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1.	Ahrné, Lilia, et al. (författare) Microwave convective drying of plant foods at constant and variable microwave power 2007 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 25:42193, s. 1149-1153 Tidskriftsartikel (refereegranskat)abstract Microwave convective drying of plant foods is a promising process due to the shorter drying time and better product quality. High microwave power decreases the drying time but causes charring of the product. In this work, microwave drying under constant and variable microwave power were compared. Temperature-sensitive products, such as plant foods, are especially affected by microwave power during the final drying period. Therefore, drying at variable microwave power was found to be a more suitable drying process. Air (temperature and velocity) has an important role during microwave drying, not only as carrier of evaporated moisture but also as it contributes to a more homogeneous and faster drying.
2.	Ananías, Rubén A., et al. (författare) Collapse of Eucalyptus nitens Wood after Drying Depending on the Radial Location Within the Stem 2014 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 32:14, s. 1699-1705 Tidskriftsartikel (refereegranskat)abstract Collapse is almost certain to occur in the industrial drying of Eucalyptus nitens, and as such this prevents the lumber manufacturing industry in Chile from producing commercial solid wood products from this species. This problem is still unsolved, and different studies to reduce collapse are currently underway. In this exploratory study, shrinkage and collapse after drying of Eucalyptus nitens was measured for boards cut from different radial locations within the stem (core, transition and outer wood from pith to bark) and having different annual ring orientation (flat-sawn and quarter-sawn). Even though exploratory, the results appear to confirm that pieces that were cut from the center of the trees were less susceptible to collapse than the pieces cut from the transition zone between the center and the periphery. On average, collapse in transition wood was approximately 50% higher than the collapse observed in wood cut from the central zone of the trees.
3.	Ananías, Rubén A., et al. (författare) Drying Schedules for Canelo Wood 2013 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 31:3, s. 282-285 Tidskriftsartikel (refereegranskat)abstract Canelo wood is a highly valued native species in Chile that shows delicate marbling patterns with a pinkish soft silver luster. Due to its decorative qualities, canelo wood is dried for the manufacture of furniture and musical instruments. However, canelo wood lacks vessels cells that typically transport the water in hardwoods. Per its drying behavior, canelo wood is considered a transition species between hardwoods and softwoods. Therefore, this article reports drying schedules that were developed for drying 25-mm and 50-mm canelo lumber. In addition, this article reports experimental overall mass transfer coefficients, so that drying times for each of the drying stages can be easily estimated
4.	Ananías, Rubén A., et al. (författare) Energy Consumption in Industrial Drying of Radiata Pine 2012 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 30:7, s. 774-779 Tidskriftsartikel (refereegranskat)abstract This article reports the results of an exploratory study designed to reduce heat and electricity consumption in industrial drying of radiata pine. The experiments were performed with slight modifications of the standard drying schedules used by the sawmill to dry radiata pine in 100-m 3 industrial kilns. The heat and electricity consumption were determined with data collected during the drying runs and calculations based on mathematical models. The results showed that depending on the case, heat and power consumption were respectively reduced by up to 14 and 35%.
5.	Ananías, Rubén A., et al. (författare) Testing New In-Kiln Meter for Monitoring Lumber Moisture Content during Drying 2013 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 31:3, s. 277-281 Tidskriftsartikel (refereegranskat)abstract The objective of this study was to test a new in-kiln sensor for monitoring lumber moisture content during industrial drying. The theoretical foundation of the technology was already known, because it is based on electrical conductivity, but the mechanism of implementation was new and required validation. For this reason, the technology was compared with two other widely used methods for assessing lumber moisture content, namely, the oven-drying and electrical capacitance methods. The tests were performed in a 120-m3 industrial kiln operated by a sawmill in the eighth region of Chile, and the results showed that the average moisture content at the end of drying was satisfactorily determined by the new in-line sensor. As predicted by theory, the sensor was not able to accurately measure moisture content above 25%, but it was still able to provide the equivalent of a drying curve for monitoring of the drying process
6.	Anderberg, Anders, et al. (författare) Drying and hydration of cement based self-leveling flooring compounds 2007 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; vol 25:no 12, s. 1995-2003 Tidskriftsartikel (refereegranskat)abstract Water in building materials not only influences important physical properties and chemical processes but is also related to the well-being of the occupants of a building. The drying of cementitious materials is complex, involving several different drying processes. The conditions for each drying process change as the material changes its properties as it goes from a particle suspension in the fresh state to a fine porous material in the hardened state. The present article describes and quantifies the drying processes of cement-based self-leveling flooring compounds (SLCs) and relates them to the extent of reaction, which here is quantified by isothermal calorimetry. The relative importance of the different drying processes is discussed and a model for the drying of the SLCs is proposed.
7.	Antti, Lena, et al. (författare) Investigation of the heating of wood in an industrial microwave applicator : theory and practice 2000 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 18:8, s. 1665-1676 Tidskriftsartikel (refereegranskat)abstract In this work a comprehensive set of experimental results are used as an excellent means to understand the coupling that exists between the material and the electromagnetic fields in a specific industrial microwave applicator. The analysis of the infrared images allows an accurate map of the power and temperature distributions within the wood sample to be determined. This map, together with the simulation results of a previously developed computational electromagnetic model, can provide a detailed understanding of the design features of the microwave applicator. In particular, it is possible to locate the occurrence of localised hot spots and to examine the uniformity of the heat distribution throughout the sample. The simulation results provide the evolution of the electromagnetic fields inside the entire applicator and the sample. The coupling of theory and practice is the best way to proceed in optimising the design and for proposing new applicator geometry that can heat the material more effectively.
