INVESTIGATION OF THE SPECIFIC CONTACT SURFACE OF A COMBINED FILTER LAYER BASED ON GLASS FIBER AND BASALT

ABSTRACT

This article investigates the microstructural characteristics of a combined filter layer composed of glass fibre, basalt, and polyester, which is specifically designed for the purification of gas streams contaminated with loam dust. Within the scope of this research, sample layers with varying thicknesses of 1.0, 1.2, and 1.5 mm, corresponding to areal masses of 390, 450, and 525 g/m², were carefully selected for examination. The microstructural properties of these samples were thoroughly analysed using an SM001-SYANS microscope at a magnification of 300x, employing a comprehensive image-analysis method. Throughout the analytical process, several key parameters were accurately determined, including the equivalent diameter of the open zones, the respective area, the precise proportion of open zones, the fraction of the area occupied by fibres, the density of the contact points, the specific contact surface area, and the overall volumetric density of the filter layer. Based on the detailed computational results, it was established that as the thickness of the filter layer increased from 1.0 mm to 1.5 mm, the total contact surface area correspondingly expanded from 1.98 m²/m² to 2.66 m²/m². Furthermore, the empirical findings conclusively revealed that the basalt-glass interface constituted the largest proportion of the total contact area within the evaluated composite structure.

АННОТАЦИЯ

В данной статье подробно исследуются микроструктурные характеристики комбинированного фильтрующего слоя на основе стекловолокна, базальта и полиэстера, специально предназначенного для высокоэффективной очистки газовых потоков, загрязненных суглинистой пылью. В рамках проведенного исследования были отобраны образцы фильтрующих слоев с различной толщиной (1,0; 1,2 и 1,5 мм), что соответствует их поверхностной плотности в 390, 450 и 525 г/м². Микроструктура данных образцов была тщательно проанализирована с использованием микроскопа SM001-SYANS при 300-кратном увеличении, с применением комплексного метода анализа изображений (image-analysis). В процессе аналитической работы были точно определены несколько ключевых параметров, включая эквивалентный диаметр открытых зон, их площадь, долю открытых зон, долю площади, заполненной волокнами, плотность распределения точек контакта, удельную поверхность контакта, а также общую объемную плотность фильтрующего слоя. На основе детализированных результатов вычислений было установлено, что по мере увеличения толщины слоя с 1,0 мм до 1,5 мм общая площадь контактной поверхности пропорционально возрастает с 1,98 м²/м² до 2,66 м²/м². Кроме того, полученные эмпирические данные убедительно продемонстрировали, что на контактную границу «базальт – стекло» приходится наибольшая доля от общей площади контакта в исследуемой композитной структуре.

Keywords: glass fiber, basalt fiber, polyester, combined filter fabric, comparative contact area, open zones, microstructure, image-analysis, soot dust, fabric filter, aerodynamic drag, dust collection efficiency.

Ключевые слова: стекловолокно, базальтовое волокно, полиэстер, комбинированная фильтрующая ткань, сравнительная площадь контакта, открытые зоны, микроструктура, анализ изображений, сажевая пыль, тканевый фильтр, аэродинамическое сопротивление, эффективность пылеулавливания.

Introduction

The effective purification of dust-laden gas streams generated within industrial facilities holds paramount importance, particularly concerning the assurance of ecological safety, the protection of atmospheric air, and the enhancement of operational stability in technological processes. Fabric filters are extensively employed in this context, especially for the filtration of gas streams laden with finely dispersed solid particles of varying dimensions, such as loam dust. However, it is crucial to recognise that the filtration efficiency of a given material is dictated not solely by its inherent chemical composition, but also by its complex microstructural characteristics. These include the spatial arrangement of the fibres, the specific geometry of the open zones, the frequency of contact points, and the overall density of the filter layer [1,2,3].

In light of these considerations, the development of a combined filter fabric — achieved by embedding a mixed intermediate layer of basalt and glass fibres between primary polyester support layers — and the subsequent analysis of its structural properties represent a highly relevant pursuit from both scientific and practical standpoints. An increased concentration of internal structural contacts within such a composite filter layer can significantly expand the active surface area available for the capture and retention of particulate matter. Concurrently, this structural configuration is anticipated to exert a highly positive influence on both the mechanical stability and the prolonged service life of the filtration system.

