Transparent Air Research Articles

Modified PVDF/PMMA/SiO2 composite nanofibrous membrane in airborne filtration: Transparency, mechanical properties and filtration performance

A comprehensive study on four modified Polyvinylidene Fluoride (PVDF) nanofibrous membrane was conducted to fabricate transparent air filters for the first time when adding Polymethyl methacrylate (PMMA) and SiO2. The modified PVDF nanofibrous membrane properties were extensively characterized using scanning electron microscopy, infrared analysis, crystallinity, and investigated the optical transparency, mechanical properties, and filtration performance. The enhancement of PMMA is greater than the weaken of SiO2 with the PVDF/PMMA/SiO2 membrane average transparency of 70.48 %. The PVDF membrane mechanical strength enhanced by SiO2 and weakened by PMMA is visualized by a Weibull two-parameter distribution model. The PVDF/PMMA/SiO2 membrane filtration efficiency is 94.12–96.39 %, and the impressive quality factor (Qf) of 0.074 Pa⁻1 is superior to other three modified membranes in filtration performance while maintaining the sufficient ultimate tensile strength (UTS) of 20.41±0.28 MPa.

Transparent and antibacterial air filters based on nanofiber/nets membrane

Air pollution is a serious human health issue worldwide, especially the pollution of particulate matter (PM) and the spread of airborne bacteria. However, most existing filters are opaque, have limited filtration efficiency and no antimicrobial properties. We report an electrospinning/netting technology to prepare high-performance and transparent air filters with antibacterial properties. By regulating the ejection and phase separation of charged droplets, nanofiber/nets (NFN) membrane is created. The resulting NFN filter has integrated properties of low packing density (0.32 g cm−3), high porosity (85 %), desirable pore size (280 nm), robust tensile strength (12.8 MPa) and high PM0.3 removal efficiency (99.996 %). Furthermore, the NFN filter also exhibits ideal transparency (90 %) and excellent bactericidal rate (99.99 %). This work should be a positive attempt to develop efficient, transparent and antibacterial filtration materials.

Transparent Nanofibrous Membranes with Optimized Optical Channel Structure for Window Screens

AbstractNanofibrous membranes, characterized by their flexibility, high porosity, and tunable structure, are emerging as a promising contender for advanced transparent materials with sufficient breathability and pliability. However, the considerable surface light reflection and internal light scattering of nanofibrous membranes pose a challenging task in achieving transparency. In this study, transparent nanofibrous membranes are fabricated by constructing a topological structure with optimized optical transmission channels, which provide the minimum equivalent thickness to minimize light loss in nanofibrous membranes. The resultant fabricated membrane exhibits a high light transmittance of up to 81%, along with a sufficient porosity of 84% and flexibility. Additionally, the membrane demonstrated effective PM0.3–10 removal efficiency (>91%), low air pressure drops (<110 Pa), high air permeability (≈104 mm s−1), and good waterproof performance. Therefore, the prepared transparent nanofibrous membrane may serve as a transparent air filtration window screen to enhance indoor comfort for people.

LES OF HUMID AIR NATURAL CONVECTION IN CAVITY WITH CONDUCTING WALLS

The differentially heated cubic cavity (DHCC) is a common benchmark for studies in application to natural convection, for instance, in passive cooling and ventilation. This system, consisting of an enclosed cavity with two opposing vertical walls maintained at two different constant temperatures, is sensitive to boundary conditions and exhibits complex flow features resulting in changes to the heat transfer. As these effects have previously only been studied in isolation, in the present study, for the first time, the DHCC has been investigated in the presence of humid air and nonadiabatic passive boundaries simultaneously at Ra = 1.58 × 10<sup>9</sup>. In the benchmark study on the DHCC, the cavity depth exceeds the width and height by a factor of 2, so the flow is nearly two dimensional in the midplane. In the present study, periodic boundary condition has been applied to the passive vertical boundaries of a cubic cavity. The findings suggest the effect of inclusion of gas radiation is more prominent than considering transparent humid air. Heat transfer is affected by vortices in the cavity corners and by conduction at the passive walls. The effects are demonstrated by the temperature changes between different cases and the flow structures.

