A kind of puffed fiber filter layer for oil fume purification, filtering method and application

Abstract

The application discloses a kind of puffed fiber filter layer for oil fume purification, filtering method and application, belong to kitchen oil fume purification technical field.The filter layer is formed by puffed fiber material staggered laying and fixed into integral three-dimensional through net structure, and solid carbon dioxide particles are encapsulated in the fiber, and the particle periphery is formed into semi-closed covering structure by puffed fiber material.When hot air current of oil fume passes, solid carbon dioxide particles gradually sublimate and absorb heat, form low-temperature condensation environment and carbon dioxide gas microenvironment, to promote condensation of condensation oil fume components, oil drop coagulation and gravity diversion dripping, thereby improve the pre-capture ability of submicron oil mist particles, and reduce the risk of combustion-supporting in oil accumulation and grease deposition area in fan inner cavity.

Description

Technical Field

[0001] This invention belongs to the field of kitchen fume purification and aerosol filtration and separation technology, specifically relating to an expanded fiber filter layer for fume purification, a filtration method, and its application in range hoods or commercial kitchen exhaust equipment. Background Technology

[0002] During Chinese cooking, cooking oil evaporates, decomposes, and undergoes a phase change and condensation at high temperatures, easily forming a mixed oil fume aerosol containing gaseous oil fumes, misty oil droplets, and liquid condensed grease. This type of oil fume aerosol contains a certain proportion of submicron oil mist particles. These particles are small in size and have strong airflow ability, making them easy to pass through ordinary pre-filters and enter the inner cavity of range hood fans.

[0003] Ordinary metal filters, ordinary synthetic fiber filters, or conventional porous filter media typically rely mainly on inertial impaction, pore sieving, surface adhesion, or single adsorption to intercept oil fume particles. For larger oil droplets, the above-mentioned filtration structures can provide some blocking effect; however, for condensable submicron oil mist particles, the capture stability of a single filtration mechanism is insufficient, and some fine oil fume components may still enter the fan casing, impeller, and inner cavity with the airflow, and condense and accumulate oil during subsequent cooling.

[0004] Furthermore, in traditional porous filter media, grease tends to accumulate on the fiber surface or inside the pores during long-term use. As grease gradually accumulates, local channels in the filter layer are prone to blockage, leading to increased air resistance, decreased airflow, and shortened maintenance cycles. Some grease-laden areas also pose a risk of combustion in medium- and high-temperature oil fume environments. Existing oil fume filter materials rarely simultaneously address the low-temperature condensation and capture of condensable oil fume components, the coagulation and guidance of oil droplets, and the regulation of the gas environment in grease-laden areas. Therefore, it is necessary to provide an oil fume filter material that can create a low-temperature condensation environment within the oil fume filter layer while also considering oil droplet guidance and operational safety. Summary of the Invention

[0005] To address the problems of unstable capture of condensed submicron oil mist particles by the aforementioned pre-filter materials for oil fumes, increased air resistance due to grease retention within the filter material pores, and the potential for fine oil fume components to still enter the fan cavity, this invention provides an expanded fiber filter layer for oil fume purification. The expanded fiber filter layer is primarily composed of expanded fiber material, which is interlaced and fixed to form an integral three-dimensional interconnected mesh structure. The expanded fiber material possesses micron-level unevenness on the fiber surface, nano-level interconnected capillary channels within the fibers, and deep gradient micropores formed by the interlacing of fibers.

[0006] The micron-level unevenness of the fiber surface forms a primary surface adhesion interception zone. The nanoscale interconnected capillary channels inside the fiber form a secondary nanocapillary condensation and adsorption zone. The deep gradient micropores form a tertiary gradient microporous rigid barrier zone. The primary surface adhesion interception zone, the secondary nanocapillary condensation and adsorption zone, and the tertiary gradient microporous rigid barrier zone are mechanistic partitions formed by the progressive development of the microstructural scale within the same integral three-dimensional interconnected network structure, rather than a spatially layered composite structure formed by stacking different materials.

[0007] Solid carbon dioxide particles are dispersed and encapsulated within the expanded fiber filter layer. These solid carbon dioxide particles are embedded in at least one location within the nanoscale interconnected capillary channels and the deep gradient micropores. The outer periphery of each solid carbon dioxide particle is formed by a semi-closed coating structure of expanded fiber material. This semi-closed coating structure restricts the concentrated release of the solid carbon dioxide particles at once and allows them to gradually sublimate under the influence of the hot airflow of cooking fumes.

[0008] As the hot oil fume stream passes through the expanded fiber filter layer, solid carbon dioxide particles gradually sublimate and absorb heat through the semi-enclosed coating structure, forming a low-temperature condensation environment in localized areas of the expanded fiber filter layer. This low-temperature condensation environment makes it easier for condensable oil fume components to condense on the fiber surface or within capillary channels, thereby increasing the probability of oil mist particles being adhered, capillary agglomerated, and blocked by micropores. The carbon dioxide gas generated by the sublimation of solid carbon dioxide particles also forms localized gas disturbances and a carbon dioxide gas microenvironment in the grease deposition area. These localized gas disturbances promote oil droplet coalescence and gravity-guided dripping, while the carbon dioxide gas microenvironment reduces the risk of combustion in the grease deposition area.

[0009] Preferably, the porosity ε of the expanded fiber filter layer is 75%–95%, the specific surface area S is 20–60 m² / g, and the number of interleaved layers N is 4–12; the pore size of the nanoscale through capillary channel is 30 nm–500 nm, and the pore size of the deep gradient micropore is 0.2 μm–0.6 μm.

[0010] More preferably, the porosity ε of the expanded fiber filter layer is 82%–92%, the specific surface area S is 28–45 m² / g, and the number of staggered layers N is 6–8; the pore size of the deep gradient micropores is 0.3 μm–0.4 μm.

[0011] Preferably, the expanded fiber material uses food-grade modified PET or food-grade modified PPS as the base material. The thermal decomposition temperature of the food-grade modified PET base material is ≥280℃, the thermal decomposition temperature of the food-grade modified PPS base material is ≥350℃, and the flame retardancy rating of the expanded fiber material is V0.

[0012] Preferably, the solid carbon dioxide particles have a particle size of 5 μm–50 μm, and the doping amount of the solid carbon dioxide particles is 1 wt%–8 wt% of the mass of the expanded fiber material. More preferably, the solid carbon dioxide particles have a particle size of 10 μm–30 μm, and the doping amount of the solid carbon dioxide particles is 2 wt%–6 wt%.

