Woven Screens Research Articles

Computational modelling and experimental validation of pressure drop through multi-layered woven screens for polymer melts

Woven screens are commonly used in filtration processes that involve molten polymer. Predicting the initial pressure drop across these screens is crucial for selecting an appropriate filtration system as it directly affects the efficiency and cost-effectiveness in industrial processes. Existing computational models for predicting pressure drop through woven screens have not been developed for multi-layered configurations. This study develops an accurate and reliable methodology for using computational fluid dynamics (CFD) to model the pressure drop across a multi-layered screen. The computational model is validated through an experimental set-up.

Liquid – Solid mass transfer characteristics of a heterogeneous reactor made of separated horizontal woven screens impinged by a submerged jet

The mass transfer characteristics of a submerged liquid jet impinging on a stack of separated screens were investigated by the electrochemical limiting current technique. The effects of changing the jet velocity, the nozzle diameter, and the screens’ porosity were studied. The present mass transfer data were found to be much higher than the data obtained by previous studies on jet impinging on flat surfaces. The mass transfer data also revealed that using the impinging jet greatly enhanced the mass transfer at screen surfaces with respect to other conventional forced convection methods used in previous studies. The mass transfer data were correlated by the equation: ShR=0.253Sc0.33ReN0.66ε0.745 for the conditions: Sc=1898, 8071 ≤ ReN≤ 33631, 0.668≤ε≤ 0.809. The importance of the above equation in the scale up and design of electrochemical and catalytic reactors suitable for diffusion-controlled reactions was highlighted. The calculated high energy utilization efficiency (kA/e) of the reactor lends support to its use in practice in preference to reactors made of flat surfaces impinged by a submerged jet. By supporting catalyst on the screens, the reactor also can replace stirred slurry reactors usually used in conducting biochemical and photochemical reactions in order to eliminate the time consuming and the costly step of separating the final product from the catalyst particles.

Effect of Roller Shades on Chromaticity and Colour Rendering Performance of Transmitted Daylight

Several studies have focused on the performance of roller shades in terms of glare, outdoor vision, daylight availability and energy performance. Currently, other parameters linked to visual amenity, such as chromaticity and colour rendition, are becoming relevant. When solar radiation passes through a window, it changes its spectral composition due to the presence of the solar shading system and the glazing. Against this background, the present study focuses on the spectral transmittance of eleven woven screen fabrics and its influence on the chromaticity and colour rendition. Results show that dark-coloured woven screen shades provide higher correlated colour temperature (CCT) values (range 6470 K - 6479 K) and therefore would produce “cooler” visual environments, while light-coloured woven screen shades provide lower CCT values (range 5210 K - 5644 K) creating “warmer” visual environments. Regarding colour rendering metrics, the light transmitted through all the studied woven shades shows excellent colour rendition. Finally, it is concluded that the combined analysis of optical properties, spectral data and its impact on parameters that determine the quality of lighting in an interior space enables an understanding of woven screens performance, which results in the possibility of taking appropriate decisions when selecting woven shades.

Using Symbolic Regression Models to Predict the Pressure Loss of Non-Newtonian Polymer-Melt Flows through Melt-Filtration Systems with Woven Screens

Abstract When selecting a melt-filtration system, the initial pressure drop is a critical parameter. We used heuristic optimization algorithms to develop general analytical equations for estimating the dimensionless pressure loss of square and Dutch woven screens in polymer processing and recycling. We present a mathematical description – without the need for further numerical methods – of the dimensionless pressure loss of non-Newtonian polymer melt-flows through woven screens. Applying the theory of similarity, we first simplified, and then transformed into dimensionless form, the governing equations. By varying the characteristic independent dimensionless influencing parameters, we created a comprehensive parameter set. For each design point, the nonlinear governing equations were solved numerically. We subsequently applied symbolic regression based on genetic programming to develop models for the dimensionless pressure drop. Finally, we validated our models against experiments using both virgin and slightly contaminated in-house and post-industrial recycling materials. Our regression models predict the experimental data accurately, yielding a mean relative error of MRE = 13.7%. Our modeling approach, the accuracy of which we have proven, allows fast and stable prediction of the initial pressure drop of polymer-melt flows through square woven and Dutch weave screens, rendering further numerical simulations unnecessary.

