Arrhenius Modeling Research Articles

FEM-based Arrhenius modeling of the thermal effects of a heating pipeline and pavements on underground power cables

It is well-known that, in thermal aging management of underground power cables, analytical Arrhenius models can include the thermal effect of a heating pipeline on the lifespan of power cables through a rise in the soil temperature and an appropriate ampacity de-rating factor. However, the thermal effect of a pavement on the lifespan of power cables installed below that pavement cannot be taken into account using any de-rating factor. Accordingly, this paper proposes FEM-based Arrhenius models to analyze the thermal effects of one heating pipeline and several different types of pavements on the thermal lifespan of an underground line of 110 kV consisting of cables with cross-linked polyethylene (XLPE) insulation. Each proposed Arrhenius model is created using both IEC 60287 and IEC TR 62095, as well as combining the traditional Arrhenius model with an appropriate FEM-based steady-state thermal model. An experimental background consisting of the existing thermal aging tests with XLPE insulation is also used. Different pavements are represented by different values of thermal and surface radiation properties, namely: thermal conductivity, solar absorptivity, and thermal emissivity. The pavement surface radiation properties are specified within the frames of the most unfavorable summer conditions, and the most common winter conditions. Moreover, different distances between the 110 kV cables and the heating pipeline are considered. Finally, it is found that: the considered thermal effects can shorten the expected total service lifespan of the 110 kV cables in the area adjacent to the heating pipeline by up to 297.5 h; the pavement surface radiation properties do not affect the consumption of total thermal lifespan; as well as the largest consumption of total thermal lifespan occurs when the 110 kV cables are at the smallest distance from the heating pipeline.

Modeling the response of blended PVC/PET fabrics to fire environments

The fire behavior of fabrics with uncertain composition of polyvinyl chloride and polyethylene terephthalate blends presents numerous kinetic and flame spread modeling challenges. Such fabrics have extensive usage in light-weight shelters or for protective-coverings. This study details thermogravimetric analysis and one-sided heating experiments carried out for three different PVC/PET blended fabrics. A challenge with characterizing these materials is the relative contributions of PVC and PET are unknown. Only approximate ranges are often provided by manufacturers. In addition, the char/species yields are not known since blended materials (with additives) perform very differently from homogeneous PVC or PET samples. To unravel initial mass fractions and char/species yields, a new non-linear regression analysis is developed to process TGA mass loss data. This analysis is verified by Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy to confirm relative amounts. The output of the regression analysis provides important kinetic rate parameters for Arrhenius modeling used in FEA. To verify this approach, FE model predictions are compared to experiments showing good agreement to measured fabric temperature and mass loss. These results confirm the utility of using non-linear regression analysis for providing kinetic and composition information for constructing thermal degradation models of blended PVC/PET fabrics subject to fire environments.

Modeling the long-term 2-8 °C stability profiles of a live, rotavirus vaccine candidate (RV3-BB) in various liquid formulations via extrapolations of real-time and accelerated stability data

To accelerate the formulation development of live-virus vaccine (LVV) candidates, more rapid approaches to rank-order formulations and estimate their real-time storage stability losses are needed. In this case-study, we utilize new and previously described stability data of a live, rotavirus vaccine candidate (RV3-BB) in three different liquid formulations to model and compare predicted vs. experimental RV3-BB stability profiles. Linear-regression extrapolations of limited real-time (2-8 °C) stability data and Arrhenius modeling of accelerated (15, 25, 37 °C) stability data provided predictions of RV3-BB real-time stability profiles (2-8 °C, 24 months). Good correlations of modeled versus experimental stability data to rank-order the RV3-BB formulations were achieved by employing (1) a high-throughput RT-qPCR assay to measure viral titers, (2) additional assay replicates and stability time-points, and (3) a −80 °C control for each formulation to benchmark results at each stability time-point and temperature. Instead of accumulating two-year, 2–8 °C storage stability data, the same rank-ordering of the three RV3-BB formulations could have been achieved by modeling 37°, 25°, 15° (and 2–8 °C) stability data over 1, 3 and 12 months, respectively. The results of this case-study are discussed in the context of accelerating LVV formulation development by expeditiously identifying stable formulations, estimating their shelf-lives, and determining vaccine vial monitoring (VVM) designations.

