Effect Of Particulate Contamination Research Articles

Simplified and Detailed Analysis of Data Center Particulate Contamination at Server and Room Level Using Computational Fluid Dynamics

Abstract Continuous rise in cloud computing and other web-based services propelled the data center proliferation seen over the past decade. Traditional data centers use vapor-compression-based cooling units that not only reduce energy efficiency but also increase operational and initial investment costs due to involved redundancies. Free air cooling and airside economization can substantially reduce the information technology equipment (ITE) cooling power consumption, which accounts for approximately 40% of energy consumption for a typical air-cooled data center. However, this cooling approach entails an inherent risk of exposing the ITE to harmful ultrafine particulate contaminants, thus, potentially reducing the equipment and component reliability. The present investigation attempts to quantify the effects of particulate contamination inside the data center equipment and ITE room using computational fluid dynamics (CFD). An analysis of the boundary conditions to be used was done by detailed modeling of ITE and the data center white space. Both two-dimensional and three-dimensional simulations were done for detailed analysis of particle transport within the server enclosure. An analysis of the effect of the primary pressure loss obstructions like heat sinks and dual inline memory modules inside the server was done to visualize the localized particle concentrations within the server. A room-level simulation was then conducted to identify the most vulnerable locations of particle concentration within the data center space. The results show that parameters such as higher velocities, heat sink cutouts, and higher aspect ratio features within the server tend to increase the particle concentration inside the servers.

Effect of Particulate Contaminants on the Development of Biofilms at Air/Water Interfaces.

The development of biofilms at air/water or oil/water interfaces has important ramifications on several applications, but it has received less attention than biofilm formation on solid surfaces. A key difference between the growth of biofilms on solid surfaces versus liquid interfaces is the range of complicated boundary conditions the liquid interface can create that may affect bacteria, as they adsorb onto and grow on the interface. This situation is exacerbated by the existence of complex interfaces in which interfacially adsorbed components can even more greatly affect interfacial boundary conditions. In this work, we present evidence as to how particle-laden interfaces impact biofilm growth at an air/water interface. We find that particles can enhance the rate of growth and final strength of biofilms at liquid interfaces by providing sites of increased adhesive strength for bacteria. The increased adhesion stems from creating localized areas of hydrophobicity that protrude in the water phase and provide sites where bacteria preferentially adhere. This mechanism is found to be primarily controlled by particle composition, with particle size providing a secondary effect. This increased adhesion through interfacial conditions creates biofilms with properties similar to those observed when adhesion is increased through biological means. Because of the generally understood ubiquity of increased bacteria attachment to hydrophobic surfaces, this result has general applicability to pellicle formation for many pellicle-forming bacteria.

Effect of particulate contamination on adhesive ability and repellence in two species of ant (Hymenoptera; Formicidae)

Tarsal adhesive pads are crucial for the ability of insects to traverse their natural environment. Previous studies have demonstrated that for both hairy and smooth adhesive pads, significant reduction in adhesion can occur because of contamination of these pads by wax crystals present on plant surfaces or synthetic microspheres. In this paper, we focus on the smooth adhesive pads of ants and study systematically how particulate contamination and the subsequent loss of adhesion depends on particle size, particle surface energy, humidity and species size. To this end, workers of ant species Polyrhachis dives and Myrmica scabrinodis (Hymenoptera; Formicidae) were presented with loose synthetic powder barriers with a range of powder diameters (1-500 μm) and surface energies (PTFE or glass), which they would have to cross in order to escape the experimental arena. The barrier experiments were conducted for a range of humidities (10-70%). Experimental results and scanning electron microscopy confirm that particulate powders adversely affect the adhesive ability of both species of ant on smooth substrates via contamination of the arolia. Specifically, the loss of adhesion was found to depend strongly on particle diameter, but only weakly on particle type, with the greatest loss occurring for particle diameters smaller than the claw dimensions of each species, and no effect of humidity was found. We also observed that ants were repelled by the powder barriers which led to a decrease of adhesion prior to their eventual crossing, suggesting that insect antennae may play a role in probing the mechanical fragility of substrates before crossing them.