[0013] Preferably, the thickness of the semi-enclosed coating structure is 0.5μm–3μm. Under oil fume operating conditions of 80℃–240℃, the solid carbon dioxide particles are slowly released and sublimated through the semi-enclosed coating structure, with a 50% cumulative release half-life of 400h–600h, and the local temperature of the expanded fiber filter layer is reduced by 10℃–40℃.

[0014] Preferably, the expanded fiber material, after melt extrusion, high-temperature expansion, and stretching, forms a micron-level uneven surface morphology, nano-level interconnected capillary channels, and deep gradient micropores within the fiber. During the high-temperature expansion or stretching process, the pre-cooled solid carbon dioxide particles enter at least one of the nano-level interconnected capillary channels or the deep gradient micropores, forming the semi-closed encapsulation structure with the expanded fiber material.

[0015] This invention also provides a method for filtration using expanded fiber for oil fume purification, wherein the filtration method employs the aforementioned expanded fiber filter layer doped with solid carbon dioxide for oil fume purification. The filtration method includes: introducing an oil fume airflow into the expanded fiber filter layer; adhering and intercepting oil mist particles in the oil fume airflow through the micron-level uneven morphology of the fiber surface; capillary condensation and adsorption of residual gaseous oil fume and free oil mist particles after adhesion and interception through nano-level interconnected capillary channels within the fiber; blocking residual oil mist particles after capillary condensation and adsorption through deep gradient micropores; causing the solid carbon dioxide particles to gradually sublimate and absorb heat under the action of the hot oil fume airflow through a semi-closed encapsulation structure, forming a low-temperature condensation environment in a localized area of ​​the expanded fiber filter layer, causing condensable oil fume components to condense on the fiber surface or within the capillary channels; the carbon dioxide gas generated by the sublimation of the solid carbon dioxide particles forms a localized gas disturbance and carbon dioxide gas microenvironment in the grease deposition area, the localized gas disturbance promoting oil droplet coalescence and gravity-guided dripping, and the carbon dioxide gas microenvironment reducing the combustion risk in the grease deposition area.

[0016] This invention also provides the application of the above-mentioned solid carbon dioxide-doped expanded fiber filter layer for oil fume purification in range hoods or commercial kitchen exhaust equipment. The expanded fiber filter layer is disposed between the air inlet of the range hood and the inner cavity of the fan, serving as a pre-filter unit. The expanded fiber filter layer is used to capture condensed oil fume components and submicron oil mist particles before the oil fumes enter the inner cavity of the fan, reducing the amount of grease entering the inner cavity of the fan and lowering the risk of oil accumulation in the fan casing, impeller, and inner cavity.

[0017] The technical effects and advantages of this invention are as follows: This invention disperses and encapsulates solid carbon dioxide particles within nanoscale interconnected capillary channels and / or deep gradient micropores in an expanded fiber filter layer, forming a semi-closed encapsulation structure through the expanded fiber material. This structure allows the solid carbon dioxide particles to gradually sublimate under the influence of hot oil fume flow, rather than being rapidly and centrally released, thus facilitating the formation of a relatively stable low-temperature condensation environment in localized areas of the filter layer.

[0018] This invention utilizes the low-temperature condensation environment created by the endothermic sublimation of solid carbon dioxide, making it easier for condensable oil fume components to condense on the fiber surface or within capillary channels. This effect, combined with the adhesion effect of the micron-level uneven morphology on the fiber surface, the capillary coagulation effect of the nano-level interconnected capillary channels inside the fiber, and the barrier effect of the deep gradient micropores, can improve the filter layer's ability to capture submicron oil mist particles.

[0019] This invention utilizes the localized gas disturbance generated by carbon dioxide vaporization to promote the coalescence of tiny oil droplets, making it easier for the oil droplets to flow and drip along the fiber surface and capillary channels due to gravity. This effect reduces the continuous retention of grease within the filter layer pores, lowers the risk of clogging during long-term operation, and helps maintain a low increase in air resistance.

[0020] The primary surface adhesion interception zone, the secondary nanocapillary condensation adsorption zone, and the tertiary gradient microporous rigid barrier zone of this invention belong to the same mechanistic partitioning within a single integral three-dimensional interconnected network structure, eliminating the need for layering different materials to form a spatially layered composite structure. Therefore, this invention can achieve progressive oil fume capture through adhesion, condensation, and barrier while maintaining the overall structural stability of the filter layer.

[0021] This invention creates a carbon dioxide gas microenvironment in the grease deposition area. This carbon dioxide gas microenvironment helps reduce the risk of combustion in the grease deposition area. This effect is not equivalent to making an absolute fireproof or fire-extinguishing commitment to the filter layer, but rather, together with the V0-level flame retardant properties of the expanded fiber material, it improves the operational safety of the filter layer in medium- and high-temperature oil fume environments.

[0022] The expanded fiber filter layer containing solid carbon dioxide particles in this invention achieves a 99.76% interception efficiency for 0.5μm oil mist particles and a 99.5% grease separation rate under test conditions of a face wind speed of 1.0 m / s, an oil fume temperature of 180℃, and an actual solid carbon dioxide particle encapsulation content of approximately 4 wt%. After 1000 hours of continuous operation, the wind resistance increase is only 2.1%, and the local temperature drop on the fiber surface is 15℃–30℃. These results demonstrate that this invention can improve the pre-collection capability of oil fumes while maintaining a low wind resistance increase. Attached Figure Description

[0023] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0024] Figure 1 A schematic diagram showing the particle size distribution of Chinese cooking fumes and the range of filtration targets; Figure 2 The curves showing the filtration efficiency at each stage as a function of key parameters; Figure 3 This is a contour map of oil-oil separation degree. Figure 4 A comparison chart of key performance characteristics of different filter media; Figure 5 This is a graph showing the change in air resistance during the continuous operation of the expanded fiber filter layer. Figure 6 The curves showing the relationship between filtration efficiency and particle size at different wind velocities; Figure 7 A breakdown diagram showing the contribution of different filtration actions to the overall capture efficiency; Figure 8 This is a comparison chart of the filtration performance of the expanded fiber filter layer before and after solid carbon dioxide doping. Detailed Implementation

[0025] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0026] The present invention will be further described below with reference to the embodiments and accompanying drawings. The following embodiments are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or conventional adjustments made by those skilled in the art to the type of substrate, the number of fiber layers, the particle size of solid carbon dioxide particles, the actual encapsulation amount of solid carbon dioxide particles, and the installation method without departing from the technical concept of the present invention should all fall within the scope of protection of the present invention.

