Air Knife Research Articles

Large-area high-efficiency perovskite solar cells based on perovskite films dried by the multi-flow air knife method in air

Multi-flow air knife (MAK): a novel method for large area perovskite film production.

NUMERICAL ANALYSIS OF EDGE OVER COATING AND BAFFLE EFFECT ON HOT-DIP GALVANIZING

In hot-dip galvanizing process, air jet wiping control is so crucial to determine the coating thickness and uniformity of the zinc layer on the steel strip. A numerical simulation of gas-jet wiping in hot-dip galvanizing was conducted to minimize the occurrence of edge over coating (EOC). The causes of EOC were identified by contrasting and analyzing the airflow fields on the strip edge with and without a baffle. The factors influencing the airflow field on the strip edge during the change in the gap between the baffle and the strip edge were also analyzed. The effect of the distance between the air knife and the strip was evaluated. Technological parameters with on-site guidance role were obtained by combining them with the actual production to elucidate the role of the baffle in restraining the occurrence of EOC. The uniform distribution of pressure and coating thickness on the strip is achieved when the distance of the baffle from the strip edge is about 0.3 times of the jetting distance.

Combustion of Boron and Boron-Containing Reactive Composites in Laminar and Turbulent Air Flows

ABSTRACTCombustion of boron and reactive composite powders of Al·B·I2 and Mg·B·I2 in air is characterized experimentally. Composite materials are prepared by mechanical milling of elemental starting materials. Particle size distributions for each material and fractal dimensions of the particle agglomerates are characterized using electron microscopy. All powders are injected into a CO2 laser beam and ignited. A turbulent flow pattern is generated just above the laser beam using a cylindrical air knife. Combustion of individual particles is characterized optically in laminar and turbulent flows. Measured particle size distributions are correlated with the measured distributions of the burn times for each powder. Thus, particle burn times are obtained as a function of the particle size. For boron, the exponent of the power law describing the effect of particle size on its burn time is close to 1 for all flow conditions. Temperatures of the burning particles are also measured. It is observed that both boron particle burn times and temperatures are reduced markedly in turbulent flows. For laminar flow, two stages in the produced emission patterns are identified for burning boron particles. The first stage, accompanied by higher temperatures, is suppressed in the turbulent flow. Conversely, neither burn times nor temperatures are affected substantially by the flow conditions for both Al·B·I2 and Mg·B·I2 powders. For Al·B·I2 and Mg·B·I2 composite powders the exponents of the power law describing the effect of particle size on its burn time are close to 1.7 and 2, respectively. Combustion temperatures in air vary around 1800 K and 2300 K for Al·B·I2 and Mg·B·I2 powders, respectively.

One-step deposition by slot-die coating of mixed lead halide perovskite for photovoltaic applications

Recent advances in the performance and stability of lead halide perovskite solar cells announce a promising future for this technology. As the understanding of lab scale device fabrication progresses technology developments in the area of up-scaling are required to demonstrate their viability on an industrial and pre-commercial scale. These developments include replacing slow spin coated deposition techniques with continuous roll to roll compatible slot-die methods. In this work we demonstrate the suitability of a one-step slot-die coating method for the deposition of lead halide perovskite layers, in particular for infiltration into a mesoporous titania scaffold. Appropriate crystallisation dynamics of the perovskite are achieved by careful control of the substrate temperature in combination with a post-processed rapid air knife application. We show that devices fully processed in air using this method deliver a photovoltaic conversion efficiency up to 9.2%, this is comparable to those manufactured using a spin coating process.

An analysis of the gas-solid plug flow formation: New insights into the coal failure process during coal and gas outbursts

Researches on the failure process of coal during coal and gas outbursts are of great importance in underground mining. Based on the theories of coal spherical shell failure, coal spallation and coal powder pneumatic conveying, the flow state and transport mechanism of coal and gas outbursts were studied. This paper concludes that in the outbursts' development stage, with the front of the outburst being gradually exposed to air, the gas gradient behind the outburst acts as a reciprocating air knife of high pressure that cuts the ejected coal powders, thus forming a plug flow with a high solid-gas ratio and a low speed. By referring to the laboratory results from other researchers and data recorded from field outbursts, an appropriate explanation was obtained for the wave-like coal powder distribution and the sound explosion using the dense-phase plug flow pneumatic conveying theory, which conversely confirms the possible existence of the plug flow.