Flow Physics of Wicking into Woven Screens with Hybrid Micro-/Nanoporous Structures.

Wicking within woven screens has attracted considerable attention due to its important role in applications concerning phase-change heat transfer and phase separation. In the present study, horizontal spreading experiments are conducted to investigate the wicking performance of woven screens by measuring the volumetric liquid intake into the screens and the liquid propagation fronts through two perpendicular high-speed cameras. Woven screens with micro (single- and multilayer)- and nano (plain, etched, and fluoridated)-porous structures are manipulated through diffusion bonding and chemical processes. The macroscopic observation indicates the substantial enhancement of the wicking capability in multilayer structures, where the interlayer microchannels could compensate for the essential deficiency of single-layer screens by providing low-resistance flow passages. Wicking capability of water is enhanced by the hydrophilic nanograsses along the wires. Furthermore, flow mechanisms within the screens are analyzed by comparisons between apparent and saturated wicking distances. In multilayer structures, the liquid spreads along the entire cross-sectional area in etched screens, while it spreads primarily along the interlayer microchannels in plain and fluoridated screens. The influence of various fluids on the wicking behavior within the woven screens is found to be fully represented by a unique parameter that captures the effects of surface tension and dynamic viscosity in the radial flow model. This work deepens the understanding of the capillary-driven flow within the woven screens with hybrid micro-/nanoporous structures and provides guidance for the design and manufacture of highly efficient wicking structures.

Robust foil regenerator flow loss and heat transfer tests under oscillating flow condition

A regenerator works as an energy storage component in a Stirling engine. Thus, it is one of the most critical components that makes the Stirling engine highly efficient. Traditionally, the regenerators are made of wire media such as woven screens and random fibers. These wire regenerators experience considerably high flow losses through the regenerator due to the flow separation and the resulting vortices. The high flow losses associated with the flow separation and vortices result in a lower engine efficiency. This research is to test a new robust foil regenerator to investigate its feasibility for free-piston Stirling engine applications. The robust foil regenerator is configured with parallel flow channels and stiffening ribs. Comparing to complex flows patterns in woven screen and random fiber regenerators, the flows in the parallel plates are simple and the flow losses are considerably small, and the heat transfer coefficient is also relatively small. To test the regenerator experimentally, a regenerator test rig was manufactured. To verify the accuracy of the test rig, a woven screen regenerator was made and tested prior to the robust foil regenerator test. The friction factor correlation of the woven screen regenerator shows a good agreement with the published regenerator correlations. The robust foil regenerator tests were conducted under the oscillating flow condition with different Reynolds numbers. The flow losses were measured with dynamic pressure transducers and the friction coefficient was derived from measured pressure drop. The measured temperature difference over the regenerator was used to calculate the heat transfer coefficient and Nusselt number. The figure of merit with two methods of NPH/NTU ratio and j/f ratio was calculated to evaluate the suitability of the robust foil regenerator. The results show that the robust foil regenerator has considerably higher figure of merit and therefore, better performance than other types of regenerator.