[0027] It should be noted that, Figures 1 to 8 This document is provided to aid in understanding the scope of oil fume filtration, performance test results, operational stability, and application installation methods of this invention. The accompanying drawings are only used to illustrate the relative relationships between technical features, data trends, or installation location relationships, and do not represent the actual microstructure of the expanded fibers, the actual number of solid carbon dioxide particles, the actual proportion of pores, or the precise distribution of the oil fume flow field.

[0028] Please see Figure 1 This diagram illustrates the particle size distribution of Chinese cooking fumes and the range of objects to be filtered. Figure 1This is to illustrate that the small-sized condensed oil fume components and submicron oil mist particles in Chinese cooking fumes are the main filtration targets of this embodiment. The subsequent performance test selects 0.5μm oil mist particles as the evaluation target in order to verify the pre-capture capability of the filter layer for particles near the critical penetration particle size.

[0029] In this invention, the integral three-dimensional interconnected mesh structure refers to an integral filtration structure formed by interlacing and fixing the same type of expanded fiber material. The integral three-dimensional interconnected mesh structure can be formed by interlacing multiple layers of expanded fibers, but its primary surface adhesion interception zone, secondary nanocapillary condensation adsorption zone, and tertiary gradient microporous rigid barrier zone are not formed by stacking different materials. Instead, they are mechanistic partitions within the same filtration layer, formed by the micron-level uneven morphology of the fiber surface, the nano-level interconnected capillary channels inside the fiber, and the deep gradient micropores formed by fiber interlacing.

[0030] In this invention, the semi-closed coating structure refers to a partially encapsulated area formed by the fiber substrate portion, which is in a softened, expanded, or stretched state, surrounding the solid carbon dioxide particles after they enter the nanoscale interconnected capillary channels or deep gradient micropores of the expanded fiber. This semi-closed coating structure is not a completely sealed structure; it still retains micropores, microcracks, or fiber gaps. This structure can limit the concentrated release of solid carbon dioxide particles during preparation or initial use, and allows the solid carbon dioxide particles to gradually sublimate under the influence of hot airflow.

[0031] In this invention, the actual encapsulation amount refers to the proportion of the mass of solid carbon dioxide particles retained in the expanded fiber filter layer to the mass of the expanded fiber material after expansion, stretching, and interleaving. Since some solid carbon dioxide particles sublimate during feeding, dispersion, and expansion, the actual encapsulation amount is usually lower than the amount of material fed. The actual encapsulation amount can be determined by the mass change before and after preparation, the mass released by thermogravimetric analysis, or an equivalent mass balance method.

[0032] Example 1: This example prepares a PET expanded fiber filter layer with an actual encapsulation amount of 2wt% of solid carbon dioxide particles.

[0033] This embodiment uses food-grade modified PET as the substrate. 1.0 wt% of a fatty acid ester surface modifier is added to the food-grade modified PET. The fatty acid ester surface modifier is used to improve the affinity of the fiber surface for oil mist particles. The substrate is melted at 280°C and extruded through an extruder to form nascent fibers.

[0034] Before adding the solid carbon dioxide particles, the particles are pre-cooled to -78.5°C. The particle size of the solid carbon dioxide particles is controlled to be 15μm–25μm. The pre-cooled solid carbon dioxide particles are added to the substrate melt or the nascent fiber expansion zone through a low-temperature feed port. The amount of solid carbon dioxide particles fed is adjusted according to the sublimation loss so that the actual encapsulation weight after preparation is 2wt% of the mass of the expanded fiber material.

[0035] Nascent fibers containing solid carbon dioxide particles are expanded at a temperature of 200°C. During expansion, nanoscale interconnected capillary channels and microporous structures are formed inside the fiber matrix. Some of the solid carbon dioxide particles enter the nanoscale interconnected capillary channels or deep gradient micropores under the action of airflow and melt shearing.

[0036] The expanded fibers containing solid carbon dioxide particles were stretched and shaped at a stretch ratio of 5:1. The stretching process oriented and connected the capillary channels inside the fibers, and formed a local coating area on the periphery of the solid carbon dioxide particles in the fiber matrix. This local coating area is connected with the surrounding capillary channels, micropores and fiber gaps, forming a semi-closed coating structure.

[0037] The stretched and shaped expanded fibers containing solid carbon dioxide particles are laid in 7 layers in an alternating pattern and fixed by hot pressing to obtain an integral three-dimensional through-mesh expanded fiber filter layer.

[0038] Example 2: This example prepares a PET expanded fiber filter layer with an actual encapsulation amount of 4wt% solid carbon dioxide particles.

[0039] This embodiment uses food-grade modified PET as the substrate. 1.0 wt% of a fatty acid ester surface modifier is added to the food-grade modified PET. The substrate is melted at 280°C and extruded through an extruder to form nascent fibers.

[0040] Before adding the solid carbon dioxide particles, pre-cool them to -78.5℃. The particle size of the solid carbon dioxide particles is controlled to be 15μm–25μm. The pre-cooled solid carbon dioxide particles are then added to the substrate melt or the nascent fiber expansion zone through a low-temperature feed port. The amount of solid carbon dioxide particles added is 5wt% of the mass of the expanded fiber material. After adding the solid carbon dioxide particles, the dispersion time is 10 minutes.

[0041] Nascent fibers containing solid carbon dioxide particles are expanded at a temperature of 200°C. During expansion, nanoscale interconnected capillary channels and microporous structures are formed inside the fiber substrate. Some of the solid carbon dioxide particles enter the nanoscale interconnected capillary channels or deep gradient micropores under the action of airflow and melt shear. Because the solid carbon dioxide particles undergo partial sublimation in this process, the actual encapsulation weight after preparation is approximately 4 wt% of the mass of the expanded fiber material.

[0042] The solid carbon dioxide particles are not simply attached to the outer surface of the filter layer, but rather at least partially enter the nanoscale interconnected capillary channels inside the expanded fibers or are located near the deep gradient micropores formed by the interlacing of fibers. This embedding method allows the solid carbon dioxide particles to gradually sublimate and be released from inside the filter layer under the action of hot airflow from the oil fume, thereby creating a low-temperature condensation environment and a carbon dioxide gas microenvironment on the fiber surface, near the capillary channels, and in the grease deposition area.