PEMODELAN PERSAMAAN ARRHENIUS UNTUK MEMPREDIKSI UMUR SIMPAN PENYEDAP RASA CANGKANG RAJUNGAN

The aim of this research is to determine the shelf life of seasoning of swimming crab shell in metalized packaging, which is stored at various temperatures using the Arrhenius modeling. Seasoning are packaged using metalized packaging with a thickness of 0.06 mm, which is stored at 25 ºC, 35ºC, and 45ºC for 8 weeks with 75% humudity. The parameters used for measuring shelf life are initial moisture content, critical water, and changes in water content during storage. In addition, analysis of hygroscopicity and water activities (aw) value of seasoning as supporting parameters were also carried out. The results showed that seasoning that the seasoning of the swimming crab shells was classified as a hygroscopic product, had moisture content, and aw values a low during storage. The longest shelf life of the swimming crab shell seasoning is storage at 25ºC, reaching 62 weeks based on moisture content parameters.

Enhanced oil recovery performance of gemini surfactant-stabilized nanoemulsions functionalized with partially hydrolyzed polymer/silica nanoparticles

Nanoemulsion flooding is a novel route to enhanced recovery of petroleum resources over conventional water-flood by effective detachment and mobilization of residual oil trapped within rock-pores. In this article, we conducted experimental investigations to test the functionality of robust nanoemulsions comprising of gemini surfactant/polymer/silica nanoparticle assemblies; and explained mechanistic behavior of nanoemulsion-assisted oil displacement on a molecular scale. The presence of nano-sized oil droplets was confirmed by light scattering and CryoTEM imaging. Pseudoplastic behavior of nanoemulsions was identified, and viscous activation energies were determined using Arrhenius modeling. Viscoelasticity studies confirmed that elastic modulus dominated over viscous modulus, indicating that deforming forces do not exceed inter-droplet repulsions and interfacial stresses. Hence, nanoemulsion (oil) droplets retain their structural integrity under varying shear conditions. Core-flooding experiments showed that enhanced oil recoveries (EOR) of nanoemulsions improved over conventional aqueous fluids to 21–27% range of original oil in place (OOIP).

An Extrapolation of a Radical Equation More Accurately Predicts Shelf Life of Frozen Biological Matrices.

Arrhenius modeling of analyte recovery at increased temperatures to predict long-term colder storage stability of biological raw materials, reagents, calibrators, and controls is standard practice in the diagnostics industry. Predicting subzero temperature stability using the same practice is frequently criticized but nevertheless heavily relied upon. We compared the ability to predict analyte recovery during frozen storage using 3 separate strategies: traditional accelerated studies with Arrhenius modeling, and extrapolation of recovery at 20% of shelf life using either ordinary least squares or a radical equation y = B1x(0.5) + B0. Computer simulations were performed to establish equivalence of statistical power to discern the expected changes during frozen storage or accelerated stress. This was followed by actual predictive and follow-up confirmatory testing of 12 chemistry and immunoassay analytes. Linear extrapolations tended to be the most conservative in the predicted percent recovery, reducing customer and patient risk. However, the majority of analytes followed a rate of change that slowed over time, which was fit best to a radical equation of the form y = B1x(0.5) + B0. Other evidence strongly suggested that the slowing of the rate was not due to higher-order kinetics, but to changes in the matrix during storage. Predicting shelf life of frozen products through extrapolation of early initial real-time storage analyte recovery should be considered the most accurate method. Although in this study the time required for a prediction was longer than a typical accelerated testing protocol, there are less potential sources of error, reduced costs, and a lower expenditure of resources.

Effect of High pH Found in Low-Level Radioactive Waste Leachates on the Antioxidant Depletion of a HDPE Geomembrane

AbstractAntioxidant depletion from a high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) immersed in three different high pHs solutions is examined over a 3-year period. The three solutions had the same concentration of inorganic salts but a range of pH (9.5, 11.5, and 13.5) likely to encompass those found in low-level radioactive waste leachate and other geoenvironmental applications. Increasing the pH from 9.5 to 13.5 increased the antioxidant depletion rates detected by both standard and high-pressure oxidative induction time tests (Std-OIT and HP-OIT) and also increased the residual HP-OIT values. Arrhenius modeling is used to predict the length antioxidant depletion stage for each solution.