Investigation of the Performance of Different Cleaning Devices in Maize Grain Harvesters Based on Field Tests

HighlightsThe effects of different factors on the performance of cleaning devices are investigated.The loss percentage is negatively correlated to the moisture content of maize grain.The cleaning performance is affected by the plant spacing and the ear mass of maize.The long-toothed scale screen has the best performance in throwing impurities.Abstract. The direct harvest of maize grain achieves high working efficiencies and low harvest costs; thus, direct harvest will become increasingly common for harvesting maize in the future. To investigate the loss percentage of maize grain (LPOMG) and the impurity percentage of maize grain (IPOMG) for harvesting in the northeast reclamation area in China, field tests were completed with various moisture contents of maize grain (MCOMGs), maize varieties, types of cleaning screens, and travel speeds of the harvesters. The results showed that the LPOMG of Xianda 205 maize with an MCOMG of 30.49% was the lowest at 0.37% and the IPOMG of Xianda 205 maize with an MCOMG of 22.62% was the lowest at 0.14% when the maize mixture was cleaned with the common scale screen in the S660 harvester. The LPOMG of Hayu 189 maize was the lowest at 0.19% when using the S660 harvester at a travel speed of 1.0 m s-1, and the IPOMG of Xianda 205 maize was the lowest at 0.28% when using the S660 harvester at a travel speed of 2.0 m s-1; the different varieties of maize mixtures were cleaned with the common scale screen. The LPOMG of Xianda 205 maize cleaned with the stepped woven screen was the lowest at 0.25% when using the GK100 harvester at a travel speed of 1.0 m s-1, and the IPOMG of Xianda 205 maize cleaned with the long-toothed scale screen was the lowest at 0.10% when using the 7088 harvester at a travel speed of 2.0 m s-1. This study provides a reference for selecting a suitable maize variety, type of screen, and the earliest harvest time for direct harvesting of maize grain. Keywords: Cleaning, Field test, Harvesting maize, Impurity, Loss.

Empirical Formulae for Determining Pressure Drop Across a 20-Layer Flooded-Bed Scrubber Screen

The use of a woven wire-mesh screen as part of a flooded-bed dust-scrubbing system is very popular in the underground coal mining industry. It is used in combination with a demister (mist eliminator) to remove dust from the dust-laden air. A study was conducted to measure the pressure drop across a flooded-bed wire-mesh screen at different airflow rates in one-phase (dry) and two-phase (wet) conditions. Two empirical relationships between pressure drop and air velocity were developed for dry and wet conditions, respectively. In both cases, the form of the empirical relationships was found to be similar to relationships given by Sabri Ergun for high velocity non-Darcy single and multi-phase flow through porous media. The experiments were repeated on a reduced-scale model of the wire-mesh screen, and the pressure-velocity relationships obtained from the full-scale prototype experiments were tested. The test results show validation of the full-scale empirical formulas on the small-scale model with an insignificant variation. This paper presents the empirical equations for pressure drop across the wire-mesh screen in dry and wet conditions. Researchers can use these equations as a tool to predict total pressure drops for wire-mesh screens of different scale sizes.

Electrochemical removal of copper from a simulated wastewater using a rotating tubular packed bed of woven screens electrode Removal of heavy metals using packed bed rotating electrode

Copper removal from a simulated wastewater was investigated by using rotating tubular packed bed of woven screens electrode as a cathode in a new design of electrochemical reactor. Effects of electrolysis operating parameters like current (0.5–2.5 A), rotation speed (150–750 rpm), and initial copper concentration (100–500ppm) were investigated. Optimization of process parameters was carried out by adopting response surface methodology (RSM) combined with Box–Behnken Design (BBD) where copper removal efficiency was selected as a response function. The results indicated that current has the main effect on the copper removal efficiency followed by rotation speed and concentration. The results of regression analysis revealed that the experimental data could be fitted to a second-order polynomial model with a value of determination coefficient (R2) equal to 0.9894 and Fisher test at value of 51.57 for. The optimum conditions of the process parameters based on RSM method were an initial copper concentration of 205 ppm, current of 2.5A, and rotation speed of 750 rpm utilizing cathode composed of screens with mesh no. 30 where a final copper concentration less than 2 ppm was obtained after 30 min.

