A thin layer of high density filler

Abstract

The present invention discloses a thin layer high-density filler, which is based on a plain woven metal wire mesh filler and is made by optimizing a weaving method, a weaving density and a bundling method. The novel weaving technique makes the thin layer high-density filler have a larger number of wefts than the plain woven metal wire mesh filler under the same number of warps, and has the characteristics of high specific surface area, high mass transfer efficiency, low flow pressure drop and the like. There are a large number of micropores on the surface of the thin layer high-density filler, and the wettability is excellent. Moreover, due to the large density of the wefts, the lateral diffusion effect of the liquid inside the filler can be greatly enhanced. The performance is particularly outstanding in processes such as large spray density distillation, and the pressure drop is about 30%-50% lower than that of ordinary plain woven fillers. The filler of the present invention mostly uses stainless steel wire as a raw material, which has the advantages of low cost, large flux, stable performance and low metal permeation rate. Therefore, it has an irreplaceable position in the field of heat pump distillation, separation of high-purity electronic chemicals, separation of intermediates and isomer separation production.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical production equipment, is applicable to mass transfer and heat transfer devices, and specifically relates to a thin layer high-density filler. Background Art

[0002] Metal mesh packing is widely used in chemical, oil refining, pharmaceutical and other production fields due to its large specific surface area, small flow pressure drop, high mass transfer efficiency and easy assembly. With the development of the times, the requirements for comprehensive green development of the chemical industry and high efficiency and energy saving of separation equipment are becoming increasingly urgent. Recently, due to the popularization of heat pump distillation process, a low pressure drop and high efficiency tower internal is urgently needed. Therefore, the research and development of new low pressure drop and high efficiency packing is a research hotspot in the chemical separation industry.

[0003] Metal mesh packing has the advantages of high separation efficiency, low cost, and relatively low pressure drop, and is often used in the separation and purification process of high-end electronic chemicals. The number of theoretical plates and energy consumption required for distillation separation increase exponentially with the increase of product purity. Therefore, when distilling and purifying it, metal mesh packing with a very high specific surface area is often used to improve the separation efficiency, and heat pump distillation is used to reduce energy consumption. However, conventional metal mesh packing has relatively high mass transfer efficiency while having high pressure drop and low processing efficiency, which leads to problems such as excessive investment in heat pump distillation process and failure to achieve optimal heat recovery. To solve this defect, we propose a packing with an innovative weaving technique - thin layer high-density packing. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a thin layer high-density filler that is easy to weave and has a simple structure, low pressure drop and high flux. The filler has small mesh holes, large specific surface area, better wettability, easier liquid film formation, lower flow pressure drop and higher mass transfer efficiency. The present invention improves the shortcomings of ordinary plain woven metal wire mesh fillers such as large mesh holes, high pressure drop, poor liquid wettability and low efficiency by adopting a new weaving method.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention provides a thin layer high-density filler, which is formed by stacking multiple thin layer high-density wire mesh sheets and has a cylindrical three-dimensional space structure. Each wire mesh sheet of the thin layer high-density filler is woven by a new weaving technique and has a corrugated structure. The corrugated structures of adjacent thin layer high-density wire mesh sheets are arranged at 90 degrees and fixed together by a special bundling method. Adjacent wire mesh sheets are fixed by spot welding, and the filler as a whole is connected and fixed together by multiple screws of different lengths.

[0007] The thin layer of high-density wire mesh is woven using a new weaving technique, specifically: a single or multiple closely fitting wefts and a single or multiple closely fitting warps are woven in a one-jump-four, one-jump-two, two-jump-two or other weaving method to achieve the interlaced superposition of multiple warps and multiple wefts, and different strengths of tension are used in the weaving process according to the different densities of the warp and weft lines, and the general tension shall not exceed 8 pounds. By increasing the number of weft lines, the density of the warp and weft lines is changed, thereby lengthening the warp lines, reducing the metal bending angle, and reducing the problem of thickening the metal wire mesh and increasing the aperture due to metal stress, so that the metal wire mesh has a thinner thickness, a three-dimensional mass transfer space and a larger apparent specific surface area.

