MODELING VACUUM-CONTACT DRYING OF WOOD: THE WATER POTENTIAL APPROACH

ABSTRACT

A two-dimensional mathematical model for vacuum-contact drying of wood is presented. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady state conservation equation of dry air. Most of the model parameters were determined during independent experiments. The set of equations is then solved in a coupled form using the finite element method. The validation of the model is performed using experimental results obtained during vacuum-contact drying of sugar maple sapwood. The experimental and calculated data are in good agreement. Nevertheless, some discrepancies are observed which can be attributed to the boundary conditions used and to the fact that heat transfer by convection was neglected.     

COMPARISON OF TWO ANALYTICAL METHODS FOR THE DETERMINATION OF AZAARENES IN ATMOSPHERIC PARTICULATE MATTER

In this paper, the development of an analytical method for the separation and quantification of 20 azaarenes is described. Two methods are compared: high performance liquid chromatography with fluorescence detection (HPLC-fluorescence) and gas chromatography with mass spectrometry detection (GC-MS).

Although HPLC-fluorescence was proven to be the most sensitive method, GC-MS was selected in particular for the efficiency of the separation of the 20 azaarenes. The detection limits of the HPLC-fluorescence and GC-MS methods varied between 0.04 μ g.L^?1 (dibenz[a,c]acridine) and 1.30 μ g.L ^?1 (acridine) and between 1.50 μ g.L ^?1 (benz[c]acridine) and 2.56 μ g.L ^?1 (dibenz[a,c]acridine) respectively.

The GC-MS method was applied to particulate matter (PM ₁₀ ) samples collected over 48–72 h periods between April 2006 and February 2007 in Strasbourg (East of France). Before analysis aerosol samples were Soxhlet extracted and concentrated to a final volume of about 1 mL of hexane.

The seasonally mean concentrations of all azaarenes for this urban site have shown a seasonal variation in which the maximum concentration occurred in the winter (6.0 ng.m ³ ) and the minimum in the summer (0.90 ng.m³). For all the seasons the 2 rings species were the predominant azaarenes while the > 4 rings species were the less abundant.     

Influence of chitosan characteristics on coagulation and flocculation of organic suspensions

Several samples of chitosan with different degrees of deacetylation and of different molecular weights were tested for the coagulation–flocculation of organic suspensions. Organic suspensions were prepared by mixing mushroom powder with tap water. Experiments were carried out at pH 5, pH 7, and pH 9. Because decreasing the pH reduced the amount of chitosan required to reach the required turbidity, at pH 9, a high concentration of chitosan was required to achieve the required treatment levels, whereas the difference was less significant between pH 7 and pH 5 (the required concentration of chitosan was halved). Though viscosity, correlated to the molecular weight of chitosan, affected treatment performance, its influence on the efficiency of coagulation–flocculation could be substantially reduced by slightly increasing the concentration of the polymer. This is of importance in the processing of industrial effluents: the aging of a chitosan solution, which may cause partial depolymerization, and loss of viscosity, will have a limited impact on process efficiency. The degree of deacetylation also has a limited effect on treatment performance, especially when the degree of deacetylation exceeds 90%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2070–2079, 2005     

The Influence of Cooling Rate on the Specific Volume of Isotactic Poly(propylene) at Elevated Pressures

Summary: We used a custom designed dilatometer to measure quantitatively the time evolution of the specific volume of (semi‐crystalline) polymers for an unusual combined wide range of cooling rates and elevated pressures, covering processing conditions. For an isotactic poly(propylene), applying the Schneider rate equations for quiescent crystallization, experimental results are compared to numerical predictions. Average cooling rates imposed during crystallization of the material vary from 0.1 to 35 °C · s^?1 while pressures range from 20 to 60 MPa. The results show the well‐known profound influence of pressure and cooling rate on the specific volume. An increasing cooling rate shifts the crystallization temperature T_c towards lower temperatures, increases the final specific volume, and the transition due to crystallization is more gradual and widespread. For the highest cooling rate applied, the shift in T_c is as much as 30 °C, while the final specific volume increases up to 1.4%. Increasing pressure has an opposite effect on the shift in T_c, while the final specific volume, after pressure release, also increases. Finally, a comparison of numerical predictions with experimental data shows that the crystallization temperature T_c is consistently predicted too low, and that the predictions at high cooling rate are sensitive to (small) variations in model parameters.

Influence of cooling rate on the specific volume of iPP.     

Oxygen Vacancy Relaxation and Domain Wall Hysteresis Motion in Cobalt-Doped Barium Titanate Ceramics

Mechanical and dielectric loss measurements were carried out in the BaTiO₃ ceramics doped with Co at frequencies between 0.01 Hz and 1 MHz as a function of temperature from −150° to 150°C. The relaxation peak observed in the ferroelectric phase with an activation energy of 0.27 eV is assumed to be related to the motion of oxygen vacancies. This peak could be because of the reorientation of an electrical dipole made of oxygen vacancies and Co³⁺ ions in the lattice. Furthermore, another loss peak located just below the Curie temperature T _c could be interpreted as hysteretic motion of the domain walls in a regime where the domain wall density is changing.     

