Stainless Steel Screen Research Articles

PEM Fuel Cell Stack Development Based on Membrane-Electrode Assemblies of Ultra-Low Platinum Loadings

We are attempting to scale-up our single cell technology, based on ultra-low platinum loadings, to develop a polymer electrolyte membrane (PEM) fuel cell stack for stationary power generation. We describe initial work on scale-up to a manifolded single cell based on a 100 cm2 active area, with the intention of combining multiples of such cells to create stacks. The cells, which are fed by pressurized H2 and air, utilize membranes catalyzed by ultra-low platinum loadings (0.14 mg Pt/cm2) and metal serpentine channel or screen flow-fields to minimize costs, while maintaining desirable power density. We describe some initial promising results from testing of stainless steel screens as flow-fields in such cells, achieving 0.5 W/cm2 under mild flow and pressurization conditions.

Hydrogen evolution on electrodeposited nickel-cobalt-molybdenum in alkaline water electrolysis

The hydrogen evolution reaction (HER) was conducted on nickel-cobalt-molybdenum electrodes in a 30 wt% KOH solution at temperatures from 298 to 353 K. These nickel- and cobalt-based ternary materials were electrodeposited on a stainless steel screen, initially at a current density of 0.5 A cm −2 and subsequently at 2 A cm −2. They showed good adhesion to the substrate, high surface roughness and they enhanced the HER in water electrolyssi compared with nickel, cobalt, nickel-molybdenum and cobalt-molybdenum deposited electrodes, having comparable or even higher deposit loadings. The HER enhancement on the ternary materials with respect to nickel-molybdenum and cobalt-molybdenum was attributable to their large surface area. On the ternary materials, two Tafel slopes were distinguished on the HER polarization in the low and high HER overpotential ranges. However, no conventionally proposed relation between TAfel slope and temperature was found; the transfer coefficient increased with temperature under the experimental conditions.

PLANT FE, AL AND CR CONCENTRATIONS IN VEGETABLES AS INFLUENCED BY SOIL INCLUSION

ABSTRACTSoil entrapment by plant tissue is often ignored when the tissue is analyzed. This leads to errors in interpretation of results. Plant tissue samples were taken from vegetables grown in experimental field plots in Norfolk, VA, Riverhead, NY, and Geneva, NY. At harvest, plant tissues were washed with deionized water, cut into small pieces, oven dried (VA) or freeze dried (NY), ground to pass a 0.0841‐cm stainless steel screen and stored in glass bottles. The surface 15 cm of each soil was sampled. Subportions of tissue and soil were analyzed for a number of elements by inductively coupled argon plamsa emission spectrometry (ICP‐ES) and electrothermal atomic absorption (ETAA). Titanium (Ti) concentrations in the soil and plant tissue were used as a measure of soil inclusion. As much as 76% of the Al, 100% of the Cr, and 70% of the Fe in the vegetable samples could be accounted for by soil particulate inclusion by the plant tissue during its growth.

Contact resistance of 500 mesh regenerator screens

The electrical contact resistance of stainless steel screen stacks at room temperature and at liquid nitrogen temperature has been measured as a function of externally applied mechanical load (weight). The data show a nearly linear voltage versus current function at small loads (up to 100 mA). The force has been varied up to a specific load of 1 N cm −2. From the data the (apparent) thermal conductance is deduced via the Lorenz number and via the (average) elastically deformed contact domain area of the Hertz theory. The conductances obtained appear to be consistent with literature data for thermal contact conductances of similar systems.

Isolation of Cryptosporidium parvum oocysts from fecal samples--the combination of ether extraction and discontinuous sucrose gradients

