Rear Side Surface Research Articles

Effectiveness of N95 Mask in Preventing COVID-19 Transmission.

N95 mask has emerged as a potential measure to mitigate the airborne transmission of respiratory disease such as COVID-19. Herein, we experimentally investigated the impact and interaction of pure water droplets as surrogate to respiratory droplets with the different layers of a commercially available N95 mask to demonstrate the penetration and passage-capability of respiratory fluids through the different layers. The penetration of an impacting droplet through the mask layers was characterized by elucidating the ejection of secondary droplets from the rear-side surface of the target mask material. In addition, the passage of respiratory fluids through the mask layers was characterized by capillary imbibition of the droplet liquid through the pores, as a function of wettability of the mask material. Droplet impact at Weber numbers We = 208 and 416 has been considered in the present study; the chosen We range corresponds to that of cough droplets realized in real respiratory events. Each layer of the N95 mask is hydrophobic that prevents capillary imbibition through the pores: a sessile droplet placed over the surface exhibits classical diffusion-limited evaporation. Droplet impact experiments on N95 mask layer surfaces reveal that a single layer allows liquid penetration at We = 416; while a combination of five layers, as is the case of a commercially available N95 mask, blocks the penetration completely, consistent with the widely known effectiveness of N95 masks. Herein, we devote special attention to compare the so-obtained efficiency of N95 masks to that of a recently designed two-layer cloth mask containing an intermediate High-Efficiency Particulate Air (HEPA) filter layer (Narayan et al. in Phys Fluids 34:061703, 2022). We conclusively show that the performance of the designed cloth mask is identical to that of a commercially available N95 mask. The assessment of mask effectiveness further includes examination of breathability and comfort by means of passage of air through them. A comparative study has been presented herein for a clear demonstration of effectiveness of different masks in preventing air-borne transmission of COVID-19.

Assessing effectiveness and comfortability of a two-layer cloth mask with a high-efficiency particulate air (HEPA) insert to mitigate COVID-19 transmission

A face mask is essential personal protective equipment to mitigate the spread of COVID-19. While a cloth mask has the least ability to prevent the passage of infectious respiratory droplets through it compared to surgical and N95 masks, the surgical mask does not fit snugly and causes significant air leakage. The synthetic fibers in the latter reduce comfortability and are an allergen for facial eczema. Moreover, the N95 mask causes CO2 inhalation and reduces heat transfer in the nose. Therefore, the objective of the present work is to improve the effectiveness of a two-layer cloth mask by introducing an intermediate, high-efficiency particulate air (HEPA) filter layer. A significant volume of impacted droplets penetrates through a single-layer cloth mask, ejecting secondary droplets from the rear side. However, a two-layer cloth mask prevents this ejection. Despite slowing down the liquid penetration, capillary imbibition through cloth due to its hydrophilicity causes the transport of the liquid into the second layer, resulting in a thin-liquid layer at the mask's rear-side surface and contaminating it. Conversely, the HEPA filter inserted in the cloth mask prevents the imbibition, making the second cloth layer free of contamination. We attribute the impedance to the imbibition by the intermediate HEPA filter layer to its hydrophobic characteristics. We experimentally and analytically assess the role of wettability on capillary imbibition. The breathability measurements of masks show that the HEPA inserted in the cloth mask does not reduce its breathability compared to that of the surgical mask.

Quality and flexural strength of laser-cut glass: classical top-down ablation versus water-assisted and bottom-up machining.

The growing applicability of glass materials drives the development of novel processing methods, which usually lack comprehensive comparison to conventional or state-of-art ones. That is especially delicate for assessing the flexural strength of glass, which is highly dependent on many factors. This paper compares the traditional top-down laser ablation methods in the air to those assisted with a flowing water film using picosecond pulses. Furthermore, the bottom-up cutting method using picosecond and nanosecond pulses is investigated as well. The cutting quality, sidewall roughness, subsurface damage and the four-point bending strength of 1 mm-thick soda-lime glass are evaluated. The flexural strength of top-down cut samples is highly reduced due to heat accumulation-induced cracks, strictly orientated along the sidewall. The subsurface crack propagation can be reduced using water-assisted processing, leading to the highest flexural strength among investigated techniques. Although bottom-up cut samples have lower flexural strength than water-assisted, bottom-up technology allows us to achieve higher cutting speed, taper-less sidewalls, and better quality on the rear side surface and is preferable for thick glass processing.

Effect of a horizontal hole on flow structures around a wall-mounted low-aspect-ratio cylinder

To control the vortex structures and separation region of a low-aspect-ratio cylinder wake, a passive flow control method that is to drill a horizontal hole from the front side surface to the rear side surface was proposed for a short circular cylinder having an aspect ratio H/D = 1 with height H and diameter D of 70 mm. The PIV measurements were performed at Reynolds number of 8570 in a circulation water tunnel in order to compare the flow characteristics between the controlling and no-controlling wakes. Furthermore, to study the position effect of the horizontal hole, three kinds of the hole positions having different height h from wall were tested. It was found that the jet flow from a horizontal hole leads to suppress the vortex formation and to reduce the rear separation region. The vorticity, Reynolds shear stresses and TKE were evidently suppressed by the jet flow of the horizontal hole in the rear recirculation zone, resulting in the reduction of the drag acted on the cylinder. Meanwhile, the instantaneous large-scale vortical structures of the rear recirculation zone were broken down into several small-scale vortices by the jet. As increasing the height of hole, the downwash flow is evidently suppressed and the upwash flow is increased. Spanwise vortex shedding is altered from symmetric to asymmetric arrangement.

