Fiber Mass Concentration Research Articles

Detection and comparison of fiber count concentration in processing environment of asbestos and man-made mineral fiber

Objective: To connect with the measurement data of asbestos dust fiber concentration in foreign countries, improve the accuracy of asbestos fiber detection in China, and understand the dust exposure in the working environment of asbestos and man-made mineral fiber production and processing sites in Zhejiang Province. The fiber count concentrations of working environment in glass fiber, ceramic fiber and asbestos processing plants were measured and compared. Methods: The dust concentration in the working environment of two glass fiber factories, one ceramic fiber factory and eight asbestos products processing factories was measured. The total dust mass concentration was measured according to GBZ/T 192.1-2007, and the fiber count concentration was measured by phase contrast microscope. Kruskal Wallis was used to test and compare the dust concentration in the working environment of each post. The correlation between asbestos mass concentration and fiber count concentration was analyzed by Spearman correlation. Results: Under the phase contrast microscope, there were many short and fine asbestos fibers in the field of vision, and there were many impurities around. The average dust concentration of asbestos processing plant was 3.2 f/ml, and the dust concentration of cotton ginning was the highest (6.68 f/ml) . There was a significantly positive correlation between asbestos fiber count concentration and mass concentration (r=0.535, P=0.033) . The average fiber count concentration of glass fiber factory was 0.001 f/ml, and the highest was 0.005 f/ml. The average fiber count concentration of ceramic fiber factory was 0.001 f/ml, and the highest was 0.006 f/ml. Conclusion: The fiber count concentration in the working environment of asbestos factory in Zhejiang Province is obviously over the standard, which is one of the important reasons for the high incidence of mesothelioma in this area. Short and small asbestos fibers are easy to be ignored when counting. It is necessary to improve the actual operation process of fiber counting to form a laboratory standard in China.

The shear and compressive yield stress of fibrillated acacia pulp fiber suspensions

Abstract The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress P y {P_{y}} and shear yield stress τ y {\tau _{y}} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of τ y / P y {\tau _{y}}/{P_{y}} were also examined and the variation of τ y / P y {\tau _{y}}/{P_{y}} became largely dependent on the fiber morphology and mass concentration.

Polymeric Films with Electric and Magnetic Anisotropy Due to Magnetically Assembled Functional Nanofibers

We demonstrate the fabrication of free-standing polymeric nanocomposite films, which present magnetic and electrically conductive anisotropic properties. Magnetically functionalized carbon nanofibers are dispersed in a polymeric solution and, upon casting under a weak external magnetic field, are easily oriented and permanently assembled in a head-to-tail orientation in the polymer film during solvent evaporation. Magnetic and conductive property studies reveal that the resulting films have a high degree of anisotropy in both cases, thus allowing their use in functional complex devices. As a proof of concept, we demonstrate the potential application of these films as flexible THz polarizers. The detailed study shows that very high attenuation values per unit film thickness and fiber mass concentration are achieved, paving thus the way for cost-effective fabrication of substrate-free systems that have advantage over conventional devices realized so far.

A successive iteration method on predicting properties of turbulent fiber suspensions and its application to pipe flows

The modified Reynolds-averaged equation of motion for the turbulent fiber suspensions and the equation of probability distribution function for mean fiber orientation are derived. A successive iteration method is used for solving these equations. The method is applied to a turbulent pipe flow, and the probability distribution for mean fiber orientation, the streamwise mean velocity, the root mean square (rms) velocity fluctuations and the Reynolds stress are calculated. A satisfactory agreement between numerical and experimental results indicates that the method is reasonable and reliable, and can be methodologically applied to any incompressible turbulent flows of fiber suspensions. The results on the pipe flows show that most fibers orient along the flow. The rms radial velocity fluctuations are smaller than the rms streamwise velocity fluctuations. The maximum of rms velocity fluctuation appears in the near wall region. As the fiber mass concentration increases, the steepness of mean velocity profile increases, while the rms velocity fluctuation and the Reynolds stress decrease. The fibers suppress the turbulence and result in a reduction in Reynolds stress, and the effect of suppression and the amount of reduction are directly proportional to the fiber mass concentrations. The Reynolds number has less effect on the velocity profile. As the Reynolds number increases, the mean velocity profile becomes blunter, and the rms velocity fluctuations and the Reynolds stress increase. The effect of fiber aspect ratio on the mean velocity is more obvious than that of Reynolds number. As the fiber aspect ratio decreases, the mean velocity profile becomes blunter, and the rms velocity fluctuations and Reynolds stress decrease.