Methodology for Determining Heat Losses through Translucent Construction

The purpose of this work is to determine the heat transfer coefficient of translucent fences, considering the number of storeys of buildings, climatic factors, such as wind velocity and outdoor temperature. To achieve this goal, the following tasks were solved: analysis of heat transfer in translucent enclosures as a quasi-stationary process; analysis of heat transfer processes in translucent barriers, which are a combination of solid transparent plates and air gaps connected by a frame structure; determination of the heat transfer coefficient on the glass surface depending on climatic factors and the radiant component. The most important result is the empirical dependence of the heat transfer coefficient on the outer surface of the window block on the Reynolds criterion, the dependences for determining the heat transfer coefficient of window blocks are improved, considering climatic parameters. The heat transfer coefficient of the window block as a whole is presented in the form of analytical ratios, considering the location of the building and its height, changes in wind velocity and outdoor temperature. This methodology was tested on the example of a civil administrative building, for which the heat transfer coefficients of window structures of non-standard series were evaluated. The significance of the research results lies in the possibility of using the obtained dependencies to assess the thermal characteristics of window structures of non-standard shapes. The dependences of the heat transfer coefficient on wind speed and outside air temperature given in the paper can be used in the energy audit of buildings.

Scalable, solvent-free transparent film-based air filter with high particulate matter 2.5 filtration efficiency

Over the course of the COVID-19 pandemic, people have realized the importance of wearing a mask. However, conventional nanofiber-based face masks impede communication between people because of their opacity. Moreover, it remains challenging to achieve both high filtration performance and transparency through fibrous mask filters without using harmful solvents. Herein, scalable transparent film-based filters with high transparency and collection efficiency are fabricated in a facile manner by means of corona discharging and punch stamping. Both methods improve the surface potential of the film while the punch stamping procedure generates micropores in the film, which enhances the electrostatic force between the film and particulate matter (PM), thereby improving the collection efficiency of the film. Moreover, the suggested fabrication method involves no nanofibers and harmful solvents, which mitigates the generation of microplastics and potential risks for the human body. The film-based filter provides a high PM2.5 collection efficiency of 99.9 % while maintaining a transparency of 52 % at the wavelength of 550 nm. This enables people to distinguish the facial expressions of a person wearing a mask composed of the proposed film-based filter. Moreover, the results of durability experiments indicate that the developed film-based filter is anti-fouling, liquid-resistant, microplastic-free and foldability.

Performance improvement for chilled water air conditioning cooling coils with various dimple fin geometries

The present research inspected the thermal and flow behavior of finned coiled tube heat exchangers in crossflow for chilled water air conditioning systems. The investigation variables cover the impacts of several variables, such as fin dimple shape, the number of fins, and the Reynolds number of water and air sides on the thermal-hydraulic aspects of a finned cooling coiled tube heat exchanger. The goal is to enhance this famous finned cooling coiled tube heat exchanger using dimples concerning the same coiled tube heat exchanger without dimples. Six test specimens were fabricated, three with fin dimple geometries as sharp-sided triangle dimples, curved-sided triangle dimples, and teardrop dimples. The other specimens with three different fin numbers 140, 155, and 170. The test runs were experimented in a transparent air duct with air Reynolds numbers ranging from 1540 to 6205, while the chilled water flow side has experimented with Reynolds numbers ranging from 3350 to 16250. The findings revealed that a higher Nusselt number and flow area goodness factor is achieved by a heat exchanger (D) with a curved-sided triangle fin dimple shape. The energy efficiency ratio for a cooling coil with a fin number of 170 is higher than that of cooling coils with fin numbers 140 and 155 by approximately 24.68% and 12.94%, respectively. Correlations of energy efficiency ratio, effectiveness, flow area goodness factor, and friction factor are extracted according to the experimental results with deviations.