[0008] Furthermore, the one-hop-four, one-hop-two, and two-hop-two modes are specifically:

[0009] One jump four means that a single or multiple closely fitting wefts or warps are regarded as a group. The first group of wefts first crosses the first group of warps, and then crosses the second to fifth groups of warps, repeating the process of first crossing one group and then crossing four groups many times; the second group of wefts first crosses the third group of warps, and then crosses the fourth to seventh groups of warps, repeating the process of first crossing one group and then crossing four groups many times; the third group of wefts first crosses the first to fourth groups of warps, and then crosses the fifth group of warps, repeating the process of first crossing one group and then crossing four groups many times; the fourth group of wefts first crosses the second group of warps, and then crosses the third to sixth groups of warps, repeating the process of first crossing one group and then crossing four groups many times; the fifth group of wefts first crosses the fourth group of warps, and then crosses the fifth to eighth groups of warps, repeating the process of first crossing one group and then crossing four groups many times; multiple groups of wefts repeat the above process in sequence, and finally weave a single piece of one jump four thin-layer high-density filler wire mesh.

[0010] One jump two means that a single or multiple closely fitting wefts or warps are regarded as a group. The first group of wefts first crosses the first group of warps, and then crosses the second and third groups of warps, repeating multiple times to cross one group first and then two groups; the second group of wefts first crosses the second group of warps, and then crosses the third and fourth groups of warps, repeating multiple times to cross one group first and then two groups; the third group of wefts first crosses the first and second groups of warps, and then crosses the third group of warps, repeating multiple times to cross one group first and then two groups; multiple groups of wefts repeat the above process in sequence, and finally weave a single piece of one jump two thin layer high-density filler wire mesh.

[0011] Two jumps and two means that a single or multiple closely fitting wefts or warps are regarded as a group. The first group of wefts first crosses the first and second groups of warps, and then crosses the third and fourth groups of warps, repeating multiple times to cross two groups first and then two groups; the second group of wefts first crosses the second and third groups of warps, and then crosses the fourth and fifth groups of warps, repeating multiple times to cross two groups first and then two groups; multiple groups of wefts repeat the above process in sequence, and finally weave a single piece of two jumps and two thin layers of high-density filler wire mesh.

[0012] Furthermore, based on a novel weaving method of a thin layer of high-density wire mesh sheet, a large number of flat strip-shaped micropores and regular patterns exist on the surface of the thin layer of high-density filler.

[0013] Furthermore, after the warp and weft threads of the thin-layer high-density silk screen are woven, the bending angles of the warp and weft threads are less than 90°.

[0014] Furthermore, the special bundling method refers to that the thin layer high-density filler wire mesh sheets are fixed to each other by spot welding, and the filler as a whole is connected in series by multiple screws of different lengths to ensure the structural stability of the wire mesh filler.

[0015] Furthermore, the vertical inclination angle of the thin layer high-density wire mesh single piece is between 0° and 90°, the height of each plate of thin layer high-density filler is between 20mm and 500mm, and the diameter of the wire used for weaving is between 0.08mm and 2.5mm.

[0016] Furthermore, the material of the thin layer high-density wire mesh is stainless steel wire, carbon wire or polymer wire. The specific material can be divided into various types of stainless steel wires such as 304 (0Cr19Ni9), 316 (022Cr17Ni12Mo2), PTFE and non-metallic wires such as carbon wire and polymer wire according to the separation process application scenario.

[0017] Furthermore, the thin layer high-density wire mesh sheets can be adjusted according to production needs by changing the peak height and peak angle of the corrugated structure of the thin layer high-density wire mesh sheets to adjust the number of wire mesh sheets and thus adjust the specific surface area of ​​the thin layer high-density filler.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The new weaving process greatly reduces the internal pore size of the metal wire mesh packing, effectively avoiding the problem of increased pressure drop caused by gas phase passing through the mesh due to excessive pore size, which causes reverse mixing of liquid phases. In addition, since the gas phase cannot break through the liquid film, the surface of the wire mesh forms a stable liquid film flow, which greatly enhances the mass transfer efficiency of the packing.

