Increasing global competition, high stumpage and energy prices, and the slowing housing market have challenged the U.S. hardwood lumber industry during the past several years. Many wood product manufactures are trying to remain in business by implementing continuous improvement programs like lean manufacturing. However, the lumber drying process where lumber is kiln-dried in large batches, can significantly increase manufacturing and inventory lead-time; and is a process that tends to limit how lean the remaining process can become. Vacuum drying has the potential to reduce drying times, reduce batch sizes and achieve product quality comparable or superior to conventional drying. The overall goal of this research was to evaluate how vacuum-drying technology could support further lean implementation in manufacturing of hardwood products. Specifically, to estimate conventional and vacuum drying times, quality, and costs for drying 4/4 red oak lumber; to determine by the use of feasibility analysis (cash flow, net present value, and internal rate of return) differences between conventional and vacuum drying for 4/4 red oak lumber; and to determine if the high capital cost of vacuum drying equipment can be justified with the reduction of WIP and cycle time, while meeting desired throughput. The study includes a cost analysis of vacuum and conventional drying, and a determination of the potential financial gains associated with the reduced drying times via vacuum drying. It was determined that vacuum drying quality was equal or better than conventional drying with less checking, end splits, drying stress and shrinkage. Compared to conventional drying, vacuum drying times with air drying and without air drying were 67% less and 70% less, respectively. Conventional and vacuum with no air drying scenarios were determined to be financially feasible when compared using Net Present Value and Internal Rate of Return analysis. However, vacuum drying with no air drying had better NPV and IRR values than conventional drying. The scenario of vacuum with air drying was not feasible. Two case studies, each employing the three drying scenarios (conventional drying, vacuum with air drying, and vacuum without air drying), were used to determine the impact of cycle times and work in process. It was determined that the cycle times for vacuum drying were 87% and 95% less than conventional drying for the first case study and 51% and 90% less than conventional drying for the second. WIP was 48% and 84% less in the first case study and 43% and 92% less than conventional drying for the second. Cycle time was reduced by 87% and 51% for Plant C and D, respectively. Finally it was determined that the reduction of WIP represented a cost saving of 73% and 76% for the two case studies. The reduction in costs, faster drying rates, and equal quality, and reduced cycle times make vacuum drying a potential technology available for improvement of the competitiveness for flooring manufacturers. / Master of Science

The objective of this research based on both the theory and experimentation was to prove that the total pressure difference is the primary driving force during the vacuum drying. The theoretical drying rates of diffusion, free water bulk flow and water vapor bulk flow were calculated and compared. The concept of equilibrium moisture content under the vacuum was developed. The theoretical maximum moisture content drop in one cycle was calculated using energy balance. The model was developed for the vacuum drying to understand the mechanism of the vacuum drying including the boiling front and its movement. To evaluate the effect of the sample size on the drying rate, four different thicknesses (1, 1.5, 2, 2.5 inches) and three different lengths (5, 10, 15 inches) were used. In the cyclic drying, the specimens were heated to the 60 C. The vacuum was pulled to about 18 mm Hg. The vacuum pump was kept running for 140 minutes. It was found that in cyclic vacuum drying, drying rate was not affected by the thickness. However, it was affected by the length. The cyclic drying curve consisted of two distinct parts. The fast drying period lasted about 10 to 20 minutes. The slow drying period occurred next when the pressure inside wood got close to the ambient pressure. In end grain vacuum drying, the specimens were coated with wax, wrapped in the plastic film and inserted into a rubber tube to prevent the moisture loss from the side surfaces during drying. The specimen size was 1×1×10 inches. Red oak and white oak were sealed and dried in both cyclic and continuous vacuum drying. The results showed that sealed specimens dried almost as fast as unsealed specimen. There was little moisture loss from the side surfaces. There was a moisture gradient along the length in both cyclic drying and continuous vacuum drying. Red oak specimens of 2.5×1.5×10 inches were used to study the boiling front in the vacuum drying. In order to detect the boiling phenomenon, the saturation pressures were calculated and were compared with the pressures at the same time and the same location. Boiling occurred during drying and the boiling front retreated to the center of wood as drying proceeded. The retreating speed depended on the heat supply and the permeability. Vacuum drying at room temperature was investigated. The specimens were dried at 20 C and pressure near 18 mm Hg. The results showed that wood can be vacuum dried at room temperature with little or no degrade at a reasonable drying rate. All experimental results support the objective of this study that the primary driving force is the total pressure difference. / Ph. D.

