Fouling Conditions Research Articles

An Evaluation of Fouled Ballast in a Laboratory Model Track Using Ground Penetrating Radar

Abstract Ground penetrating radar (GPR) was used to evaluate fouled ballast in a prototype model railway track designed and constructed at the University of Wollongong. To simulate actual conditions, the track consisted of a layer of sub-grade, a capping layer, and a layer of ballast. The track was then divided into seven fouled ballast sections and two clean ballast sections, nine in all. Radar detectable geotextile was embedded under the ballast to highlight the interface between the ballast and capping layer, and then different frequency antennae were used to capture the reflected GPR signals so that the fouled ballast could be evaluated. The design and construction of the model track and the analysis and interpretation of collected GPR data are presented in this paper. Clear patterns of texture observed from the GPR images illustrate the different fouling conditions. The relative dielectric permittivity of each sub-section was also calculated and compared, which proved that it can be used to classify clean and fouled ballast.

Fouling behavior of electroacidified soy protein extracts during cross-flow ultrafiltration using dynamic reversible–irreversible fouling resistances and CFD modeling

The transient membrane fouling during the concentration by cross-flow ultrafiltration of soy protein extracts subjected to electroacidification is examined by combining experimentation with computational fluid dynamics (CFD) modeling. Transient reversible (water removal) and irreversible (chemical removal) membrane fouling resistances, permeate flux, protein concentration and protein concentration dependent viscosity were obtained experimentally. A detailed fouling resistance model to describe the reversible and the irreversible fouling resistances was developed in terms of the microscopic local transient and spatial pressure difference, permeate velocity, protein concentration and initial fouling resistance conditions. This fouling resistance model is used in a boundary condition for the permeate velocity when solving the momentum and protein concentration continuity equations with CFD. The model estimates agree with experimentally measured permeate flux, protein concentration and transient irreversible and reversible fouling resistances. In particular, the model estimated accurately the transient reversible and irreversible fouling resistances, a limitation of most previously published models. The model shows considerable axial variation of the reversible fouling resistance and the protein concentration at the membrane surface which supports the inadequacy of the film theory and the assumptions for constant properties. In contrast, the irreversible fouling resistance remains relatively constant with axial position suggesting protein adsorption.

Gait and force analysis of provoked pig gait on clean and fouled rubber mat surfaces

Materials that increase floor friction forces in absorption of foot pressure could reduce the risk of slipping, i.e. promote walking safety. The effects of fouled rubber mat floor condition on the gait of 10 pigs walking in a curve, using kinematics and kinetics to record gait parameters and slip frequency, are described and compared with clean conditions. Pigs adapted to fouled floor conditions through reduced walking speed (10%), prolonged swing and stance time, and a higher number of 3-limb support phases, but kept stride length and diagonality constant. This adaption produced a threefold reduction in lateral horizontal forces and kept braking and propulsion forces constant, resulting in a constant peak utilised coefficient of friction (UCOF) level in fore limbs but a 31% reduction in UCOF in hind limbs. The better traction for pigs walking on rubber matting compared with concrete is due to a more effective transmission of forces from the limb to the elastomer, dissipating the forces into energy within the material, and thus impeding the effect of centripetal force, with less displacement of body centre of gravity and less forward and backward slip. Pig forward slip frequency on fouled rubber matting was 65 and 51% lower for fore and hind limbs respectively compared with pigs walking a curve on fouled concrete. The soft flooring material improved gait adaption and could thus improve walking safety.

Behaviors of commercialized seawater reverse osmosis membranes under harsh organic fouling conditions

Reverse osmosis performance is often limited by membrane fouling, which reduces the permeate flux and membrane life-span, requires costly pretreatment, higher operating pressure, and frequent chemical cleaning; results in increased water cost. Organic fouling is inevitable in seawater reverse osmosis (SWRO) desalination plants because certain amount of humic substances — organic foulants — naturally exists in seawater. In this study, the effect of harsh organic fouling condition on performance of four commercialized SWRO membranes was compared. The performance here was defined as flux, salt rejection and boron rejection. The performance variation pattern was similar for all tested membranes. Contact angles of clean and fouled membranes were measured and analyzed to gain insight into the fouling mechanism. The results provided the clue to investigate the interaction of humic acid and membrane surfaces, how important are membrane surface properties in the interaction.