[0020] Compared with ordinary plain woven wire mesh packing, thin layer high density packing adopts a new weaving technique. The new weaving process makes the number of wefts of thin layer high density packing and ordinary plain woven wire mesh packing increase several times under the condition of the same number of warps, which is conducive to the formation of liquid film on the surface of the wire mesh and the lateral diffusion of liquid. In addition, the regular flow channels formed on the surface of the wire mesh further make the liquid phase quickly and evenly distributed in the radial and lateral directions, and enhance the liquid renewal rate on the packing surface; thus, it is conducive to the improvement of mass transfer efficiency;

[0021] The new weaving process changes the tension and the span so that the wire bending angle is less than 90°, making the filler itself have a smaller thickness and a larger mass transfer surface area, thereby enhancing the mass transfer efficiency.

[0022] In summary, the thin layer high-density filler of the present invention is based on the plain woven metal wire mesh filler, and is made by optimizing the weaving method, weaving density and flat stamping process. The new weaving technique makes the thin layer high-density filler have the advantages of ultra-high specific surface area and three-dimensional mass transfer space under the same number of warps compared with the plain woven metal wire mesh filler. Compared with ordinary plain woven metal wire mesh fillers, thin layer high-density wire mesh fillers have the characteristics of high specific surface area, high mass transfer efficiency, low flow pressure drop, etc., so they can be widely used in heat pump distillation energy-saving processes, thereby reducing the pressure difference between the top of the tower and the bottom of the tower, reducing the temperature difference and reducing the compressor power, and achieving better heat utilization. And the thin layer high-density filler is mostly woven with metal wire, and there are a large number of flat strip-shaped micropores on its surface with excellent wettability, and because the weft density is large, it can greatly enhance the lateral diffusion effect of the liquid inside the filler, so the separation performance is particularly outstanding in processes such as large spray density distillation, and the pressure drop is about 30%-50% lower than that of ordinary plain woven fillers. The filler of the present invention mostly uses stainless steel wire as raw material, which has the advantages of stable performance and low metal leakage rate. Therefore, it has an irreplaceable position in the field of fine chemicals, separation of high-purity electronic chemicals, separation of intermediates and separation of isomers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The weaving pattern of the thin layer of high-density wire mesh is mesh configuration-1 (one jump four);

[0024] Figure 2 The weaving pattern of the thin layer of high-density wire mesh is mesh configuration-2 (one jump two);

[0025] Figure 3 The weaving pattern of the thin layer of high-density wire mesh is mesh configuration-3 (one jump four);

[0026] Figure 4 This is a detailed diagram of a thin layer of high-density filler;

[0027] Figure 5 This is a front view of the thin layer high-density filler;

[0028] Figure 6 This is a top view of a thin layer of high-density filler;

[0029] Figure 7 The pressure drop comparison diagram of thin layer high density packing and flat woven packing under 0 spray density under two types;

[0030] Figure 8It is a comparison chart of pressure drop of thin layer high density packing and flat woven packing under 10 spray density under two types;

[0031] Fig. 9 The pressure drop comparison diagram of thin layer high density packing and flat woven packing under 20 spray density under two models;

[0032] Fig.10 This is a comparison chart of the pressure drop of thin-layer high-density packing and flat-woven packing under 30 spray density under two models;

[0033] Fig.11 It is a comparison chart of pressure drop of thin layer high density packing and flat woven packing under 40 spray density under two types;

[0034] Fig.12 It is a comparison chart of pressure drop of thin layer high density packing and flat woven packing under 50 spray density under two types;

[0035] Fig.13 It is a comparison chart of pressure drop of thin layer high density packing and flat woven packing under 60 spray density under two types;

[0036] Fig.14 This is a comparison chart of the efficiency of thin-layer high-density packing and flat-woven packing under 10 spray density under two models;

[0037] Fig.15 This is a comparison chart of the efficiency of thin-layer high-density packing and flat-woven packing under 20 spray density under two models;

[0038] Fig.16 This is a comparison chart of the efficiency of thin-layer high-density packing and flat-woven packing under 30 spray density under two models;

[0039] Fig.17 This is a comparison chart of the efficiency of thin-layer high-density filler and flat-woven filler at a spray density of 40 under two models. DETAILED DESCRIPTION