<p>Istraživanja u okviru disertacije usmerena su na razvoj vakuumskog postupka su&scaron;enja voća. Konstruisan je prototip laboratorijske vakuumske su&scaron;are i optimizovan proces su&scaron;enja vi&scaron;anja i borovnica. U cilju optimizacije procesa su&scaron;enja ispitan je uticaj nezavisno promenljivih procesa, temperature i pritiska, na parametre kvaliteta osu&scaron;enog voća (aktivnost vode, sadržaj ukupnih fenola, ukupnih monomernih antocijana i vitamina C, antioksidativnu aktivnost, promenu boje, teksturu i sposobnost rehidratacije). Proces su&scaron;enja optimizovan je kori&scaron;ćenjem metode odzivnih povr&scaron;ina (engl. Response Surface Methodology, RSM).<br />Rezultati istraživanja pokazuju da tehnika su&scaron;enja voća u vakuumu daje odlične rezultate u pogledu očuvanja visokovrednih komponenata voća i ima perspektivu za &scaron;iru primenu u zanatskim i poluindustrijskim postrojenjima.</p> / <p>Research in the framework of the thesis focuses on the development of fruit vacuum-drying process. Laboratory vacuum dryer prototype was constructed. Cherries and blueberries vacuum drying process was optimized. In order to optimize the drying process, the influence of independent variables of the process (temperature and pressure) on the quality parameters of dried fruit (water activity, total phenol content, total monomeric anthocyanins and vitamin C, antioxidant activity, colour change, texture, and rehydration capability) was investigated. The drying process was optimized using Response Surface Methodology (RSM).<br />There is the possibility of application of the results in plants at semi-industrial and industrial level.</p>

As the environmental concern grows, researchers try to find material which can be environmental friendly and biodegradable to some extent. At present, flax fibre cannot fully replace glass fibre. Some attempts have been made to replace the glass fibre.<p> Studies show the physical and mechanical properties of natural fibres are comparable with glass fibre, so it can replace glass fibre in the process of making biocomposites. <p> The properties of biocomposites depend on the fibre used. Research shows that to get a better biocomposite, the fibre has to be chemically treated to improve adhesion between fibre and polymer matrix. After the chemical treatment, the fibre has to be dried to minimum moisture content so the drying of flax fibre is essential in the process of making biocomposites. <p> In this research, oilseed flax fibre is dried and drying characteristics were investigated. After drying, the physical properties of the fibre were tested and analysed.<p> The fibre was dried using three different drying methods, namely, microwave, microwave-convection, and microwave-vacuum environments. Curve fitting with four empirical methods has been carried out to determine the drying constant, coefficient of determination and standard error values. The results showed that microwave-vacuum drying method is more efficient (in terms of final moisture content) than microwave and microwave-convection drying. Although microwave-vacuum drying took the most time and did not result in promising colour values, the maximum moisture removal is achieved because fibres can be dried for a longer period of time with a comparatively low temperature.<p> The results of physical properties were analysed for untreated and treated and dried flax fibre. The tensile strength and elastic modulus of untreated and treated fibre did not show any significant change. Because the diameter of flax fibre cannot be consistent, a range of values can be obtained. The diameter range of fibre bundle 30-300 µm was examined for these tests. The tensile strength obtained from these fibre bundles ranged between 16 to 667 MPa and elastic modulus values were 2 GPa up to 63 GPa.<p> The scanning electron micrograph (SEM) was also analysed for untreated and treated-dried fibre. The fibre which was dried with high power or longer period of time showed black spots, probably due to local heating. The fibre dried with microwave-vacuum developed some black spots which were clearly seen in the SEM.<p> Differential scanning calorimetric data showed a shift in temperature of degradation. In this research, degradation temperature of cellulose was found 350(+/-10)°C for the treated and dried flax fibre.<p> In conclusion, the flax fibre has a potential to be used in biocomposite production. The microwave-vacuum works best for drying where the fibre can be dried up to a less than 1% of moisture content.