Gas dispersion in horizontal pulp-fibre-suspension flow

Dispersion of gas into pulp-suspension horizontal flow was investigated downstream of 90° tees for ranges of fibre mass concentrations (0–3.0%), superficial liquid/pulp velocities (0.5–5.0m/s) and superficial gas velocities (0.11–0.44m/s) based on a gas mixing index, derived from the standard deviation of cross-sectional local gas holdup obtained from electrical resistance tomography. Mixing for dilute suspensions was similar to that for water, but differed significantly for higher suspension concentrations. Mixing worsened with increasing fibre mass concentration for the bubble flow regime, likely due to dense fibre networks in the core of the pipe causing bubbles to congregate near the wall. When buoyancy was significant, gas uniformity improved with increasing pulp concentration, since robust fibre networks caused liquid/pulp slugs to flow at the top of the pipe, whereas stratified flow was approached at lower concentrations. Mixing was less dependent on superficial liquid/pulp velocity at higher pulp concentrations, due to less variation in flow regimes.

Reducing ring spun yarn hairiness via spinning with a contact surface

In this study, spinning with a contact surface was introduced as a simple and energy-saving method to reduce spun yarn hairiness. Theoretical analysis indicated that yarn hairiness could be reduced via a sufficient long contact surface applied in other part of yarn formation zone in addition to spinning triangle. Then, a simple contact apparatus was installed on ring frame to validate the theoretical analysis. Results proved that yarn hairiness was reduced via a contact surface in the yarn formation zone. However, unevenness was deteriorated for most yarns spun with contact apparatus during the spinning, which might be due to fiber mass concentration. Most of yarns spun with contact apparatus had a lower strength than the conventional yarns. This might be because evenness deterioration to decrease yarn strength overpowered hairiness reduction to increase yarn strength for most yarns spun with a contact surface.

Mechanical Properties of Hybrid Cementitous Composites

Pulverised stem fibres of the natural sponge plant, SP, (Acanthus montanus) and stranded coconut fibre, CF, (Cocos nucifera) from the coir tree were used as reinforcements for thin cement sheets in this research work. The mixture of cement and pulverised waste paper, which formed the matrix, was maintained constant while the fibre mass concentration of both fibres were varied. The slurry formed by adding water to the mixture of the matrix materials and the reinforcement fibres, was poured into rectangular mould and consequently pressed to eject excess water. De-moulded samples were allowed to cure in the laboratory for twenty-eight days before flexural and compressive tests were carried out. The analysis of the experimental results established that sample coded as S4, with 30% CF and 70% SP, showed the most promising result. This implied that particulate reinforcement in cement matrix composite contributed to higher and improved flexural load bearing capacity and ductility when utilised in a higher proportion than long fibres.

Yield stress of pretreated corn stover suspensions using magnetic resonance imaging

Cellulose fibers in water form networks that give rise to an apparent yield stress, especially at high solids contents. Measuring the yield stress and correlating it with fiber concentration is important for the biomass and pulp industries. Understanding how the yield stress behaves at high solids concentrations is critical to optimize enzymatic hydrolysis of biomass in the production of biofuels. Rheological studies on pretreated corn stover and various pulp fibers have shown that yield stress values correlate with fiber mass concentration through a power-law relationship. We use magnetic resonance imaging (MRI) as an in-line rheometer to measure velocity profiles during pipe flow. If coupled with pressure drop measurements, these allow yield stress values to be determined. We compare our results with literature values and discuss the accuracy and precision of the rheo-MRI measurement, along with the effects of fiber characteristics on the power-law coefficients.

The effect of off‐wall clearance of a side‐entering impeller on the mixing of pulp suspensions in a cylindrical stock chest

AbstractFor a side‐entering impeller of diameter D, the clearance from the off‐wall (E) is characterised by E/D and it affects the mixing quality attained in a pulp stock chest. For agitation of pulp suspensions, mixing can be characterised by the size of cavern produced by the impeller. In this work, we have investigated cavern size as a function of the impeller off‐wall clearance in a laboratory‐scale cylindrical stock chest. Hardwood pulp suspensions of Cm = 2%, 3%, and 4% (fibre mass concentration) were agitated using an axial flow impeller with E/D varied from 0.14 to 0.68. Cavern size was measured using electrical resistance tomography (ERT) in batch operation and dynamic mixing tests in continuous operation, with cavern size increasing with increasing E/D. At E/D = 0.14, throttling of the impeller suction occurred which reduced cavern size. Computational fluid dynamic (CFD) simulations for steady state operation under‐predicted the cavern size, but correctly captured the trend in cavern size variation with E/D. The measured cavern volumes compared well with predictions of an axial force model that accounted for interaction between the cavern and the vessel walls only when impeller throttling was absent.