[0040] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0041] like Figure 1-Figure 6As shown, the present invention is a metal wire mesh packing with a three-dimensional spatial structure and a high specific surface area, which is composed of multiple thin layers of high-density metal wire mesh sheets stacked together. The new thin layer of high-density wire mesh sheets are flattened and punched into a corrugated shape, and the intersections of the corrugated thin layer of high-density wire mesh sheets are fixed to each other by welding, and are connected in series by multiple screws of different lengths. Then, the vertically arranged thin layer of high-density metal wire mesh strips are formed into a disc-shaped regular packing. The mesh configuration of the thin layer of high-density packing is shown in FIG. Figure 1-Figure 3 , the actual details of the thin layer high density filler are as follows Figure 4 As shown, the front view and top view of the thin layer high density filler are shown in Figure 5 and Figure 6 , hoops can be installed on the outside of thin layers of high-density fill.

[0042] The following is a detailed description of the B-type and Y-type thin-layer high-density fillers and ordinary BX500 and CY700 fillers in this application, which is convenient for comparison with cases. The B-type and Y-type thin-layer high-density fillers adopt a new one-jump-four weaving method, and ordinary BX500 and CY700 fillers use ordinary plain woven metal wire mesh filler sheets. Among them, the B-type thin-layer high-density filler and the ordinary BX500 filler have the same peak height of 6.2±0.07mm, wave spacing of 10.2±0.07mm, corrugation inclination of 30°, tooth angle of 78.9±1°, and nominal specific surface area of ​​507.9 m 2 / m 3 , wire diameter 0.156mm, B-type thin layer high density packing porosity 96.83%, ordinary BX500 packing porosity 97.64%. Among them, Y-type thin layer high density packing and ordinary CY700 packing have the same peak height of 4.5±0.05mm, wave spacing of 7.2±0.05mm, corrugation angle of 45°, tooth angle of 77.3±1°, and nominal specific surface area of ​​711.4 m 2 / m 3 , wire diameter 0.156mm, the porosity of Y-type thin layer high-density filler is 95.29%, and the porosity of ordinary CY700 filler is 95.79%. Example 1

[0043] By magnifying and observing the intersection of ordinary plain woven metal wire mesh filler sheets, it is found that the weft line width is narrow, and the warp lines need to bend more in a shorter distance when they are staggered and superimposed. Therefore, the material stress of the warp lines will cause the wire mesh to become thicker and the aperture to become larger. Thin layer high-density filler wire mesh materials use different weaving techniques. By magnifying the intersection, it is found that the thin layer high-density filler widens the weft lines, so that the warp lines span a larger length when the warp and weft lines are staggered and superimposed, resulting in less bending, thus solving the problem that material stress will cause the wire mesh to become thicker and the aperture to become larger. When the mesh number per unit area is the same and the wire diameter is the same as 0.20 mm, the surface area of ​​thin layer high density packing and ordinary plain woven wire mesh packing in the range of 10 mm * 10 mm is compared. It is calculated that the surface area of ​​thin layer high density packing is 57.26% larger than that of ordinary plain woven wire mesh packing. Because the specific surface area is equal to the surface area divided by the volume, the larger the surface area is under the same volume, the larger the specific surface area is. The specific surface area is positively correlated with the mass transfer performance, so the thin layer high density packing has the advantage of high mass transfer efficiency. Example 2

[0044] The wet tower pressure drop of B-type and Y-type thin-layer high-density packings was compared with that of ordinary BX500 and CY700 packings at different spray densities. The packing pressure drop test was carried out in a 600 mm diameter organic glass tower. The air inlet device in the tower adopted a metal double-row blade gas distributor, the bottom support device of the packing adopted a grid support, and the top liquid distribution device adopted a tube-type liquid distributor. The experimental system adopted an air-water system. In the experiment, water was sent from the tower bottom to the top liquid distributor by a centrifugal pump, and its liquid flow was measured by a rotor flowmeter. The liquid flow was controlled by changing the gate valve opening to change the spray density of the liquid in the tower. The gas was sent into the tower bottom by a centrifugal fan, and its gas flow was measured by an orifice flowmeter in the form of pressure drop. The gas flow in the tower was controlled by changing the butterfly valve opening. The tower was equipped with a total height of 2400 mm packing. After removing some end effect elimination packing, the pressure packing height was 1800 mm. The packing layer pressure drop was measured by a micro differential pressure gauge and a U-tube differential pressure gauge.