Practical study on the electrochemical simultaneous removal of copper and cadmium from simulated wastewater using rotating tubular packed bed cathode

The simultaneous removal of copper and cadmium from a simulated wastewater using rotating tubular packed bed of woven screens electrode was investigated. The effect of weight present of each metal on the removal efficiency and current efficiency was studied. The experiments were carried out at current 1.5 A, rotation speed 450 rpm, pH=2, and total concentration of metals (300 ppm) at different weight percent of each metal. The results showed that the removal efficiency of copper increased from 93.5 % to 99.33% as its weight percent increased from 20% to100%. In a similar fashion, the removal efficiency of cadmium increased from 80% to 90% as its weight percent increased from 20% to100 %. The results confirmed that the removal efficiency of any metals decreased in the presence of other metal. The results established that current efficiency for the simultaneous removal of copper and cadmium decreased with increasing of electrolysis time and Cd percent weight or decreasing of Cu weight percent. Current efficiency is higher at the initial stage of electrolysis and then declined with increasing time for all weight percent of metals.

A heuristic method for modeling the initial pressure drop in melt filtration using woven screens in polymer recycling

This paper addresses the use of heuristic optimization algorithms to generate generally valid analytic equations for estimating the initial pressure drop of square and Dutch woven screens in polymer recycling. We present a mathematical description of the isothermal initial pressure drop of non‐Newtonian polymer melt flows through woven screens without the need for numerical methods. We first performed numerical CFD simulations to create a set of 9,000 physically independent modeling set‐ups as a basis for heuristic modeling. Then, we applied symbolic regression based on genetic programming to develop pecScreen models, achieving coefficients of determination R2 > 0.9995. For verification of our models, we performed experiments using both virgin and slightly contaminated in‐house and post‐industrial recycling materials. The experimentally determined data are in good agreement with the approximation results, which yielded a coefficient of determination R2 of 0.926. Our modeling approach, the accuracy of which we have proven, allows fast and stable computational modeling of the initial pressure drop of polymer melt flows through woven screens. POLYM. ENG. SCI., 59:1105–1113 2019. © 2019 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.

Pressure drop analysis of oscillating flows through a miniature porous regenerator under isothermal and nonisothermal conditions

In this paper, we present an experimental study on the pressure, pressure drop, velocity and friction factor in a regenerator made from an array of pillars in reciprocating flow conditions. The fluid used in the experiment is air. We show that the pressure drop depends on the porosity, frequency and stroke. We observe a phase shift between the crank angle sinusoidal variation of the piston and the pressure variation that increases with frequency. We also observe that the instantaneous friction factor is higher in the discharge phase than in the suction phase, and higher in the acceleration than in the deceleration phase. Friction factor in oscillating flow appears to be higher than friction factor in steady unidirectional flow for the highest porosity. For the lower porosities, we observe that the pressure drop and friction factors are similar for maximum Reynolds numbers lower than 5000. An experimental correlation for the friction factor of the regenerator is derived in order to design a millimetric Stirling engine. The friction factor is compared with friction factors reported for woven screens, metal felts and involute foil regenerators.

Pressure drop measurements for woven metal mesh screens used in electrical safety switchgears

The paper deals with an experimental investigation of the pressure drops and friction factors induced by sets of metal woven screens in the case of an incompressible fluid flow, namely water flow. These woven screens are of metallic type and are used in electrical safety devices, especially at the end of exhaust duct of low voltage circuit breakers. In a first step, the whole of the set-up is used to check some approximations dedicated to pressure drops due to sphere beds around 275µm and 375µm as diameters. Results are discussed in terms of Darcyan and non-Darcyan permeabilities compared with published data and are analyzed in terms of the Blake-type friction factor. In the second step, the pressure drops are measured for stacks composed of eight different woven screens (of plain dutch type) formed with millimetric wires. Various formulations of the pressure drops and friction factors published elsewhere are tested with a special care dedicated to the choice of the geometry for the flow pattern (hydraulic diameter, spherical diameter, cylindrical diameter) and to the consideration of laminar and turbulent contribution. We then give the formulation that characterizes the fluid flowing through stacks of woven screens used in electrical safety applications.