[0043] The expanded fibers containing solid carbon dioxide particles were stretched and shaped at a stretch ratio of 5:1. The stretching process oriented and connected the capillary channels within the fibers, creating a localized coating region around the solid carbon dioxide particles. This localized coating region communicates with the surrounding capillary channels, micropores, and fiber gaps, forming a semi-closed coating structure. The thickness of the semi-closed coating structure was controlled within the range of 0.5 μm–3 μm.

[0044] The stretched and shaped expanded fibers containing solid carbon dioxide particles are laid in 7 layers in an alternating pattern and fixed by hot pressing to obtain an integral three-dimensional through-mesh expanded fiber filter layer containing solid carbon dioxide particles.

[0045] Example 3: This example prepares a PET expanded fiber filter layer with an actual encapsulation amount of 6wt% solid carbon dioxide particles.

[0046] The substrate, melt extrusion conditions, expansion temperature, draw ratio, number of staggered layers, and fixing method in this embodiment are basically the same as in Example 2. The difference is that this embodiment increases the amount of solid carbon dioxide particles fed in, so that the actual encapsulation amount of the prepared solid carbon dioxide particles is 6 wt% of the mass of the expanded fiber material.

[0047] In the filter layer obtained in this embodiment, solid carbon dioxide particles are dispersed and encapsulated in nanoscale interconnected capillary channels and deep gradient micropores, and the outer periphery of the particles is formed by a semi-closed encapsulation structure of expanded fiber material.

[0048] Example 4: This example prepares a PET expanded fiber filter layer with an actual encapsulation amount of 8wt% solid carbon dioxide particles.

[0049] The substrate, melt extrusion conditions, expansion temperature, draw ratio, number of interleaved layers, and fixing method in this embodiment are basically the same as in Example 2. The difference is that this embodiment further increases the amount of solid carbon dioxide particles fed in, so that the actual encapsulation amount of the prepared solid carbon dioxide particles is 8 wt% of the mass of the expanded fiber material.

[0050] This embodiment illustrates the filter layer performance under a relatively high actual encapsulation volume of solid carbon dioxide particles. While this embodiment is still a implementation of the technical solution of this invention, its initial air resistance is relatively high, therefore it is not a preferred embodiment of this invention.

[0051] Example 5: This example prepares a PPS expanded fiber filter layer containing solid carbon dioxide particles for use in commercial kitchen exhaust equipment.

[0052] This embodiment uses food-grade modified PPS as the substrate. 1.5 wt% of a fatty acid ester surface modifier is added to the food-grade modified PPS. The substrate is melt-extruded at 320°C to form nascent fibers.

[0053] At an expansion temperature of 200℃, solid carbon dioxide particles pre-cooled to -78.5℃ with a particle size of 20μm–30μm are added to the substrate melt or the expansion zone of the nascent fiber at a feed rate of 5wt%, and dispersed for 12 minutes. Subsequently, the nascent fiber containing the solid carbon dioxide particles is expanded at high temperature, which forms nanoscale interconnected capillary channels and deep gradient micropores inside the fiber, and allows some of the solid carbon dioxide particles to enter the above-mentioned channels or micropores.

[0054] The expanded fibers were stretched and shaped at a stretch ratio of 6:1. After stretching and shaping, the solid carbon dioxide particles were semi-enclosed by the expanded fiber material. Subsequently, the stretched and shaped fibers were laid in eight layers in an alternating pattern and fixed by ultrasonic spot welding to obtain an integral three-dimensional through-mesh expanded fiber filter layer.

[0055] The filter layer obtained in this embodiment has a porosity ε of 90%, a specific surface area S of 38 m² / g, an interleaved layer number N of 8 layers, and an actual encapsulation amount of solid carbon dioxide particles of approximately 5 wt%. This filter layer is suitable for commercial kitchen exhaust conditions with a face wind speed of 1.2 m / s–1.5 m / s and an oil fume temperature of 180℃–220℃.

[0056] Comparative Example 1: This comparative example prepared a basic expanded fiber filter layer that does not contain solid carbon dioxide particles.

[0057] This comparative example uses food-grade modified PET as the substrate. 1.0 wt% of a fatty acid ester surface modifier was added to the food-grade modified PET. The substrate was melted at 280°C and extruded through an extruder to form nascent fibers.

[0058] The nascent fibers were fed into a 190°C expansion zone for 20 seconds. During the expansion process, 0.3 wt% azodicarbonamide was added to the substrate as a foaming agent. Upon thermal decomposition, the foaming agent formed micropores and nanoscale interconnected capillary channels within the fibers. Due to the varying degrees of expansion in different regions of the fiber substrate during thermal expansion, a micron-level uneven morphology was formed on the fiber surface.

[0059] The expanded fibers were stretched and shaped at a stretch ratio of 5:1. During the stretching process, some of the capillary channels inside the fiber were elongated and connected along the axial direction, and the pore size of some micropores was further refined, thereby forming deep gradient micropores. After stretching, the fibers were shaped at about 170°C to stabilize the surface morphology and internal capillary channel structure.

[0060] The stretched and shaped expanded fibers are laid in 7 layers in an alternating pattern and fixed by hot pressing to obtain an integral three-dimensional through-mesh expanded fiber filter layer that does not contain solid carbon dioxide particles.

[0061] This comparative example is used to illustrate that, under the same or similar expanded fiber structure conditions, without the presence of solid carbon dioxide particles, the filter layer cannot form a low-temperature condensation environment and a carbon dioxide gas microenvironment resulting from the slow release and sublimation of solid carbon dioxide.

[0062] Performance Testing: Unless otherwise specified, the following performance testing conditions are: face wind speed 1.0 m / s, oil fume temperature 180℃, test particle size 0.5 μm, and the effective filtration area of ​​each sample is the same. During testing, the oil mist particle concentration upstream and downstream of the filter layer are measured separately, and the interception efficiency of 0.5 μm oil mist particles is calculated. Grease separation degree is calculated by collecting the amount of grease trapped by the filter layer and the amount of residual grease downstream. Wind resistance is measured by the pressure difference between the upstream and downstream of the filter layer. The wind resistance increase over 1000 hours is calculated by the change in wind resistance before and after continuous operation.