The Effect of Fouling on Low Temperature Heat Exchangers Performance Based on Exergy Analysis

By analyzing heat and exergy transfer processes of heat exchangers operating below the surrounding temperature, the effect of fouling on the low temperature heat exchangers performance has been conducted. Taking the parallel flow, counter flow, and cross flow low temperature heat exchangers as examples, the effects of some non-dimensional parameters on the low temperature heat exchangers performance under the fouling condition are given by introducing exergy transfer units number.

Railroad Ballast Evaluation Using Ground-Penetrating Radar

Ballast fouling in the railroad substructure is detrimental to the effectiveness of the railroad track and its structural capacity. The early detection of ballast fouling is of utmost importance to the safety of the rail system and its life-cycle cost-effectiveness. Ground-penetrating radar (GPR), a nondestructive evaluation tool, has shown its potential as a means of assessing the condition of the railroad substructure rapidly, effectively, and continuously. However, an unknown ballast dielectric constant and an unclear interface between clean and fouled ballast limit the accuracy of GPR assessment. In the present study, controlled laboratory testing was conducted to measure accurately the dielectric constants of two common ballast types, granite and limestone, under various fouling and moisture conditions. In addition, a time–frequency method, short-time Fourier transform (STFT), was used to demonstrate graphically the frequency energy variation with the depth of the ballast under various conditions. This method indirectly reflects the ballast fouling condition. To validate the effectiveness of STFT for ballast fouling assessment, field GPR data from the Orin Subdivision in Wyoming were analyzed with the STFT technique and laboratory-measured dielectric constants. Comparison of the ground truth data and GPR measurements proved that the STFT method is effective and that its results are reasonably accurate when it is used to locate fouling and trapped water within ballast, especially when the laboratory-predicted ballast dielectric constants are used in the analysis.

Assessment of the Performance of Membranes Type Koch in Hartha Power Plant

This paper deals with the assessment of the performance of reverse osmosis membranes type (TFC-Koch) model (8822XR-365) which are used in water desalination unit in Hartha power plant, one of the electrical power plant in the south Iraq. This unit has a capacity of 100 withdraws water from Shat Al-Arab River as a raw water having total dissolved solid (TDS) ppm, and consists of two stages with total recovery and salt rejection of about 60% and 95%, respectively. The first array contains twelve vessels and the second six vessels. Each vessel contains six elements, 8 inches in diameter and 40 inches in length. The performance of the reverse osmosis (RO) membranes is based on surveying the chemical analysis of different ions present in water for both permeate and rejected streams from the unit log book, and only those readings where the overall recovery was 60% were selected. The results depicted that the reduction of membrane efficiency is attributed to the membrane blockage due to scaling and fouling. Under high fouling conditions the permeate flow rate is reduced and accordingly a high feed pressure is required to produce the design flow rate of permeate or percent recovery. A simulation of the behavior of RO membranes was conducted using standard Saehane software and compared with predicted model that was developed by the same authors. The results revealed that the reduction in water flow in both elements one and two in each vessel in the first array is attributed to the high permeate water flux through these two elements beyond the operation limits. Accordingly it is necessary to replace these two elements or change their position relative to other elements periodically.

The use of proactive in-water grooming to improve the performance of ship hull antifouling coatings

The US Navy operates a large number of ships, however, unlike most commercial vessels they typically spend long periods of time in port where they may become fouled. This study investigated the feasibility of applying light cleaning (grooming) to maintain four surfaces free from fouling. The test surfaces were an ablative copper antifouling (AF) coating, a silicone fouling release (FR) coating, a two part marine epoxy, and a solid sheet of polytetrafluoroethylene plastic. The surfaces were exposed to static immersion in seawater on the East coast of Florida for 120 days and subjected to 3, 6, 12, and 24-day grooming intervals. Pre-groomed and post-groomed fouling conditions on each test surface were assessed and the maximum required lateral forces at each grooming event were measured. The results showed that grooming prevented or reduced the development of biofilm on the ablative copper coatings. The FR coatings that were groomed at the 3- and 6-day interval remained free from fouling until exposure to severe fouling pressure, which caused the 6-day interval to develop a small amount of fouling. Both the polytetrafluoroethylene and epoxy surfaces became fouled at all grooming frequencies, but fouling was reduced for the 3-day grooming frequency. The lateral forces required to groom the surfaces, with the exception of the FR coatings, increased with time. The results demonstrated that frequent grooming can have prolonged, positive effects on the AF performance of coatings.