The apparent yield stress of pulp fiber suspensions

The apparent yield stress is one of the most important rheological properties of pulp suspensions in designing process equipment for the pulp and paper industry. Therefore, determining a reliable apparent yield stress measurement technique is of importance, not only for pulp suspensions but for any fluid exhibiting yielding behavior. In this work two established and extensively used methods for determining apparent yield stress are compared with a velocity profile determination technique using ultrasonic Doppler velocimetry. The apparent yield stresses are determined for various commercial pulp suspensions at fiber mass concentrations ranging from 0.5 to 5 wt %. The results are compared and models are proposed to represent the apparent yield stress of pulp suspensions as a function of fiber mass concentration. It is concluded that the apparent yield stress measurements obtained using the local velocity profile determination technique are the most reliable.

Computational modelling of industrial pulp stock chests

AbstractAgitated pulp stock chests are the most widely used mixers in pulp and paper manufacture. Stock chests are used for a number of purposes, including attenuation of high‐frequency disturbances in pulp properties (such as mixture composition, fibre mass concentration, and suspension freeness) and are designed using semi‐empirical rules based largely on previous experience. Tests made on both laboratory and industrial‐scale pulp chests indicate that they are subject to non‐ideal flows, including channelling and creation of dead zones.In the present work, a commercial computational fluid dynamic (CFD) software (Fluent) is used to model two industrial pulp stock chests. The first chest is rectangular, agitated using a single side‐entering impeller, and feeds a mixture of chemical pulps at 3.5% mass concentration (Cm) to a papermachine. The second chest has rectangular geometry, with a mid‐feather wall used to direct suspension flow through a U‐shaped trajectory past four side‐entering impellers. This chest is used to remove latency from a Cm = 3.5% thermomechanical pulp suspension ahead of stock screening.For CFD computations, pulp rheology was described using a modified Hershel–Buckley model. Steady‐state simulations were made corresponding to process conditions during mill tests. The calculated steady‐state flows were then used to determine the dynamic response of the virtual chests and then compared with experimental measurements and found to agree reasonably well. The computed flow fields provided insight into mixing processes occurring within the chests, showing cavern formation around the impellers (which reduced the agitated volume available for mixing). Mass‐less particle tracking, using the steady‐state flow field, gave insight into the stagnant regions and bypassing zones created in the vessels. This paper discusses difficulties encountered in characterising the mixing (both experimentally and computationally) and the limitations of the industrial data.

Measuring Flow Velocity in Pulp Suspension Mixing Using Ultrasonic Doppler Velocimetry

Ultrasonic Doppler velocimetry (UDV), a non-invasive fluid flow measurement technique suitable for use in opaque systems, was used to measure pulp suspension flow velocity in a rectangular 1 : 11-scale agitated pulp stock chest. The flow characteristics of a Maxflo impeller were measured as a function of fibre mass concentration, fibre type and impeller speed. Using the velocity profiles measured, the impeller pumping rate and flow number were calculated as a function of suspension yield stress (itself a function of fibre mass concentration and fibre type). The flow number was found to decrease as the suspension yield strength increased. For example, when the mass concentration of a hardwood pulp was increased from 0% (water) to 3.3%, the flow number decreased from 0.64 to 0.43. UDV was also used to identify regions of poor mixing by measuring flow profiles at critical locations within the vessel. This study also demonstrates the ability of UDV to measure the cavern size of the pulp suspension during agitation.

Mathematical modeling of turbulent fiber suspension and successive iteration solution in the channel flow

The modified Reynolds mean motion equation of turbulent fiber suspension and the equation of probability distribution function for mean fiber orientation are firstly derived. A new successive iteration method is developed to calculate the mean orientation distribution of fiber, and the mean and fluctuation-correlated quantities of suspension in a turbulent channel flow. The derived equations and successive iteration method are verified by comparing the computational results with the experimental ones. The obtained results show that the flow rate of the fiber suspension is large under the same pressure drop in comparison with the rate of Newtonian fluid in the absence of fiber suspension. Fibers play a significant role in the drag reduction. The amount of drag reduction augments with increasing of the fiber mass concentration. The relative turbulent intensity and the Reynolds stress in the fiber suspension are smaller than those in the Newtonian flow, which illustrates that the fibers have an effect on suppressing the turbulence. The amount of suppression is also directly proportional to the fiber mass concentration.