Performance Improvement of High Efficiency Mono-Crystalline Silicon Solar Cells by Modifying Rear-Side Morphology

In this work, aluminum oxide films with excellent passivation effects were prepared on the rear-side surface of passivated emitter and rear cells (PERCs) using a self-developed spatial atomic layer deposition system. Various rear-side surface morphologies were obtained through different etching treatments. We compared the PERCs with standard etching treatment and further polishing processes on rear-side surfaces. Experimental results show that compared with the unpolished cell, the polished cell attained superior electrical performance, particularly in open-circuit voltage (Voc) and short-circuit current density (Jsc), because of the more effective rear-side surface passivation and reabsorption of long-wavelength light. The improvement in Voc and Jsc raised the conversion efficiency to 19.27%. This study verifies that despite polished cells requiring complex processes, the polishing treatment displays application potential for achieving high efficiency in the solar industry.

Multifunctional PECVD Layers: Dopant Source, Passivation, and Optics

In this study, the feasibility of creating one dielectric layer system acting simultaneously as antireflection coating, phosphorous doping source, masking against metal plating, and surface passivation is presented. Moreover, a similar layer stack is described, which behaves as rear-side surface passivation, boron dopant source, and internal reflection mirror. The optical characteristics of these layers are especially investigated and optimized for a solar cell's front- and rear-side coating. By consequent use of the multifunctional layers, a totally diffused solar cell with rear-side passivation and local rear contacts can be produced using only one wet chemical bath sequence, one multilayer vacuum step, and one high-temperature process. We present the first proof of concept for such a solar cell production using multifunctional plasma-enhanced chemical vapor deposition layers resulting already in a conversion efficiency of 18.3%.

Firing stability of SiN y/SiN x stacks for the surface passivation of crystalline silicon solar cells

In the photovoltaic industry contacts to crystalline silicon are typically formed by firing of screen-printed metallization pastes. However, the stability of surface passivation layers during high temperature contact formation is a major challenge. Here, we investigate the thermal stability of the surface passivation by amorphous silicon nitride double layers (SiN y /SiN x ). The SiN y passivation layer is silicon rich with refractive index larger than 3. Whereas the SiN x capping layer has a refractive index of 2.05. Compared to pure hydrogenated amorphous silicon, the nitrogen in the SiN y passivation layer improves the firing stability. We achieve an effective surface recombination velocity after a conventional co-firing process of (5.2±2) cm/s on p-type (1.5 Ωcm) FZ-silicon wafers at an injection density of 10 15 cm −3. An analysis of the improved firing stability is presented based on FTIR and hydrogen effusion measurements. The incorporation of an SiN y /SiN x stack into the passivated rear of Cz silicon screen-printed solar cells results in an energy conversion efficiency of 18.3% compared to reference solar cells with conventional aluminum back surface field showing 17.9% efficiency. The short circuit current density increases by up to 0.8 mA/cm 2 compared to conventional solar cells due to the improved optical reflectance and rear side surface passivation.

Physical properties of industrial 19% rear side passivated Al-LBSFR- solar cells

Abstract With the objective of high efficiency solar cells rear side passivation with local aluminium back surface field and dielectric reflection (Al-LBSFR) were developed at Centrotherm and cell efficiencies of 19.4% were achieved. In this paper major physical properties of the developed technology, named centaurus technology, are presented. A low reflection on the solar cell front side is achieved by a textured surface, which enables in particular an inclined light entry at the solar cell front side, which is mandatory for a total light reflection on the solar cell dielectric rear side. Likewise a smooth instead of a textured rear side surface was more suitable for a high rear reflection and also more appropriate for better rear surface passivation. In addition, the influence of the rear side local BSF and metallization fraction was identified as a possible Voc limitation in combination with the front emitter saturation currents. Lower temperature coefficients of the cell power output or cell efficiency and of the open circuit voltage were evaluated for Al-LBSFR cells.

Influences of various vortex structures on the dispersion and deposition of small ash particles

Numerical simulations were conducted to study the influences of various vortex structures on the dispersion and deposition processes of 1 μm to 10 μm diameter fly ash particles on the rear side surface of a boiler tube. Turbulent gas flow was simulated with detached eddy simulation (DES) method and vortex structures in the wakes were modeled. Results suggested that the motions of particles in the near wake region were controlled by different vortex structures, and the impact efficiency and deposit concentration on the rear side surface induced by the vortices varied considerably at different velocities. The results of volume percentages distribution of the deposited particles with various diameters simulated were in good agreement with the experimental data.