Wire Screen Research Articles

A comparative study of porous medium CFD models for flow diverter stents: Advantages and shortcomings.

In computational fluid dynamics, there is a high interest in modeling flow diverter stents as porous media due to its reduced computational loads. One of the main difficulties of such models is proper parameter setup. Most authors assume flow diverter's wire screen as an isotropic and homogeneous medium, while others proposes anisotropic configurations, yet very little is discussed about the effect of these assumptions on model's accuracy. In this paper, we compare the effect of different models on hemodynamics in relation to their parameters. The fidelity and efficiency of the different models to capture wire screen effect on fluid flow are quantitatively analyzed and compared.

Simulation and experimental investigation of fluid flow in porous and non-porous solar air heaters

The porous absorber in the solar air heater gives considerable temperature increment which is shown by computational fluid dynamic simulation and verified experimentally. Experimental analysis on porous (wire screen) and non-porous solar air heaters were carried out to study the heat transfer and friction factor characteristics. The analysis encompasses the investigation on effect of mass flow rate on air temperature increment, thermal efficiency and pressure drop across the test section. The heat transfer parameter is established in terms of Colburn (Jh) factor for porous bed solar air heaters. The effect of friction factor on different geometries for a range of operating Reynolds number (194–591) is presented. Two wire screen matrix (WSM) solar air heater WSM-I and WSM-II were investigated which has different diameter, pitch and porosity. Thermal efficiency increased on introducing the packed wire-screen matrix diagonally in the air flow path. The increase in thermal efficiency for WSM-I and WSM-II were found to be 5–17% and 5–20% respectively with the mass flow rate ranging from 0.01 kg/s to 0.055 kg/s. The collector heat removal factor was found to be 0.95 ± 0.021 for wire mesh absorber and 0.72 ± 0.0073 for conventional type. The pressure drop across the length of the duct was studied to be in the range of 15 ± 0.28 Pa to 17 ± 0.28 Pa and 7 ± 0.16 Pa to 11 ± 0.28 Pa for WSM-I and WSM-II respectively and for conventional type it was between 5 ± 0.20 Pa and 10 ± 0.28 Pa.

The Influence of Rotational Speed on the Wall Thickness and Mechanical Characteristic of Rotomouldable Plastics

This study is interested in the main parameter of this technique that uses a cubic container with an internal dimension of 100 mm and a cylindrical container 100 mm in diameter. We implemented the work in the fifth stage: In the first stage, we designed and manufactured the multi-axial system. In the second stage, the specimens were moulded from polyester, PVC, and polyethylene at a rotational speed axis of 5–120 rpm. The results from this stage indicated that the optimal rotational speed of the steady quality in dimensions and properties of the parts are 85, 100 and 115 rpm. The third stage was concerned with the effect of the speed of rotation on the thickness of the wall. The rotational speed of the axes was changed, and the thickness of the moulded walls was measured. The laboratory measurements revealed that the maximum compression ratio with the change of speed is at the speed of 115 rpm. The fourth stage was concerned with the effect of the speed of rotation on the value of tensile strength. The rotational speed of the axes was changed, and the tensile strength of the mould was measured. The tests revealed an improvement in the tensile strength at the speed of 115 rpm compared with the other speeds. The fifth stage utilised a cylindrical mould, which was re-worked in the previous stages, to investigate the effect of the speed of rotation on the thickness of the wall and mechanical specifications. Based on the conducted experimental tests, the influence of the rotational speed, which characterized the moulding process, on selected geometrical features of the mould was studied and analysed theoretically and numerically. The results showed an increase of about 5% in the compression ratio with increased rotation speed within the range of 85 to 115 rpm. There was also an improvement of about 7% in the tensile strength with increased rotational speed from 85 to 115 rpm. These results are due to the increase in the centrifugal force on the wall of the mould during the process. Also, the study was characterized by the production of the composite of polyethylene reinforced by iron screen wire, with improvement in the mechanical properties by about 300% compared to the base material.Â

A porous media model for CFD simulations of gas-liquid two-phase flow in rotating packed beds