As the environmental concern grows, researchers try to find material which can be environmental friendly and biodegradable to some extent. At present, flax fibre cannot fully replace glass fibre. Some attempts have been made to replace the glass fibre.<p> Studies show the physical and mechanical properties of natural fibres are comparable with glass fibre, so it can replace glass fibre in the process of making biocomposites. <p> The properties of biocomposites depend on the fibre used. Research shows that to get a better biocomposite, the fibre has to be chemically treated to improve adhesion between fibre and polymer matrix. After the chemical treatment, the fibre has to be dried to minimum moisture content so the drying of flax fibre is essential in the process of making biocomposites. <p> In this research, oilseed flax fibre is dried and drying characteristics were investigated. After drying, the physical properties of the fibre were tested and analysed.<p> The fibre was dried using three different drying methods, namely, microwave, microwave-convection, and microwave-vacuum environments. Curve fitting with four empirical methods has been carried out to determine the drying constant, coefficient of determination and standard error values. The results showed that microwave-vacuum drying method is more efficient (in terms of final moisture content) than microwave and microwave-convection drying. Although microwave-vacuum drying took the most time and did not result in promising colour values, the maximum moisture removal is achieved because fibres can be dried for a longer period of time with a comparatively low temperature.<p> The results of physical properties were analysed for untreated and treated and dried flax fibre. The tensile strength and elastic modulus of untreated and treated fibre did not show any significant change. Because the diameter of flax fibre cannot be consistent, a range of values can be obtained. The diameter range of fibre bundle 30-300 µm was examined for these tests. The tensile strength obtained from these fibre bundles ranged between 16 to 667 MPa and elastic modulus values were 2 GPa up to 63 GPa.<p> The scanning electron micrograph (SEM) was also analysed for untreated and treated-dried fibre. The fibre which was dried with high power or longer period of time showed black spots, probably due to local heating. The fibre dried with microwave-vacuum developed some black spots which were clearly seen in the SEM.<p> Differential scanning calorimetric data showed a shift in temperature of degradation. In this research, degradation temperature of cellulose was found 350(+/-10)°C for the treated and dried flax fibre.<p> In conclusion, the flax fibre has a potential to be used in biocomposite production. The microwave-vacuum works best for drying where the fibre can be dried up to a less than 1% of moisture content.

Ce travail de thèse porte sur l’étude de l’effet du traitement par champs électriques pulsés (CEP) sur l’amélioration de la congélation des tissus végétaux. Pour l’ensemble de notre étude, nous avons démontré que l’effet des champs électriques pulsés est complexe. Le prétraitement entraîne une électroperméabilisation des membranes. Les analyses calorimétriques ont mis en évidence que l’électroperméabilisation conduit à une augmentation de la teneur en eau liée. Les transferts de matière entre les milieux intra et extracellulaires sont intensifiés. Cela conduit à une modification dynamique de la composition des deux compartiments au cours de la congélation. En effet, les essais réalisés sur le cryo-pressage assisté par CEP démontrent que les températures de fusion sont plus basses et que le jus récupéré est beaucoup plus concentré. Il a été constaté que le temps de congélation d’un échantillon soumis préalablement à un prétraitement par champs électriques pulsés est sensiblement plus court que celui d’un échantillon sans prétraitement. D’autre part, l’électroperméabilisation facilite les transferts de matière avec le milieu extérieur. Le prétraitement par CEP accélère notamment l’imprégnation des tissus végétaux par des cryoprotectants, l’évaporation de l’eau libre et la sublimation de l’eau congelée. Finalement, le prétraitement par champs électriques pulsés induit des modifications de la structure des échantillons, de leur composition et influence favorablement les transferts couplés de masse et d’énergie. / This work is focused on the study of the effects of pulsed electric fields (PEF) on the improvement of plant tissues freezing. These studies have demonstrated that the effects of the PEF are rather complex. The PEF treatment results in membrane electro-permeabilization. Calorimetric analyses showed that the electro-permeabilization leads to an increase in bound water content. It also results in acceleration of mass transfer processes between intra- and extracellular parts of a tissue. The dynamic modification of the composition of these two parts during the freezing was observed. Experimental tests using the PEF-assisted cryo-pressing demonstrated that the melting temperatures were lower and that the extracted juice was much more concentrated as compared to untreated tissues. Moreover, the PEF-treatment allowed significant decreasing of freezing time. Furthermore, the electro-permeabilization facilitates the mass transfer with the external medium. The PEF treatment accelerates the impregnation of plant tissues by cryoprotectants, evaporation of free water and sublimation of frozen water. Finally, the treatment by PEF induces changes in the structure of the samples, their composition and positively influences both the mass and energy transfers.