Effect of leachate composition on the long-term performance of a HDPE geomembrane

Aging of the same geomembrane immersed in the same four synthetic municipal solid waste leachates tested by Rowe et al. (2008) for 2.65 years is continued for an additional 6.5 years (i.e., providing data over more than 9 years of aging). The additional data is used to (a) update the initial estimates for antioxidant depletion stage, and (b) investigate the effect of leachate constituents on the timing and magnitude of the changes in the physical properties of the geomembrane. While all the examined leachates had surfactant and trace metals in common, reduced Leachate 1 (full leachate) had salts and volatile fatty acids (VFAs), Leachate 2 was not reduced and had neither salts nor VFAs, reduced Leachate 3 had salts, reduced Leachate 4 had VFAs, and Leachate 5 was similar to Leachate 2 except that it was reduced. Incubation in all leachates gave very similar predictions of the antioxidant depletion stage, however, the salts in Leachates 1 and 3 are shown to have the largest effect on the geomembrane mechanical properties, especially stress-crack resistance, resulting in a shorter time to nominal failure than for leachates without salts. Furthermore, reduced Leachates 1 and 3 showed faster degradation in stress-crack resistance than Leachate 2 which was not reduced and without salts. Arrhenius modeling is used to extrapolate the time to nominal failure (i.e., a reduction in stress-crack resistance to 150 h) at a range of temperatures.

Effect of high temperatures on antioxidant depletion from different HDPE geomembranes

The effect of elevated temperatures, typically 95–115 °C, on antioxidant depletion from a high-density polyethylene (HDPE) geomembrane (GMB) incubated in air, water and synthetic leachate is examined. It is shown that the antioxidant depletion in synthetic leachate at 95–115 °C is consistent with what would be expected from Arrhenius modeling based on data from lower temperatures (25–85 °C). A similar finding is reached for incubation in air. However, when incubated in water the antioxidant depletion is more complicated. At temperatures above 100 °C a four-parameter exponential model was needed to fit oxidative induction time data that exhibited quite different early-time and later-time depletion rates. The early-time depletion rate decreases with an increase of the temperature while the later-time depletion rates follow the more typical pattern of increasing with increasing temperature. Three additional HDPE GMBs with different antioxidant packages are examined at elevated temperatures in air. The GMB with the lowest initial standard (Std) oxidative induction time (OIT) and without hindered amine light stabilizer (HALS) has the longest antioxidant depletion stage based on Std-OIT at these elevated temperatures. GMBs stabilized with HALS showed only a slight change in their high pressure OIT during the current study. It is shown also that degradation in physical properties can start at Std-OIT values above the residual OIT values.

Arsenic removal from groundwater by acclimated sludge under autohydrogenotrophic conditions

Arsenic in the environment is attracting increasing attention due to its chronic health effects. Although arsenite (As(III)) is generally more mobile and more toxic than arsenate (As(V)), reducing As(V) to As(III) may still be a means for decontamination, because As(III) can be removed from solution by precipitation with sulfide or by adsorption or complexation with other metal sulfides. The performance of As(V) bio-reduction under autohydrogenotrophic conditions was investigated with batch experiments. The results showed that As(V) reduction was a biochemical process while both acclimated sludge and hydrogen were essential. Most of the reduced arsenic remained in a soluble form, although 20% was removed with no addition of sulfate, while 82% was removed when sulfate was reduced to sulfide. The results demonstrated that the reduced arsenic was re-sequestered in the precipitates, probably as arsenic sulfides. Kinetic analysis showed that pseudo first-order kinetics described the bio-reduction process better than pseudo second-order. In particular, the influences of pH and temperature on As(V) reduction by acclimated sludge under autohydrogenotrophic conditions and total soluble As removal were examined. The reduction process was highly sensitive to both pH and temperature, with the optimum ranges of pH 6.5–7.0 and 30–40°C respectively. Furthermore, Arrhenius modeling results for the temperature effect indicated that the As(V) reduction trend was systematic. Total soluble As removal was consistent with the trend of As(V) reduction.