Consequently, the primary objective of this research is to calculate the specific contact surface areas of the composite filter layer based on glass and basalt fibres, and to critically evaluate the geometry of its open zones. Furthermore, the study aims to determine the profound impact of these microstructural parameters on the overall dust capture efficiency, aerodynamic resistance, and long-term operational characteristics of the filter. To achieve these objectives, sample layers varying in both mass and thickness were rigorously examined utilising advanced microscopic imaging and comprehensive image-analysis techniques. Based upon the empirical data derived from these analyses, the feasibility of selecting the most optimal constructive variant for the filter fabric was carefully evaluated.

As previously noted, the ultimate efficiency achieved in the purification of loam dust-contaminated gas streams using fabric filters is directly contingent not only upon the chemical composition of the filtration medium but also intimately linked to its underlying microstructural architecture. Addressing this specific context, a combined filter fabric was methodically constructed by interposing a mixed filtration layer — comprising basalt and glass fibres — between the fundamental polyester support layers (Figure 1). Subsequently, a comprehensive evaluation was conducted to ascertain exactly how this precisely engineered microstructure influences the overarching operational dynamics of the fabric filter.

Figure 1. Exterior view of combined filter fabric with fiberglass, basalt and polyester base

Materials and methods

In this approach, primary attention was directed towards the mutual contact surface of the fibres, the precise geometry of the open zones, the equivalent size of these open zones, and the overall volumetric density of the filter layer. For the purpose of microscopic analysis, samples corresponding to a surface area of 1 m² with respective areal masses of 390, 450, and 525 g/m² were meticulously extracted and brought to a compacted state. Consequently, these compacted fibres formed uniform filtration layers with thicknesses of 1.0, 1.2, and 1.5 mm, corresponding strictly to their respective fibre masses. Within this experimental framework, the average equivalent diameter of the fibres was established as 9 μm for the basalt fibres and 11 μm for the glass fibres, while the applicable mass coefficients were accepted as 0.8667, 1.0, and 1.1667, respectively [4].

The fundamental practical significance of this comprehensive analysis lies in its capacity to facilitate the selection of the most optimal microstructural configuration for the filter fabric, specifically tailored for the capture of loam dust. Specifically, the frequency of contact points generated by the mutual spatial arrangement of basalt and glass fibres, alongside the resultant proportion of open zones, directly impacts the primary operational parameters of the fabric filter; these encompass dust retention efficiency, aerodynamic resistance, the rate of dust cake formation, regeneration stability, and the overall service life of the material. For this very reason, the detailed microscopic analysis of the mixed layer comprising basalt and glass fibres is considered an absolutely essential stage for the structural and constructive optimisation of the filter fabric [5].

In the course of this study, the complex microstructure of the mixed filtration layer, constructed from both glass and basalt fibres, was rigorously evaluated. High-resolution images were captured using an SM001-SYANS optical microscope at a magnification of 300x, and subsequently analysed employing an advanced image-analysis methodology. Figure 2 vividly illustrates the detailed process of image-analysis processing applied to the individual particles and structural elements.

During the systematic analytical procedure, multiple critical variables were quantified: the equivalent diameter of the open zones, their respective cross-sectional area, the relative fraction of open zones within the analysed surface area, the proportion of the area wholly occupied by solid fibres, the spatial density of the contact points, the specific contact surface area, and the overall volumetric density of the filtration layer. To ensure precise measurements, a scale coefficient was meticulously applied to accurately convert standard pixel dimensions into actual micrometres;

Initially, the acquired microscopic images for each individual sample underwent thorough examination, wherein the metrological linkage of the visual representation was definitively established through the use of a calibrated scale bar. Following this calibration step, the discrete open zones situated between the interwoven fibres were carefully isolated, allowing for the accurate computational assessment of their equivalent diameter and total area. Ultimately, the equivalent diameter of the distinct open zones interspersed between the fibres was determined using the following mathematical formula, expressed in micrometres (μm):

Figure 2. View of the fiber layer magnified 300 times and image-analyzed using the SM001-SYANS microscope

The equivalent diameter of open zones was determined according to the following formula, μm [6];

                                          (1)

where d_o.z.d represents the equivalent diameter of the open zone, expressed in µm; and A_o denotes the cross-sectional area of the open zone, which is determined in direct correlation with the equivalent diameter of the open zones identified as a result of the comprehensive analysis, measured in µm² [7];

                                             (2)

Following this systematic procedure, the relative proportion of open zones with respect to the total analysed surface area, the corresponding fraction of the region entirely occupied by the solid fibres, and the overarching spatial density of the structural contacts were meticulously determined. Consequently, the specific proportion of these open zones was carefully calculated utilising the subsequent mathematical expression, denoted as a percentage (%) [8];

                                      (3)

where P_o.u represents the relative proportion of the open zone, expressed as a percentage (%); and A_t.y. denotes the total analysed surface area, measured in µm².

