纖維濾材3D模擬於空氣過濾效能之研究

Abstract

熔噴不織布是由超細纖維堆疊構成，具有多孔性及孔徑分布範圍廣泛的特性，且其流動孔道相互連通，可減緩因孔洞阻塞造成壓差增加的情形。由大量纖維組成的結構，可供捕集顆粒的表面積廣大，具備有效捕捉汙染物的能力。對於濾材的效能通常考量兩個重要參數，分別是滲透度及過濾效率，過去已有許多研究預測纖維濾材在這兩方面的過濾效能，考量不同纖維排列型態推導理論模型，其中許多理論模型會再經由實驗數據進行優化。

數值模擬則是另一種可用於預測纖維濾材滲透度及過濾效率的方式，但其準確性受模型的結構特性影響。根據規格所列熔噴不織布的結構參數，發現選定建立模型的參數具有難度。本研究藉由不同結構參數之熔噴不織布，提出使用GeoDict®軟體建立對應模型的流程，並透過軟體提供的模組與建立的濾材模型進行數值模擬，預測熔噴不織布的滲透度、最易穿透粒徑(MPPS)及過濾效率。有關滲透度的預測，本研究比較多個無量綱滲透度的理論預測與數值模擬計算之結果。由於使用的熔噴不織布具有多分散纖維直徑，本研究進一步探討適用於濾材模型的等效直徑，數值模擬搭配3種等效直徑計算的無量綱滲透度與部分理論預測結果相近。針對過濾效率及最易穿透粒徑的預測，藉由單根纖維過濾效率和等效直徑計算纖維濾材的過濾效率，與數值模擬所得的數據點進行比較。除纖維體積占比較高的模型外，其餘模型的最易穿透粒徑之數值模擬結果與理論預測接近；數值模擬所得的過濾效率變化趨勢與理論預測曲線相符。由理論預測與數值模擬進行比較分析的結果，說明本研究方法建立的模型具準確性，使數值模擬可有效預測過濾效能，達成降低實驗成本的目標。最後，藉由這些濾材模型進行相關應用分析與討論。

Melt-blown nonwoven fabric consists of stacked ultrafine fibers. It exhibits porosity with a broad pore size distribution, and its interconnected flow channels can help mitigate the increase in pressure drop caused by pore blockage. The structure composed of a large number of fibers provides an extensive surface area for particle collection, making it effective in capturing contaminants. Two critical parameters commonly considered in evaluating the performance of filter media are permeability and filtration efficiency. In the past, numerous studies have predicted the filtration performance of fibrous filter media in these two aspects by deriving theoretical models that consider various fiber arrangement structures. Many of these models were further refined using experimental data.

Numerical simulation is an alternative method for predicting the permeability and filtration efficiency of fibrous filter media. However, its accuracy is influenced by the structural characteristics of models. Given the structural parameters of the melt-blown nonwoven fabrics outlined in the specifications, it was found that selecting appropriate parameters for the model construction presented difficulties. Based on the melt-blown nonwoven fabrics with varying structural parameters, this study proposes a procedure for constructing corresponding models via GeoDict® software. Numerical simulations are then performed using the software’s modules and these constructed filter media models to predict the permeability, most penetrating particle size (MPPS), and filtration efficiency of the melt-blown nonwoven fabrics. In terms of permeability prediction, this study compares various theoretical predictions of dimensionless permeability with results obtained from the numerical simulations. Because the melt-blown nonwoven fabrics employed exhibit polydisperse fiber diameters, this study further investigates the equivalent diameters applicable to the filter media models. The dimensionless permeability calculated through the numerical simulations in conjunction with three of these equivalent diameters shows good agreement with certain theoretical predictions. To predict the filtration efficiency and the most penetrating particle size, the filtration efficiency of the fibrous filter media is calculated based on the single fiber filtration efficiency and the equivalent diameters. It is then compared with data points obtained from the numerical simulations. Except for the models with the high fiber volume fraction, the numerical simulation results of the most penetrating particle sizes for the other models are close to the theoretical predictions. The trends in the filtration efficiency obtained from the numerical simulations agree with the theoretical prediction curves. The results of the comparative analysis between the theoretical predictions and the numerical simulations demonstrate the accuracy of the models constructed using the procedure proposed in this study, thereby enabling numerical simulations to predict filtration performance effectively and achieving the objective of reducing experimental costs. Finally, these filter media models are utilized to analyze and discuss related applications.