Simulation of the flow through woven fabrics

Filament-level three-dimensional simulations of the flow through single layer woven fabrics were done using FLUENT^TM. For screen Reynolds numbers, Re_s, between 50 and 300, CFD simulations reproduce experimental measurements of wind tunnel screen pressure drops to within ±10%. Simulations of woven fabrics with geometric non-uniformities have also been undertaken. In these simulations one or more strands of the fabric is shifted laterally relative to its undisturbed location. If the filament displacement, normalized by the centre-to-centre separation between filaments, is ε, the enhancement in the flow rate through the enlarged opening in the fabric is given by approximately 2ε. A very simplified model of the geometry is consistent with this enhanced flow rate. The findings of this research are relevant to both wind tunnel and papermachine forming fabric design.     

Numerical Study of Heat Transfer and Fluid Flow in Multiple turbulent Impinging Jets

ABSTRACT

Impingement flows have been studied extensively for various geometries and configurations, but because of the complexity of the turbulent flow and its strong dependence on the geometry of the flow, further investigation is required to identify the suitable model for specific cases. This paper presents a study of various k–E turbulence models in order to identify the best model for an array of multiple confined impinging slot jets, with exhaust ports in the confinement surface located symmetrically between adjacent jets. Such a configuration is used in a novel drum dryer for black liquor. The “High Reynolds number” turbulence models including the standard k–E model fail to predict heat transfer to impingement surface accurately although they do predict the flow field reasonably well. On the other hand, the “Low Reynolds number” models yield considerably better results for both fluid flow and heat transfer. All computed results are compared with experimental data reponed in the literature. This work was motivated by the need to select an optimal multiple impinging jet configuration for a novel drum dryer for Kraft black liquor. It is also pertinent to impingement dryers for paper, films, textiles etc.     

A Novel Method for Enhanced Recovery of Lignin from Aqueous Process Streams

Abstract

This study demonstrates that acid precipitation of lignin in the presence of magnetite followed by an applied magnetic field provides a simple method for enhanced lignin recovery from an aqueous stream. The extraction procedure was shown to be sensitive to the relative charge of magnetite and solution pH. Under optimized conditions, 93 wt.% of the softwood lignin from a kraft cooking liquor could be recovered employing this novel separation approach.     

Temperature dependence of cellulase hydrolysis of paper fiber

The hydrolysis of cellulosic fiber used in papermaking by cellulase enzymes was studied as a function of fiber length and temperature. The rate of hydrolysis of the fines fraction increased with temperature but that of the longer fiber was relatively temperature independent. The binding of enzyme to the fiber was proportionately almost three times higher for the fines fraction. Binding of these enzymes to cellulose is known to be inversely temperature dependent, whereas the catalytic step should have a direct dependence on temperature. It is proposed that the two effects offset each other for the longer fiber where there is more free enzyme present as compared to the situation with fines. A similar effect was noted for the hydrolysis of cellulosic paper mill sludge where the rate of hydrolysis of the longer fiber was relatively temperature independent. A practical outcome is that the cost of heating long-fiber sludges to 50 °C, the reported optimum temperature for the enzyme, can be avoided.     

Flax fibers as a raw material: How to bleach efficiently a non-woody plant to obtain high-quality pulp

Fiber crops constitute a good alternative to wood fiber for manufacturing pulp and paper. In fact, fiber plants like flax surpass wood fiber in some technical respects and also in the environmental benignity of their processing. In this work, flax fiber was subjected to environmentally friendly bleaching sequences in order to obtain a high-quality pulp. The totally chlorine-free sequences (TCF) used for this purpose (LE and LRE) included an enzyme treatment with laccase in the presence of HBT as mediator (L stage), an alkaline extraction (E stage) and a reductive treatment with NaBH₄ (R stage). The operating conditions for the L stage (laccase and HBT doses, reaction time and oxygen pressure) were optimised by using a sequential statistical plan to assess their influence on pulp properties after the E stage.Mathematical models accurately predicting brightness and kappa number in terms of the previous four variables were developed based on which the most influential factors were the laccase and HBT rates, and treatment time. By contrast, oxygen pressures of 0.2–0.6 MPa in the reactor had no effect on brightness or kappa number. The flax pulp obtained contained some oxidized cellulose that was partially degraded in the alkaline extraction step and reduced viscosity as a result. The viscosity loss associated with the presence of oxidized cellulose in the control and enzyme-treated pulp samples was efficiently recovered by using a reductive stage with sodium borohydride. Effluent was also analysed in order to assess the environmental impact of the process.     

FLOWS WITH INERTIA IN A THREE-DIMENSIONAL RANDOM FIBER NETWORK

A fiber web is modeled as a three-dimensional random cylindrical fiber network. Nonlinear behavior of fluid flowing through the fiber network is numerically simulated by using the lattice Boltzmann (LB) method. A nonlinear relationship between the friction factor and the modified Reynolds number is clearly observed and analyzed by using the Fochheimer equation, which includes the quadratic term of velocity. We obtain a transition from linear to nonlinear region when the Reynolds numbers are sufficiently high, reflecting the inertial effect of the flows. The simulated permeability of such fiber network has relatively good agreement with the experimental results and finite element simulations.     

脱墨化学品的脱墨选择性研究

本文介绍了四类脱墨化学品对脱墨选择性的研究。结果认为脂肪酸一表面活性剂添加2％硅酸盐能最有效地提高脱墨效率和提高浮选浆得率。     

废纸碎解时的油墨剥离动力学

本文介绍了废纸碎解时油墨物理剥离的动力学以及其他有关油墨的附着、碎片化、研细和再沉积等的规律.     

新闻纸回用时TMP物化性能的变化

介绍了新闻纸中TMP在回用时受回用次数的影响。回用次数增加时，TMP的总电荷会增加，氧／碳比率会增加，纸页密度会增加和抽出物含量会降低，但纸页粗糙度会有所增加，抗张指数等强度指数都会有所下降。     

Viscous flow of a Newtonian fluid in a curved channel with flexible moving porous walls

We consider flow of a viscous Newtonian fluid in a curved channel with moving porous walls; the upper wall is flexible and its position in unknown a priori. This work is motivated from a papermaking application namely roll forming. We solve the leading order terms in equations of motion using perturbation methods and present analytical expressions for the variation in channel size, pressure, and viscous shear. The stability of the solution is also examined and we report the conditions for marginal stability.