The fraction of the zone filled with fibers was determined by the following formula, % [9];

                                         (4)

where P_t.q denotes the proportion of the layer fully occupied by the interwoven fibres, expressed as a percentage (%); Furthermore, the spatial contact density of the structural fibres was precisely determined according to the following mathematical formula, also expressed as a percentage (%):

                                             (5)

Where N_k.y represents the contact density, measured in μm^-2; and n_k.y. denotes the total number of individual contact points.

In the subsequent analytical stage, the distinct types of structural contacts—specifically comprising basalt-basalt, glass-glass, and basalt-glass interactions—were quantified individually. Following this meticulous classification, the overall total contact surface area was accurately derived through the mathematical summation of these respective components. Ultimately, the specific contact surface area of the fibrous layer under the evaluated conditions is systematically determined according to the following formula, expressed in m²/m² [5];

                                        (6)

Where S_n.k. represents the specific contact surface area under the calculated conditions, expressed in m²/m²; S_b.k. denotes the specific contact surface area under the baseline conditions, expressed in m²/m²; M_n.k. corresponds to the specific areal mass for the relevant evaluated state, measured in g/m²; M_b.k. indicates the fundamental baseline areal mass, measured in g/m².

Furthermore, the total contact surface area per 1 m² of the composite filtration layer, which is fundamentally constructed from a precise blend of basalt and glass fibres, was accurately determined in accordance with the following mathematical formula, with the final value expressed in m² [10]:

                             (7)

In the final phase of the analytical methodology, the overarching volumetric density was precisely determined based upon the areal mass corresponding to a 1 m² surface area and the measured thickness of the filtration layer. Following this crucial determination, all calculated indicators were subjected to a rigorous and systematic comparative analysis. In order to effectively compare and visualise the comprehensive computational results, a correlational graph was meticulously constructed. Consequently, Figure 3 clearly illustrates the functional dependency of the evaluated microstructural parameters upon the total contact surface area, whilst the exhaustive set of overall experimental findings is comprehensively documented in Appendix D.

Figure 3. Graph of dependence of basalt and glass fiber parameters on contact surface change

Results and discussion

The computational results, coupled with the graphical correlations prominently illustrated in Figure 3, clearly demonstrate that for a fibre layer with a measured thickness of 1.0 mm, the total contact surface area amounted to 1.98 m²/m². For thicknesses of 1.2 mm and 1.5 mm, this specific value progressively increased to 2.28 m²/m² and 2.66 m²/m², respectively. Concurrently, a detailed breakdown of the internal interactions revealed that the basalt-basalt contact surface area expanded from 0.57 to 0.77 m²/m², whilst the glass-glass contact surface area experienced an increment from 0.38 to 0.51 m²/m². Most notably, the basalt-glass contact surface area exhibited the most substantial growth, increasing consistently from 1.02 to 1.38 m²/m². This empirical evidence strongly indicates that as the physical thickness of the filtration medium increases, there is a corresponding and significant enhancement in the potential for mutual compaction and internal cohesion among the heterogeneous fibres distributed within the mixed layer [11,12].

In the comprehensive evaluation of the geometry pertaining to the open zones, the cross-sectional areas strictly corresponding to their equivalent diameters were precisely calculated to be 706.9, 1809.6, 2463.0, 4778.4, 6647.6, 8659.0, and 11309.7 µm². These specific quantitative metrics successfully facilitated a robust morphological assessment of the open zones, thereby providing a highly reliable basis for their mutual comparative analysis. Furthermore, these calculated parameters inherently denote that the intricate pore system embedded within the filter layer is formed in a distinctly irregular and heterogeneous manner. In turn, this observed structural heterogeneity serves as a crucial analytical factor for rigorously evaluating the precise extent to which the underlying microstructure influences the spatial distribution and flow dynamics of the dust-laden air stream across the entire active surface of the filter.