Modeling of Replacement Alternatives for Power Transformer Populations

The age of the majority of power transformers installed in the western electricity network reaches 30 to 60 years and replacement on short term seems eminent. A technically sound policy concerning the replacement of these assets requires a model that estimates the life expectancies of individual components and from that calculates parameters related to the behavior of a population of assets as a whole. A probabilistic approach is adopted and is applied to thermal degradation of the transformer paper insulation. In this paper, we will focus on the determination of the population reliability from individual reliabilities. These individual reliabilities are based on Arrhenius modeling of paper insulation degradation, including the inherent uncertainty in the parameters involved. A statistical failure model is used to obtain the population reliability figures. The modeling method is demonstrated on two populations of power transformers in The Netherlands to evaluate the different replacement alternatives. Using the model, strategies can be defined to maximize transformer utilization and postpone replacement. The downside is the need to replace the complete fleet in a relatively short time afterwards.

LONG-TERM SAFETY, HIGH-RESOLUTION IMAGING, AND TISSUE TEMPERATURE MODELING OF SUBVISIBLE DIODE MICROPULSE PHOTOCOAGULATION FOR RETINOVASCULAR MACULAR EDEMA

To determine the long-term safety of high-density subvisible diode micropulse photocoagulation (810 nm), compare the clinical findings with computational modeling of tissue hyperthermia and to report results for a subset of eyes treated for diabetic macular edema (ME) documented pre- and postoperatively by spectral-domain optical coherence tomography. All eyes treated for ME from diabetic retinopathy (diabetic ME) and branch retinal vein occlusion between April 2000 and January 2010 were reviewed for subvisible diode micropulse laser-induced retinal damage. Therapeutic outcomes were reviewed for a subgroup treated for diabetic ME with pre- and postoperative spectral-domain optical coherence tomography. Laser-induced retinal thermal effects were modeled computationally using Arrhenius formalism. A total of 252 eyes (212 diabetic ME, 40 branch retinal vein occlusion) of 181 patients qualified. None of the 168 eyes treated at irradiance <350 W/cm2 and 7 of 84 eyes at ≥ 590 W/cm2 had retinal damage (P = 0.0001) (follow-up 3-120 months, median, 47). Sixty-two eyes of 48 patients treated for diabetic ME with pre- and postoperative spectral-domain optical coherence tomography with median 12 months follow-up had no retinal injury by infrared, red-free, or fundus autofluorescence photos; fluorescein angiography or indocyanine green angiography; or spectral-domain optical coherence tomography. Central foveal thickness (P = 0.04) and maximum macular thickness decreased (P < 0.0001). Modeling of retinal hyperthermia demonstrates that the sublethal clinical regimen corresponds to Arrhenius integral >0.05, while damage is likely to occur if it exceeds 1. Subvisible diode micropulse can effectively treat retinovascular ME without laser-induced retinal damage, consistent with Arrhenius modeling of pulsed hyperthermia.

Effects of Thickness on the Aging of HDPE Geomembranes

The results of an accelerated aging test program to evaluate the effect of thickness on the depletion of antioxidants from high-density polyethylene HDPE geomembranes and subsequent degradation of the physical properties are reported. Three commer- cially available HDPE geomembranes having nominal thicknesses of 1.5, 2.0, and 2.5 mm were examined. The geomembranes were immersed in a synthetic leachate at 85, 70, 55, and 22° C and tested for oxidative induction time, crystallinity, melt index MI, tensile properties, and stress-crack resistance. The antioxidant depletion rate for the 1.5 mm geomembrane was faster than for the 2.0 and 2.5 mm geomembranes. Antioxidant depletion time was predicted at representative landfill temperatures of 20- 60° C using Arrhenius modeling and was found to increase with geomembrane thickness for the three geomembranes examined. Based on the results of crystallinity, MI, and stress-crack resistance, the degradation of the geomembrane was slowest for the thickest geomembrane. These results suggest that a thicker geomembrane may have a longer service life other things being equal.

