the experiments, a physical model of the process of removing moisture from the bulk layer of biomass was formulated. According to the results of the experiments, it was found that before burning forest biomass in boilers of thermal power plants, it is most advantageous to carry out drying in conditions of relatively moderate (at 333≤Tg ≤ 353 K) ambient temperatures. The studies carried out provide grounds for justifying the use of forest combustible material as fuel (or one of the components of the fuel mixture) at thermal power plants currently operating on coal.

Drying processes are known to be widely used in industry and agriculture. The object of drying can be either raw materials such as boards, workpieces, and parquet frieze or semi-finished products (peeled or planed veneer and chopped wood), as well as finished products (plywood, chairs, armchairs, etc.). Wood drying is quite a complex manufacturing process accompanied by a number of physical phenomena such as heat exchange of the material (object of drying) with the drying agent (environment), moisture evaporation (water) from the surface of the dried material to the environment, heat transfer throughout the material (thermal conductivity), deepening of the surface of evaporation inside the object of drying due to moisture transfer. Drying processes are analyzed according to the curves of the change of the average humidity of the material (the object of drying) over time (so-called "drying curves") and temperature changes (curves), as well as the rate of change in moisture content in time. The authors have established that drying of various materials applying various methods of heat transfer (convection, thermal radiation, conduction) under constant regime parameters consists of three drying periods such as the period of initial warming, periods of constant and falling drying rates. Various methods of rational use of heat, as well as methods and means of intensifying the wood drying process are known nowadays, although the problem of reducing the energy costs of wood drying remains. Therefore, the main purpose of new developments in this work is the creation of equipment that can solve this problem. The review of issues related to the energy efficiency of drying chambers has shown that there exist enough ways and opportunities of its increasing. The concept of rational use of heat designing of drying chamber in order to reduce specific heat consumption costs is considered in this paper. It is reasonable to combine the methods for determining camera performance with the compilation of the main indicators of the cost of heat energy, going to drying lumber. The proportion of the chamber's parts balance varies substantially, depending on the type and design of the chamber, drying modes, lumber characteristics etc.

Modern technological wood drying equipment is not sufficient to ensure the constancy of the humidity dimensional products throughout the volume, which often leads to deviations from the specified limits of moisture content. This leads to losses not only in materials, but also in heat and electricity. This is especially true for expensive wood products. This article describes the main methods of moisture measurement used in wood moisture meters design. The advantages of combined measurement methods in solving the moisture measuring problems are reviewed. A block diagram of a digital moisture meter with a combined capacitive converter is proposed, which makes it possible to compensate for the thickness instability error of thin sheet materials during their production. The proposed device can be used not only in woodworking enterprises, but also in other industries when measuring the humidity of any thin sheet materials, in particular, when measuring the fabrics humidity.

Wood drying is known to be a complicated heat and mass transfer process. Although many scientific publications, textbooks, manuals and monographs are devoted to many processes of drying veneer, chopped wood and lumber, convective drying of profile workpieces is not sufficiently investigated yet in literature sources, because profile workpieces such as shoe pads, profile elements of joiner's and furniture and furniture products and firewood have an alternating cross-section, which also varies along the length of the workpieces. Therefore, the process of wood drying, including profile billets (wood) from massive wood is considered. It consists of such thermal technological operations as initial heating, steaming and drying, and intermediate heat-treatment and conditioning in the process of drying of firewood are not considered. The regularities of the external and internal movement of heat and moisture in the processes of heating and drying of wood are studied. As a result, the basic equation of the kinetics of the drying process is defined to establishe the relationship between heat exchange and moisture exchange in the form of the ratio of the amount of heat consumed to heating the wood and the evaporation of moisture and the drying rate. The differential equation of convective diffusion together with the equation of mass transfer of the stationary process of moisture transfer due to the difference in the concentration of the diffusion substance (in this case, the moisture) and the equation of the first Fick law, which allowed deriving the values of the mass transfer criteria of Nusselt, Fourier, Peckel and Prandtl, were used. The authors have also determined that the necessary prerequisite for the similarity of the processes of mass deducing is the observance of aerodynamic similarity, which is described by the Reynold and Froude criteria. Finally, we have synthesized on the basis of the above-described physical-mathematical model of the drying process in the form of dependencies between the Nusselt criterion and the Fourier, Reynold and geometric similarity criteria. The obtained dependence can be described by all thermal process operations of the drying process.