8.	Bengtsson, Peter, 1974- (författare) Experimental Analysis of Low-Temperature Bed Drying of Wooden Biomass Particles 2008 Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 26:5, s. 602-610 Tidskriftsartikel (refereegranskat)abstract This report investigates the low-temperature bed drying of biomass particles for use in a gasification process. Experimental drying equipment capable of drying up to 0.25 m 3 of biomass batchwise was constructed. The experimental result indicates that the drying equipment and applied method are appropriate to evaluate different drying parameters and their influence on the drying course. Drying parameters such as air temperature, air velocity, bed height, and type of wood are studied regarding the drying rate, final moisture content in the material, and bed pressure drop. The constant-rate and falling-rate drying period are studied to obtain an energy efficient drying process. Measurements show that the drying zone (where the actual drying occurs) progresses irregularly through the bed.
9.	Bengtsson, Peder, et al. (författare) Performance Study of a Closed-Type Heat Pump Tumble Dryer Using A Simulation Model and an Experimental Set-Up 2014 Ingår i: Drying Technology. - : Taylor & Francis Group. - 0737-3937 .- 1532-2300. ; 32:8, s. 891-901 Tidskriftsartikel (refereegranskat)abstract In the interests of competitiveness, manufactures of tumble dryers are seeking to reduce both their electricity use and the drying time. This study examines how the cylinder volume of the compressor and the total heat transfer of the condenser influence the drying time and electricity use in a heat pump tumble dryer. A transient simulation model was developed and compared to an experimental set-up with good similarity. The simulations show that increasing the cylinder volume of the compressor by 50% decreases the drying time by 14% without using more electricity.
10.	Berg, C G A, et al. (författare) Transport equations for moist air at elevated wet bulb temperatures 2004 Ingår i: Drying Technology. - 1532-2300. ; 22:1-2, s. 201-224 Tidskriftsartikel (refereegranskat)abstract In meteorological applications psychrometers are used both as a humidity transfer standard and as a measurement instrument. Unfortunately wet bulb temperature, t(wb), is not a thermodynamic property and consequently, in equation linking vapor pressure and temperature, the psychrometer constant, from now on called the psychrometer coefficient, a, must be experimentally evaluated. Both theoretical formulations and experimental results show that the psychrometer coefficient, a, depends on a number of parameters. In this work a thermodynamic model of the coupled heat and mass transfer formulation of an adiabatic drying process is derived to state the adiabatic saturation temperature, t(as). Derived equations are also used in a couple of calculated examples to show to the reader why some psychrometric relations tend to be less usable at high wet bulb temperatures. The authors have found, based on the calculations, that the past conclusions of experimental studies of adiabatic evaporation from a water surface in humid air may verify both an assumption that the apparent heat transfer coefficient, is greater than the apparent mass transfer coefficient, alpha'(tot), (i.e., alpha(tot) > alpha'(tot) and t(wb) > t(as)) as well as an assumption that the apparent heat transfer coefficient is smaller than the apparent mass transfer coefficient (i.e., alpha(tot) < alpha'(tot) and t(wb) < t(as)) although pure analogy considerations propose that the apparent heat transfer coefficient is smaller than the apparent mass transfer coefficient (i.e., alpha(tot) < alpha'(tot) and t(wb) < t(as)).
11.	Berghel, Jonas, et al. (författare) An Experimental Study on the Influence of Using a Draft Tube in a Continuous Spouted Bed Dryer 2014 Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 32:5, s. 519-527 Tidskriftsartikel (refereegranskat)abstract Further increasing the production of processed biofuel also increases the demands on drying capacity. With the aim of increasing the heat capacity flow, experimental tests have been performed on the process of drying sawdust in a continuous spouted bed dryer with nine different draft tube designs. The results showed that a draft tube with an increased length and an increased disengagement height decreased the dry substances' flow rate throughout the dryer. The results also showed that the mass of the material in the dryer was approximately the same in all the tests. This means that the draft tubes, no matter their size, do not influence the amount of material in the dryer.
12.	Berghel, Jonas (författare) The Effect of Using a Heating Tube in an Existing Spouted Bed Superheated Steam Dryer 2011 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 29:2, s. 183-188 Tidskriftsartikel (refereegranskat)
13.	Brülls, Mikael, et al. (författare) Ice sublimation in vial lyophilization. 2009 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 27:5, s. 695-706 Tidskriftsartikel (refereegranskat)abstract Ice sublimation in vial lyophilization was studied experimentally and theoretically. A theoretical dynamic and two-dimensional axisymmetric model that comprised both the vial and its content was developed. The model included the curvature of the bottom of the vial, the temperature of the ice surface as a function of the chamber pressure, and physical models for the heat of sublimation, thermal conductivity of gases at low pressure, thermal conduction, and thermal radiation. The coefficients in the model were based on physical constants, except for vials on the periphery of the shelf, where an overall heat transfer coefficient derived from experimental data was used to model the transport of heat from the walls of the freeze dryer. The study demonstrated that the sublimation was, apart from the shelf temperature and the chamber pressure, also influenced by the curvature of the bottom of the vial, the position on the shelf, and the atmosphere in the freeze dryer.