Monitoring kraft recovery boiler fouling using principal component analysis

Researchers analyzed high resolution operational data from three recovery boilers using the principal component analysis (PCA) feature of a multivariate statistical analysis program to identify major operating variables that contributed to fouling and plugging. The results show that PCA can be used to visualize the variability relative to long-term fouling trends in the boilers and to graphically distinguish changes in the boiler fouling condition caused by operational variability over a short period. This represents a major step forward in identifying operating variables that might be adjusted to minimize fouling, and in developing an online fouling monitoring technology based on PCA.

A Comprehensive Study on the Asymmetric Internal Spur Gear Drives through Direct and Conventional Gear Design#

An optimum design for an internal gear pair for the desired values of input parameters has been attempted through a direct gear design approach using area of existence, which is enclosed between the isograms of a desired contact ratio, a definite pitch point contact, an interference free drive and a fouling free condition. By synthesizing several sets of asymmetric pinion cutters for specific values of input parameters, the respective gear and pinion generated by them have been analyzed for a balanced and lowest possible maximum fillet stress to decide the optimum one. A conventional gear design process has also been suggested with stub tooth concept in this regard.

Mechanisms underlying the effects of membrane fouling on the nanofiltration of trace organic contaminants

The influence of membrane fouling on the retention of four trace organic contaminants – namely sulfamethoxazole, ibuprofen, carbamazepine, and triclosan – by nanofiltration membranes was investigated in this study. Humic acid, alginate, bovine serum albumin, and silica colloids were selected as model foulants to simulate various organic fractions and colloidal matter that are found in secondary treated effluent and surface water. The effects of membrane fouling on the separation process was delineated by comparing retention values of clean and fouled membranes and relate them to the membrane properties (under both clean and fouled conditions) as well as physicochemical characteristics of the trace organic contaminants. Membrane fouling was dependent on the physicochemical properties of the model foulants. Initial foulant–membrane interaction could probably be a major factor governing the process of membrane fouling particularly by the organic foulants. Such membrane–foulant interaction was also a dominating factor governing the effects of membrane fouling on the membrane separation efficacy. In good agreement with our previous study (Nghiem and Hawkes, 2007 [1]), the effects of fouling on retention were found to be membrane pore size dependent. In addition, results reported here suggest that these effects could also be foulant dependent. It was probable that the influence of membrane fouling on trace organic retention could be governed by four distinctive mechanisms: modification of the membrane charge surface, pore blocking, cake enhanced concentration polarisation, and modification of the membrane hydrophobicity. The presence of the fouling layer could affect the retention behavior of charged solutes by altering the membrane surface charge density. While the effect of surface charge modification was clear for inorganic salts, it was less obvious for the negatively charged pharmaceutical species (sulfamethoxazole and ibuprofen) examined in this investigation, possibly due to the interference of the pore blocking mechanism. Evidence of the cake enhanced concentration polarisation effect was quite clear, particularly under colloidal fouling conditions. In addition, organic fouling could also interfere with the solute–membrane interaction, and therefore, exerted considerable influence on the separation process of the hydrophobic trace organic contaminant triclosan.

Underneath Ranefer's floors – urban environments on the desert edge

The city of Akhetaten, modern day Amarna, was founded by the monotheist pharoah Akhenaten as his new capital ca. 1353 BC, and abandoned within about 25 years. Much of the site has been excavated over the past century and few deposits remain undisturbed. In one house, however, that of the king's chief charioteer, Ranefer, rebuilding had sealed occupation debris beneath the final mud brick house floors and in the desiccating conditions of the desert, these preserved extensive insect faunas, which for the first time provide detailed data on living conditions and pest infestation in a major pharaonic urban centre. Pests of stored products include the grain weevil, Sitophilus granarius, the lesser grain borer, Rhizopertha dominica, and flour beetles, Tribolium castaneum, as well as more general pests, such as the lesser mealworm, Alphitobius diaperinus, and the biscuit beetle, Stegobium paniceum. Flies include the house fly, Musca domestica, and the puparia of a flesh fly, Sarcophagidae, burrowed vertically into the mud-brick floor in a room corner, perhaps beneath abandoned offal or meat. The taphonomy of the insect assemblages would suggest that much consisted of material dumped into the house plot, either during a phase of abandonment or to level up the area before the later house, that of Ranefer, was constructed. Trampled surfaces within the midden, often consolidated with desert sand, indicate foul damp conditions and also imply that the process was intermittent. Living conditions in the city of Akhenaten are likely not to have been as salubrious as contemporary tomb paintings might suggest.