A calf and 50 mice were infected with Cryptosporidium parvum, and their fecal materials were collected and treated with ether extraction (EE), followed by discontinuous sucrose gradients (DSG) method. EE method was to remove some of fat or lipid from feces. Sediments were washed by centrifugation (1,500 x g for 10 min., 3 times) in phosphate-buffered saline and then these washed sediments were sieved sequentially through stainless steel screens with a final mesh of 250 (61 microns porosity) to remove other debris. After sieving, the materials were suspended in 2.5% potassium dichromate solution. Oocysts were counted by using a hemocytometer and the recovery rate of pure oocysts was calculated on the basis of the count. Following centrifugation (1,500 x g for 30 min.) by DSG method, most oocysts were recovered at the interface between a gravity of 1.103 and 1.064. The recovery rates of pure oocysts from the fecal suspension of the calf (3.8 x 10(7)/ml) and the mouse (3.2 x 10(6)/ml) treated with EE method were 81.6% and 51.6%, respectively. It is suggested that the recovery rate was dependent on the number of oocysts in each suspension treated with EE method. To get the 50% recovery rate, there must be more than 2 x 10(6) oocysts per ml of the fecal suspension treated with EE method. By the combination of the two methods it was possible to isolate C. parvum oocysts from normal feces of the calf and mouse as well as from diarrheic feces.

The Effective Pore Radius of Screen Wicks

The effective pore radius in screen-wick heat pipes was investigated, which is very important for the prediction of maximum heat transfer rates due to capillary limitation. An equation for the effective pore radius of the screen wicks was derived based on the model of the screen geometry. The capillary height for stainless steel and phosphor bronze screens was measured using water, ethyl alcohol, and Freon 113 as the test liquids. The effect of surface treatment (acid cleaning and oxidation) on the capillary height was also examined. From the comparison of the experimental data for water and ethyl alcohol with those for Freon 113, it was indicated that the contact angle was 24.2° for water and 16.9° for ethyl alcohol. Consequently, it was found that the effective pore radius of the screen wicks could be predicted fairly well from the expression presented in this study, and that the contact angle should be taken into consideration to evaluate the maximum capillary pressure accurately.

Two stage pulse tube refrigerator with double rotary valves

We have constructed a two stage pulse tube refrigerator equipped with two rotaryvalves. The first stage regenerator was made of stainless steel tube 39mm OD, 0.5mm thickness and 180mm long packed 1735 stainless steel screens of 200 mesh and the second stage regenerator was made of stainless steel tube 18mm OD, 0.3mm thickness and 250mm long packed with stainless steel screen of 250 mesh and lead shots of about 0.3 mm diameter. The performance was investigated by changing the ratio of the stainless steel mesh and lead shots of the second regenerator and the volumes of first and second pulse tubes. The second stage cold end reached below 20K.

An Ammonia Abatement System for Whole-Body Small Animal Inhalation Exposures to Acid Aerosols

AbstractConducting whole-body acid aerosol inhalation exposures of laboratory animals is complicated by ammonia arising from the excrement of the test animals which is sufficient to completely neutralize much of the acid aerosol. The neutralization of acid by ammonia can only be controlled by the use of head-only exposure systems (Schlesinger et al., 1983), which are tedious for repetitive exposures for large numbers of rodents, or by complete elimination of ammonia as it is formed during the whole-body exposure. This latter approach appears to be most appropriate; therefore, the development of a small animal whole-body ammonia reduction system (SAWBARS) for inhalation exposures was desirable for long-term rodent exposure studies.The removal of ammonia was accomplished by designing and fabricating stainless steel excreta pan manifolds to exhaust ammonia from the pans as it was generated. These manifolds were situated between neomycin-treated paper lining the excreta pans and a stainless steel screen that ...

Separation of oil from oil/water emulsions using an electroflotation cell with insoluble electrodes

Finely dispersed oil was separated from oil-water emulsions in an electroflotation cell equipped with a lead anode and stainless steel screen cathode. The effect of operating parameters such as current, oil concentration, flotation time, and height, on the performance of the electroflotation cell was examined. Oil removal reached 60% at optimum conditions; 70% in the presence of NaCl (3.5% by wt); and 88% in the presence of both NACl and an optimum concentration of a flocculant. Electrical energy consumption varied from 0.46 to 10.63 kWh/m 3 according to experimental conditions. The performance of the oil removal process was also represented as a first order kinetic rate model. The constants obtained fit the experimental data well, with their values varying from 1.305 × 10 −5 to 9.94 × 10 −5 m/s. Good correlation was found for the change in percentage oil removal with a wide range of operating parameters.