14.	Carlsson, Peter, 1950-, et al. (författare) Optimization of Drying Schedules Adapted for a Mixture of Bords with Distribution of Sapwood and Heartwood 2002 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 20:2, s. 403-418 Tidskriftsartikel (refereegranskat)abstract A distributed optimization model for wood drying with several different boards simultaneously is presented. Optimization is performed with a gradient-based program. During optimization, convex subproblems are created and transformed to the dual problem and solved. Arbitrary outtakes and board dimensions are possible, as well as different material data and distribution of sapwood and heartwood. It is also possible to optimize drying schedules where drying of boards with variations in environmental conditions is simulated. A two-dimensional orthotropic drying model is used in the moisture transport and structural analysis, where the variation in radial and tangential directions are considered. The influence of temperature and moisture content on material data and mechanical properties is also taken into account. The drying schedules achieved are optimized to minimize drying time for a representative mixture of boards. A numerical example is presented where the drying schedule is optimized for two boards with different outtakes and distributions of sapwood and heartwood. Optimization is performed with two computers in a network. Drying starts from the fibre saturation point in these simulations.
15.	Carlsson, Peter, et al. (författare) Optimized wood drying 2000 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 18:8, s. 1779-1796 Tidskriftsartikel (refereegranskat)abstract Nonlinear programming methods are used to create effective drying schedules for boards. A two-dimensional. orthotropic drying model is connected to an optimization routine that solves convex sub-problems. The iterative optimi7ation program calculates the drying schedule. i.e. the variation of temperature and humidity with time, that gives the shortest drying time for a board with prescribed upper and lower level of the moisture content. To demonstrate the capability of the technique. numerical results are presented.
16.	Elustondo, Diego, et al. (författare) Comparative analysis of three methods for stochastic lumber drying simulation 2005 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 23:1-2 Spec. issue, s. 131-142 Tidskriftsartikel (refereegranskat)abstract This article describes a novel stochastic model designed to simulate systems that cannot be analyzed as a unit, but as a collection of a large number of similar components. In order to state advantages and disadvantages, the proposed method is compared with two other published models. The first is a symbolic mathematical relationship designed to predict average moisture content and standard deviation after conventional drying of lumber. Since this model is exact, it was used as reference to evaluate the accuracy of the other approximate numerical methods. The second model is entirely random, and it emulates a real system behavior in which the parameters and conditions randomly change from one component to the other. The proposed method is based on numerical integration of the parameter's frequency distribution curves, which always produce the same and most probable result for the same parameters and conditions. The three methods were applied for simulation of conventional lumber drying, and the results were compared both qualitatively and numerically
17.	Elustondo, Diego, et al. (författare) Drying Western Red Cedar with Superheated Steam 2014 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 32:5, s. 550-556 Tidskriftsartikel (refereegranskat)abstract This exploratory study evaluated the possibility of drying 50-mm-thick western red cedar with superheated steam. Since there are no industrial facilities in Canada drying western red cedar with superheated steam, the study was designed to explore the potential of this technology in terms of lumber quality, moisture content distribution, and drying time. The experiments showed that the 50-mm-thick product can be dried in less than three days without jeopardizing lumber quality (in comparison with the two weeks that is currently required in conventional kilns), and the percentage of pieces that remained wet after drying was within the 10% to 15% range that is typically tolerated in industry.
18.	Elustondo, Diego, et al. (författare) Evaluation of three semi-empirical models for superheated steam vacuum drying of timbers 2003 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 21:5, s. 875-893 Tidskriftsartikel (refereegranskat)abstract Superheated steam drying at sub-atmospheric pressure (SSV) has been successfully employed in Europe and Asia for drying some types of timbers, showing that drying time could be reduced by 50% with respect to conventional drying without significant losses in the quality of the final product. This reduction is the consequence of a different heat and mass transfer control mechanism. Since SSV drying is carried out in absence of gaseous air, diffusion of the generated vapor is not a limiting factor and drying rate becomes more dependent on heat transference. Therefore, classical interpretation of timber drying as a process based on moisture migration control is not applicable to SSV. This work is targeting the development and validation of a simplified semi-empirical model for SSV drying of timbers. Mathematical representation of the proposed model is uncomplicated and straightforward to apply, and the comparison between model predicted and experimental data showed a high degree of agreement under variable drying conditions.
19.	Elustondo, Diego (författare) Guest Editorial : R&D Needs in Wood Drying Technology 2014 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 32:6, s. 629-630 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
20.	Elustondo, Diego, et al. (författare) Opportunities to reduce energy consumption in softwood lumber drying 2006 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 24:5, s. 653-662 Tidskriftsartikel (refereegranskat)abstract While a few years ago the cost and availability of energy was not an important issue for the Canadian lumber industry, this situation has recently changed. Today, companies that have operated trouble-free for many years using the same technologies and practices may now have to adapt to the rising cost of fossil fuels and concerns about greenhouse gas emissions. This article addresses this problem for the particular case of the softwood lumber industry. The study describes the most important sources of energy losses in conventional drying and proposes a number of strategies and technologies to reduce kiln energy demand
21.	Elustondo, Diego, et al. (författare) Optimum operating conditions in drying foodstuffs with superheated steam 2002 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 20:2, s. 381-402 Tidskriftsartikel (refereegranskat)abstract It is inferred from experimental data that in drying foodstuffs with superheated steam, the initial drying rate has a direct effect on the rate at which the overall drying takes place. That is, the faster the initial drying rate, the shorter the overall drying time. This criterion is very convenient because at the beginning, water moistens the sample external surface so evaporation does not depend on internal sample characteristics, but only on external convective heat and mass transfer rates. Mass and energy balance equations are solved and the result converted into a general initial drying rate equation, in which all dryer characteristics are grouped into one dimensionless parameter. The initial drying rate equation is mathematically maximized and the optimum working conditions determined. The result shows that initial drying rate always increase with increases of either the superheated steam temperature or velocity, but once these two variables are fixed, there exists at least one "optimum" pressure at which the initial drying rate is a maximum. Finally, the initial drying rate and optimum condition equations are applied to three model dryers, a dryer for a flat sheet, a fixed bed dryer and a rotary dryer. In each case, numeric values are computed and plotted as drying rate versus pressure curves, in which the optimum drying rate is also included. Also presented is a chart to compare the optimum pressures as functions of temperature and steam velocity for the three dryers.