The rotating packed bed (RPB) is a promising advanced reactor used in industrial gas-liquid two-phase reaction processes because of its high phase contact efficiency and mixing efficiency. Investigation of RPBs using CFD simulations will improve the understanding of physical behaviours of gas and liquid flows in such reactors. Currently, CFD simulations on the RPBs only focus on the volume of fluid (VOF) method. However, the VOF method is not suitable for simulations of pilot-scale 2D and 3D RPBs due to the limitations in computer resources, while the Eulerian method using a porous media model is a promising alternative method but it is rarely reported. The reason is that there are no suitable porous media models that accurately describe the drag force between the gas and liquid, the gas and solids and the liquid and solids due to the high porosity and the stacked wire screen packing used in RPBs. Therefore, the purpose of this paper is to propose a new model for modelling RPBs. The new proposed model is based on the Kołodziej high porosity wire screen one-phase porous media model. In this work, two experimental counter-current gas–liquid flow cases from the literatures have been used for validating the CFD simulation results. Finally, the new model has been compared with the current porous media models for traditional spherical or structured slit packed beds, which are the Attou, Lappalainen, Iliuta and Zhang models. The simulation results show that the proposed new model is the most appropriate and accurate model for the simulation of RPBs among all the models investigated in this paper.

Effect of Low Temperature on a 4 W/60 K Pulse-Tube Cryocooler for Cooling HgCdTe Detector

Temperature is an extremely important parameter for the material of the space-borne infrared detector. To cool an HgCdTe-infrared detector, a Stirling-type pulse-tube cryocooler (PTC) has been developed based on a great deal of numerical simulations, which are performed to investigate the thermodynamic behaviors of the PTC. The effects of different low temperatures are presented to analyze different energy flows, losses, phase shifts, and impedance matching of the PTC at a temperature range of 40–120 K, where woven wire screens are used. Finally, a high-efficiency coaxial PTC has been designed, built, and tested, operating around 60 K after a number of theoretical and experimental studies. The PTC can offer a no-load refrigeration temperature of 40 K with an input electric power of 150 W, and a cooling power of 4 W at 60 K is obtained with Carnot efficiency of 12%. In addition, a comparative study of simulation and experiment has been carried out, and some studies on reject temperatures have been presented for a thorough understanding of the PTC system.

Wind tunnel experiments on effects of woven wire screens and buffer zones in mitigating risks associated with firebrand showers

The benefits of using wire screens to mitigate wildfire spread are well known and many standards mandate their use in wildland fire prone areas. However, some recent studies show that firebrands can penetrate through screens. The penetrated firebrands are smaller in size, have less potential to ignite fuel beds and have a shorter burn-out time. This leads to the idea that a combination of a buffer zone and screens might be able to serve as a wildfire barrier. This study aims to explore the effectiveness of such an approach for two screens with a relatively short buffer zone. The results show that the combination is very effective in reducing firebrand intensity but falls short of full protection. The study suggests the combination of screens and a wider buffer zone is a promising approach to mitigate the spread of wildfires.

How does the packing density of a metal screen affect the mechanism for catching highly charged nanoparticles?

Highly charged aerosol nanoparticles of a molecular size (< 5 nm) exhibit complex behaviors caused by random (Brownian) motion and electrostatic interactions (image force) with solid surfaces. The classical single fiber theory, however, can only partially describe the complex filtration mechanism of highly charged nanoparticles. We began this study by employing the Langevin Dynamics (LD) Method to simulate the random motion and deposition of highly charged nanoparticles on a single fiber. The single fiber efficiencies predicted by the LD simulation did not agree with data from experiments using electrosprayed highly charged molecular ions. To explain this mismatch and search for other factors that could potentially affect the capturing mechanism, we investigated the influence of the mesh structure. While the image force exerted a significant influence as the packing density decreased, the influence tended to oppose the theoretical predictions. These results suggested that the fiber-fiber interaction in a wire screen with high packing density significantly influences the collection of multiply charged molecular ions. A new theoretical model describing the influence of inter-fiber interaction will be required to clarify how highly charged molecular ions are captured by image force.

Modelling droplet sliding angle on hydrophobic wire screens

This work presents a detailed investigation of the droplet lower and upper contact angles on hydrophobic wire screens with different properties such as wire diameter, wire spacing, or Young–Laplace contact angle. Numerical simulation and experiment were considered to better our understanding of the factors impacting droplet sliding on a hydrophobic screen, and to quantify their importance. To conduct the numerical simulations, the screens’ geometry was programed in the Surface Evolver code, and the droplet shape was obtained by minimizing the total energy of the droplet–screen system iteratively using the code’s finite element solver. Good general agreement was observed between the results of our numerical simulations and experimental data. Most interestingly, it was observed that droplet sliding angle increases with increasing the wire spacing in screens with a given wire diameter. To explain this counterintuitive observation, detailed quantitative information is presented in terms of the three-phase contact line on the droplet’s receding side as well as the penetration of the air–water interface into the void space between the wires. The results of our study are discussed in the context of the contemporary literature.