[0063] The particle size of solid carbon dioxide particles can be 5μm–50μm. When the particle size is less than 5μm, the sublimation loss of solid carbon dioxide particles during feeding, dispersion, and expansion is relatively large, and it is not conducive to forming a stable semi-closed coating structure. When the particle size is greater than 50μm, solid carbon dioxide particles have difficulty entering the vicinity of nanoscale interconnected capillary channels or deep gradient micropores, which easily causes local blockage and increases the initial air resistance of the filter layer. Therefore, this invention controls the particle size of solid carbon dioxide particles to 5μm–50μm, and more preferably 10μm–30μm.

[0064] Please see Figure 2 This figure shows the curves of how the filtration efficiency at each stage changes with key parameters. Figure 2This is used to illustrate the influence trends of parameters such as specific surface area, capillary pore size, number of staggered layers, and deep micropore size on the primary surface adhesion interception zone, the secondary nanocapillary condensation adsorption zone, and the tertiary gradient microporous rigid barrier zone. These three filtration processes participate in the capture sequentially as the airflow passes through the same integral three-dimensional interconnected mesh structure, rather than existing in isolation.

[0065] In performance evaluation, the overall filtration efficiency η_f can be characterized by a cascade filtration relationship. η_f = 1 - (1 - η1)(1 - η2)(1 - η3), where η_f is the overall filtration efficiency of the expanded fiber filter layer, η1 is the adhesion efficiency of the primary surface adhesion interception zone, η2 is the capillary condensation adsorption efficiency of the secondary nanocapillary condensation adsorption zone, and η3 is the barrier efficiency of the tertiary gradient microporous rigid barrier zone. This formula is used to illustrate the cascade superposition relationship of the three filtration actions and is not intended to limit the filtration efficiency of each stage to a fixed value.

[0066] Please see Figure 3 This figure is a contour map of oil separation degree. Figure 3 This is used to illustrate that the overall filtration efficiency and the ability of oil droplet coagulation, diversion, and dripping jointly affect the degree of grease separation; when the filter layer can promote the timely coagulation of captured grease and diversion along the fiber channels, the grease separation effect is more stable.

[0067] In one embodiment, the grease separation degree η_total can be characterized by the following formula: η_total = η_f·δ, where η_total is the grease separation degree, η_f is the overall filtration efficiency, and δ is the grease agglomeration and dripping correction coefficient. The grease agglomeration and dripping correction coefficient δ is used to characterize the effect of grease agglomeration, diversion, and gravity dripping of captured grease in the filter layer on the grease separation effect; preferably, δ ≥ 0.99.

[0068] Please see Figure 7 This figure is a breakdown of the contribution of different filtration processes to the overall capture efficiency. Figure 7 This is used to help explain the contribution of surface adhesion, capillary coagulation, and microporous barrier effects in the basic expanded fiber structure, as well as the low-temperature condensation and local gas disturbance effects after the introduction of solid carbon dioxide particles, to the overall capture effect.

[0069] When solid carbon dioxide particles are dispersed and encapsulated in the expanded fiber filter layer, the solid carbon dioxide particles gradually sublimate and absorb heat, forming a low-temperature condensation environment. Simultaneously, the carbon dioxide gas creates localized gas disturbances in the grease deposition area. The filtration effect containing solid carbon dioxide particles can be characterized by the following formula: η_co2 = η_base + Δη_cond + Δη_turb, where η_co2 is the overall efficiency of the filter layer containing solid carbon dioxide particles, η_base is the overall efficiency of the basic expanded fiber filter layer without solid carbon dioxide particles, Δη_cond is the efficiency increment brought about by the low-temperature condensation environment, and Δη_turb is the efficiency increment brought about by the localized gas disturbance promoting oil droplet coagulation and flow guidance. The above formula is used to illustrate the contribution relationship of different effects to the overall filtration effect and is not intended to limit the parameters to a fixed proportional relationship.

[0070] Table 1 Sample preparation parameters Comparative Example 1 Solid carbon dioxide-free basic filter layer PET — 0wt% 190℃ 5:1 7th floor Hot pressing Example 1 Low-doped filter layer PET 15μm–25μm 2wt% 200℃ 5:1 7th floor Hot pressing Example 2 Preferred filter layer PET 15μm–25μm 4wt% 200℃ 5:1 7th floor Hot pressing Example 3 Highly doped filter layer PET 15μm–25μm 6wt% 200℃ 5:1 7th floor Hot pressing Example 4 Highly doped boundary filter layer PET 15μm–25μm 8wt% 200℃ 5:1 7th floor Hot pressing Example 5 Commercial high temperature filter layer PPS 20μm–30μm Approximately 5wt% 200℃ 6:1 8 floors Ultrasonic spot welding

[0071] As shown in Table 1, Examples 1 to 4 all used PET substrate, and expanded fiber filter layers with different doping levels were formed by adjusting the actual encapsulation amount of solid carbon dioxide particles. Example 5 used PPS substrate to adapt to the exhaust conditions of commercial kitchens with higher oil fume temperatures and larger air volumes.

[0072] Table 2 Filter layer structural parameters Comparative Example 1 85% 28m² / g 30nm–500nm 0.3μm–0.4μm — ≥280℃ V0 Example 2 85% 30m² / g 30nm–500nm 0.3μm–0.4μm 0.5μm–3μm ≥280℃ V0 Example 5 90% 38m² / g 30nm–500nm 0.3μm–0.4μm 0.5μm–3μm ≥350℃ V0

[0073] As shown in Table 2, both Examples 2 and 5 formed micron-level uneven morphology on the fiber surface, nanoscale interconnected capillary channels inside the fiber, and deep gradient micropores. Solid carbon dioxide particles were embedded in at least one of the nanoscale interconnected capillary channels and deep gradient micropores, forming a semi-closed encapsulation structure with expanded fiber material. This semi-closed encapsulation structure restricts the one-time release of solid carbon dioxide particles and allows them to gradually sublimate under the action of hot airflow from the oil fume.