22.	Elustondo, Diego, et al. (författare) Predicting thermal efficiency in timber radio frequency vacuum drying 2004 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 22:4, s. 795-807 Tidskriftsartikel (refereegranskat)abstract In this work, the efficiency of transforming dielectric energy into evaporated water is analyzed for the case of timber radio frequency vacuum drying. Based on well-known heat and mass transfer equations, a simplified mathematical model is proposed that estimates the drying efficacy in regards to the thermo-physical properties of wood. Although not exact, the theoretical results are close to the experimental observations and elucidate some phenomena like the tendency of the timber to dry from inside to outside, and the drying rate increase with the rise of the timber gas permeability. The theoretical efficiency model also predicts a range of wood permeability values for which the drying efficiency changes from 100 to 0%, thus providing a quantitative scale for classifying the spectrum of "difficult-to-dry" all the way to "easy-to-dry" wood species when using radio frequency vacuum technology
23.	Elustondo, Diego, et al. (författare) Stochastic numerical model for radio frequency vacuum drying of timbers 2002 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 20:9, s. 1827-1842 Tidskriftsartikel (refereegranskat)abstract A new numeric method to simulate stochastic dispersion (a natural phenomenon that occurs when a magnitude cannot be associated to a specific value, but to the probability of being within a range of values) is proposed and applied to predict Radio Frequency Vacuum (RFV) drying of timber. A theoretical formulation of the method is described and complemented to take into account the frequency distribution of the timber initial moisture content, so that it can be applied to industrial runs. Experimental data obtained from mixed western hemlock and amabilis fir dried in a commercial RFV kiln are used to validate the stochastic model, and the results are compared through moisture content histograms and probability charts. A numerical example is shown in order to provide an idea of the movement of the moisture profiles during RFV drying.
24.	Elustondo, Diego, et al. (författare) Visual Method to Assess Lumber Sorting Before Drying 2013 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 31:1, s. 32-39 Tidskriftsartikel (refereegranskat)abstract This article explores the possibility of using a simplified but intuitive method to quickly assess the potential benefits of sorting lumber before industrial kiln drying. The method consists of using scatter plots to visualize the probability of obtaining a certain drying result, such as final moisture content, as a function of a property of the green lumber that can be measured in practice. The method was first validated with four drying runs of 116 mm × 52 mm hemlock lumber: one run contained unsorted lumber and the others contained the same type of lumber but sorted into low, medium, and high groups depending on the electrical capacitance of the green wood. After validation, the scatter plots were used to assess the benefits of two typical industrial sorting strategies, namely, sorting by electric capacitance and sorting by weight. It was found that both methods have the potential to increase lumber production and reduce over dried lumber in approximately the same magnitude. For a typical industrial schedule, sorting into three groups reduced the drying time by approximately 10% and over dried lumber to practically zero
25.	Eriksson, John, 1973, et al. (författare) A Mass Transport Model for Drying Wood under Isothermal Conditions 2007 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 25:3, s. 433-439 Tidskriftsartikel (refereegranskat)abstract Mass transport in wood during drying can have different mechanisms at different periods of drying. Depending on the current moisture content (MC) and the structure of the wood, the driving forces for the mass transport are essentially different. Above the fiber saturation point (FSP), the lumens are partially saturated and the transport of liquid (free) water occurs as a consequence of capillary action. On the other hand, below the FSP, bound water within the cell walls is conveyed by diffusion, and water vapor in the lumens moves under influence of pressures gradient. Based on these considerations, a unified model is presented that takes into account the transport of the different moisture phases. Simulation of the drying of a Norway spruce sample at 50°C from about 135 to 7% MC is carried out using the finite element method (FEM). Comparison between the simulated average MC and the experimental observations obtained from X-ray computed tomography (CT) shows reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation. Finally, the influence of absolute permeability on the average MC is studied.
26.	Fredriksson, Maria, et al. (författare) A method for determination of absorption isotherms at high relative humidity levels: measurements on lime-silica brick and Norway spruce (Picea abies (L.) Karst.) 2016 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 34:1, s. 132-141 Tidskriftsartikel (refereegranskat)abstract The relationship between the relative humidity and the moisture content of a material for relative humidity levels close to 100% can be studied using the pressure plate technique. However, this method is designed for desorption experiments and modifications are necessary in order to perform absorption experiments. This paper presents a method to condition samples to a uniform moisture content by absorption with the pressure plate technique. The specimens were suspended in magnetic clamps until the ceramic plate had equilibrated with the applied pressure and modifications were made so that water could circulate through the pressure plate cell.