A study on hot-air drying basil (Ocimum basilicum) leaves was carried out by obtaining sorption isotherms, thin-layer drying kinetics and drying in vibrofluidized equipment under temperatures from 30 to 60 °C. Experimental data of sorption isotherms and moisture variations on thin-layer drying were fitted to empirical equations to predict the equilibrium moisture content and the drying kinetics. The moisture reduction and homogeneity in vibrofluidized drying were compared to data obtained in a conventional fluidized dryer. The application of mechanical vibration under an amplitude of 5 mm and a dimensionless vibration ratio equal to 1.0 produced leaves uniformly dried and with adequate moisture for storage. The volatile constituents of basil essential oil were well preserved after vibrofluidized drying and were not significantly affected by the air temperature. The effect of the drying temperature on most colour parameters was not significant, but the loss of the green colour was slightly smaller at 30 °C.

The process of wood drying is studied in supercritical (SC) CO2 and SC-CO2 containing 5 vol % ethanol at temperatures of 323, 343, and 353 K and pressures of 10, 20, and 30 MPa. It is established that 40–87% of moisture is removed from wood in the first cycle of drying. An increase in the duration of the decompression stage of the drying process decreases the number of cracks in the wood samples. The solubility of propiconazole is studied in SC-CO2 at 323, 343, and 353 K in the pressure range of 10–30 MPa using a dynamic method. Rather high saturation concentrations of (3–5) × 10–3 mol/mol CO2 are obtained, which indicates the potential benefits of using SC-CO2 as a solvent in wood impregnation with propiconazole. Continuous impregnation is achieved when impregnating wood with propiconazole from SC-CO2. The impregnation efficiency increases with increasing pressure and duration of the process.

In this study, a simplified two-dimensional axisymmetric finite element analysis (FEA) model was developed, using COMSOL Multiphysics® software, to simulate the water vapor separation in a moisture-selective hollow-fiber membrane for the application of air dehumidification in wood drying processes. The membrane material was dense polydimethylsiloxane (PDMS). A single hollow fiber membrane was modelled. The mass and momentum transfer equations were simultaneously solved to compute the water vapor concentration profile in the single hollow fiber membrane. A water vapor removal experiment was conducted by using a lab-scale PDMS hollow fiber membrane module operated at constant temperature of 35 °C. Three operation parameters of air flow rate, vacuum pressure, and initial relative humidity (RH) were set at different levels. The final RH of dehydrated air was collected and converted to water vapor concentration to validate simulated results. The simulated results were fairly consistent with the experimental data. Both experimental and simulated results revealed that the water vapor removal efficiency of the membrane system was affected by air velocity and vacuum pressure. A high water vapor removal performance was achieved at a slow air velocity and high vacuum pressure. Subsequently, the correlation of Sherwood (Sh)–Reynolds (Re)–Schmidt (Sc) numbers of the PDMS membrane was established using the validated model, which is applicable at a constant temperature of 35 °C and vacuum pressure of 77.9 kPa. This study delivers an insight into the mass transport in the moisture-selective dense PDMS hollow fiber membrane-based air dehumidification process, with the aims of providing a useful reference to the scale-up design, process optimization and module development using hollow fiber membrane materials.

This study aims to review variation pattern of moisture content ratio of grains in deep-bed drying process, guide the drying technology design, realize real-time tracking and regulation in drying process, improve the quality of drying process and reduce energy consumption. Based on the moisture diffusion model in thin layer drying process, the principle of mass conservation of deep drying process, state function and irreversible thermodynamics analytic method, we have established and solved basic equations of deep-bed drying of grains, obtained the moisture content ratio of grains and analysis formula of drying velocity distribution in processes of concurrent flow drying, counter flow drying, cross-flow drying and standing drying and resolved the sustained decreasing drying process of grains in the concurrent flow drying and extreme point of drying rate in the counter-flow drying. Under the same conditions of temperature, humidity and air output, the drying velocity in counter-flow drying significantly higher than that in the concurrent flow drying. It means the energy utilization effects in counter-flow drying is better than that in the concurrent flow drying. Drying characteristics of grains in cross-flow drying and standing flow drying are the same, while drying rates in inlet-air side and outlet-air side vary widely. It means that when the layer thickness is 0.5m and the moisture content is over 20%, the drying rate in outlet-air side is nearly zero and the drying uniformity is bad. Tests on 5HP-3.5 recirculation drier shows that maximum deviation between analytic value and measured value in deep drying process is 0.69% and the range scope is -0.27%-0.69%. From the drying characteristics of grains, deviations mainly come from instrument detection deviations. The analytic method has important significance for realizing real-time tracking and regulation in drying process, guiding drying technology design, reducing energy consumption, increasing drying rate and drying machine capacity.