[0074] When the porosity of the expanded fiber filter layer is below 75%, the resistance to airflow through the filter layer tends to increase; when the porosity is above 95%, the deep gradient micropores formed by the interwoven fibers reduce their ability to block submicron oil mist particles. When the specific surface area is below 20 m² / g, the contact area for capturing oil mist particles on the fiber surface is insufficient; when the specific surface area is above 60 m² / g, the fiber structure is too dense, and the increase in wind resistance during long-term operation tends to increase. Therefore, this invention controls the porosity ε to 75%–95% and the specific surface area S to 20–60 m² / g, and further preferably the porosity ε to be 82%–92% and the specific surface area S to be 28–45 m² / g.

[0075] Table 3 Results of Solid Carbon Dioxide Particle Slow Release and Temperature Drop Tests Comparative Example 1 0wt% 180℃ — 0℃ No sustained release formed Example 1 2wt% 180℃ Measurable sustained release 8℃–15℃ Low temperature drop Example 2 4wt% 180℃ Approximately 500 hours 15℃–30℃ The sustained release and temperature drop are relatively balanced. Example 3 6wt% 180℃ 400h–600h range 25℃–35℃ Temperature drop increases but wind resistance rises Example 4 8wt% 180℃ 400h–600h range 30℃–40℃ High temperature drop but large initial wind resistance

[0076] As shown in Table 3, solid carbon dioxide particles, after being encapsulated by a semi-enclosed coating structure, can gradually sublimate and release under constant temperature conditions of 180℃. The 50% cumulative release half-life in Example 2 is approximately 500 hours, indicating that the solid carbon dioxide particles are not released all at once during the initial heating stage, but rather slowly under the action of the semi-enclosed coating structure. As the actual encapsulation amount of solid carbon dioxide particles increases, the local temperature drop of the filter layer increases accordingly.

[0077] The local temperature reduction of 10℃–40℃ mainly corresponds to the implementation method where the actual encapsulation amount of solid carbon dioxide particles is not less than about 4wt%. When the actual encapsulation amount is 2wt%, the filter layer can still form a certain low-temperature condensation environment, but the local temperature drop is relatively low. As the actual encapsulation amount of solid carbon dioxide particles increases, the local temperature drop increases, but the initial air resistance of the filter layer may also increase accordingly. Therefore, the present invention further preferably uses an actual encapsulation amount of solid carbon dioxide particles of 2wt%–6wt%, more preferably about 4wt%.

[0078] Table 4 Performance test results of the filter layer under different actual encapsulation amounts of solid carbon dioxide particles Comparative Example 1 0wt% 99.37% 82Pa 2.8% 0℃ Example 1 2wt% 99.52% 83Pa 2.5% 8℃–15℃ Example 2 4wt% 99.76% 86Pa 2.1% 15℃–30℃ Example 3 6wt% 99.78% 91Pa 2.0% 25℃–35℃ Example 4 8wt% 99.79% 98Pa 2.0% 30℃–40℃

[0079] As shown in Table 4, with the increase in the actual encapsulation amount of solid carbon dioxide particles, the local temperature drop of the filter layer increases, and the interception efficiency of 0.5μm oil mist particles improves. In Example 2, the actual encapsulation amount of solid carbon dioxide particles was 4wt%, the interception efficiency of 0.5μm oil mist particles reached 99.76%, the wind resistance increase over 1000 hours was 2.1%, and the initial wind resistance was 86Pa. Compared with Comparative Example 1, Example 2 shows improvements in both interception efficiency and long-term wind resistance stability.

[0080] Table 4 also shows that when the actual encapsulation amount of solid carbon dioxide particles increases to 6wt% and 8wt%, the local temperature drop of the filter layer continues to increase, but the improvement in the interception efficiency of 0.5μm oil mist particles slows down, while the initial wind resistance increases significantly. Therefore, a higher actual encapsulation amount of solid carbon dioxide particles is not necessarily better. Considering the interception efficiency, initial wind resistance, and the wind resistance increase over 1000 hours, the optimal actual encapsulation amount of solid carbon dioxide particles is 2wt%–6wt%, and more preferably around 4wt%.

[0081] Please see Figure 5 This figure shows the change in air resistance during the continuous operation of the expanded fiber filter layer. Figure 5Corresponding to the 1000h wind resistance increase data in Table 4, this illustrates that when the actual packaging amount of solid carbon dioxide particles is moderate, the filter layer can maintain a low wind resistance growth trend under long-term oil fume conditions; when the actual packaging amount is too high, the initial wind resistance increases and the overall balance decreases.

[0082] Table 5. Comparison of overall performance between Example 2 and Comparative Example 1 0.5μm oil mist particle interception efficiency 99.37% 99.76% Low-temperature condensation environment increases the probability of oil mist capture. Oil separation 99.1% 99.5% Enhanced oil droplet coagulation and diffusing capacity Initial wind resistance 82Pa 86Pa Initial wind resistance increased slightly 1000h drag increase 2.8% 2.1% Long-term congestion trend decreases Local temperature drop 0℃ 15℃–30℃ Formation of a low-temperature condensation environment

[0083] As shown in Table 5, under the same test conditions, compared with Comparative Example 1, Example 2 improved the interception efficiency of 0.5μm oil mist particles from 99.37% to 99.76%, the grease separation rate from 99.1% to 99.5%, and the wind resistance increase over 1000 hours from 2.8% to 2.1%. This result indicates that after the semi-enclosed coating structure slowly releases and sublimates, solid carbon dioxide particles can form a low-temperature condensation environment in a localized area of ​​the filter layer, making it easier for condensable oil fume components to condense on the fiber surface or within the capillary channels. Simultaneously, the localized gas disturbance generated by carbon dioxide vaporization promotes oil droplet coalescence and gravity-guided dripping, thereby reducing the tendency for the filter layer to clog during long-term operation. The performance differences corresponding to Table 5 can be combined with… Figure 8 To understand.

[0084] Please see Figure 4 This figure is a comparison chart of the key performance characteristics of different filter media. Figure 4 The solid carbon dioxide-doped expanded fiber filter layer used to illustrate this embodiment has a more balanced overall performance compared with ordinary metal mesh, ordinary chemical fiber filter mesh or conventional porous filter media in terms of 0.5μm oil mist particle interception efficiency, grease separation degree, 1000h wind resistance increase and local temperature drop.

[0085] Please see Figure 8 This figure shows a comparison of the filtration performance of the expanded fiber filter layer before and after solid carbon dioxide doping. Figure 8 This corroborates Table 5, demonstrating that after solid carbon dioxide particles are slowly released and sublimated through a semi-enclosed coating structure, the low-temperature condensation environment and local gas disturbance can jointly improve oil mist particle capture, grease separation, and long-term wind resistance stability.