In VitroCharacterization of a Bone Marrow Stem Cell-Seeded Collagen Gel Composite for Soft Tissue Grafts: Effects of Fiber Number and Serum Concentration

Cell-seeded collagen hydrogels have been used in the engineering of many tissue types, from skin and vasculature to spinal cord. One of the primary limitations of collagen-based hydrogels for use in tissue-engineered grafts is that cells seeded within the gel cause it to contract as much as 70%. By forming a composite gel by adding short collagen fibers, Gentleman et al. (Tissue Eng. 10, 421, 2004) determined that the contraction due to fibroblasts was decreased and permeability was increased. Before these composite hydrogels can be used to design soft tissue replacements, however, the effect of fiber number and serum concentration should be addressed. Consequently, short collagen fibers were included in adult rat bone marrow stem cell-seeded hydrogels for composite support. The mass of fibers was varied from 1.6 to 31.3 mg per gel, and the effect of serum concentration in the growth medium was examined. It was determined that increasing fiber mass and decreasing serum concentration significantly decreased contraction, which plateaued after day 10. Cell number increased throughout the experiment, demonstrating the compatibility of bone marrow stem cells with the collagen composite gels. By using short collagen fibers to create a collagen composite gel, preservation of the original dimensions can be achieved without compromising cellular viability.

Suspension yield stress and the dynamic response of agitated pulp chests

Agitated pulp chests act as low-pass filters attenuating high-frequency variability and thus complimenting the action of control loops which attenuate slow disturbances. Dynamic tests made on industrial and scale-model chests show that non-ideal flows, including short-circuiting, recirculation, and dead zones, are common and significantly reduce the ability of the chest to attenuate fluctuations. In this paper, we explore the effect of suspension yield stress on the extent of non-ideal flow and upset attenuation by conducting dynamic tests using two different pulp suspensions: a long-fibred softwood pulp and a shorter-fibred hardwood pulp. Dynamic tests were also made as a function of the fibre mass concentration, with the yield stress used to characterize the dynamic behaviour observed in mixing. It was found that while the yield stress plays a significant role determining the mixing of pulp suspensions, the dynamic behaviour of pulp mixing could not be fully described by yield stress alone. Tests show that when the surface of the cavern created by the impeller approaches the pulp outlet, which was located on the impeller wall, the percentage of short-circuiting approached zero.

The Effect of Operating Conditions and Design Parameters on the Dynamic Behaviour of Agitated Pulp Stock Chests

AbstractAgitated pulp chests provide attenuation of high‐frequency disturbances in pulp properties ahead of many pulping and papermaking unit operations. The effect of process and design variables on the extent of non‐ideal flows was examined in a laboratory‐scale pulp chest. Dynamic tests were made using the frequency‐modulated random binary input of a brine solution with the pulp feed to determine the magnitude of non‐ideal flows (channeling, recirculation and stagnant zones). Results showed that the degree of upset attenuation is a function of impeller momentum flux and fibre mass concentration and that existing design criteria underpredict the power needed to produce a fully mixed system.

The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method.

This paper describes experiments carried out in the laboratory to clarify interpretation of the role of sampling flow rate and wind speed on the efficiency of sampling airborne asbestos fibres in workplaces. The experiments were carried out with test clouds of UICC amosite and UICC chrysotile with aerodynamic characteristics sufficiently close to those of workplace dusts to allow direct comparison to be made, at least as far as the immediate aims of this enquiry are concerned. It was shown unambiguously, for conditions of practical interest, that there were no significant effects of sampling flow rate and wind speed on the measurement of fibre mass concentration and fibre number concentration respectively. Thus, any observed bias in the measurement of fibre concentration by manual counting must instead be attributable to psychological effects relating to the density of fibres on the filter. On the basis of these results, it is suggested that recommended procedures which impose limitations on sampling flow rate or face velocity are unnecessarily restrictive. Rather it is preferable to tighten up the prescribed limits on fibre density on the filter.