27.	Fritzell, Emma, 1979, et al. (författare) Drying kinetics and equilibrium moisture content of MDF fibres 2009 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 27:9, s. 993-998 Tidskriftsartikel (refereegranskat)abstract An experimental device was constructed to study the drying kinetics of wood fibers under controlled conditions. The device consisted of a drying chamber in which a net basket filled with the fiber material was connected to a load cell. The drying medium was then forced through the basket at controlled levels of humidity and temperature. Experiments were performed with spruce fibers and the drying medium at varying temperature (50-170° C) and relative humidity (1-86%). In general, the drying rate increased with increasing temperature and decreasing relative humidity. A constant drying rate period was observed in all cases. The critical moisture content was approximately 1.25. The characteristic drying curve has a slight downward concave shape. The equilibrium moisture contents obtained at ambient temperature agree well with data in the literature. © 2009 Taylor & Francis Group, LLC.
28.	Frodeson, Stefan, 1968-, et al. (författare) The Potential of Using Two-Step Drying Techniques for Improving Energy Efficiency and Increasing Drying Capacity in Fuel Pellet Industries 2013 Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 31:15, s. 1863-1870 Tidskriftsartikel (refereegranskat)abstract The use of wood fuel pellets has increased worldwide in recent years, and pellet producers conclude that the lack of drying capacity is a barrier to increased production. In this study, we develop a concept of two different dryers called the two-step drying technique. The aim is to show the potential for increasing the drying capacity and improving energy efficiency when introducing a second dryer into the pellet plant. The study is theoretical and based on an industrial packed moving bed dryer. It shows that the drying capacity increased by 22% when a pneumatic second dryer was used.
29.	Frühwald, Eva (författare) Effect of high-temperature drying and restraint on twist of Norway spruce 2007 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 25:1-3, s. 489-496 Tidskriftsartikel (refereegranskat)abstract During drying, timber distortion is a major defect mainly due to shrinkage anisotropy, differences in longitudinal shrinkage, and spiral grain. The distortion can be reduced by external restraint and use of appropriate kiln schedules. The research presented here is part of a project on the improvement of shape stability of Norway spruce by high-temperature drying. The effects of drying temperatures between 80 and 170 degrees C and restraint on the extent of twist in Norway spruce were investigated on 30 cm lengths. Results show that significant twist reduction could be achieved in restrained specimens sawn from core wood. This effect was permanent even after exposure to subsequent moisture cycling. In addition to high-temperature drying, heat-treated material (Thermowood (R)) was also investigated. As for the high-temperature dried material, twist amplitude in moisture cycling was highest for pith-in specimens. Increased heat-treatment temperature reduced the twist amplitude, thus improving the shape stability. However, for the material dried in this study, shape stability was not influenced by the drying temperature.
30.	Gamero, Rafael, et al. (författare) Internal mass transfer during isothermal drying of a porous solid containing multicomponent liquid mixture 2005 Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 23:9-11, s. 1939-1951 Tidskriftsartikel (refereegranskat)abstract Internal mass transfer in a porous solid partially saturated with multicomponent liquids has been experimentally and theoretically studied. Isothermal drying experiments were performed using a jacketed wind tunnel where the transient composition profiles and total liquid content of a cylindrical sample were determined. Sand samples wetted with the ternary liquid mixtures watermethanol-ethanol and 2-propanol-methanol-ethanol were dried at two different initial compositions and temperatures. A mathematical model including mass transfer by capillary movement of the liquid and interactive diffusion in both gas and liquid phase was developed. To simulate the capillary movement of liquid mixtures, parameters experimentally determined for single liquids where weighed according to liquid composition. A fairly good agreement between theoretical and experimental liquid composition profiles was obtained provided that axial dispersion is included in the model.
31.	Granstrom, Karin, et al. (författare) Emissions from sawdust in packed moving bed dryers and subsequent pellet production 2016 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 34:3, s. 258-266 Tidskriftsartikel (refereegranskat)abstract This study quantifies emissions of hydrocarbon terpenes from the drying of sawdust in packed moving bed dryers, through the production chain to the finished pellets, and determines the parameters suitable for emission control. The terpene content in softwood sawdust and pellets was analyzed using gas chromatography. The distribution of VOC emissions over the bed was measured with a flame ionization detector. After drying, 30-40% of the initial terpenes remain in the wood, 20-30% remain after grinding, and 10-15% remain after pelleting. Dryer emissions correlate with residence time and final sawdust moisture content. Pellet press emissions correlate with pellet moisture content.
32.	Hajiyan, Ebrahim, 1992-, et al. (författare) High temperature drying of sawn timber—A review 2024 Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. Forskningsöversikt (refereegranskat)abstract Sawn-timber drying is the wood industry’s most time- and energy-consuming process. This process can be more efficient than the conventional method by elevating the dry-bulb temperature to above 100 °C in a high-temperature drying (HTD) process, which for some species shortens the drying process by up to 50% without deteriorating the quality. Comprehending the complex correlation between the wood drying physics at high temperatures and the anatomical features of the specific species, along with its mechanical and physical properties, is crucial, as it limited its application from being broadly implemented in industry and the necessity of generalizing this method for wood species. The present study has been conducted to comprehensively review and tackle the challenges of applying this method on various species and the consequences, such as high moisture content gradients resulting in stress residual, unevenness, and color changes. Energy, environment, and economic (3E) assessments of HTD were evaluated. The accelerated drying process in HTD reduces heat losses and air leaks, resulting in higher energy efficiency than the conventional methods. Furthermore, it was proved to be 20% economically in the long term. Confliction in reported studies, such as HTD's effect on permeability and volatile organic compound (VOC) emissions, was raised, highlighting the importance of further studies for generalizing this method to adapt appropriate drying schedules, focusing on Scandinavian species by referring to previous industrial trials.