[0086] Table 6 Comparison of Residential Range Hood Solutions and Commercial Kitchen Exhaust Solutions Representative sample Example 2 Example 5 Substrate Food-grade modified PET Food-grade modified PPS Actual encapsulation volume of solid carbon dioxide particles Approximately 4wt% Approximately 5wt% Number of layers 7th floor 8 floors Fixing method Hot pressing Ultrasonic spot welding Headwind speed 1.0m / s 1.2m / s–1.5m / s Oil fume temperature 180℃ 180℃–220℃ 0.5μm oil mist particle interception efficiency 99.76% ≥99.8% Oil separation 99.5% ≥99.6%

[0087] As shown in Table 6, Example 2 is suitable for common oil fume conditions in household range hoods, while Example 5 is suitable for conditions with larger air volume and higher oil fume temperature in commercial kitchen exhaust equipment. Food-grade modified PET substrate is used to balance processability, low wind resistance, and filtration efficiency under household range hood conditions; food-grade modified PPS substrate is used to improve heat resistance stability under commercial kitchen exhaust conditions.

[0088] Filtration Method Example: This example illustrates the filtration method of the expanded fiber filter layer obtained in Example 2.

[0089] During operation, the oil fume airflow first enters the air inlet side of the expanded fiber filter layer. Some of the oil mist particles in the oil fume airflow come into contact with the micron-level unevenness of the fiber surface. The oleophilic regions on the fiber surface have an adhesive effect on the oil mist particles, causing some of the oil mist particles to remain on the fiber surface.

[0090] After being intercepted by surface adhesion, the oil fume airflow continues to enter the nanoscale interconnected capillary channels inside the fiber. The nanoscale interconnected capillary channels generate capillary condensation and adsorption on residual gaseous oil fumes and free oil mist particles, causing some oil fume components to condense and remain in the capillary channels.

[0091] After being adsorbed by capillary condensation, the oil fume airflow continues to pass through deep gradient micropores formed by interwoven fibers. These deep gradient micropores block residual oil mist particles, reducing the probability of submicron oil mist particles penetrating the filter layer and entering the fan cavity.

[0092] When the hot airflow of cooking fumes acts on the expanded fiber filter layer containing solid carbon dioxide particles, the solid carbon dioxide particles gradually sublimate and absorb heat through the semi-enclosed coating structure, forming a low-temperature condensation environment in a localized area of ​​the filter layer. This low-temperature condensation environment makes it easier for condensable oil fume components to condense on the fiber surface or within the capillary channels. The carbon dioxide gas generated by the sublimation of the solid carbon dioxide particles creates localized gas disturbances in the grease deposition area, promoting oil droplet coalescence and gravity-guided dripping, and forming a carbon dioxide gas microenvironment.

[0093] In this embodiment, the face velocity of the oil fume airflow can be 0.5 m / s–2.0 m / s, and the oil fume temperature can be 80℃–240℃. Within the above operating range, the expanded fiber filter layer can pre-capture condensable oil fume components and submicron oil mist particles, and reduce the risk of grease entering the fan cavity.

[0094] Please see Figure 6 This figure shows the relationship between filtration efficiency and particle size at different wind speeds. Figure 6 This is to illustrate that within the oncoming wind speed range of 0.5 m / s–2.0 m / s, the filter layer can still maintain a high collection efficiency for oil mist particles around 0.5 μm. When the wind speed increases, the residence time of particles in the filter layer is shortened. Therefore, it is necessary to maintain the collection effect through fiber surface adhesion, capillary agglomeration, deep microporous barrier, and low-temperature condensation environment formed by solid carbon dioxide particles.

[0095] Application Example 1: This example illustrates the application of the expanded fiber filter layer obtained in Example 2 in a household range hood.

[0096] In household range hoods, the expanded fiber filter layer is positioned between the air inlet and the fan cavity, serving as a pre-filter unit. The expanded fiber filter layer can be installed in the traditional filter location or within an independent support frame behind the air inlet. The edges of the filter layer can be secured with clips, pressure frames, or sealing rings to reduce the amount of cooking fumes bypassing the filter layer and directly entering the fan cavity.

[0097] When installing the filter layer, its air inlet side faces the direction in which the fumes enter, and its air outlet side faces the inner cavity of the fan. An oil guide edge or oil collection groove can be installed at the lower edge of the filter layer to allow oil droplets condensed within the filter layer to be discharged downwards along the direction of gravity. The oil collection groove can be connected to the existing oil collection cup of the range hood, or it can be installed separately as a detachable oil collection structure.

[0098] During operation, the oil fume airflow first passes through the expanded fiber filter layer. This filter layer pre-captures condensable oil fume components and submicron oil mist particles. Solid carbon dioxide particles gradually sublimate under the influence of the hot oil fume airflow; the low-temperature condensation environment promotes the condensation of oil fume components, and the disturbance of carbon dioxide gas promotes oil droplet coalescence and guided dripping. Through this process, the expanded fiber filter layer reduces the amount of grease entering the fan casing, impeller, and inner cavity, thereby reducing the risk of oil accumulation in the fan's internal cavity and extending the cleaning and maintenance cycle.

[0099] Application Example 2: This example illustrates the application of the expanded fiber filter layer obtained in Example 5 in a commercial kitchen exhaust system.

[0100] In commercial kitchen exhaust systems, the expanded fiber filter layer can be installed within the exhaust hood, pre-filter box, or airflow channel at the front end of the fan. For high-volume applications, multiple filter layer units can be installed side-by-side according to the cross-sectional area of ​​the exhaust channel. Adjacent filter layer units should maintain a sealed connection to prevent the oil fume from flowing around the filter. A flow equalization plate can be installed upstream of the filter layer to make the airflow distribution into the filter layer more uniform.

[0101] When commercial kitchen exhaust systems are in operation, the temperature of the oil fume airflow can range from 180℃ to 220℃, and the oncoming wind speed can range from 1.2 m / s to 1.5 m / s. Using the PPS substrate filter layer obtained in Example 5, the filter layer achieves an interception efficiency of over 99.8% for 0.5 μm oil mist particles and an grease separation rate of over 99.6%. These results demonstrate that the filter layer is suitable for high-flow-rate, high-concentration, and medium-to-high-temperature oil fume conditions.