Prediction of ultrafiltration permeate flux decline by means of a shear induced diffusion model with empirical estimation of the gel layer concentration

In this work, the shear-induced diffusion model has been used to predict flux decline in ultrafiltration. Two types of monotubular ceramic membranes were used in the experiments: Carbosep M2 ZrO2-TiO2 membranes with a MWCO of 15 kg/mol (Orelis, S.A., France) and TiO2–Al2O3 Tami MSKT membranes of 5 kg/mol (Tami, S.A., France). Polyethylene glycol (PEG) of 35 kg/mol was used in the preparation of the feed aqueous solution. The experiments were performed at constant temperature (25°C) and at different feed flow rates (1–3 m/s), transmembrane pressures (TMPs) (0.1–0.5 MPa) and feed concentrations (5–15 g/L). In this work the gel layer concentration was empirically estimated form steady-state permeate flux values. Model predictions were compared with the experimental results and discussed. For the Carbosep M2 membranes, model predictions were better for high TMPs and low crossflow velocities. For Tami MSKT membranes, model predictions for initial permeate flux decline were worse when fouling was severe (high TMPs and feed concentrations and low crossflow velocities) than in the case of mild fouling conditions. An explanation for this is given in this paper.

Gait and force analysis of provoked pig gait on clean and fouled concrete surfaces

Gait and force analysis have proven to be useful methods in linking claw injuries to surface material conditions. To determine the relationship between claw disorders and floor properties such as friction and surface abrasiveness, the factors controlling gait must be characterised. The effects of fouled concrete floor conditions on the gait of 10 pigs walking in a curve, using kinematics and kinetics to record gait parameters and slip frequency are described and compared with clean conditions. Pigs adapted to fouled floor conditions by reducing their walking speed and stride length, using a higher number of 3-foot support phases and by lowering diagonality. This adaption produced lower vertical forces, a twofold reduction in propulsion and outward stabilisation force and a threefold increase in braking force, without reducing the peak utilised coefficient of friction (UCOF). The UCOF values for both limbs of the curve walking pigs exceeded the recorded dynamic coefficient of friction and the corresponding UCOF values for pigs walking a straight line in fouled floor condition. As UCOF increased and available friction from the fouled floor surface decreased, this resulted in higher forward and backward slip frequencies in both limbs for pigs walking in a curve. Pigs provoked to walk in a curve can adapt to fouled floor condition, but if the floor is heavily fouled this adaption is not sufficient to ensure safe walking.

Effect of free calcium concentration and ionic strength on alginate fouling in cross-flow membrane filtration

Extracellular polymeric substances (EPS) are generally negatively charged polymers. Membrane fouling in membrane bioreactors (MBRs) by EPS is therefore influenced by the water chemistry of the mixed liquor (calcium concentration, foulant concentration and ionic strength). We used alginate as a model compound to study this fouling in detail. Flux-step experiments were performed with a flat sheet test cell, varying the free calcium concentration, total ionic strength and alginate concentration. There was a strong relation between calcium concentration and fouling rate. An increased ionic strength had no impact on fouling rate in low fouling experiments, but decreased fouling with 66–72% at high fouling conditions. Reversibility of the fouling decreased with increasing calcium concentrations to values as low as 3%. Several fouling mechanisms were identified and the reducing effect of increased ionic strength on alginate fouling was explained by competition for carboxyl groups on the alginate polymer. Further research will focus on the interaction of polysaccharides with other compounds typically present in the MBR supernatant (e.g. proteins, humic acids and sludge particles) and a more detailed analysis of the fouling layer.

Experimental Investigation of Crystallization Fouling on Grooved Stainless Steel Surfaces During Convective Heat Transfer

The beneficial aspects of enhanced or extended heat transfer surfaces may be offset if operated under fouling conditions. In this article, preliminary experimental results for crystallization fouling of CaSO4 solutions onto surfaces with different structures are reported. Flat stainless steel plates (50 mm × 59 mm) with “V”-shaped grooves on the side of fluid flow were used as heat transfer surfaces. Experiments were carried out under both clean and fouling conditions to discern how the same surface structures perform under such circumstances. In addition, the impact of both the direction of grooves with respect to fluid flow (crossed, longitudinal, and mixed flow grooves) and the groove dimensions has also been investigated. Fouling trends are discussed in terms of induction time and fouling rate. Significant differences have been found for the various flow conditions.