Experimental investigation on Influencing Factors of air curtain systems barrier efficiency for mine refuge chamber

Air curtain systems for mine refuge chambers prevent harmful gases in the tunnel from entering the chambers, but their barrier efficiency is affected by their structural parameters, installation location and air flow angle as well as the size of the chamber door. Previous studies focused on air curtain systems installed on the top of the door frames of the mine rescue capsule, but no studies have investigated air curtain systems installed on two or three sides of the door frames. To improve the barrier efficiency of air curtain systems for refuge chambers, this study conducted an experimental investigation of the effects of the structural parameters, installation location, and air flow angle on the barrier efficiency for a constant size of the door frame. The results demonstrate that air curtain systems with air curtains installed on two sides of the door frame behind the door wall that ejected air parallel to the door frame provided a relatively good barrier effect; an air curtain system that used pipeline air curtains with a nozzle diameter of 1mm and a nozzle distance of 15mm exhibited a relatively good barrier effect and a barrier efficiency of 55–60%. In air curtain systems that use air knives, the air knife gap should be 0.1–0.2mm wide. Under reasonable parameters and installation conditions, there was no significant difference between the barrier effects against CO2 of air curtain systems that use pipeline air curtains and those that use air knives.

Influence of air knives on liquid zinc flow in galvanising bath

Liquid zinc flow in a galvanising bath was numerically modelled for four cases, and flow field using three-dimensional views was analysed. Flow pattern analysis shows that there are two vortexes (circulations) close to the zinc flow surface and another two below them, which are attributed to strip movement and two guide rolls. Jets from air knives will generate high pressure and zinc backflow. Based on the results of the jets study, the impact of air knives on zinc flow in a galvanising bath was studied on the lengthwise and widthwise section views. It was found that high pressure and zinc backflow due to jets from air knives have little influence on the flow patterns far away from the strip outlet. It was also found that zinc backflow has little influence on the zinc flow surface far away from the strip outlet, while high pressure and zinc backflow together have some influence, that is, the jets of air knives can effectively influence the zinc flow around the strip outlet. This work lays the foundation for the optimisation of the galvanising process to improve the coating quality of steel strips.

Технологические особенности агрегатов непрерывного горячего цинкования стальной полосы

The article describes technological features of a continuous hot-dip galvanized steel strip used in domestic enterprises. Basic technological operations of the galvanizing process are discussed, such as preparation of the strip surface, its thermochemical treatment, melt galvanizing, formation of the coating with air knives, cooling of the strip after galvanizing, editing and finishing of the galvanized strip. It is shown that furnaces of both vertical and horizontal types are installed in new units. Advantages and disadvantages of vertical-type furnaces compared with the horizontal ones are considered. It is shown that the peculiar feature and the advantage of modern units of hot-dip galvanizing is a continuous modular design that allows to produce a strip with different types of coatings at one unit. The use of various types of zinc coatings can improve technological and operational properties of the galvanized sheet. Chemical compositions and application fields of the four most common zinc-based coatings, namely zinc, zinc-iron, zinc-aluminum and aluminum-zinc compound are analysed. It is stated that on modern lines of hot dip the galvanizing coating is applied to the strip on both sides. However, currently, technologies of one-sided zinc coating on a steel strip are developed, the application of which will reduce the consumption of expensive zinc, and consequently, the cost of the finished product. Some promising methods and equipment for unilateral galvanizing are shown and described.

Development of an air-knife system for highly reproducible fabrication of polydimethylsiloxane microstencils

In this study, an air-knife system was developed for the automated fabrication of polymer microstencils with microscale perforated patterns. Blowing compressed N2 gas through the air knife provided a uniform laminar gas flow of high intensity suitable for perforating holes in the stencil. The polydimethylsiloxane (PDMS) stencil was replicated from a master mold prepared by photolithography. When the prepolymer of PDMS was spin-coated onto the master mold, a thin layer of the prepolymer remained on top of the master's structure and consequently prevented the formation of the perforated patterns. This residual layer was easily removed by the presented air knife. The air-knife system controlled the flow rate of N2 gas and the conveying speed of the master mold; therefore, the system possessed high reproducibility compared to manual gas blowing. Its use reduced the fabrication time for perforated biocompatible polymer microstencils, allowing for their mass production via an automated system. The validity of this suggested method was proven through experiments and was evaluated by application in various fields.