33.	Hansson, Lars, et al. (författare) Modeling microwave heating and moisture redistribution in wood 2008 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 26:5, s. 552-559 Tidskriftsartikel (refereegranskat)abstract A finite element model was developed to describe and explain microwave heating of wood and the following moisture redistribution in wood. Dielectric and thermal properties are of great importance, since they are continuously affected during the process by moisture content, density, grain direction, temperature, and more. Computer tomography was used to detect wood density and moisture content. Heat distribution was verified by fiber-optic temperature sensors. The tests were performed in a designed microwave dryer based on 1-kW generators, 2.45GHz. The results show that finite element modeling is a powerful tool to simulate heat and mass transfer in wood, providing the material is well described.
34.	Hashimoto, A, et al. (författare) Simulation of Convective Drying of Wet Porous Materials 2003 Ingår i: Drying Technology. - 1532-2300. ; 21:8, s. 1411-1431 Tidskriftsartikel (refereegranskat)abstract A simulation model for convective drying of wet porous materials was developed. For the simulation, we measured the moisture diffusivities within them and applied a modified Dubinin-Astakhov equation to the moisture sorption data for a membrane filter. The simulation results not accounting for internal mass transfer resistance were quite different from the experimental ones. The drying characteristics calculated by a shrinking core model with effective moisture diffusivity represented a much lower drying rate and much higher temperatures, respectively, than the experimental ones. This meant that we must consider the plural moisture transport mechanisms within the samples. Therefore, we calculated the drying rate and temperatures with an apparent overall mass transfer coefficient damping with a decrease in the moisture content. The results accounting for the hygroscopic effects broadly agreed with the experimental ones by the evaluation.
35.	Holmberg, André, et al. (författare) Water vapor sorption and diffusivity in bark 2016 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 34:2, s. 150-160 Tidskriftsartikel (refereegranskat)abstract Physical properties of importance in drying processes have been compiled for bark, including spruce, pine, and birch in Sweden. Water vapor sorption isotherms were determined for the bark of these trees. At 95% relative humidity and 25 degrees C, outer birch bark reached a moisture ratio (kg water/kg dry mass) of 5%, whereas inner birch bark, spruce bark, and pine bark reached moisture ratios of 21, 28, and 25%, respectively. The transverse water vapor diffusivity in samples of spruce bark, pine bark, inner birch bark, and outer birch bark were determined to be 1.1-1.710(-6), 2.2-9.210(-7), 1.5-2.610(-6), and 4.3-1310(-8)m(2)/s, respectively. The in-plane diffusivity was of the same magnitude as the transverse diffusivity in inner birch bark, whereas in outer birch bark the in-plane diffusivity was several times higher than the transverse diffusivity. These data can be used to model the drying behavior and can thus aid in the design of efficient bark drying processes.
36.	Holtz, Emma, et al. (författare) The role of processing parameters on energy efficiency during microwave convective drying of porous materials 2009 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 27:2, s. 173-185 Tidskriftsartikel (refereegranskat)abstract A small-scale microwave convective dryer was built to study the effects of microwave power level, air temperature, and air velocity on drying kinetics, temperature development, and specific energy consumption (MJ/ kg evaporated water) using statistical designs. Increased microwave power had a large significant effect on moisture loss and temperature development and it reduced specific energy consumption. Increased air temperature and air velocity increased specific energy consumption, as their effect on drying kinetics was smaller in the system used. Low air temperature slowed the drying process, without affecting the relationship between average sample temperature and average moisture content during drying.
37.	Huttunen, Marcus, et al. (författare) Modeling fixed-bed drying of bark 2017 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 35:1, s. 97-107 Tidskriftsartikel (refereegranskat)abstract A model for fixed-bed drying of bark has been developed. The model takes heat and mass transfer between the air and bark into account and the volumetric heat transfer coefficient was used as fitting parameter in the model. The assumption of adiabatic saturation of the air leads to too high drying rates but a model with three size fractions shows good agreement both between experimental laboratory data and data from an industrial dryer. A sensitivity analysis for different air temperatures, air velocities, and bed heights show how the dryer capacity depends on these parameters.
38.	Karlsson, Magnus, et al. (författare) Static and dynamic modeling of cardboard drying - Part 1: Theoretical model 2005 Ingår i: Drying Technology. - 1532-2300. ; 23:1-2, s. 143-163 Tidskriftsartikel (refereegranskat)abstract A general, dynamic model describing the drying mechanisms of paper has been developed. The model includes shrinkage and predicts temperature, moisture, and pressure profiles. It has been evaluated against steady-state as well as dynamic measurements on a multicylinder paper dryer. The results revealed critical sections where low web strength and maximum gas pressure occur. Measurements of the outer cylinder temperature provide reliable information on the accuracy of the predicted moisture profile since they show the position where the paper surface is dry.