Guest room safety management of resort hotels as destination in Thailand (A case study of Khao Kor District, Phetchabun Province)

The purpose of this study is to study the satisfaction level of guest room safety management of resort hotels in Khao Kor District, Phetchabun Province. A researcher adopted a quantitative methodology used a questionnaire with the accidentally-met Thai 387 tourists travelling to Khao Kor District during winter season which is considered as a high season in the area. The data from the questionnaire then is analyzed as descriptive statistics. Some interviews are conducted with the tourists to have more fruitful information. General information is analyzed by using descriptive statistics describing percentages. Information on satisfactions of in-room safety management of hotels in Khao Kor District, Phetchabun Province is analyzed by using mean (X) and standard deviation (S.D.). The results revealed that the tourists are satisfied with the good condition and secured-lock guestroom door at most (X = 4.88), followed by the safe from outside danger of guestroom balcony (X = 4.84), the good condition and safe from danger of mosquito wire screens and curved steels (X = 4.74) respectively. Although the least satisfaction of the tourists about in-room safety management is light and well-ventilated guestroom toilets and clean sanitary ware (X=4.05), it is still in high level. Some useful suggestions from the tourists about the in-room safety management of hotels in Khao Kor District, Phetchabun Province are the hotels should have a safety instruction in English and Chinese version because it will be useful for international tourists in case of emergency, a floor plan and fire exit way should be clear both picture and wordings so it will be easy to evacuate safely. In the meantime, next researcher should conduct other kinds of hotels in Khao Kor District such as guesthouses that are quite popular among the tourists to be aware of safety management may have.

Effective factors on the performance of woven wire screens against leaf firebrand attacks

Firebrand spotting is the dominant wildfire propagation mechanism. The use of wire screens to prevent firebrand entry into structures is recommended or mandated by many standards. The existing standards address only one feature of screens which is opening size. This experimental study aims to explore several other factors that may influence the performance of wire screens and may need to be incorporated in codes and standards development process for structures located in wildfire-prone areas. The results demonstrate a previously unreported shattering mechanism in the case of Eucalyptus populnea (from the Myrtle family) leaf firebrands under a moderate wind speed of 14.5 m s−1. The results also show that screen porosity, screen type and wind speed would be appropriate to be addressed in developing standards, but there is no need for concern about screen orientation as long as the screen is placed perpendicular to the wind direction during the experiment.

Numerical simulation of flows over vacuometers by means of the Monte-Carlo method of direct statistical simulation

An upper atmosphere probe is considered. For the atmosphere parameters, a reconstruction method using the density data by a vacuometer located behind a wire screen is constructed. In the context of the Monte-Carlo method of direct statistical simulation, we propose a simplified simulation algorithm for the interactions of a molecule with the wire screen treated as a semipermeable membrane. To obtain a relationship between the transmitter reading and the parameters of the undisturbed atmosphere, we numerically simulate the flow over the transmitter.

Prediction of Darcy Permeability and Forchheimer’s Coefficient of Porous Structures Relevant to Regenerator of a Stirling Cryocooler Using a Correlation Based Method

A regenerative heat exchanger is the most vital component in the design of a Stirling cryocooler. Computational Fluid Dynamics (CFD) is the best technique for the design and prediction of the performance of a regenerator. The reliability of the simulation results depend on the accuracy of the Darcy permeability [Formula: see text] and Forchheimer’s inertial coefficient [Formula: see text] used for modeling the momentum transfer in porous media. Usually these coefficients are calculated from pressure drop data obtained from experiment. Because of the requirement of sophisticated equipments for the measurement and analysis of data, experimental study becomes expensive. This paper proposes a friction factor correlation-based method for the prediction of directional permeability and Forchheimer’s inertial coefficient of wire mesh structures relevant to Stirling cryocooler. The friction factor for the flow of helium through #325, #400 and #635 SS wire matrices with porosities of 0.6969, 0.6969 and 0.6312 are calculated using standard correlations and compared with the friction factor given by Clearman et al. based on steady flow experimental study. The friction factor obtained from Blass and Tong/London correlations are in agreement with that of Clearman et al. The viscous and inertial resistances are calculated from the friction factor obtained from Blass and Tong/London correlations. Using these values, the regenerator was modeled as a porous media in Fluent. From the steady flow simulation, pressure drop at different mass flow rates (0.08–1.44[Formula: see text]g/s) is obtained. The maximum deviation of predicted pressure drop from the reported experimental data is 15.14%. The Darcy permeability [Formula: see text] and Forchheimer’s inertial coefficient [Formula: see text] obtained from correlation-based method was used for modeling the oscillatory flow of helium through a #400 regenerator. The pressure amplitude and phase at regenerator exit were obtained at different frequencies. The average deviation of predicted pressure amplitude from the experimental data is 15.83%. The model could predict the phase angle also accurately. Therefore, the proposed method can be used to calculate the hydrodynamic parameters of woven wire screen matrices applied to Stirling cryocoolers.