[0045] The test results are as follows: under the same test conditions, the pressure drop of B-type thin layer high-density packing and ordinary BX500 packing is about 30% lower than that of ordinary BX500 packing; under the same test conditions, the pressure drop of Y-type thin layer high-density packing and ordinary CY700 packing is about 50% lower than that of ordinary CY700 packing. The specific data are as follows: Figure 7-Figure 13, and the pressure drop of thin-layer high-density packing changes more slowly with the spray density. This phenomenon is because the thickness of the B-type and Y-type thin-layer high-density packing mesh is about 33% thinner than that of the ordinary BX500 and CY700 packing mesh, and the surface of the B-type and Y-type thin-layer high-density packing mesh has multiple micro-channels with liquid diversion function, so that the gas-liquid two-phase flow state can be achieved more perfectly, reducing the impact between the gas and liquid, and greatly reducing the pressure drop. Example 3

[0046] The mass transfer efficiency of B-type and Y-type thin-layer high-density packings was compared with that of ordinary BX500 and CY700 packings by oxygen desorption. The oxygen desorption test was conducted using an oxygen-water system, and the change in oxygen content in the water after the system passed through the packing was used as the rating standard for mass transfer efficiency. The test was conducted in a steel tower with a diameter of 600 mm. The air inlet device in the tower used a metal double-row blade gas distributor, the bottom support device of the packing used a grid support, and the liquid distribution device used a tube-type liquid distributor. In the experiment, water was sent from the tower bottom to the absorption tower through a centrifugal pump, and oxygen was introduced into the absorption tower through an oxygen cylinder to make the liquid reach an oxygen-enriched state, and then the oxygen-enriched water was introduced into the liquid distributor. The liquid flow rate was measured by a rotor flowmeter, and the liquid flow rate was controlled by changing the gate valve opening to change the spray density of the liquid in the tower. The gas was sent into the tower bottom by a centrifugal fan to send high-pressure air, and the gas flow rate was measured by an orifice flowmeter in the form of pressure drop, and the gas flow rate was controlled by changing the butterfly valve opening. The tower is filled with a total height of 1100 mm of filler as test filler.

[0047] The test results are as follows: under the same test conditions, the mass transfer performance of B-type thin layer high density packing and ordinary BX500 packing is about 20% higher than that of ordinary BX500 packing; under the same test conditions, the mass transfer performance of Y-type thin layer high density packing and ordinary CY700 packing is about 30% higher than that of ordinary CY700 packing; the specific data are as follows: Figure 14-17 This phenomenon is because the B-type and Y-type thin-layer high-density packing wire mesh has better liquid lateral distribution ability than ordinary BX500 and CY700 packing wires, and contains a large number of flat strip-shaped micropores inside, which are easier to form films and not easy to break, so that the mass transfer efficiency is significantly increased.

[0048] In summary, compared with ordinary plain woven metal wire mesh fillers, the thin layer high density fillers of the present invention have greatly improved performance in terms of filler wire mesh structure stability, flow pressure drop, operation flexibility and mass transfer efficiency. The parameters of the thin layer high density filler wire diameter, wave crest, disk height, wave pitch, tooth angle, corrugation inclination, porosity, etc. are adjusted according to actual process conditions. Within the parameter range of the claims, the present invention can produce the above-mentioned beneficial effects.