39.	Karlsson, Magnus, et al. (författare) Static and dynamic modeling of cardboard drying - Part 2: Simulations and experimental results 2005 Ingår i: Drying Technology. - 1532-2300. ; 23:1-2, s. 165-186 Tidskriftsartikel (refereegranskat)abstract A general, dynamic model describing the drying mechanisms of paper has been developed. The model includes shrinkage and predicts temperature, moisture, and pressure profiles. It has been evaluated against steady-state as well as dynamic measurements oil a multicylinder paper dryer. The results revealed critical sections where low web strength and maximum gas pressure Occur. Measurements of the outer cylinder temperature provide reliable information on the accuracy of the predicted moisture profile since they show the position where the paper surface is dry.
40.	Lindell, Kristian, et al. (författare) A modular process modeling tool for the analysis of energy use and cost in the pulp and paper industry 2006 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 24:11, s. 1335-1345 Tidskriftsartikel (refereegranskat)abstract A novel process modeling tool to facilitate the study of how various process changes in the paper dryer section affect the mill-wide energy system has been developed. A model library with steady-state block models describing paper dryers, heat recovery equipment, and auxiliary systems on component level have been developed using the software Extend. Process models are then created from these block models using graphical programming. In this article, the characteristics of the developed tool are described and a case study where the tool is shown to be useful for analyzing the energy performance of a hybrid dryer section is presented.
41.	Ljung, Anna-Lena, et al. (författare) Discrete and continuous modelling of heat and mass transport in drying of a bed of iron ore pellets 2012 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 30:7, s. 760-773 Tidskriftsartikel (refereegranskat)abstract Drying of a porous bed of iron ore pellets is here considered by modeling a discrete two-dimensional system of round pellets. As a complement to the two-dimensional model, a continuous one-dimensional model enabling fast calculations is developed. Results from the discrete model show that the temperature front advances faster in areas with large distances between the pellets. In areas with low flow speed, the temperature of the pellets increases with a relatively slow rate. The water inside these pellets will therefore remain for a long time. The continuous model fits the discrete model very well for a regular distribution of equal-sized particles. A discrete model with irregular packing will, compared to the continuous model, show a larger variation in the distribution of temperature and moisture content in the final phase of drying.
42.	Ljung, Anna-Lena, et al. (författare) Evaporation of a sessile water droplet subjected to forced convection in humid environment 2019 Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 37:1, s. 129-138 Tidskriftsartikel (refereegranskat)abstract The evaporation of a sessile droplet is here investigated numerically with a design of experiment approach. Boundary conditions are chosen based on forced convection in humid air, i.e., mimicking the conditions inside a dishwasher. Computational fluid dynamic simulations of an axisymmetrical droplet placed on a heated plate show that relative humidity, initial contact angle, plate temperature, and temperature difference between plate and air all have significant effect on the initial evaporation rate. For the studied conditions, relative humidity is the most significant factor while the magnitude of the velocity and type of internal flow are insignificant within a 95% confidence interval.
43.	Ljung, Anna-Lena, et al. (författare) Influence of air humidity on drying of individual iron ore pellets 2011 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 29:9, s. 1101-1111 Tidskriftsartikel (refereegranskat)abstract The influence of air humidity on drying is investigated at four inlet air dew points; T dp = 273, 292, 313, and 333 K. A numerical model taking into account capillary transport of liquid and internal evaporation is applied to a spherical geometry representative for an individual iron ore pellet. Drying simulations are carried out with commercial computational fluid dynamic (CFD) software and the boundary conditions are calculated from the surrounding fluid flow. The results indicate that the effect of air humidity arises from the start of the first drying period, that is, the surface evaporation period, whereas the difference is reduced at the end of the period due to a prolonged stage of constant rate drying attained at high saturations. At low saturations, there is no constant drying stage because the surface becomes locally dry before the pellet temperature has stabilized at the wet bulb temperature. The magnitudes of the drying rates and moisture contents are rather similar at the time when internal drying becomes dominating (i.e., when the total surface evaporation rate is zero) for the respective dew points, yet the drying time is increased at high saturations. It was also found that the moisture gradients at the surface and inside the pellet increased with drying rate.
44.	Ljung, Anna-Lena, et al. (författare) Influence of plate size on the evaporation rate of a heated droplet 2015 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 33:15-16, s. 1963-1970 Tidskriftsartikel (refereegranskat)abstract The purpose of this study is to numerically investigate how the width of a plate influences natural convection around a droplet. Droplets evaporating on hot surfaces has many applications including drying of dishes and paint. Evaporation rate and deposition of particles withheld in the fluid is of great importance in both cases. As a first step to investigate how the drying rate and deposition mechanisms can be controlled, this work aims to investigate how the external flow around a water droplet influences the evaporation rate. Natural convection caused by the hot plate on which the droplet rests is considered and the effect of different widths is examined. Results show that an extension of the plate past the droplet will increase the maximum velocity in the domain due to natural convection while the flow close to the surface is decreased due to the no slip condition and temperature gradient. A decrease of the evaporation rate is therefore observed when the plate is extended past the droplet as compared to the case when the plate and droplet have the same diameter. Simulations furthermore show that the results from the heat and mass transfer analogy only compare well to the results of Fick's law when the droplet and plate has the same width.