Drying is widely used in a variety of thermal energy applications ranging from food drying to wood drying. Utilization of high amount of energy in the drying industry makes drying one of the most energy-intensive operations in pellet production. Thermodynamic analysis has appeared to be an essential tool for system design, analysis and optimization of thermal systems. The aim of current paper is to make an algorithm to evaluate wood chip drying process energy and exergy efficiency. Energy and exergy efficiency evaluation consist of the drying process energy and exergy balance analysis. On the basis of the results of the study it can be concluded that under the given assumptions drying process energy efficiency varies between 22.69 % and 10.25 % but the exergy efficiency varies between 16.47 % to 0.7 %. Decrease of drying air mass flow increases the energy and exergy efficiency. This is because less heat is required to heat drying smaller air mass flow. Decreasing drying air humidity ratio of air before dryer, increases energy and exergy efficiency. This is because the drying air with smaller humidity ratio content are able to attract more moisture from the drying product.

The aim of the article is to present the results of moisture content of wood during and after the high temperature steam and air-steam mixture drying processes and after an open air drying process. The knowledge of moisture content changes of wood in the process of its drying is one of important parameter to economy drying process and to keep the quality of dried wood. Wood samples, namely spruce (Picea abies K.) and beech (Fagus silvatica L.) from the northern part of Poland, were subject of steam, air-steam mixture and air drying respectively with a temperatures about 105, 80 and 25°C. The samples of thickness 70 mm and length about 1050 of spruce and about 1500 mm of beech were used. They were machined by the modern narrow-kerf frame sawing machine. Temperature of the cross-section of dried wood was measured by thermocouples, wood moisture content was determined during process using moisture sensors. Measurements of moisture content for steam dried and air dried samples, as reference, allowed t...

Shengli lignite coal, originated from inner Mongolia China, contains significantly high amount of moisture (more than 30%) which can cause spontaneous combustion or other application problems. Thus...

Drying behavior of corn (Zea mays L) was studied in a hot air-infrared dryer. The effects of inlet air temperature (40, 50 and 60 °C), infrared radiation intensity (1000, 2000 and 3000 W/m2), and modes of drying bed (fixed and vibratory) were investigated on grain moisture variation during drying process. Corn kernels were dehydrated from the initial moisture content of 24.5 ± 0.5% (w.b) to final moisture content of 14 ± 0.2%. The thin layer drying characteristics was experimentally investigated and appropriate mathematical drying models were correlated with temperature and radiation intensity. Among models fitted to experimental data, the Page model was found to be the best model for describing drying behavior of corn in thin layer drying form. The effective moisture diffusivity ranged from 0.6170 × 10−8 to 4.6432 × 10−8 m2/s for the fixed bed mode and 0.8021 × 10−8 to 5.5533 × 10−8 m2/s for the vibratory bed mode.

We proposed a generalized procedure of convective fruit drying, which takes into account comprehensive combination of thermal-physical and physical-chemical properties of fruit with their kinematic heat and mass exchange characteristics. We developed a mathematical model of heat, moisture and mass exchange for convective fruit drying, which considers moisture-yielding velocity of the dried material in the operation zone of the heat carrier under conditions of diffusion process of moisture transfer in the dried material. The given model allows us to determine heat and mass exchange characteristics and intensity of the drying process. We proposed the systems of differential equations of heat and moisture transfer in the process of convective fruit drying for parabolic and uniformed original distribution of temperature and moisture content. As a result of the solution of a system of differential equations, we obtained appropriate dependences to determine the energy of bound moisture, moisture content on the surface and in the center of the material, difference of moisture content between the surface and central layers, as well as critical moisture content. The obtained results may be used when predicting the heat and mass exchange processes, for improvement of technology and equipment for fruit drying in the solar dryer, for increasing technological and energy efficiency of the process.