Regarding the volumetric density, the systematic analysis determined a precise value of 390 kg/m³ for the 1.0 mm sample, 375 kg/m³ for the 1.2 mm sample, and 350 kg/m³ for the 1.5 mm sample. This particular experimental finding clearly demonstrated that as the filtration layer progressively thickens, its overarching macrostructure naturally adopts a relatively more voluminous and less densely packed configuration. Therefore, it was definitively established that during the critical selection process of an appropriate filtration medium, it is absolutely essential to evaluate not merely the fundamental mass or the nominal thickness in isolation, but rather to conduct a holistic assessment that concurrently integrates the specific contact surface area, the relative proportion of open zones, and the overall volumetric density [14,15].

With specific regard to the filtration of loam dust, the practical and operational significance of these analytical results lies primarily in the fact that a mixed layer possessing a larger specific contact surface area naturally generates a significantly greater internal active surface dedicated to the highly effective capture and retention of solid particulate matter. Consequently, a deliberate reduction in the calculated proportion of open zones substantially mitigates the underlying probability of coarse and medium-dispersed particles penetrating and passing entirely through the filter fabric. However, it is imperative to acknowledge that this internal structural tightening, in turn, leads to a considerable and measurable increase in the aerodynamic resistance of the filter layer. As a direct result of these competing factors, while the overall operational efficiency of the device in terms of absolute dust capture is markedly augmented, the filtration system may simultaneously underperform from the distinct perspective of fluid throughput and volumetric productivity. Conversely, in filter layers that are inherently characterised by a comparatively small specific surface area, the available contact surfaces for particle interception are strictly limited; a condition that unequivocally exerts a profoundly negative impact upon the ultimate purification degree achieved by the respective filter fabric.

Finally, the prominent fact that the highest overall proportion of internal structural connections was directly attributed to the basalt-glass type of contacts clearly indicates that within this specific mixed composite structure, the mutual physical bonding of the differing fibres is exceptionally robust, thereby ensuring a superior degree of mechanical stability for the entire filter layer. On this solid foundational basis, the comprehensive microstructural analysis provided a highly reliable and predictive means to prospectively evaluate the multifarious operational factors that directly dictate the performance of the fabric filter. These critical factors encompass the fundamental dust capture efficiency, the recorded aerodynamic resistance during both the initial and active operational phases, the precise kinetic rate of dust cake formation, the subsequent recovery capacity following cyclic regeneration, and ultimately, the prolonged operational service life of the entire filtration system [16].

Conclusion

The conducted microscopic analysis establishes a robust scientific foundation for the practical application of a combined filter fabric—fundamentally based on basalt, glass fibre, and polyester—in the highly effective purification of gas streams contaminated with loam dust. The comprehensive analytical results have clearly demonstrated that the intricate microstructure of the mixed-fibre intermediate layer, particularly regarding its specific contact surface area, the exact geometry of its open zones, and its overall volumetric density, constitutes one of the primary and most critical factors determining the fundamental operational properties of the filter. Furthermore, the synergistic utilisation of basalt and glass fibres significantly multiplies the internal structural contacts within the fabric filter, thereby vastly expanding the active surface area available for optimal dust retention and substantially enhancing the overarching mechanical stability of the filtration layer.

From a strictly practical perspective, this rigorous microstructural analysis holds paramount importance for accurately evaluating, managing, and optimising the following key operational parameters of the fabric filter:

− Dust capture efficiency;

− Aerodynamic resistance;

− Air permeability;

− Uniform formation of the solid dust cake;

− The precise degree of filter recovery subsequent to pulse-jet cleaning procedures;

− The prolonged operational service life of the filtration system.

Consequently, through the systematic microstructural analysis of the mixed composite layer comprising basalt and glass fibres, it becomes entirely feasible to select the most optimal structural design for the filter fabric, specifically tailored for the interception of loam dust; in other words, to successfully identify the absolute finest balance between achieving exceptionally high filtration efficiency and maintaining fundamentally acceptable pressure losses. Building directly upon the aforementioned empirical and analytical findings, a comprehensive computational scheme of the device has been meticulously developed. This scheme was specifically designed in order to provide a robust theoretical justification for the aerodynamic resistance of the advanced bag filter unit, which is suitably equipped with the engineered filter fabric prepared on the basis of glass fibre, basalt, and polyester.

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