Experimental investigation on the effect of wire mesh at the nozzle exit on heat transfer from impinging square jets

This paper reports the results of an investigation carried out to study the effect of a wire screen mesh installed at the nozzle exit on the heat transfer performance of a square jet. Towards this, experiments are carried out to cool an electrically heated flat plate with an impinging air jet issued from a square orifice. Three wire meshes with area based porosity values of 0.35, 0.41 and 0.66 respectively are employed in this study. Heat transfer characteristics are presented as stagnation point and local Nusselt numbers. The heat transfer characteristics of the jets with and without the wire meshes are compared at (i) the same mass flow rate of the jet fluid and (ii) the same power consumption of the jet across the nozzle. To support the heat transfer results, mean velocity and turbulence intensities are measured along the jet centerline with a hot-wire anemometer. The effect of dimensionless jet-to-plate distance (2–8.5) on the heat transfer rate is studied as well.

Boiling on fins with wire screen of variable effective conductivity

The high scale of integration of modern equipment used for medical, military and other purposes puts heavy demands as regards the removal of great heat fluxes. This can be achieved only in exchangers that apply the phase change phenomena. Among many methods to improve boiling heat transfer, the wire mesh covering demonstrates some advantages due to the possibilities of designing the desired microstructure parameters, availability on the market, and low cost. The wire mesh microstucture with specified geometrical parameters produces anisotropy in conductivity. The different arrangement of the mesh layers relative to the direction of the heat flux is a cause of the change of temperature distribution within the layer. The consequence is a respective change in the discharge conditions of the gas phase and liquid feed. The experiments were conducted on fins covered with a single layer of copper mesh with lumen of 38 % and boiling FC-72 at ambient pressure. Compared with the smooth surface, the wire mesh structures yield an increase in the heat transfer rate at boiling. It is also shown that nucleate boiling is initiated at lower wall superheat. Formulas for longitudinal and perpendicular thermal conductivity are given for different mesh structure arrangements.

Inclusion of Wire Twisting Effects in Cable Impedance Calculations

Cable-series impedance modeling is widely applied in electromagnetic transients simulations and power-loss calculations. The calculations are usually performed in a 2-D frame using the finite-element method or alternative approaches, such as MoM-SO, thereby losing the 3-D effects imposed by twisting wire screens and armors. One of the implications of using 2-D modeling for three-core and closely packed single-core cables is that currents will always circulate among the individual wires of each wire screen or armor. However, in the case of twisted screens/armors where the wires are insulated from each other, such current circulation will in reality not exist. As a result, the calculated impedances become incorrect as well as the induced currents and losses on individual conductors. A procedure is introduced for preventing such false current circulations in a 2-D calculation frame by simple manipulation of the system impedance matrix. The approach is demonstrated for the modeling of single-core and three-core cables, with and without external armor. It is shown that the representation of the wire screen/armor armor with respect to current circulations can substantially influence the calculated result, both for the 50/60 Hz impedance and the cable transient behavior. The use of tubular screen representations is also investigated.

Performance evaluation of oscillating flow regenerators filled with particles, wire screens and high porosity open-cell foams

The porous matrix filled in oscillating flow regenerators has a significant influence on the performance of the regenerators. In this study, we firstly simulated the heat exchange process of the oscillating flow regenerators with particles, wire screens and high porosity open-cell foams with water as the working fluid using a generalized one-dimensional two-phase thermal-hydraulic model. Then, a detailed evaluation on the performance of these three types of regenerators was carried out regarding unit volume weight, regenerator effectiveness, specific pumping power and the proposed comprehensive performance factor by us as evaluation criteria. The comprehensive performance factor proposed by us is suitable for the performance evaluation and optimizing design of the oscillating flow regenerators because it not only considers the heat exchange ability of the thermal energy by introducing the entransy, but also solves the mismatching between the thermal energy and the pumping power in quality by division operation instead of weighted average algorithm. The evaluating results indicate that high porosity open-cell foams are the optimal choice for the porous matrix used to oscillating flow regenerators from multiple perspectives. The greatest advantage of foams is their high porosity and low pressure drop compared to the other porous structures. This study could also provide a guideline for the other fields involving the porous matrix.