[0049] The embodiments described above are only used to explain the present invention and cannot be understood as limiting the present invention. Referring to the drawings, the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification, and are not used to limit the limiting conditions under which the present invention can be implemented, so they have no technical substantive significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

Claims

1. A thin layer high density filler, characterized in that: The thin layer high-density packing is formed by stacking multiple thin layer high-density wire mesh sheets, and has a cylindrical three-dimensional space structure; each wire mesh sheet of the thin layer high-density packing is woven by weaving techniques and has a corrugated structure, and the corrugated structures of adjacent thin layer high-density wire mesh sheets are arranged at 90 degrees and fixed together by bundling; The thin layer of high-density wire mesh is woven by a weaving technique, specifically: a single or multiple closely fitting wefts and a single or multiple closely fitting warps are woven in a one-jump-four, one-jump-two or two-jump-two weaving method to achieve the interlaced superposition of multiple warp lines and multiple weft lines, and different strengths of tension are used in the weaving process according to the different densities of the warp and weft lines, and the tension generally does not exceed 8 pounds; the one-jump-four, one-jump-two, and two-jump-two weaving methods are specifically: One jump four is to regard a single or multiple closely fitting wefts or warps as a group, and cross the first group of wefts over the first group of warps first, and then cross the second to fifth groups of warps, and repeat this process of crossing one group first and then four groups many times; The second group of weft threads first crosses the third group of warp threads, and then crosses the fourth to seventh groups of warp threads, and repeats multiple times to cross one group first and then four groups; the third group of weft threads first crosses the first to fourth groups of warp threads, and then crosses the fifth group of warp threads, and repeats multiple times to cross one group first and then four groups; the fourth group of weft threads first crosses the second group of warp threads, and then crosses the third to sixth groups of warp threads, and repeats multiple times to cross one group first and then four groups; the fifth group of weft threads first crosses the fourth group of warp threads, and then crosses the fifth to eighth groups of warp threads, and repeats multiple times to cross one group first and then four groups; the above process is repeated in sequence for multiple groups of weft threads, and finally a single piece of high-density filler silk screen with four thin layers is woven; One jump two is to regard a single or multiple closely fitting wefts or warps as a group, and first cross the first group of wefts over the first group of warps, and then cross the second and third groups of warps, repeating multiple times to cross one group first and then two groups; the second group of wefts cross the second group of warps first, and then cross the third and fourth groups of warps, repeating multiple times to cross one group first and then two groups; the third group of wefts cross the first and second groups of warps first, and then cross the third group of warps, repeating multiple times to cross one group first and then two groups; multiple groups of wefts repeat the above process in sequence, and finally weave a single piece of one jump two thin layer high-density filler screen; Two jumps and two is to regard a single or multiple closely fitting wefts or warps as a group, and cross the first group of wefts over the first and second groups of warps first, and then the third and fourth groups of warps, and repeat this process many times, first crossing two groups and then two groups; the second group of wefts cross the second and third groups of warps first, and then the fourth and fifth groups of warps, and repeat this process many times, first crossing two groups and then two groups; the above process is repeated in sequence for multiple groups of wefts, and finally a two-jump two-thin layer high-density filler wire mesh single piece is woven.

2. A thin layer high-density filler according to claim 1, characterized in that: The bundling method refers to that thin-layer high-density wire mesh sheets are fixed to each other by spot welding and connected in series by multiple screws of different lengths, thereby ensuring the structural stability of the wire mesh filler.

3. A thin layer high-density filler according to claim 2, characterized in that: After the warp and weft threads of the thin-layer high-density silk screen are woven, the bending angles of the warp and weft threads are less than 90°.

4. A thin layer high density filler according to claim 2, characterized in that: Based on the weaving method of a thin-layer high-density wire mesh single sheet, a large number of flat strip-shaped micropores and regular patterns exist on the surface of the thin-layer high-density wire mesh single sheet under different tensile forces.

5. A thin layer high density filler according to claim 2, characterized in that: The vertical inclination angle of the thin layer high-density wire mesh single piece is between 0° and 90°, the height of each plate of thin layer high-density filler is between 20mm and 500mm, and the diameter of the wire used for weaving is between 0.08mm and 2.5mm.

6. A thin layer high density filler according to claim 2, characterized in that: The material of the thin layer high-density wire mesh single piece is stainless steel wire, carbon wire or polymer wire.

7. A thin layer high density filler according to claim 2, characterized in that: By changing the peak height and peak angle of the corrugated structure of a thin layer of high-density wire mesh single piece, the number of wire mesh single pieces is adjusted, and then the specific surface area of ​​the thin layer of high-density filler is adjusted.

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