平織金網背後に形成する縦渦対の可視化計測

In order to control various industrial flow fields there are two types of square lattice structure, biplane grid and woven screen. Woven screen which is used as a rectification lattice consists of the alternation of knitted circular crynders. Though the woven screen and the biplane grid have similar shape, the vortex structure behind two types of lattice is though to be different each other. However, the vortex structure formed behind these lattices is not almost known yet. It way leads to the explanation of the straightening effect of woven screen to clarify vortex structure. Therefor, the aim of this investigation is to clarify the vortex structure formed behind woven screen and the growth process in the near wake by means of flow visualization and PIV measurement using the stainless steel large model of woven screen submarged in the water tunnel flow under the low Reynolds number. As a result, two pair of longitudinal vortices behind all downstream cylinders are produced in the cross region of circulare cylinder menbers. The secondary flow which is made by four longitudinal vortices shows a plus or minus vorticity in each mesh. It becomes difficlut to confirm four longitudinal vortices in the wake region of x/d=10.0.

Experimental Measurement of Direct Thermal Radiation Through Single-Layer Square-Cell Plain Woven Screens

Australian bushfires have repeatedly killed many people and caused severe damage. Previous studies have identified direct flame contact and radiant heat as the main cause of fatalities. The role of screens to limit the radiation exposure of an object by a fire on the opposite side of the screen is well-known, but still it has not been experimentally quantified. A screen between a radiation source and an object divides the radiant heat flux (RHF) into two parts. The first part is the direct RHF (DRHF) that passes directly through the screen without any interaction. The second part is indirect RHF (IRHF), which includes both emitted and reflected RHFs by the heated screen. This experimental study deals with the DRHF, which is dependent on the screen porosity and is independent of the material composition or the surface quality of the screen. The experimental results of four square-cell, plain woven screens, with porosities ranging from 41% to 66%, show that the passing ratios (PRs) of DRHF through screens are less than those suggested by their porosity. Four empirical equations have been developed to determine the PR of the direct radiation through screen and the tunnel vision angles of the screens.

Mass transfer at a rotating tubular packed bed of woven screens in relation to electrochemical and catalytic reactor design

The mass transfer behavior of a rotating tubular packed bed of woven screens was studied using an electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide in a large excess of supporting electrolyte. Variables studied were bed rotation speed, bed thickness and mesh number of the woven screen. The mass transfer coefficient was found to increase with increasing bed rotation speed and mesh number but decreases with increasing bed thickness. The data for rotating screen bed were correlated by the dimensionless equation:Sh=4.85Sc0.33Re0.32dhd-0.25 The mass transfer coefficient at single rotating screen cylinder was found to be higher than that of rotating packed bed of screens. Both rotating single and packed bed of screens gave higher volumetric mass transfer coefficient than smooth rotating cylinder. Implication of the present results for the design and operation of electrochemical and catalytic reactors suitable for conducting liquid–solid diffusion controlled reactions such as photocatalytic reactions and immobilized enzyme catalyzed biochemical reactions was highlighted.

Possibility of a Straightening Flow-Meter by Using Woven Screen

In this paper, the possibility of the flow rate measurement for a circular pipe flow by using a wo-ven screen with the property of straightening un-uniform flows is discussed. The resistance coefficient and the flow rate coefficient are estimated from the pressure difference caused by the woven screen under the experiment ranges of the wire Reynolds number, Red = 2.2 × 102-1.8 × 103, and of the open area ratio, β = 0.28-0.65. As a result, the resistance coefficient decreases and the flow rate coefficient increases as the wire Reynolds number Red or the open area ratio β increases. In addition, both coefficients are not affected by the difference between uniform and turbulent pipe flows approaching the woven screen. Therefore, the possibility of a flow-meter having the property to straighten the un-uniform flow is expected.