Rheological behaviour of polysaccharide aqueous solutions

Several data relative to the viscosity of water-soluble polysaccharide solutions were collected from the literature and processed by different rheological models. Some relationships between the viscosity of these polymer solutions, their molecular weight and their solution concentrations, were established and their validity checked. Thus, an accurate equation correlating the viscosity and both the shear rate and the solution concentration of different water soluble polysaccharides (xanthan, hyaluronan, carboxymethylcellulose) was deduced on the basis of Cross' model which suggests two domains in which the viscosity is constant, i.e. very low and very high shear rate ranges. Then, an expression relating the zero-shear viscosity (A) and the concentration of their solutions was proposed. Finally, an alternative equation to that of Mark–Houwink correlating the molecular weight and the intrinsic viscosity of the water-soluble polysaccharides studied in this paper was found.     

The distribution of lithium intercalated in V2O5 thin films studied by XPS and ToF-SIMS

The distribution of lithium in V₂O₅/V lower oxide duplex thin films prepared by thermal oxidation of V metal was analysed by XPS and ToF-SIMS after intercalation at 2.8 V versus Li/Li⁺ and de-intercalation at 3.8 V following cycling between 3.8 and 2.8 V in 1 M LiClO₄-PC. XPS analysis of the intercalated thin film evidenced a partial reduction (43 at.% V⁴⁺) of the V₂O₅ surface, the modification of its electronic structure and the presence of Li, consistent with the formation of the δ-Li_xV₂O₅ (0.9 ≤ x ≤ 1) phase. The Li in-depth distribution measured by ToF-SIMS shows a maximum in the outer layer of V₂O₅, but Li is also found at the oxide film/metal substrate interface indicating its diffusion across the inner layer of V lower oxides. The analyses performed after de-intercalation on the samples cycled 12, 120 and 300 times reveal the effect of aging on the trapping of lithium. A significant reduction (17-22 at.% V⁴⁺) of the V₂O₅ surface was measured after 300 cycles. The Li in-depth distribution shows a maximum at the interface between the outer layer of V₂O₅ and the inner layer of lower oxides. Aging favours the accumulation of lithium at this interface with a resulting enlarged distribution enriching the sub-surface of the outer layer of V₂O₅ and the inner layer of lower oxides after 300 cycles. Lithium is also found, but in smaller quantities, at the oxide film/metal substrate interface. Measurements performed in the non-electrochemically treated surface areas of the de-intercalated samples revealed the same type of modifications, evidencing the diffusion of lithium along the interfaces where it is trapped.     

Mathematical modeling of high-pressure PEM water electrolysis

This paper is devoted to the modeling and numerical optimization of proton-exchange membrane (PEM) water electrolysers for operation at elevated pressures (up to 130 bars). The model takes into account different geometrical parameters of the PEM cell, the kinetics of the hydrogen and oxygen evolution reactions, the electro-osmotic drag of water molecules, the permselectivity of the solid polymer electrolyte and associated gas cross-over phenomena. The role of various operating parameters (such as pressure, temperature, current density, flow rate of water) on cell efficiency, faradaic yield and heat produced during water electrolysis is evaluated and discussed. The model is also used for the purpose of optimizing the performances of PEM cells. In particular, optimal values of some critical operating parameters (current density, rate of water supplied to the anodes) are recommended.     

Response of Predatory Mites to a Herbivore-Induced Plant Volatile: Genetic Variation for Context-Dependent Behaviour

Plants infested with herbivores release specific volatile compounds that are known to recruit natural enemies. The response of natural enemies to these volatiles may be either learned or genetically determined. We asked whether there is genetic variation in the response of the predatory mite Phytoseiulus persimilis to methyl salicylate (MeSa). MeSa is a volatile compound consistently produced by plants being attacked by the two-spotted spider mite, the prey of P. persimilis. We predicted that predators express genetically determined responses during long-distance migration where previously learned associations may have less value. Additionally, we asked whether these responses depend on odors from uninfested plants as a background to MeSa. To infer a genetic basis, we analyzed the variation in response to MeSa among iso-female lines of P. persimilis by using choice-tests that involved either (1) MeSa presented as a single compound or (2) MeSa with background-odor from uninfested lima bean plants. These tests were conducted for starved and satiated predators, i.e., two physiological states, one that approximates migration and another that mimics local patch exploration. We found variation among iso-female lines in the responses to MeSa, thus showing genetic variation for this behavior. The variation was more pronounced in the starved predators, thus indicating that P. persimilis relies on innate preferences when migrating. Background volatiles of uninfested plants changed the predators’ responses to MeSa in a manner that depended on physiological state and iso-female line. Thus, it is possible to select for context-dependent behavioral responses of natural enemies to plant volatiles.