Size Measurement of Radioactive Aerosol Particles in Intense Radiation Fields Using Wire Screens and Imaging Plates

Background: Very fine radiation-induced aerosol particles are produced in intense radiation fields, such as high-intensity accelerator rooms and containment vessels such as those in the Fukushima Daiichi nuclear power plant (FDNPP). Size measurement of the aerosol particles is very important for understanding the behavior of radioactive aerosols released in the FDNPP accident and radiation safety in high-energy accelerators. Materials and Methods: A combined technique using wire screens and imaging plates was developed for size measurement of fine radioactive aerosol particles smaller than 100 nm in diameter. This technique was applied to the radiation field of a proton accelerator room, in which radioactive atoms produced in air during machine operation are incorporated into radiation- induced aerosol particles. The size of 11C-bearing aerosol particles was analyzed using the wire screen technique in distinction from other positron emitters in combination with a radioactive decay analysis. Results and Discussion: The size distribution for 11C-bearing aerosol particles was found to be ca. 70 μm in geometric mean diameter. The size was similar to that for 7Be- bearing particles obtained by a Ge detector measurement, and was slightly larger than the number-based size distribution measured with a scanning mobility particle sizer. Conclusion: The particle size measuring method using wire screens and imaging plates was successfully applied to the fine aerosol particles produced in an intense radiation field of a proton accelerator. This technique is applicable to size measurement of radioactive aerosol particles produced in the intense radiation fields of radiation facilities.

Failure pressures and drag reduction benefits of superhydrophobic wire screens

This work presents a detailed study on the failure pressure of spray-coated superhydrophobic wire screens in terms of their geometric and wetting properties. Such information is needed in designing fluid–fluid or fluid–air separation/barrier media as well as drag reducing and self-cleaning surfaces, amongst many others. Good agreement has been observed between the results of our numerical simulations and the experimental data for failure pressure. In addition, the wetted area of the screens was calculated and used to predict their drag reduction benefits when used in a Couette flow configuration under different operating pressures. Interestingly, it was found that operating pressure in the Couette configuration does not significantly affect the drag reducing effects of the screens.

Investigations on a Porous Rotating Media Liquid-air Contacting Device Suitable for Various Alternative Cooling Technologies

Low energy and sustainable alternative air conditioning systems are getting more and more attention due to climate change concerns. High effectiveness, low cost and compact heat and mass exchangers play an important role in making such technology competitive with conventional technologies. This communication describes a novel counter-flow liquid-gas contacting device, which uses highly porous and rotating cylindrical contact media made from wire screens. The device can have very high surface area density, exceeding 500 m2/m3. The device can be used as a modular evaporative cooler, indirect evaporative cooler as well as liquid desiccant based air dehumidification system. Low pressure drops across device, low electrical power consumption, ability to run on solar PV cells, least chances of liquid carryover and prospective high effectiveness are the important features of this device. The small modular device with 110mm diameter and half a meter length could provide cooling at a rate exceeding 200W in evaporative cooling experiment with consumption of 10W power. The effectiveness exceeding 50% could be achieved under moderately hot and dry conditions. Better performance is expected for dry and hot summer conditions. Preliminary trials for combined direct and indirect evaporative cooling and liquid desiccant dehumidifier are also taken and encouraging results are achieved.

Preliminary design and thermal analysis of a liquid metal heat pipe radiator for TOPAZ-II power system

An alkali metal heat pipe radiator is proposed for the Russian TOPAZ-II space reactor power system to replace the original pumped loop radiator with three advantages. First, the single point failure problem of the original radiator can be avoided. Second, because only the NaK manifold needs to be armored, the specific mass would be reduced and the reliability and survivability can be improved. Third, the heat pipe has nearly isothermal characteristics and high heat transfer capabilities. In the present paper, the high temperature heat pipes using potassium as working fluid, wire screen mesh as wick layer, made of stainless steel are adopted to remove waste heat by radiation. An integral carbon-carbon fin covering and connecting heat pipes as whole heat transfer radiator is selected for its higher thermal conductivity and lower self-weight. A detailed steady state numerical calculation using the finite element method coupled with finite difference method is performed to predict the heat rejection characteristics of the heat pipe radiator. Heat transfer performances of the new concept heat pipe radiator and the pumped loop radiator are compared with key parameters. The results show that the designed heat pipe radiator satisfies the waste heat rejection requirements of the TOPAZ-II power system under the normal operating conditions and has an ideal redundancy. The isothermal and safety of heat pipe radiator is also better than that of pumped loop radiator.