[0102] In this invention, the solid carbon dioxide particles gradually sublimate under the influence of hot airflow from oily fumes, creating a carbon dioxide gas microenvironment in the grease deposition area. This carbon dioxide gas microenvironment helps reduce the risk of combustion in the grease deposition area. This effect is not equivalent to making an absolute fireproof, fire-extinguishing, or completely flame-retardant commitment to the filter layer, but rather, together with the V0-level flame-retardant performance of the expanded fiber material, it improves the operational safety of the filter layer in medium- and high-temperature oily fume environments.

[0103] In the implementation method, the gas after the solid carbon dioxide particles sublimate can also form a weakly acidic local environment with the water vapor in the oil fumes. This local environment can play a certain role in regulating the acid-base environment of the oil deposition area.

[0104] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. An expanded fiber filter layer for purifying oil fumes, characterized in that, The expanded fiber filter layer is composed of expanded fiber material, which is laid out in an interlaced manner and fixed to form an integral three-dimensional interconnected mesh structure. The expanded fiber material has a micron-level uneven surface morphology, a nano-level interconnected capillary channel inside the fiber, and a deep gradient micropore formed by the interlacing of fibers. Solid carbon dioxide particles are dispersed and encapsulated in the expanded fiber filter layer. The solid carbon dioxide particles are embedded in at least one of the nano-level interconnected capillary channels and the deep gradient micropores, and the outer periphery of the solid carbon dioxide particles is formed by a semi-closed coating structure of expanded fiber material. Under the action of hot airflow of oil fume, the semi-closed coating structure causes the solid carbon dioxide particles to gradually sublimate, forming a low-temperature condensation environment and a carbon dioxide gas microenvironment in a local area of ​​the expanded fiber filter layer. The micron-level uneven surface morphology of the fiber forms a primary surface adhesion interception. The fiber contains a secondary nanocapillary condensation and adsorption zone formed by nanoscale interconnected capillary channels within the fiber, and a tertiary gradient micropore rigid barrier zone formed by deep gradient micropores. The primary surface adhesion interception zone, the secondary nanocapillary condensation and adsorption zone, and the tertiary gradient micropore rigid barrier zone are mechanistic partitions formed by progressive microstructural scales within the same integral three-dimensional interconnected network structure, rather than spatial layered composite structures formed by stacking different materials. After melt extrusion, high-temperature expansion, and stretching, the expanded fiber material forms a micron-level uneven morphology on the fiber surface, nanoscale interconnected capillary channels within the fiber, and deep gradient micropores. Pre-cooled solid carbon dioxide particles enter at least one of the nanoscale interconnected capillary channels and deep gradient micropores during high-temperature expansion or stretching, and the expanded fiber material forms the semi-closed encapsulation structure.

2. The expanded fiber filter layer for oil fume purification according to claim 1, characterized in that, The porosity ε of the expanded fiber filter layer is 75%–95%, the specific surface area S is 20–60 m² / g, and the number of staggered layers N is 4–12; the pore size of the nanoscale through capillary channel is 30 nm–500 nm, and the pore size of the deep gradient micropore is 0.2 μm–0.6 μm.

3. The expanded fiber filter layer for oil fume purification according to claim 2, characterized in that, The porosity ε of the expanded fiber filter layer is 82%–92%, the specific surface area S is 28–45 m² / g, and the number of staggered layers N is 6–8; the pore size of the deep gradient micropores is 0.3 μm–0.4 μm.

4. The expanded fiber filter layer for oil fume purification according to claim 1, characterized in that, The expanded fiber material uses food-grade modified PET or food-grade modified PPS as the base material; wherein, the thermal decomposition temperature of the food-grade modified PET base material is ≥280℃, the thermal decomposition temperature of the food-grade modified PPS base material is ≥350℃, and the flame retardancy rating of the expanded fiber material is V0.

5. The expanded fiber filter layer for oil fume purification according to claim 1, characterized in that, The solid carbon dioxide particles have a particle size of 5μm–50μm, and the actual amount of solid carbon dioxide particles encapsulated in the expanded fiber filter layer is 1wt%–8wt% of the mass of the expanded fiber material.

6. The expanded fiber filter layer for oil fume purification according to claim 5, characterized in that, The solid carbon dioxide particles have a particle size of 10μm–30μm, and the actual encapsulation amount of the solid carbon dioxide particles is 2wt%–6wt%.

7. The expanded fiber filter layer for oil fume purification according to claim 1, characterized in that, The thickness of the semi-enclosed coating structure is 0.5μm–3μm; under the working temperature of 80℃–240℃ for oil fume, the solid carbon dioxide particles are slowly released and sublimated by the semi-enclosed coating structure, with a cumulative release half-life of 400h–600h for 50%, and the local temperature of the expanded fiber filter layer is reduced by 10℃–40℃.

8. A method for purifying oil fumes using expanded fiber filtration, characterized in that, The expanded fiber filter layer for oil fume purification according to any one of claims 1 to 7 is used. The filtration method includes: allowing oil fume airflow to enter the expanded fiber filter layer; adhering and intercepting oil mist particles in the oil fume airflow through the micron-level uneven morphology of the fiber surface; capillary condensation and adsorption of residual gaseous oil fume and free oil mist particles after adhesion and interception through the nano-level interconnected capillary channels inside the fiber; blocking the residual oil mist particles after capillary condensation and adsorption through deep gradient micropores; causing the solid carbon dioxide particles to gradually sublimate and absorb heat through a semi-closed coating structure under the action of the hot oil fume airflow, and forming a low-temperature condensation environment in a local area of ​​the expanded fiber filter layer, so that the condensable oil fume components condense on the fiber surface or in the capillary channels; the carbon dioxide gas generated by the sublimation of the solid carbon dioxide particles forms a local gas disturbance and carbon dioxide gas microenvironment in the grease deposition area, the local gas disturbance promotes oil droplet coalescence and gravity-guided dripping, and the carbon dioxide gas microenvironment is used to reduce the combustion risk in the grease deposition area.

9. The application of an expanded fiber filter layer for oil fume purification as described in any one of claims 1 to 7 in a range hood or commercial kitchen exhaust system, characterized in that, The expanded fiber filter layer is disposed between the air inlet of the range hood and the inner cavity of the fan, serving as a pre-filter unit to capture condensable oil fume components and submicron oil mist particles before the oil fumes enter the inner cavity of the fan.

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