Aging of HDPE Geomembrane in Three Composite Landfill Liner Configurations

Laboratory-accelerated aging experiments conducted to examine the depletion of antioxidant from a geomembrane (GM) underlain by a geosynthetic clay liner (GCL) are described. Three different “protection” layers between the GM and overlying gravel and leachate are examined: (1) A traditional nonwoven geotextile (GT); (2) a GT-GCL; and (3) a GT-sand-GT layer. The GT-GCL protection layer gives an antioxidant depletion rate 0.59 to 0.66 times slower than the GT layer alone. The GT-sand-GT layer gives depletion rates 0.72–0.75 times that of the conventional GT alone. Based on Arrhenius modeling, the time required for depletion of antioxidants at 35°C is estimated to be 65 years for a GM with a GT-GCL protection layer, 50 years for a GT-sand-GT layer, and 40 years for a conventional GT protection layer. These times are all significantly greater than the depletion time for GM immersed in leachate (10 years) for the geomembrane tested.

Depletion of antioxidants from an HDPE geomembrane upon exposure to acidic and alkaline solutions

Oxidation is generally recognized as the key degradation mechanism regarding the long-term durability of high-density polyethylene (HDPE) geomembranes. For protection against oxidation during their service lifetime, antioxidants are added to the formulation. In this study, a laboratory accelerated aging program was conducted to assess the depletion of antioxidant from a Korean HDPE geomembrane subjected to air oven aging followed by incubation in acidic and alkaline buffer solutions at three different temperatures. The changes in oxidative induction time (OIT) were monitored at selected time intervals. The results indicated that, for samples subjected to oven aging incubation for 90 days, the OIT percent retained is above the residual value of 55% required by the existing specifications, indicating the geomembrane still has enough antioxidants to ensure its long-term oxidation stability under field conditions. Immersion in the alkaline buffer solution was found to accelerate the antioxidant depletion rate relative to that observed in the acidic buffer solution. Greater depletion rates were recorded at higher temperature, indicating the temperature dependency of the depletion process. Arrhenius modeling was used to give estimates of the time required for depletion of antioxidants. Conservative values of the depletion time ranged from 107 to 9 years depending on temperature and exposure condition. The estimated antioxidant depletion times were longest for exposure to acidic solutions and shortest for exposure to alkaline solutions.

Depletion of Antioxidants from a HDPE Geomembrane in a Composite Liner

The results of two series of accelerated aging tests are reported. Both series of tests were conducted at temperatures of 85, 70, 55, and 26°C over a period of about 3years. In the simulated liner series, the top of the geomembrane was covered with a geotextile (protection) layer that was exposed to simulated municipal solid waste (MSW) landfill leachate while the bottom of the geomembrane was in contact with a hydrated geosynthetic clay liner. In the immersion series, the geomembrane was immersed in the simulated MSW leachate, and hence, both sides were exposed to leachate. The results from oxidative induction time tests indicate that the antioxidant depletion is about 2.2–4.8 times faster for the leachate immersed geomembrane than for geomembrane in a composite liner. The higher rates are attributed to the higher extraction of antioxidants from two sides of the geomembrane immersed in leachate. The measured antioxidant depletion rates are extrapolated to a range of temperatures (0–60°C) using Arrhenius modeling. At a liner temperature of 35°C, the calculated time for the depletion of antioxidants is about 40years for a geomembrane in a composite liner compared to 10years if it is simply immersed in leachate. These tests suggest that to obtain realistic estimates of geomembrane service life one needs data from tests that simulate the expected field conditions and that prediction based on immersion tests may underestimate the service life.

In Vitro Assessment of the Efficacy of Thermal Therapy in Human Renal Cell Carcinoma

To define the temperature-time points that result in cell death in a human renal cell carcinoma cell (RCC) line in vitro. Cellular viability and clonogenic cell survival were determined for human A498 RCC cells after thermal treatment. Various temperature (45 degrees C to 70 degrees C) and time (1 to 30 minutes) combinations were used. Cell viability was assessed by vital dye uptake and clonogenic cell survival. Mathematical Arrhenius modeling was performed to construct a graphic display of A498 cell thermal sensitivity. Temperature-time points at which 99% or greater cell death occurred according to the vital dye assay were 55 degrees C for 30 minutes, 60 degrees C for 10 minutes, and 65 degrees C for 8 minutes. Clonogenic survival studies confirmed that cells treated at these temperature-time points failed to grow even after 10 days. These in vitro results show that short exposure to temperatures higher than 70 degrees C is lethal in the A498 RCC cell line. Lower temperatures in the 60 degrees C range require more prolonged heating to cause cell death. Knowledge of these temperatures will be useful to better plan and monitor complex radiofrequency ablations.