45.	Luna, Fabio, et al. (författare) Diffusion equation applied to isothermal drying of a multicomponent liquid film 2005 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 23:11-sep, s. 1953-1975 Tidskriftsartikel (refereegranskat)abstract Liquid-side-controlled drying by convection of a multicomponent liquid film is studied. Interactive diffusion in liquid phase is considered the main mechanism for mass transfer. Assuming an isothermal drying process and a constant matrix of multicomponent diffusion coefficients, an analytical solution of the diffusion equation is developed. The equations are decoupled by a similarity transformation and solved by the method of variable separation. The solution is applied to the drying of ternary mixtures, one of them containing a component of negligible volatility. The variation of diffusion coefficients along the process trajectory was taken into account by a piecewise application of the solution in time intervals with averaged coefficients from previous time steps. Despite the simplifications made, the analytical solution gives a god insight into the selectivity of the drying process and is computationally fast. The limitations of the analytical solution and the prospect of applying the solution to the description of a nonisothermal process are discussed. It would introduce an important computational economy since the rigorous treatment of multicomponent drying leads to partial differential equations with variable coefficients, which can only be solved by time-consuming iterative procedures.
46.	Luna, Fabio, et al. (författare) Stability of the Dynamical System describing Isothermal Gas-Phase-Controlled Drying of Ternary Mixtures 1998 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 16:9-10, s. 1807-1825 Tidskriftsartikel (refereegranskat)abstract A stability analysis of the ordinary differential equations describing the process of convective gas-phase-controlled evaporation during drying of ternary mixtures was performed. The case considered was that of a gas flowing parallel to the surface of a flat solid, wetted with a liquid mixture, during drying at constant gas conditions. If evaporation is isothermal, the solutions of a system of ODEs are the trajectories in the phase plane represented by a triangular diagram of compositions. Analysis of the ternary mixture showed that the predicted ternary dynamic azeotropes were unstable nodes and composition trajectories moved away from them. On the other hand, some of the binary azeotropes could be stable nodes. Nodes represented by pure components could be either stable or unstable. Loading the gas with one of the components might give rise to additional critical points and might reverse or change the stability of the previous ones. The present stability analysis permits the prediction of the trajectories and final state in a gas-phase-controlled drying process. It is of great importance due to the critical influence of the composition of the remaining moisture on the quality and properties of the final product.
47.	Malmquist, Lars, et al. (författare) Sorption equilibrium in relation to the spatial distribution of molecules - application to desorption of potato 1996 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 14:10, s. 2293-2306 Tidskriftsartikel (refereegranskat)
48.	Martinez, D. M., et al. (författare) Dryness and physical properties of paper webs in laboratory-scale impulse processing 2001 Ingår i: Drying Technology. - 0737-3937 .- 1532-2300. ; 19:10, s. 2435-2450 Tidskriftsartikel (refereegranskat)abstract This investigation evaluates the changes in dryness and physical properties of impulse processed paper webs. A laboratory-scale platen press was used to process 60 g/m2 webs under a wide range of pressure impulses and temperatures (23-380°C). The heat transfer rate to the web was also varied by using two different platen materials (steel and copper). Both thermomechanical and bleached kraft pulps were tested, and the dryness, density, surface roughness, and Scott bond were measured for each trial. Results show that dewatering is enhanced with increased temperature, pressure, and nip residence time, while pressure pulse shape and platen material have little influence. An empirical correlation is given to relate sheet dryness to the key process variables. This correlation suggests that resulting dryness values are not unique; that is, different combinations of temperature, pressure, and nip residence time can be used to obtain a similar level of dryness. Physical reasoning was used to develop a second correlation that links the resulting dryness to the density of the completely dried web. Surface roughness decreased with increasing surface temperature, while Scott bond rose sharply under conditions of high temperature and long nip residence time.
49.	Martínez, Joaquín (författare) Closed-cycle drying of solids 1996 Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 14:5, s. 1041-1062 Tidskriftsartikel (refereegranskat)abstract The influence of the recovery system and other system parameters upon drying selectivity was studied in a closed-cycle dryer. A continuously-worked unit consisting of a single stage dryer and a ondenser was simulated. In the dryer, a thin solid wetted with a liquid mixture was dryed in contact with an inert gas flowing either parallelly or as an impinging jet Partial recycle of the exhaust gas was allowed. Two recovery systems were studied, a scrubber condenser and an indirect condenser. Both drying and condensation were described by a mathematical model considering a s-phase-controlled process. The inlet liquid composition in the scrubber condenser has the greatest influence on drying selectivity. Degree of vapour recovery, recycle ratio and other operational parameters ffect selectivity and equipment dimensions in a variable extent. The combined use of these variables constitutes a powerful method to control selectivity. The present models may be useful to aid the optimization of the system with regard to product quality in gas-phase-conirolled processes.
50.	Melander, Olof, 1971, et al. (författare) Mathematical Modeling of Heat, Mass, and Momentum Transport in MDF Fiber Drying 2011 Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 29:1, s. 64-72 Tidskriftsartikel (refereegranskat)abstract A 3D two-phase flow drying model for medium density fiberboard (MDF) fibers was developed and implemented in the Ansys-CFX commercial CFD software. The model was validated against measurement data([1]) with satisfactory results. A parameter study was done to study the effects of dryer temperature and mass loading of fibers. A realistic dryer geometry has been simulated and it has been demonstrated that the model can capture 2D and 3D flow phenomena that affect the drying results. The simulation results can be used to determine suitable ways for improving dryer efficiency.

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