Through-hole composite membrane with an ultrathin oxide shell for highly robust and transparent air filters

Exploring pore structures that are optically transparent and have high filtration efficiency for ultrafine dust is very important for realizing passive window filters for indoor air purification. Herein, a polyester track-etched (PETE) membrane with vertically perforated micropores is investigated as a cost-effective candidate for transparent window filters. The pore size, which governs transparency and filtration efficiency, can be precisely tuned by conformally depositing an ultrathin oxide layer on the PETE membrane via atomic layer deposition. The maximum visible light transmittance (∼81.2 %) was achieved with an alumina layer of approximately 55 nm, and the resulting composite membrane exhibited competitive filtration efficiency compared to commercial products. The chemically inert alumina layer also increased resistance to various external stimuli and enabled simple cleaning of the contaminated membrane surface with a solvent. The membrane installed on an insect screen effectively maintained its filtration performance (∼85 % for PM2.5) even after 10 reuse cycles under extremely harsh conditions (PM2.5 concentration: ∼5000 μg cm−3). The proposed through-hole composite membrane can expand the choice of aesthetic window filters to situations that require high outside visibility and daylighting.

Electric field activated ON/OFF surface charge polarization of transparent filter media for high-efficiency PM2.5 filtration

It is a cruel reality that the air we breathe has become an invisible but leading danger in terms of public health and the environment. Exposure to fine particulate matter (PM), and indoor volatile organic compounds (VOCs) is particularly harmful to urban residents among the different airborne pollutants. So far, different types of polymers has been widely used to fabricate filter media for clean air. Most of the developed filter are non-transparent not suitable for window. Moreover, the PMs concentration depends on different factors and fluctuates day-to-week and seasonally. Most present development air filter are non-transparent not suitable for window and single functional by their construction, high fiber diameter and large thickness. Therefore, to meet demands, we introduced a transparent advanced air filters with multi-functionality, such as in situ switch based tuning filtration efficiency, VOC adsorption capability and antibacterial properties. We have rationally designed an electric field activated ON/OFF surface charge polarization air filter composed of nanofiber/nets nanoarchitectured networks with 80% optical transparency. The electric field activated nanofiber/nets filter enhanced PM2.5 filtering efficiency from 61% to more than 95% at a low poling voltage of 0.2 kV. More importantly, here the low voltage is adequate to cause a high electric field (MV m−1) and surface charges can form on the fiber surface. In addition, due to the presence of chitosan in nanofiber/nanonet structure the filter can effectively adsorb gases such as ammonia, triethylamine, and formaldehyde and possessed anti-bacterial behaviour for P. aeruginosa and S.aureus. The approach introduced in this work has the potential to filter PMs under extremely hazardous air conditions and can reduce power consumption by turning off the power during low hazardous conditions.

Biosensing with a scanning planar Yagi-Uda antenna.

We investigate a model bioassay in a liquid environment using a z-scanning planar Yagi-Uda antenna, focusing on the fluorescence collection enhancement of ATTO-647N dye conjugated to DNA (deoxyribonucleic acid) molecules. The antenna changes the excitation and the decay rates and, more importantly, the emission pattern of ATTO-647N, resulting in a narrow emission angle (41°) and improved collection efficiency. We efficiently detect immobilized fluorescently-labeled DNA molecules, originating from solutions with DNA concentrations down to 1 nM. In practice, this corresponds to an ensemble of fewer than 10 ATTO-647N labeled DNA molecules in the focal area. Even though we use only one type of biomolecule and one immobilization technique to establish the procedure, our method is versatile and applicable to any immobilized, dye-labeled biomolecule in a transparent solid, air, or liquid environment.

Melville's Quixoticism and the Modern World-System

Melville's Quixoticism and the Modern World-System

Transparent Air Filters with Active Thermal Sterilization.

The worldwide proliferation of COVID-19 poses the urgent need for sterilizable and transparent air filters to inhibit virus transmission while retaining ease of communication. Here, we introduce copper nanowires to fabricate transparent and self-sterilizable air filters. Copper nanowire air filter (CNAF) allowed visible light penetration, thereby can exhibit facial expressions, helpful for better communication. CNAF effectively captured particulate matter (PM) by mechanical and electrostatic filtration mechanisms. The temperature of CNAF could be controlled by Joule-heating up to 100 °C with thermal stability. CNAF successfully inhibited the growth of E. coli because of the oligodynamic effect of copper. With heat sterilization, the antibacterial efficiency against G. anodireducens was greatly improved up to 99.3% within 10 min. CNAF showed high reusability with stable filtration efficiency and thermal antibacterial efficacy after five repeated uses. Our result suggests an alternative form of active antimicrobial air filter in preparation for the current and future pandemic situations.