Acoustic pressure losses in woven screen regenerators

In thermoacoustic travelling-wave engines and other Stirling cycle devices, good performance depends on the material of a regenerator being in intimate contact with the gas inside it, so that each particle of gas oscillates in temperature following the adjacent material as it is acoustically displaced. This requires that the passages are small enough for temperature waves to penetrate across the gas path with the frequencies of interest. One type of ‘regenerator’ that is commonly used for this purpose is composed of multiple layers of woven stainless steel mesh, laid on top of one another in random registration. Associated with the thermal penetration is a viscous loss of pressure and this must be quantified if efficient engines are to be designed.In the literature, reliance has been placed on the correlation of steady-flow loss data for these meshes, but for the coarser ones operating at frequencies greater than 28Hz, the assumption of quasi steady-flow is dubious and direct acoustic measurements must be made. This paper reports acoustic pressure loss data for meshes with 34 and 75 wires per inch taken in two configurations of impedance tube, and finds that the dependence on velocity is the same as in steady-flow, but that there is indeed some enhancement of loss for frequencies above 40Hz. (Separation of the mesh layers is probably responsible for the anomalously low loss coefficients that were recorded in one set of data.) It is shown that the acoustic pressure losses can be correlated in terms that give the acoustic impedance more directly than the friction factor correlations.

5:1의 형상비를 갖는 사각덕트에서 직조 스크린 리입(rib)이 열전달과 마찰계수에 미치는 영향

직조 금속 스크린 리브(rib) 이 바닥에 설치된 사각 덕트에서 열전달과 유체유동의 압력강하를 측정하기 위해 실험적 연구를 수행하였다. 시험부의 치수는 200 mm(W) <TEX>${\times}$</TEX> 40 mm(H) <TEX>${\times}$</TEX> 712 mm(L)이고 수력직경은 66.6 mm이다. 입구영역에는 1.72m 길이의 가열되지 않은 동일한 치수의 채널을 설치하였다. 메쉬가 다른 4가지의 직조금속 스크린 리브에 대해 측정하였다. 그리고 비교를 위해 일체형 리브에 대해서도 측정하였다. 국부 열전달 계수의 측정에는 스테인레스 강제 포일(foil) 히터와 T형 열전대률 이용하였다. 레이놀즈 수는 23,000에서 58,000의 범위이다. 덕트의 수력직경(<TEX>$D_h$</TEX>)에 대한 직조 금속 리브의 높이(e)의 비(<TEX>$e/D_h$</TEX>)는 0.075 이고 리브 간격(p)과 높이의 비(p/e)는 10이다. 실험 결과 메쉬가 없는 일체형 리입에서 가장 누셀트 수와 마찰계수가 컷다.

On the applicability of the Forchheimer equation in simulating flow through woven screens

Flow through woven screens is of continuing interest in many fields, including protected horticulture, in which such screens are used mainly to protect crops against insects. Screens may significantly affect crop microclimate, therefore computational fluid dynamics (CFD) simulations have been used by researchers in recent years to predict their effects on the distribution of microclimate parameters within the structures where the crop is grown. In such simulations screens are usually represented by porous media, through which the pressure drop is estimated by means of the Forchheimer equation. The applicability of the Forchheimer equation to estimate pressure drops through woven screens was investigated. Firstly, the results of CFD simulations of flow through realistic models of woven screens were validated by means of wind tunnel tests and by means of a published correlation for calculating pressure drops through such screens. The CFD tool was then used in conjunction with the wind tunnel tests and published correlation results to examine whether the coefficients in the Forchheimer equation are constant over a wide range of Reynolds numbers, and to explore the flow through the screens. It was found that the values of the Forchheimer coefficients varied with Reynolds number, and that the changes in their values can be assumed to be relatively small and not very significant but only up to a Reynolds number, Rei ≈ 130–160. Moreover, presenting the Forchheimer coefficients as functions of only porosity may lead to erroneous predictions of pressure drops.