The forest transportation represents a great proportion of raw material cost for pulp and paper production and, for this reason, the wood moisture content should be low to reduce these cost. The objective was to relate the wood moisture with fuel consumption per kilometer in each vehicle and the number of trips to supply a pulp mill. Three trees of Eucalyptus urophylla clone and three of Corymbia citriodora from seeds were used. These trees were felled and their logs removed from its base and at 50 and 100% of the commercial height. The basic density and initial moisture of wood were determined and the air drying monitored during 90 days. The fuel consumption to transport one ton of dry wood and the number of trips required to supply a pulp mill were estimated based on the number of air drying days. Air drying reduced the fuel consumption and the number of trips to supply the pulp mill. The accuracy of models to estimate the wood moisture, fuel consumption and the number of trips based in days of drying was high. Therefore, wood drying is an essential tool to reduce forest transport costs. RESUMO O transporte florestal representa uma grande proporção do custo da matéria-prima para a produção de papel e celulose, por esse motivo, o teor de umidade da madeira deve ser baixo para reduzir esses custos. O objetivo deste trabalho foi relacionar a umidade da madeira com o consumo de combustível por quilômetro em cada veículo e o número de viagens necessárias para abastecer uma fábrica de celulose. Três árvores de um clone de Eucalyptus urophylla e de Corymbia citriodora com produção seminal foram utilizadas. As árvores foram abatidas e seus troncos foram removidos de sua base e 50% e 100% da altura comercial. A densidade básica e a umidade inicial da madeira foram determinadas e a secagem ao ar foi monitorada durante 90 dias. O consumo de combustível para transportar uma tonelada de madeira seca e o número de viagens necessárias para abastecer uma fábrica de celulose foram estimados com base no número de dias de secagem. A secagem ao ar livre reduziu o consumo de combustível e o número de viagens para abastecer a fábrica de celulose. A precisão dos modelos para estimar a umidade da madeira, o consumo de combustível e o número de viagens com base nos dias de secagem apresentaram alta precisão. Portanto, a secagem de madeira é uma ferramenta essencial para reduzir os custos do transporte florestal.

Stopping the drying process prior to complete dehydration reduces energy consumption and processing time but can also improve product quality. Using hygrothermal simulations, different stopping criteria are evaluated, which are based on the final water activity and residual moisture content in the fruit. Their impact on drying time and moisture redistribution kinetics inside fruit is quantified. One of the variants leads to a significant reduction in residence time in the dryer (24%), compared to full dehydration. For this variant, drying is stopped when the average moisture content in the sample reaches the value corresponding to an equilibrium water activity of 60% in the sample, as determined from the sorption isotherm. At the same time, this variant does not induce problems with fruit spoilage, as a sufficiently low water activity is reached after moisture redistribution during relaxation in the ambient environment. In addition, the relation of the drying time to the drying air temperature was quantified for all stopping criteria, as well as the impact of the humidity of the ambient environment in which the dried fruits are placed afterwards. This study gives a better quantitative insight in when fruit drying should be stopped, given specific drying conditions, without having to compromise food safety.

While making calculations for non-steady heat-and-moisture exchange processes in building envelope constructions it is necessary to consider moisture sorption isotherms of the materials in use. Fifteen aqueous vapor sorption models have been analyzed in order to select the simplest one that represents conventional equilibrium wood moisture values in the most accurate way. Hailwood-Horrobin and Peleg modified equations with three and four empirical constants respectively are the most suitable ones for description. When selecting models for calculations in a climatically defined range of air temperature and relative humidity values, these equations might be in preference to others. The dependence of the constants in these equations on the ambient air temperature have been calculated.

This study intended to assess the effect of weather on the air-drying process of messassa wood (Brachystegia spiciformis Benth) in two areas of Mozambique (Machipanda and Beira city). First, the logs were sawn into 27 mm thick boards. Every five days the moisture content of the wood was determined by the control samples. For each region, the drying rate and wood quality post sawing and drying were estimated. The drying time differed between the regions under investigation, with Machipanda revealing the higher value. Messassa wood, which revealed a low drying rate (0.33% U/day), was categorized as slow drying wood. Both regions showed average final moisture content of 15.3% in the boards, with only slight variations in moisture inside the stacks. After outdoor drying, only a few defects were noted and as it was free from tensions, hence it was classified as good quality wood.