Influence of laser-induced plume on penetration in laser welding

The influence of a laser-induced plume on penetration is discussed in remote laser welding. Melt-runs accompanying plumes of various lengths were carried out in order to investigate the influence of plume on penetration using a 4.5 kW YAG laser and air knife. Penetration depth obviously reduced in conditions with a long plume. It is considered that the decrease of penetration depth comes from attenuation of laser power in the plume, through the decrease in weld metal cross-sectional area. Attenuation of laser power was estimated at about 7% and focus shift was estimated to be about 0.7 mm in the experimental conditions with a plume of 90-mm length, compared with the conditions with a plume of 11-mm length.

The Effect of Air Knife Flow Rate on Coating Weight and Thickness for a Hot Dipping Process Simulator

A series of air knife flow rate were conducted by a hot dipping process simulator in laboratory to study its effect on coating weight and thickness. The research results show that, when the experimental steel were immersed for 3.5s in a Zn-0.24%Al zinc bath, with atmosphere of N2-10%H2 and dew point-60°C in the whole simulation, air knife flow rate (FR) was a key factor for coating surface quality. When FR was precisely controlled by the simulator from 200~500 l/min, the coating weight and thickness decreased significantly from 159.68 to 56.19 g/m2 and 17.45 to 7.84 μm. In which the decreasing line was more obvious when FR increased from 300 to 400 l/min, that the coating thickness had a dramatic decreasing from 18.08 to 11.07μm.

Effect of uniaxial stretching on thermal, oxygen barrier, and mechanical properties of polyamide 6 and poly(m‐xylene adipamide) nanocomposite films

In this study, the effect of uniaxial stretching on the thermal, oxygen barrier and mechanical properties of aliphatic polyamide 6 (PA6) and aromatic Poly(m‐xylene adipamide) (MXD6) nylon films as well as their in‐situ polymerized nanocomposites with 4 wt% clay were studied. Cast films were prepared by extrusion process and rapidly cooled using an air knife. The precursor films were uniaxially stretched at 110°C with draw ratios varying from 1.5 to 5. DSC results showed that the cold crystallization temperature (Tcc) of the uniaxially stretched MXD6 and MXD6/clay films drastically shifted to the lower temperatures when draw ratio increased. The aromatic nylon films had lower oxygen permeability than those of the aliphatic films, due to more rigidity and chain packing. However, the oxygen permeability of the stretched films increased with draw ratio (DR) up to a critical value for each sample, while further stretching resulted in a reduction in the oxygen permeation. This phenomenon was related to the changes in free volume upon uniaxial stretching. The ability of different geometrical models to describe the experimental relative permeability data was investigated. The Bharadwaj model that took into account clay orientation was the most successful one to predict the oxygen barrier characteristics of the stretched nanocomposites at high draw ratios. The Young's modulus and tensile strength of the aliphatic and aromatic nylons increased with uniaxial deformation, while the flexibility and elongation at break of the former decreased with increasing DR. A larger increase in the Young's modulus of the uniaxially stretched nanocomposite films compared with the neat samples was observed and could be related to the improvement in the clay orientation as well as a better alignment of the crystalline phase due to incorporating the clay platelets in the polymer matrix. In contrast, the flexibility of the stretched MXD6 improved remarkably (ca., 25 times) compared with the precursor film (DR = 1) when the draw ratio increased to 1.5. This could be related to the effect of hot stretching on the enhancement of polymer chains relaxation and mobility at low draw ratios. POLYM. ENG. SCI., 55:1113–1127, 2015. © 2014 Society of Plastics Engineers

The Numerical and Experimental Study on Electromagnet-Air Knife DC Casting Process of Large-Size AA 7055 Aluminum Alloys

In this paper, Low frequency electromagnetic field and air knife are applied simultaneously to produce large-size AA 7055 aluminum alloy ingots during DC casting. Moreover, the effects of low frequency electromagnetic field and air knife on macro-physical fields during DC casting as well as microstructure and crack in the ingots are studied and analyzed by the numerical and experimental methods. Comparison of the calculated results indicates that applying electromagnetic field can modify the flow direction and increase the velocity of melt flow and homogenize the distribution of temperature in the sump, and applying air knife can homogenize the distribution of temperature and decrease the stress and strain in the solidified ingots. Further, the microstructure of the billet is refined remarkably and the crack is eliminated by applying electromagnetic field and air knife during DC casting because of modification of the macro-physical fields