High-performance anti-haze window screen based on multiscale structured polyvinylidene fluoride nanofibers

Indoor air quality (IAQ) has assumed new significance given the extensive amount of time spent indoor due to the coronavirus pandemic and particulate matter (PM) pollution. Accordingly, the development of window air filters to effectively intercept PM from outdoor air under natural ventilation conditions is an important research topic. However, most existing filters inevitably suffer from the compromise among filtration capability, transparency, and air permeability. In this study, we fabricate a high-performance transparent air filter to improve IAQ via natural ventilation. polyvinylidene fluoride (PVDF) superfine nanofibers of size 20–35 nm are prepared using extremely dilute solution electrospinning; a multi-scale nanofiber structure is then designed. By adjusting the ratio of PVDF superfine nanofibers (SNs) to PVDF coarse fibers (CNs), we balance the structure–performance relationship. Benefiting from the multiscale structural features that include a small pore size (0.72 μm) and high porosity (92.22%), the resulting filters exhibit excellent performance including high interception efficiency (99.92%) for PM0.3, low air resistance (69 Pa), high transparency (∼80%) and stable filtration after 100 h of UV irradiation. This work describes a new strategy for the fabrication of nanofibers with true-nanoscale diameters and the design of high-performance air filters.

Anaximenes’ ἀήρ as Generating Mist and Generated Air

AbstractAnaximenes is usually considered to be a material monist recognizing transparent atmospheric air as a principle (ἀρχή). In the cosmogonic explanation of the origin of the earth and the heavenly bodies, the Greek term ἀήρ turns out to mean rather ‘opaque damp mist’. However, Not only does it accord with archaic usage, but also with how it was used in his mentor, Anaximander. Yet, in cosmology ἀήρ means ‘air’ serving as stuff on which the earth and the heavenly bodies float. Hence, in keeping with contemporary usage, Anaximenes recognised two kinds of ἀήρ, distinguishing them functionally. Whereas mist is conceived of as ageneratingsubstance, air functions only ascarryingstuff.

Highly Efficient, Transparent, and Multifunctional Air Filters Using Self-Assembled 2D Nanoarchitectured Fibrous Networks.

Particulate matter (PM) pollution is a significant burden on global economies and public health. Most present air filters are heavy, bulky, and nontransparent and typically have inevitable compromise between removal efficiency and air permeability. We report a scalable strategy to create ultralight, thin, rubbery, self-assembled nanoarchitectured networks (nanonetworks) with high-efficiency and transparency (ULTRA NET) as air filters using capacitive-like electronetting technology. By controlling the ejection, deformation, and phase separation of charged droplets from a Taylor cone, our approach allows continuously welded two-dimensional nanonetworks (∼20 nm fiber diameter) to assemble into filters on a large scale. The resulting ULTRA NET filters exhibit integrated properties of desirable pore structure yet maintaining strikingly low thickness (∼350 nm) and free-standing capability, 99.98% removal efficiency, and <0.07% of atmosphere pressure for PM0.3 filtration at ∼85.6% transmittance, which enable them to serve as a multifunctional filter against PMs either in rigid solid or in soft oil forms and even biohazard pathogens. This work should serve as a source of inspiration for the design and development of high-performance fibrous materials for various filtration and separation applications.

Highly efficient transparent air filter prepared by collecting-electrode-free bipolar electrospinning apparatus

Electrospinning technology has been used for a long time. A jet from a needle was formed by applying high voltage, and then the nanofibers are deposited onto a collecting electrode (usually metal) and the excess charge is conducted away to complete the electrospinning. Alternatively, it is also possible to prevent charge accumulation from hindering the progress of electrospinning by means of charge neutralization. A bipolar electrospinning technique (B-EEM) was developed to induce jets with different charges through a set of high-voltage power supplies of opposite polarity, and the two jets neutralize each other on the insulating mesh, thus completing the electrospinning process. There is no need for a collecting electrode to complete the electrospinning process. We have found that the filters produced by the new technology have better filtration efficiency while maintaining the same transparency in relative to the original technology, and this optimization is due to the distribution modification of the nanofibers on the mesh.

