Nanofiber Media Research Articles

Semi-empirical equation for determining the pressure drop of nanofibers

Air pollution, particularly the presence of particulate matter, has been linked to increased mortality rates. Air filtration is a widely used method to reduce exposure to airborne particles and protect public health. Nanofiber filter media has gained attention due to its ability to efficiently remove nanosized particles while minimizing pressure drop. However, accurately predicting the pressure drop in nanofiber media, which is influenced by the slip flow effect, remains a challenge. In this study, a simple semi-empirical equation was developed to calculate the pressure drop across nanofiber filter media. The model considers various filter parameters such as diameter, thickness, and solidity. Existing theoretical and empirical models were compared with experimental data, revealing limitations in accurately predicting pressure drop in nanofibers. To address this, a new empirical model, proposed by Bian, was examined. However, the Bian model demonstrated limited applicability due to its specific range of solidities. Numerical simulations were conducted to obtain additional pressure drop data, and a total of 107 cases were tested across various filter parameters. The simulations were performed using the Stokes equation to account for the low Reynolds numbers associated with nanofibers. The developed semi-empirical model provides a practical tool for analyzing the effect of filter parameters on nanofiber filter media's pressure drop, aiding in the design of efficient air filtration systems.

Filtration Performance and Fiber Shedding Behavior in Common Respirator and Face Mask Materials

Wearing respirators and face masks is effective for protecting the public from COVID-19 infection. Thus, there is a need to evaluate the performance of the commonly used respirators and face masks. Two experimental systems were developed to investigate seven different mask materials, which have a fiber size range from 0.1 μm (100 nm) to 20 μm (20,000 nm). One of the systems is a computer-controlled setup for measuring the filtration performance, including size-dependent filtration efficiency and pressure drop, while the other system is for testing the fiber shedding behavior of the materials. The technique of scanning electron microscope (SEM) was applied to observe the dimensions and structures of those materials, which are made of nonwoven-fabrics electret-treated media, cotton woven fabrics, or nanofiber media. The study indicated that the 3M N95 respirator has the best overall filtration performance with over 95% efficiency and low pressure drop of 74.1 Pa. The two commercial cotton face masks have the worst filtration performance in general, with a filtration efficiency of around 25%. No broken fibers from by the seven tested respirator and face mask materials were discovered; however, dendrite structures likely shed by the SHEMA97 face mask with a size comparable to its nanoscale fibers were identified. The reason for this phenomena is presented.

Feasibility study on the application of electrospun nanofiber webs for the air sampling of crystalline silica.

The aim of the present study was to first fabricate an electrospun PVC nanofiber web and then assess its applicability in sampling and measuring the concentration of airborne crystalline silica by comparing analysis results with a commercial PVC membrane filter under different ranges of airborne silica concentration. A filtration performance comparison was also made between an electrospun PVC web with nano-sized fibers and a commercial PVC membrane filter. Overall, the measured concentration of silica by the electrospun webs was 1.022 times higher than that of the commercial PVC filter in all studied ranges of silica concentration and the nanofiber media had higher filtration efficiency and lower pressure drop compared to the PVC membrane filter. This can be considered to be due to the lower fiber diameter and greater porosity (obtained from the 2D SEM image) of the electrospun nanofiber webs. This makes them suited for air pollutant sampling and determining its airborne concentration.

Nanofibers for High Efficiency Filtration

Nanofiber is a broad phrase generally referring to a fibre with a diameter less than 1 micron. While glass fibres have existed in the sub-micron range for some time and polymeric meltblown fibres are just beginning to break the micron barrier, sub-half-micron diameters have been used for air filtration in commercial, industrial and defence applications for more than twenty years. They have been shown to deliver improved filter life, increased contaminate holding capacity and enhanced filtration efficiency. Small fibres in the sub-micron range, in comparison with larger ones, are well known to provide higher filter efficiency at the same pressure drop in the interception and inertial impaction stages of the filtration process. In particular, nanofibers provide marked increases in filtration efficiency at relatively small (and in some cases immeasurable) decreases in permeability. Nanofiber filter media have enabled new levels of filtration performance in several diverse applications with a broad range of environments and contaminants. While nano fibre size lead to a higher pressure drop, interception and inertial impaction efficiencies will increase faster, and therefore more than compensating for the rise in pressure drop. Thus, in the particle size of interest, i.e. from sub-micron upwards, better filter efficiency can be achieved at the same pressure drop, or conversely, the same filter efficiency at a lower pressure drop can be achieved with nanofibres. This paper will discuss a process for making nanofibers, as well as the benefits, limitations, construction, and applications of filters using nanofiber media.

Changes in the Spectral Features of Zinc Phthalocyanine Induced by Nitrogen Dioxide Gas in Solution and in Solid Polymer Nanofiber Media.