Properties of co-extruded nanoclay-filled aliphatic nylon (PA6)/linear low-density polyethylene and aromatic nylon (MXD6)/ linear low-density polyethylene multilayer films

In this study, coextruded multilayer films with aliphatic (polyamide 6) and aromatic (poly (m-xylene adipamide)) nylons as well as their in-situ polymerized nanocomposites with 4 wt% nanoclay, as an oxygen barrier layer (core), and a linear low-density polyethylene, as a moisture barrier layer (skin), were produced and characterized. Five-layer films were prepared by cast coextrusion and rapidly cooled using an air knife. Dynamic rheological measurements showed that the selected materials can be coextruded with a minimum interfacial instability between the melt flows in the feed block. Type of crystals, crystallinity and thermal transitions of layers were investigated using differential scanning calorimetry and modulated differential scanning calorimetry. The mechanical, optical, oxygen and water vapor barrier properties of the coextruded multilayer films were measured and discussed. Although the crystallinity of the poly (m-xylene adipamide) layer in the multilayer films was lower compared to the polyamide 6 layer, the impermeability to oxygen and water vapor was much better for the former multilayer films. In addition, substituting the neat polyamide 6 and poly (m-xylene adipamide) by their nanocomposites improved the oxygen barrier of the multilayer films by more than 50%. The series resistance model was not able to predict the barrier properties of the multilayer films due to the difference in polymer behavior for the single layer and multilayer, and boundary adjacent layer effects. The coextruded polyamide linear low-density polyethylene multilayer films showed higher toughness, tear and flex crack resistance compared to the poly (m-xylene adipamide)/linear low-density polyethylene samples. The pristine poly (m-xylene adipamide)-based multilayer film showed a lower haze compared to the polyamide 6 films due to very little crystallinity in the former.

X-ray and Trichroic Infrared Orientation Analyses of Uniaxially Stretched PA6 and MXD6 Nanoclay Composite Films

Cast films of aliphatic (PA6) and aromatic (MXD6) nylons and their in situ polymerized nanocomposites with 4 wt % clay were prepared by an extrusion process and rapid cooling using an air knife. The precursor films were then uniaxially stretched at 110 °C with draw ratios varying from 1.5 to 5. The changes in orientation of clay and crystal axes of all the crystalline phases and amorphous region were examined using X-ray diffraction and Trichroic Infrared analyses. The clay alignment was measured with three different techniques: FTIR peak deconvolution, FTIR interactive spectral subtraction and X-ray diffraction. It was found that the clay platelets are mainly oriented in the machine direction (MD) and their orientation improved upon uniaxial stretching. X-ray analysis showed that γ crystals (designated as γ1) of both nylons were mainly formed during rapid cooling of cast films. However, only the PA6/clay films showed an extra γ crystal population (designated as γ2). WAXD and FTIR analyses revealed that the c-axis of γ1 crystal population was oriented in the normal and transverse directions (ND and TD), while the c-axis of γ2 was aligned in the normal direction (ND), indicating that this later crystal population formed perpendicular to the (001) plane of the clay platelets. The orientation of γ1 and γ2 crystal populations increased after uniaxial deformation. The MXD6 showed very little crystallinity due to its higher stiffness and low relaxation rate of the aromatic chains. The amorphous region had a lower orientation in the nanocomposite films due to the spatial hindrance caused by the presence of clay platelets.

Parametric numerical study for energy savings in industrial drying process

A numerical study on the shape of a dryer was conducted with the aim of reducing the energy consumed in the actual industrial drying process. We measured the temperature distributions over the air knives in the dryer for three cases of power consumption (100%, 81%, and 67%). The measured temperature values were used as applied boundary conditions in the numerical model. To investigate the shape of the energy efficient model, three cases of the dryer’s outlet height, distance between the nozzles and the drying material, height of the dryer, and the number of heaters were selected as the geometric design parameters (X1, X2, X3). For comparing the thermal performance in each case, the temperature distribution over the conveyer line through which the drying material passes, and the inside of the dryer, was also analyzed using numerical simulations. As a result, the proposed shape of the dryer is expected to reduce power consumption while maintaining the thermal performance of the existing dryer.