Optimization of antenna configuration in multiple-frequency ground penetrating radar system for railroad substructure assessment

This paper discusses the use of ground penetrating radar (GPR) to rapidly, effectively, and continuously assess railroad track substructure conditions, especially ballast. To overcome the limited electromagnetic waves penetration for high-frequency antennae and the low resolution of low-frequency antennae, this study uses a multiple-frequency GPR system to assess railroad substructure conditions. High-frequency antennae were used to detect the scattering pattern, which is related to air void volume in railroad ballast, and low-frequency antennae are used to assess deeper substructure conditions. Considering the scattering energy attenuation is highly frequency and material dependent, a time–frequency method based on tracking the frequency spectrum and energy change over depth can be used to extract ballast fouling conditions. From GPR field collected data, ground-truth observation, and ballast gradation analysis, the multiple-frequency GPR system demonstrates a promising capability to assess railroad track substructure condition.

Force analysis of unprovoked pig gait on clean and fouled concrete surfaces

Inadequate floor properties are considered the primary cause of the majority of claw disorders in pigs but to date no clear relationship has been found between claw disorders and floor properties such as friction and surface abrasiveness. To determine this relationship, the factors controlling pig gait must be characterised. This study examined unprovoked pig gait on a concrete floor in clean conditions and compared it with gait in fouled floor conditions. Kinematics were used to record gait parameters such as walking speed, stride length, swing and stance time, stride elevation together with limb support phases, gait symmetry, diagonality and duty factor. On clean floors, pigs had an unprovoked symmetrical gait with alternating two- and three-beat support phases and a high rate of diagonality. Stride length, swing and stance time and stride elevation showed little variation. Pigs altered their gait in accordance with floor conditions to maintain gait control by reducing walking speed, lowering diagonality and employing more three-limb support phases. Pigs also shortened their stride length and prolonged their stance time.

Oxidative Regeneration of Sulfide-fouled Catalysts for Water Treatment

This study tested the stability, activity, and selectivity of an alumina-supported Pd–In bimetallic catalyst during repetitive sulfide fouling and oxidative regeneration conditions. Nitrate reduction with hydrogen was used as the probe reaction in a continuous-flow packed-bed reactor to assess changes in the catalyst structure as a result of the fouling and regeneration processes. Partial regeneration of a severely sulfide-fouled Pd–In catalyst was achieved with a NaOCl/NaHCO3 solution. However, the regenerated catalyst had a reduced activity for NO3− reduction and increased selectivity towards NH3. Analysis of the catalyst bed after regeneration experiments using XPS, ICP-MS, and BET surface area revealed that bulk structural transformations of the Pd–In bimetallic catalyst occurred, as a result of preferential Pd dissolution near the column influent. The dissolved Pd showed limited mobility in the column, and was re-deposited on the catalyst, resulting in Pd enrichment on the catalyst surface and redistribution of Pd towards the end of the column. These changes along with residual sulfur content on the catalyst surface were likely responsible for the increased selectivity towards NH3. These results indicate the importance of limiting the exposure of reduced sulfur species to Pd-based catalysts, especially when treating contaminants like NO3−, where product selectivity is a priority.

Influence of intermittent aeration and relaxation on a side-stream membrane bioreactor for municipal wastewater treatment

This paper is focusing on filtration of municipal wastewater with intermittent aeration and relaxation periods for a side-stream MBR in which filtration is performed with outside/in hollow-fibre membranes. In this semi-industrial scale side-stream MBR, hollow fibres are put in an external cartridge where sludge at low velocity and air are circulating around and inside the fibre bundle (in a confined system). Short-term experiments were performed under high fouling conditions but low energy consumption in order to determine and to characterise the influence on fouling of intermittent aeration and permeation. Discontinuous aeration is divided in two periods with two different air flow rates, a high one during a short duration and a lower one during a longer period. Relaxation was also studied by alternating on and off permeation periods. After that, aeration and permeation sequences were coupled. Results showed that for the same global air flow rate injected and for the same filtered volume, a punctually high aeration flow rate combined with a low aeration flow rate for the rest of time is better than a continuous one. Furthermore, filtration cake is removed more easily at the end of the experiment if aeration is discontinuous. Nevertheless, the aeration rate should be sufficient (above 0.112Nm3 h-1 corresponding to specific aeration demand per membrane square meter (SADm) of 0.074 Nm3 h-1 m-2 and specific aeration demand per permeate cubic meter (SADp) of 0.373 Nm 3 m-3 p) to prevent fouling. Lower fouling was obtained by discontinuous permeation in comparison to continuous permeation. Moreover specific aeration energies are only slightly higher for discontinuous permeation but the cake density is significantly lower and the deposit can be more easily removed by backwash. This study confirms the interest of operation with relaxation periods.