The changes in the spectral features of zinc phthalocyanine in the visible domain as a result of its interaction with nitrogen dioxide gas were assessed in this work. This was done both in solution and when the phthalocyanine was incorporated into a solid polystyrene polymer nanofiber matrix. The spectral changes were found to be spontaneous and marked in both cases suggesting a rapid response criterion for the detection of the gas. In particular, the functionalised nano-fabric material could serve as a practical fire alarm system as it rapidly detects the nitrogen dioxide gas generated during burning.

Respiratory source control using surgical masks with nanofiber media.

Background: Potentially infected individuals (‘source’) are sometimes encouraged to use face masks to reduce exposure of their infectious aerosols to others (‘receiver’). To improve compliance with Respiratory Source Control via face mask and therefore reduce receiver exposure, a mask should be comfortable and effective. We tested a novel face mask designed to improve breathability and filtration using nanofiber filtration.Methods: Using radiolabeled test aerosols and a calibrated exposure chamber simulating source to receiver interaction, facepiece function was measured with a life-like ventilated manikin model. Measurements included mask airflow resistance (pressure difference during breathing), filtration, (mask capture of exhaled radiolabeled test aerosols), and exposure (the transfer of ‘infectious’ aerosols from the ‘source’ to a ‘receiver’). Polydisperse aerosols were measured at the source with a mass median aerodynamic diameter of 0.95 µm. Approximately 90% of the particles were <2.0 µm. Tested facepieces included nanofiber prototype surgical masks, conventional surgical masks, and for comparison, an N95-class filtering facepiece respirator (commonly known as an ‘N95 respirator’). Airflow through and around conventional surgical face mask and nanofiber prototype face mask was visualized using Schlieren optical imaging.Results: Airflow resistance [ΔP, cmH2O] across sealed surgical masks (means: 0.1865 and 0.1791 cmH2O) approached that of the N95 (mean: 0.2664 cmH2O). The airflow resistance across the nanofiber face mask whether sealed or not sealed (0.0504 and 0.0311 cmH2O) was significantly reduced in comparison. In addition, ‘infected’ source airflow filtration and receiver exposure levels for nanofiber face masks placed on the source were comparable to that achieved with N95 placed on the source; 98.98% versus 82.68% and 0.0194 versus 0.0557, respectively. Compared to deflection within and around the conventional face masks, Schlieren optical imaging demonstrated enhanced airflow through the nanofiber mask.Conclusions: Substituting nanofiber for conventional filter media significantly reduced face mask airflow resistance directing more airflow through the face mask resulting in enhanced filtration. Respiratory source control efficacy similar to that achieved through the use of an N95 respirator worn by the source and decreased airflow resistance using nanofiber masks may improve compliance and reduce receiver exposure.

Case Studies of Air Filtration at Microscales: Micro- and Nanofiber Media

In this work, 3–D fibrous geometries are developed to resemble the microstructure of spun-bonded and electrospun filters media and used here to simulate their filtration efficiency and pressure drop. For the sake of simplicity, a continuum flow theory was considered to prevail for the case of spun-bonded media (microfiber media) whereas our electrospun media (nanofiber media) were assumed to be in a free molecular flow regime. Our simulations results are in good general agreement with the experimental data. Especially, in predicting media's pressure drop, our results show better predictions when compared to some of the existing models. We also quantitatively demonstrated that by decreasing the fiber diameter, the minimum collection efficiency of the media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies – the most penetrating particle diameter. Studying the influence of the gas temperature, we showed that filter's efficiency increases as the gas temperature increases. Conversely, the filter's pressure drop decreases by increasing the gas temperature.

A simulation of unsteady-state filtration via nanofiber media at reduced operating pressures

In this work, 3-D structures resembling nanofiber ( d f < 200 nm ) filter media are simulated and challenged with nanoparticle aerosols at reduced operating pressures. For the range of fiber diameters considered in this paper, the free molecular flow regime is dominant. Therefore, the disturbances to the air flow field caused by the fibers are neglected. Nanoparticle capture efficiency of nanofiber webs, due to Brownian diffusion and interception, is calculated for particle diameters ranging from 50 to 500 nm. Our simulations show that by decreasing the fiber diameter, the minimum collection efficiency of filtration media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies—the most penetrating particle diameter. Moreover, it is demonstrated that increasing the flow temperature enhances the nanoparticle capture efficiency of nanofiber filters. Allowing the particles to deposit on the fibers as well as each other, the caking process of such nanofiber filters is simulated for different monodisperse and polydisperse aerosols at different temperatures. The statistical information regarding the composition of nanoparticle cakes formed at high and low temperatures is presented and discussed.