Design of Compressed Air Dehumidifying Equipment for Wire Rope and Simulation of Air Knife Flow Field

Aiming at characteristics of wire rope for stringing, this text designed mechanical structure of compressed air dehumidifying device, in order to study the influence of relative angle between air knife and wire rope, jet distance and inlet pressure of air knife on blowing pressure, it designed orthogonal experiment, using Fluent to simulate flow field of air knife, then obtain the flow characteristic parameters. After analyzing simulation results, the article draws a conclusion of influence of every factor on blowing pressure and the optimal level combination, providing a basis for practical dehumidifying work.

Indoor Climate Analysis for Urban Mobility Buses: a CFD Model for the Evaluation of thermal Comfort

The aim of this work is to analyze the indoor climate in city buses; the study was developed by numerical simulation and experimental validation carried out on the urban mobility buses of the city of Rome (Italy). Several factors have contributed to increase the concern about the comfort evaluation in vehicles and particularly in city buses. Due to the rising of the mobility needs, time that people spend in vehicles has grown substantially. The thermal environment in urban buses also varies greatly: passengers are exposed to local heating and/or cooling due to vertical temperature gradients, radiant asymmetry and local unexpected airflow. The interaction of the cabin thermal environment, created by the HVAC-system, the outdoor conditions as well as the occupants is rather complex. At the moment no standards exist for assessment and classification of the thermal environment quality in vehicles. To obtain some evidences, in order to enhance the indoor climate for a city bus and to improve occupants’ comfort monitoring local temperature and air distribution around passengers, we have developed a mathematical model. The numerical model was implemented with Computational Fluid Dynamic software (CFD, Fluent Inc.): it permits the evaluation of the thermal and fluid-dynamic performances of the air conditioning system and diffusers’ distribution. To gain a deeper understanding of the local climate comfort, the numerical simulation results were experimentally validated by several measurements inside the urban buses performed under real operative conditions during the summer season.The experimental results are in good agreement with the CFD evidences. This shows that the model developed can give reliable results to optimize and locally modify the air diffusers distribution inside cabin spaces. These evidences can help to improve the air conditioning distribution as a function of the obstructions’ typical for a city bus vehicle and to reduce the draught risk related to the bus stop door apertures. One of the most important reasons of local temperature differences and unexpected air velocity gradients is due to the multi-door system apertures at each bus stop. This situation is particularly recurrent in a city area where an urban bus can afford several stops during his programmed route. For this reason it’s important to get more information about this transient localized load for the climate conditions and about the time needed to reach again the steady conditions. To avoid or, at least, reduce this kind of problem it is proposed an air knife screened doors system bus. The thermo fluid dynamic results obtained show a significant improvement in the indoor climate comfort.

Vibration Analysis of Steel Strip in Continuous Hot-Dip Galvanizing Process

In hot-dip galvanizing lines, undesirable vibration of the moving steel strip occurs due to the impingement of the high-speed turbulence jet, which leads to non-uniformity of zinc thickness, as well as splash of the liquid zinc. In this paper, the turbulent jet flow field is firstly numerically obtained using the CFD method. Then, the influence of the turbulent jet flow on the steel strip is simplified as a harmonic force at the impingement line, and the response of the steel strip is obtained by means of finite element analysis for different strip lengths, thickness and pretension forces. Influences of impingement distance, air knife slot gap and jet pressure, on vibration of the steel strip are also analyzed. The results will provide theoretical basis for the reduction of steel strip vibration in continuous hot-dip galvanizing process.

Influence of Air-Knife Wiping on Coating Thickness in Hot-Dip Galvanizing

In hot-dip galvanizing process, air jet wiping control is so crucial to decide the coating thickness and uniformity of the zinc layer on the steel strip. The mathematical models developed predict the zinc coating thickness as a function of pressure and shear stress. The required pressure and shear stress profile on the strip surface were calculated using regression analysis, and carried out using numerical simulation as FLUENT, a finite element analysis software. The influences of the outlet pressure, the nozzle to strip distance, the slot opening, the edge baffle plate, as well as the tilting angle of air knife were discussed. Combining with these results and regression analysis on the practical data, four first-order polynomial multi-parameter models were established for different targeted coating thicknesses with better regression coefficients. The validated model was used to carry out sensitivity analysis to determine the favorable controlling regime for the air jet wiping process.