Electrostatic Transparent Air Filter Membranes Composed of Metallized Microfibers for Particulate Removal.

Particulate matter (PM) from ever-increasing industrialization poses a great public health risk. Although fiber-based filters are used effectively to block PM, filters with high packing densities suffer from excessive pressure drops. Electret filters bypass intermediate- or large-sized particles and thus capture only small particles, the motion of which can be influenced by weak electrostatic fields. In this study, we demonstrate the fabrication of metallized fibers that produce intense electric fields, thereby enabling capture of PMs of a variety of sizes produced by burning incense. The filter consisting of these metallized fibers effectively removes moving particles from air. An electricity-driven filter is relatively thin and has a low packing density, making it light, portable, transparent, and inexpensive. The sizes of the pores between the metallized fibers are readily controlled by manipulating the electrospinning and electroplating times. Sufficiently large pores permit efficient airflow and thus increase permeability without risking an excessive pressure drop. The metallized fiber filter is washable and thus reusable. In this study, a PM removal rate of >97% was recorded using a filter designed under optimal conditions.

Error Analysis of Liquid Holdup Measurement in Gas-Liquid Annular Flow Through Circular Pipes Using High-Speed Camera Method

Accurate measurement of gas-liquid phase fraction is essential for the proper modelling of the pressure drop, heat transfer coefficient, mass transfer rate and interfacial area in two-phase flows. In this paper, taking the issue of optical distortion into account, an analytical model was proposed to estimate and correct the liquid holdup in gas-liquid annular flow through a circular pipe using high-speed camera method. The error in the liquid holdup measurement generated from different refractive indices among transparent circular pipe, liquid film and air core was firstly theoretically analyzed based on the geometric optics. Experimental tests were then carried out to identify the difference as well as to validate the proposed model. Results indicated that the prediction of the liquid holdup has a good performance with the experimental data (i.e., mean relative error is 4.1%) and the measured liquid holdup is larger than the real one. It was found that the measured liquid holdup is larger than the real one. Generally, when the real liquid holdup gets smaller, the discrepancy between the measured liquid holdup by image and the real liquid holdup becomes more significant. Thus, after measuring the liquid holdup from the images, the value of the measured liquid holdup must be corrected by the present model in order to obtain the real liquid holdup.

Field study of NOx degradation by a mineral-based air purifying paint

This paper studies the performance of a mineral-based transparent air purifying paint. The air pollutants removal efficiency of this photocatalytic paint was first determined following the ISO 22197-1 procedure under laboratory conditions. Subsequently, its air pollutants removal efficiency under realistic conditions was determined by outdoor monitoring with a duration of 20 months, applying a new monitoring protocol. The weather conditions, including temperature, wind flow, humidity, precipitation, and NOx concentration were continuously monitored. The efficiency of the photocatalytic paint was analyzed. The influence of the environmental parameters on the air pollutant removal efficiency as well as long term performance was discussed. The results show the excellent air purifying efficiency of this new paint, nevertheless the environmental parameters show dramatic effects on its long term performance. Furthermore, this study also confirmed the robustness of the proposed air purification performance monitoring protocol.

Development of Nata de Coco-based transparent air masks

We report the development of transparent air masks using Nata de coco as basic material. Several methods have been explored to make the transparent air masks: direct drying under sunlight, blending, combined blending and wringing, and hot press. The transparencies of the air masks samples were 54.16%, 62.5% and 66.67%, for masks produced by direct sun drying, blending, and blending-wringing methods, respectively. Meanwhile, the masks produced with hot press process showed the highest transparency, i.e. 87%. The preparation of pore size in the sample was done by several variation methods, such as coconut grater method, sandpaper method, and naphthalene insertion. Based on SEM characterization, sample from naphthalene insertion method have higher porosity which is 72.762%. The permeability of the sample was also measured to clarify pressure drop. Sample mask with naphtalene insertion has the lowest pressure drop among other samples. This indicates that the mask with naphtalene insertion method has good possibility to be applied as transparent air masks.