Use of a graded diffusion battery in measuring the activity size distributions of thoron progeny

This paper describes the performance of a graded diffusion battery in measuring the activity size distribution of 212Pb. The diffusion battery consisted of five stainless steel screens with 24, 35, 50, 200 and 635 mesh numbers and a backup filter. Calibration of the screens indicated that the collection of ultrafine particles on these screen follows the diffusion battery theory if the flow rate is kept at a level at which the flow Reynolds number (Re= d w U/ ν, where d w is the wire diameter, U is the face velocity and ν is the kinematic viscosity of air) is less than 1. The activity size distribution of 212Pb in an aging chamber was measured in ultra-pure air with dry (< 10% r.h.) and humid (40–50% r.h.) conditions. The particle size of 212Pb (about 1 nm) did not change significantly in the humid air when the mean residence time was between 0.33 and 8.3 min. However, in the dry air, the thoron progeny grew with aging time from about 1 to 3 nm. By adjusting the relative humidity and the aging time, 212Pb of activity median diameters from 1 to 3 nm could be produced. This allowed us to study the effect of the particle size of ‘unattached’ thoron progeny on the deposition efficiency in the upper respiratory tract.

Hydraulic Tests On Well Screens

Twenty-seven well screens of various types and diameters were hydraulically tested in a specially designed and constructed test rig. A relatively simple model for describing the head losses was found to adequately summarize the observations, and this yielded two empirical parameters for each well screen. A comparison of screens of the same nominal diameter revealed only small differences. Although stainless-steel screens are much rougher than glass reinforced plastic (GRP) and plastic screens, their similar hydraulic behaviour is explained by the fact that they have significantly larger internal diameters (for the same nominal diameter). Screens of different diameters differ greatly: considerable reductions in head loss can be achieved by increasing the screen diameters.

Screen heat exchanger performance comparison

The performance of stainless steel screen regenerator stacks (500 mesh) has been investigated at relatively small flow rates in comparison to conventional operation close to the laminar-turbulent transition range. A modified ‘single blow’ technique was used initially, and an additional comparative procedure is employed to deduce heat transfer rate ratios with respect to a single-wire reference case of heat transfer. The data obtained are two orders of magnitude below ‘classical’ room temperature values at low Reynolds numbers ( Re); ( Re based on the Darcy law-related characteristic length; Re < 1). The fluid is cold nitrogen from a liquid bath at atmospheric pressure.

Deposition of Fluorinated Silicon Nitride using Plasma Enhanced Chemical Vapor Deposition Technique

ABSTRACTHigh hydrogen content of ammonia/silane deposited silicon nitride films has been linked to instability in electronic devices such as MOSFET's MNOSFET's and TFT's. Fluorine has been proposed to help reduce the hydrogen content of these films. In this work, NF3 was used as a fluorinating agent. Optical and electrical properties were studied as a function of NF3 flow rate. A maximum optical gap of 5.3 eV was obtained with NF3 as compared to 3.2 eV without. The dielectric strength improved from 4 to 10 MV/cm with the addition of NF3. FTIR data show that the Si-N peak shifts to higher wave numbers and the Si-H peak drops below the detection limit with the addition of NF3. Also, the broad Si-N peak at 850 cm-1 is composed of many individual peaks which become discernable when a stainless steel screen is placed in front of the substrate. As the NF3 concentration is increased, a new peak at 1030–1060 cm-1 appears. This may be associated with a N-F vibration (1030 cm-1).

Mechanistic Considerations in the Plasma Deposition of Silicon Nitride Films

A stainless steel screen placed directly over the substrate in an RF glow discharge significantly altered plasma deposited (PD) silicon nitride film chemical composition and structure as measured by x‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy. Changes in film composition were more pronounced for PD silicon nitride films formed using as the nitrogen source gas rather than . An increase in the N:Si ratio was observed for all films deposited using the screen. This change in N:Si ratio was also reflected in an increased N‒H and decreased Si‒H bonding structure. These results are similar to those obtained previously in triode and remote plasma reactors, thereby suggesting common deposition mechanisms for films deposited in different reactor configurations.

Two-phase flow and dryout in a screen wick saturated with a fluid mixture

Experiments are performed to investigate the use of water-ethanol mixtures as a heat pipe coolant. An everted heat pipe structure consisting of a vertical tube, internally heated at the top, and around which is wrapped four layers of 325 mesh stainless steel screen, is used to measure the steady state and dryout heat fluxes as a function of mixture composition and capillary rise height. For small capillary rise heights it is observed that the maximum operating heat flux could be increased by 135% with waterethanol mixtures as compared to pure water. As the capillary rise height is increased the performance of water-ethanol mixtures becomes comparable to that of pure water. The measured dryout heat fluxes for pure water and pure ethanol are in reasonable agreement with the predictions of an analytical model which allows for two-phase flow, boiling, and dryout in the heated section of the wick.