A state-of-the-art review on the effects of particulate contamination and related topics in machine-element contacts

Contamination of machine-element contacts by solid particles is a serious problem in all industrial sectors. Particles ranging in size from nanometres to micrometres are responsible for increased wear and for even catastrophic failures of bearings, gears, seals, mechanisms, and machines. The wear such contaminants can cause is abrasion, surface indentation, flaking, and even scuffing, depending on the operating conditions and the mechanical properties of the particulates. The literature on the effects of debris particles in mechanism and machine reliability is voluminous. There are theoretical studies covering the entrainment, entrapment, and passage of particles through concentrated contacts, experimental and theoretical studies on the wear caused in such incidents, studies on the effects of air and lubricant filtration on machine life, and other related research work. The goal is to determine the consequences of having debris particles in a mechanical system and to develop methods to prevent the presence of particles in order to maximize the life expectancy of the system. This article is a review of the related research available in the literature. It covers more than 150 years of research, with the largest volume of work concentrated in the last 30 years. The review discusses over 230 of the most important publications and aims to be a definitive point of reference for the work done up to the year 2009.

Effects of Contamination on Aerospace Hydraulic Component and System Performance

Abstract Most papers concerning hydraulic systems contamination cover primarily the adverse effects of particulate contamination on hydraulic component and system performance. While that is a valid concern, the effects of other contaminants can also be serious. This paper concentrates on the adverse effects of water, free air, and chemical contaminants on military aerospace hydraulic component and systems performance. The hydraulic fluids used in the military aerospace systems are both the mineral oil-based MIL-PRF-5606 [1] and the synthetic hydrocarbon-based fire resistant hydraulic fluids MIL-PRF-83282 [2], and MIL-PRF-87257 [3]. Examples will be provided where each of the contaminants were responsible for some adverse effect and the recommended solution for the problems will be provided. Some of the problems encountered were stuck valves, spongy controls, “burnt” hydraulic fluid, and erratic actuator performance. The methodology used to identify the source of the problem will be presented. Based on the problems found, limits for these contaminants were recommended and, when followed, solved the problems for the aircraft involved. The major significance of this paper is to enlighten the aerospace hydraulic system community to the potential problems caused by contamination other than particulate contamination and to suggest solutions for these problems.

Contamination of Power Generation Lubricants

Abstract This paper examines the potential sources of fluid contamination that may occur during the manufacture, transportation, delivery, and use of a turbine oil for power generation. A turbine oil is a very precise formulation. If it becomes polluted with other lubricants or water, its performance could be compromised. The paper first identifies the potential sources of contamination that may be found when using a turbine oil. Then the consequences of contamination of the lubricant are considered. In conclusion, the paper proposes possible solutions to some of these practical problems regarding the sources of contamination. The paper will not consider the effects of particulate contamination. Because this is a well documented subject, the need for high levels of cleanliness in turbines is accepted practice.

Effect of Particulate Contamination on Pole Tip Recession in a Linear Tape Drive

Three-body abrasion is the cause of differential wear in magnetic tape heads resulting in recession of the magnetic poles with respect to the head substrate; this is called pole tip recession (PTR). The increasing head--tape spacing caused by PTR results in a lower write density, so the recession must be minimized. The three-body particles that may interact with the head--tape interface can originate from the operating environment (contaminant particles) and from the interface itself (debris particles). The effect of airborne particulate contaminants trapped at the head--tape interface (particle concentration, size, and hardness), which results in three-body abrasion, on PTR growth is studied experimentally. PTR increases with increases in any of the following: particle concentration, size, and hardness. Analytical modeling supports the experimental results. Possible mechanisms responsible for the observed behavior are discussed.