Creep Behavior of Recycled Plastic Lumber in Slope Stabilization Applications

Slender recycled plastic pins (RPPs) can be used to stabilize earthen slopes by driving the RPPs into the face of the slope to intercept the sliding surface and pin the slope. The RPPs will be subjected to lateral (bending) forces, and their ability to resist deformation will strongly influence the success of the RPPs for stabilizing slopes. Arrhenius modeling was used to predict the time for the RPPs to reach creep failure. Engineering properties and strain rate effect of four different types of RPPs were evaluated and are reported in this paper. Arrhenius modeling showed creep failure ranged from 50 to 3,900 years at field temperature and stress levels. Compressive strengths ranged from 11 to 20 MPa and compressive moduli from 580 to 1,280 MPa at 1% strain, while flexural strengths ranged from 9 to 25 MPa and flexural moduli from 620 to 1675 MPa at 1% strain.

Antioxidant Depletion Lifetime in High Density Polyethylene Geomembranes

A major issue in the use of geomembranes for waste containment is an estimate of the material's durability (i.e., its lifetime) to various aging phenomena. For high density polyethylene geomembranes, which are the focus of this study, there are three stages in assessing lifetime: depletion of antioxidants, induction time, and time to reach half-life of a relevant engineering property. This paper addresses the first stage of these three sequential processes. Twenty laboratory incubation devices were made to simulate landfill conditions. Four sets of five columns were maintained at elevated temperatures of 85, 75, 65 and 55°C. Samples were retrieved at various intervals over a 24-month incubation period. Various physical, mechanical, and chemical properties were evaluated. The depletion of antioxidants in the incubated samples was monitored using both standard and high pressure oxidative induction time tests. Arrhenius modeling was used on the data to extrapolate the antioxidant lifetime to a typical landfill site temperature of 20°C. The resulting predicted time was 200 to 215 years. Also, it should be emphasized that within this period of time the physical and mechanical properties of the incubated samples remained unchanged.

Arrhenius modeling to predict geosynthetic degradation

A methodology for the determination of the degradation of polymeric materials used in long-term applications such as landfill liners and covers, vertical and lateral expansions of solid waste facilities, retaining wall and slope reinforcement, etc., is the focus of this paper. Attention is placed on geomembrane barriers, but geotextile filters, geonet and geocomposite drains, geogrid and geotextile reinforcement and plastic pipe might also be involved. The predictive technique most widely used for polymer degradation (and explained throughout this paper) is based on a time-temperature superposition principle, and is called ‘Arrhenius modeling’ in this paper. It uses high-temperature incubation of the polymeric material in question followed by some type of laboratory testing, in order to extrapolate the experimental behavior to the site-specific, and lower, temperature. The tacit assumption involved is that the material's behavior within the high-temperature incubation range (as indicated by the activation energy, ‘E act’) is constant within this range and can be extrapolated to the lower temperature behavior of practical interest. Assuming this to be the case (it is obviously a critical assumption and promises to be difficult with oriented geosynthetic products), the nature of the experiments used to identify the amount of degradation becomes very significant. We have outlined 13 candidate tests (there are undoubtedly more) for the evaluation of polymers commonly used to manufacture geosynthetics. They are grouped in the mechanical, physical and chemical test method categories. Each test method is described in some detail. Furthermore, an attempt has been made to predict how the various responses might behave in their elevated temperature test environments. Using these trends, an Arrhenius plot can be generated, and a prediction of degradation to a site-specific temperature should be possible to obtain. It is hoped that this paper will stimulate discussion (and even controversy) and, if warranted, an intensive research effort in this area. With a strong enough effort, a single geosynthetic material can be investigated by a number of different testing techniques to see if a consensus regarding degradation times is reached. At the minimum, such a broad-based approach should identify which testing method is preferred for use in Arrhenius modeling. At this point, that particular method(s) can be used on all of the different polymer materials used in a particular application to see which one possesses the best resistance to a specific type of degradation.