Charging belt noise in a Van de Graaf accelerator

With the aid of spectrum analysis techniques it has been possible to decompose Van de Graaff terminal voltage noise into components that can be related to various mechanical properties of the charging belt. The principal mechanism for noise production is found to be loss of contact between charge applicators (screens) and the belt surface due to imperfect compliance of the applicators, resulting in a belt surface charge distribution with wavy edges and gaps. This noise source has been greatly reduced by replacing the standard stainless steel screens with beryllium-copper shim stock. By this means noise at the belt fundamental frequency has been eliminated.

Trypanosoma cruzi: Quantification in tissues of experimentally infected mice by limiting dilution analysis

A limiting dilution assay (LDA) was developed for the quantification of Trypanosoma cruzi in the heart and blood of infected mice. Three groups of swiss mice were injected ip with “CL”, “Colombiana,” and “Y” strains. At 1-day intervals after infection, blood and the heart were removed. Serial blood dilutions in LIT medium were performed and distributed in four groups of 24 microplate wells. The growth of parasite was visually checked in an inverted microscope. It was found that curves of parasitemia obtained by parasite counting in a hemocytometer or estimated by LDA were similar. A similar method was used to quantify parasites in the heart of mice. The heart was cut, washed, dried, and its weight was determined. The heart pieces were disrupted by passage through a mesh stainless-steel screen into LIT. Serial dilutions of the heart homogenate were made in LIT and added to at least 24 replicate microplate wells. Parasites were detectable earlier in the heart of mouse infected with Y strain when compared to CL and Colombiana strains. Parasites were detected in the heart of mice of all strains by 6 days after infection. This LDA for quantification of T. cruzi permits a more precise evaluation of the number of living parasites in infected tissues.

Bismuth(III) hydride generation, its separation and the determination of bismuth(III) by atomic absorption spectrometry using flow injection

A PTFE membrane backed by a stainless-steel screen was used to separate bismuth(III) hydride in a flow injection process. The atomic absorption signal gave a linear range of 0–50 p.p.b. of bismuth(III) in a sample size of 200 µl. Good precision (1.6% relative) and a low detection limit [0.17 ng of bismuth(III)] were observed. A sampling rate of up to 300 samples h–1 was obtained. Parameters and interfering ions which might affect the final atomic absorption signal of bismuth(III) were studied.

Pressure drop and He II flow through fine mesh screens

Fluid acquisition systems for He II transfer devices will utilise gallery arms to ensure that the fluid encounters the pump inlet. In near term experiments such as Superfluid Helium on Orbit Transfer (SHOOT), the preferred configuration consists of several rectangular channels which have one side made from a Dutch weave stainless steel screen having 325 × 2300 wires per inch. The effective pore diameter for this screen is about 5 μm. The present paper reports on measurements of pressure drop across a screen when it is subjected to a flow of liquid helium. The experiment measures the time rate of change of the level in two different helium reservoirs connected by a screen-blocked channel. Results with normal helium are compared with predictions based on the Armour-Cannon equations. The He II data show considerable deviation from the classical result. A discussion of the He II pressure drop results in terms of two fluid hydrodynamics is included.

An Improved Method of Making Tissue Carriers for TEM and SEM Fixation

Hazards in fixing small pieces of tissue for electron microscopy include damage, drying, or loss. Over the years, microstrainer tissue carriers have been developed to minimize these problems. Construction materials have included glass tubing, copper grids for electron microscopy, stainless steel screen, and bolting silk (Padawer 1951, Friend 1963, Bronskill 1970). Carriers made from plastic embedding molds (e.g., BEEM capsules) with either TEM grids attached to the conical tip (Buchanan 1965) or Nitex screen cloth held to one end by a retaining ring have proven to be inexpensive and popular, though the former has a very small filtration area and in the latter small tissues may be lost or crushed between the screen cloth and the bottom rim of the carrier. This note describes a carrier in which Nitex is permanently sealed to the bottom edee of a BEEM capsule cylinder.