In this paper, we review the literature published on vacuum drying of wood. Vacuum drying is not a new technology, and its use for drying wood has been suggested since the early 1900s. Technologies for vacuum drying of wood can be classified by the heating method used. In this paper, we define vacuum-drying methods in four groups: conductive heating vacuum, cyclic vacuum, superheated steam vacuum, and dielectric vacuum. Advantages of drying wood below atmospheric pressure are the ability to dry at lower temperatures (and thus lower the probability of developing some drying defects), greatly reduced drying times, color preservation, greater energy efficiency, better control of volatile organic compound emissions, and the ability to dry very large cross sections. Some characteristics that differentiate vacuum from conventional drying are that in vacuum the primary driving force is the total pressure difference, the prevailing moisture transfer mechanism is water vapor bulk flow, and there is greater water migration in the longitudinal direction. While past research has focused on increasing the understanding of the fundamental mechanisms for vacuum drying and applications to specific industries and species, more recent efforts have concentrated on improving existing methods, for example, by improving moisture control and the use of pretreatments to improve drying quality.

A modified moisture diffusion equation fits for the relationship between moisture ratio of paddy samples and drying time.The geometry of paddy kernels was assumed as homogenous finite cylinders, their moisture effective diffusivity increased with the raise of drying temperature.Most of the five paddy varieties had similar desorption rates at drying temperatures of 45-70°C.When MC of the paddy samples decreases from 20% to 13% at drying temperatures of 50-70°C, drying time should be 60-80min for less than 10% kernel damage. Moisture effective diffusivity and glass transition temperature (Tg) of paddy during drying were investigated by drying five varieties of paddy with an initial moisture content of 21.1-24.4% wet basis and a temperature range of 45-70°C in a constant temperature and blast oven. With an increase in drying temperature, the desorption rate and moisture effective diffusivity of paddy kernels increased and drying duration decreased. At a drying temperature of 45°C, the curve of the desorption rate changed slowly and drying duration was longer. Most of the five paddy varieties had similar desorption rates at drying temperatures of 45-70°C, and their moisture effective diffusivities were in the range of 2.638×10-9-2.514×10-8m2min-1 with an active energy of 6.547-36.913kJmol-1. Tg values of long-grain variety 'Zhunliang you' and two medium-grain varieties 'Zhongjia zao' and 'Dianjiang' determined using the differential scanning colorimeter method increased from 38.7°C to 51.2°C when their moisture contents decreased from 20% to 13%. Under similar conditions, differences in Tg values of the three varieties of paddy were observed. When the moisture content of the three varieties of paddy decreases from 20% to 13% at drying temperatures of 50-70°C, drying time should be 60-80minfor less than 10% damage to kernels.

In this study, fluidized bed drying experiments were conducted for poplar wood particles (Populus deltoides) at temperatures ranging from 90°C to 120°C and air velocities ranging from 2.8 m s−1 to 3.3 m s−1. The initial moisture content (MC) and the bed height of the poplar wood particles were 150% (on an oven-dry basis) and 2 cm, respectively. The results showed that the drying rate increased by increasing the drying temperature and air velocity. The constant drying rate period was only observed at the early stages of the drying process and most of the drying processes were found in the falling rate period. The experimental data of the drying process were put into e11 models. Among these models, Midilli, Kucuk, and Yapar (2002) and Henderson and Pabis (1961) were found to satisfactorily describe the drying characteristics of poplar wood particles. The effective moisture diffusivity of wood particles increased from 7E-6 to 8.46E-6 and 7.65 E-6 to 1.44E-5 m2 s−1 as the drying air temperature increa...

A new technique, micro-explosion, was used to pretreat fast-growing poplar wood and improve membrane porosity. Poplar lumber with a thickness of 20 mm was pretreated 10 times at pressures of 0.4, 0.6, 0.8 and 1.0 MPa. Subsequently, the test and control groups were dried in air to equilibrium moisture content. Several slices of 2–3 mm long at depths of 0, 2, 4, 6 and 8 mm were cut from the samples of both the pretreated and control groups for use in the scanning electron microscope. Numerous fine fractures were found at the weak parts of the cells, the pit membranes, following an instantaneous exhaust process which used pressurized air. With the increase in depth, the fractures became fewer and finer. Regardless of the fracture extent, at each level of pressure, the fractures could reach a depth of 8 mm. According to the diversity of fracture extent and location, the fractures could be classified into three main types: radial fracture opening along the pit membrane, ring fracture opening along the pit membrane and crush. The SEM photographs illustrated that the large capillary system of the micro-explosion-treated samples was widened, which could reduce resistance to moisture movement. Thus, micro-explosion treatment could be applied not only in the wood drying industry, but also to wood impregnation, as an effective method for improving impregnation efficiency.