Effect of particulate concentration, materials and size on the friction and wear of a negative-pressure picoslider flying on a laser-textured disk

The effect of particulate contamination on friction and wear between a negative-pressure picoslider and a laser-textured disk has been studied. Particles of different concentration, materials and size were injected at the head-disk interface consisting of disks with various textures and slider types at different speeds. Durability increases and coefficient of friction decreases as the disk speed is increased in a contaminated environment. Frictional characteristics and durability in the data zone were better than those in the laser-textured zone. It was also found that durability of head-disk interface (HDI) decreased as the particle concentration increased. Hard particles and large particles made the HDI failure early and resulted in an extensive damage to the slider and disk surfaces. The interface durability with the picoslider was better than that with the nanoslider at any condition in a contaminated environment. Based on the test results, the mechanisms are proposed to explain the reasons why durability with the picoslider is superior to that with the nanoslider and the mechanism of the HDI failure with the picoslider is also presented.

Effect of particulate contamination on the friction and wear of a magnetic head-rigid disk interface

Particulate contamination studies were carried out with laser-textured and mechanically textured magnetic rigid disks and nanosliders. The effects of particle concentration and its size, particle material, duration of exposure to contamination, interface speed and disk textures were studied. The head-disk interface (HDI) durability increased as particle concentration decreased. The effect of different hard-particle materials was attributed to how easily it can form agglomerates. Data indicate that limited-time exposure to a class 10 000 environment will not deter tribological performance of the HDI. In a contaminated environment, head flying in the data zone exhibited higher durability than that in the-lase textured zone. However, the mechanically textured disk and the data zone of laser-textured disks showed comparable durability in the presence of contamination. The HDI damage mechanism and pattern changed as the disk speed changed. A failure mechanism to show how the airborne particles interact with the interface is presented. The effects of the HDI geometry, flying height, pitch angle which controls the air flow pattern govern the failure mechanism in the flying mode.

Effect of Particulate Contamination in Grease-Lubricated Hybrid Rolling Bearings

The presence of hard contaminants in lubricated rolling bearings is a major cause of premature failure, for example by fatigue or by abrasive wear of rolling elements, races or cages. However, the introduction of much harder ceramic (usually silicon nitride) balls or rollers running against steel races, in the hybrid bearing concept, is likely to change the interactions of hard particulate contaminants with the bearing components. The performance of all-steel and hybrid rolling bearings was investigated in the presence of two well-defined particulate contaminants. Experiments were carried out with grease-lubricated thrust bearings, contaminated with titania (anatase) and silica (quartz) particles. A significant beneficial effect was observed in the hybrid bearings in the presence of fine (<5 μm) anatase particles, as lower cage wear and running temperature were recorded. This improvement was associated with the formation of thin and relatively soft titania films on the silicon nitride ball surfaces. In the all-steel bearings, silica particles caused severe wear of the balls and cage, whereas in the hybrid bearing no wear could be detected on the balls, and cage wear was significantly lower than for the all-steel bearing. The wear losses of the steel race-ways were similar in both cases. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997

A kinetic model for low-pressure glow discharges in the presence of dust particles

A kinetic model for low-pressure dusty plasmas is developed. The Boltzmann and the dust charging balance equations are solved self-consistently. The dependence of the dust particle surface potential on plasma parameters and the effects of particulate contamination on the electron energy distribution are investigated for direct-current argon glow discharges. It is shown that the dust particle surface potential obtained from this model is higher than that obtained for a Maxwellian electron distribution, and that the higher energy portion of the electron distribution is reduced in the presence of dust particles. Electron-dust collection and electron - atom inelastic collisions are the main electron energy loss processes, and the electron energy loss due to electron-dust elastic collision is negligibly small for under the discharge conditions considered in this work, where E is the externally applied electric field and N is the argon atom density.

The Effects of Particulate Contamination in Rolling Bearings—a State of the Art Review

The role played by particulate contamination in rolling contacts has formed the subject of much research in recent years. Bearing-steel quality has improved to a level where the long established sub-surface-inclusion based fatigue failures are being replaced by surface or near-surface initiated failures caused by surface defects resulting mainly from rolled-in debris particles. The paper reviews the reasons and mechanisms involved, and shows how particle material, size, concentration and hardness can all have effects on bearing reliability.