The skill in optimized lumber drying lies in controlling the rate of evaporation to match the rate at which moisture reaches the surface; the aim is to minimize the moisture gradient without damaging the lumber. Adjustable speed drives have proven themselves as a method for reducing energy consumption by reducing fan speed in the later stages of drying to match the rate of evaporation. Little work has been done to investigate how lower air velocities over the lumber stack during the later stages of drying affects quality of the final product in terms of moisture content distribution, shrinkage, and degrade. This study was undertaken to examine the impact of airflow using an adjustable speed drive on the final quality of 50 × 152.5 mm Pacific Coast Hemlock.

At logging and at the subsequent wood and wood semi-products treatment the fine grained loose waste is arising, e.g. wood dust, saw dust, shavings, chips, bark etc. One of possibilities of its meaningful utilization is the briquetting technology, which product are briquettes determined for energetic utilization (combustion). This report contains the results of tests carried out with the aim to assess the influence of moisture on the briquettes final properties. For the tests the platan tree chips of four moisture levels, namely 5.7 %, 7.7 %, 15.7 % and 23.9 % were used. The basic physical-mechanical properties were the evaluation criteria. Following properties were determined: ash amount, gross calorific value, total moisture content, density, rupture force, length, diameter, weight and mechanical durability. From the results of carried out tests it follows that the best properties were reached at briquettes made from chips of moisture 7.7 %. At higher or lower moisture the briquettes properties were sharply failing (namely rupture force and density).

Moist irregular wood chips or wood bark are used in packed beds for reducing odour and other gaseous emissions from waste gases. Moisture control of packing materials is essential for effective waste gas treatment. Therefore, simple experiments have been carried out to determine the influence of moisture content in a biofiltration bed made up of a mixture of irregular wood chips and wood bark in proportion 50:50 by mass on the pressure drop of air flowing through that bed. Nine moisture content levels varying from 8.1% to 64.5% (w.b.) were tested. The limiting empty bed residence time (EBRT) has been determined for each level. The influence of moisture content on true density, porosity and specific surface of the bed was determined. Above the moisture content of 28.3% (w.b.) there was a drastic change in the physical parameters of the biofilter packing. For moisture contents ≤28.3% (w.b.) the pressure drop increased slightly, while at values greater than 28.3% (w.b.) the opposite trend was observed. The Ergun equation was used to describe the relationship between the pressure drop through the bed and the superficial air velocity. For moisture contents ≤28.3% (w.b.) an approximate Ergun-type equation was proposed to describe pressure drop through the bed and the superficial air velocity.

Our drying model explicitly accounts for the three forms of moisture in low-rank coals – monolayer, multilayer, and bulk – as a basis to predict the distinctive drying behavior and energy requirements of individual low-rank coal samples. The mass loadings of the moisture forms are estimated from a database of equilibrium moisture contents that were correlated to parameters from a coal’s proximate and ultimate analyses. The drying analysis is validated with laboratory tests on steam drying in autoclaves and a fluidized bed that cover broad ranges of steam pressures and temperatures for an assortment of Australian brown coals. Then the analysis determines which forms of moisture and operating conditions most affect drying times. For some selections of samples, drying time will be proportional to total moisture, and for others, there will be exceptions. One key aspect is whether or not the target moisture level requires removal of any monolayer moisture at all. Coals with abundant bulk and multilayer moisture can achieve targets on residual moisture by vaporizing only a portion of the multilayer moisture. Consequently, their drying times will be relatively modest. But coals with little bulk moisture and relatively abundant monolayer moisture will require relatively long drying times simply because monolayer moisture is always released much more slowly than multilayer moisture. Hence, the levels of the three forms of moisture in any particular coal sample are determining factors for drying times.

In this paper, we consider the problem situation related to the drying of wood, which requires significant energy costs. To solve the problem, the traditional technology of wood drying is analyzed and the main shortcomings are identified. The use of an electro-osmotic phenomenon is proposed to remove moisture from the mass of wood, which will reduce energy consumption for wood drying.