Temperature Measurements with Depth and Physical Evidence for the Effect of High Temperature Gradients on Top-Down Fatigue Cracking

2020 ◽  
Vol 2674 (4) ◽  
pp. 384-396
Author(s):  
Adrian Ricardo Archilla
Keyword(s):  
High Temperature ◽  
High Surface ◽  
Fatigue Cracking ◽  
Time Of Day ◽  
Temperature Gradients ◽  
Temperature Measurements ◽  
Measured Temperature ◽  
Horizontal Shear ◽  
Top Down ◽  
Shear Strains

This paper presents the results of pavement temperature measurements with depth over a year obtained with a setup emulating the heat flow on a pavement with 305 mm (12 in.) of hot mix asphalt (HMA) and 152 mm (6 in.) of aggregate base. Several findings related to top-down fatigue cracking (TDFC) in Hawaii were obtained from these measurements. It was observed that pavement temperatures near the surface, which were both the lowest and the highest in the HMA depending on the time of day, were rarely below 20°C, and thus, that most cracking in Hawaii occurs at higher temperatures. It was also observed that passing rains can cause sudden temperature drops of the order of 15°C within short periods (15 min). HMA moduli estimated using measured temperature profiles indicate that high temperature gradients may lead to inverted moduli profiles that when loaded cause the highest tensile and shear strains to occur near the surface, and that these may be a main reason for TDFC in the state. The simulated stresses and strains under high temperature gradients also indicate they may be conducive to delamination problems related to large horizontal shear strains generated near the surface and combined with nearly vertical but small tensile strains at the layer interface. The observation that cracking suddenly and consistently stops under overpass bridges and immediately resumes after them provides strong evidence consistent with the findings of the stress/strain distributions generated from profiles with high surface temperature and high temperature gradients potentially causing TDFC. The paper provides recommendations for further study.

A Dynamic Modeling Methodology to Estimate the Magnitude of Unwanted Liquid Flows in High Temperature Boiler Components

2020 ◽  
Vol 12 (5) ◽  
Author(s):  
Gary de Klerk ◽  
Pieter Rousseau ◽  
Louis Jestin
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Fatigue Cracking ◽  
Momentum Equation ◽  
Temperature Gradients ◽  
Root Cause ◽  
Modeling Methodology ◽  
Tracking Model ◽  
Liquid Flows ◽  
Control Volumes

Abstract Due to the penetration of variable renewable energy (VRE) sources into electricity supply grids, conventional coal fired power plants need to operate with greater flexibility while remaining reliable and conserving the lifetime of components. Thick-sectioned components are prone to thermal fatigue cracking as a result of through-wall temperature gradients. These temperature gradients can be significantly amplified during quenching when components at high temperature are unintentionally exposed to colder liquid or steam. Such quench events are known to occur during two-shift operation of a large once-through coal fired tower type boiler. The purpose of this study is to develop and demonstrate a model that can be used to determine the root cause and magnitude of quenching. The model is developed using the least level of detail to make it readily usable by power plant engineers. Two different approaches are used. A liquid tracking model (LTM) was developed from first principles that approximates the liquid level in the superheater as a function of time. The model is presented and verified by comparison with real-plant data. The second approach was to configure a model in flownex, which is a commercially available software package. The LTM model with eight control volumes provided better steam temperature results and was able to simulate the correct superheater pressure behavior without solving the momentum equation. The models proved that a separator overflow was the cause of quenching for this particular case study.

Top-Down Fatigue Cracking in High-Temperature Environments

2015 ◽  
Vol 2507 (1) ◽  
pp. 128-137 ◽  
Author(s):  
Adrián Ricardo Archilla
Keyword(s):  
High Temperature ◽  
Traditional Approach ◽  
Fatigue Cracking ◽  
Temperature Profiles ◽  
Top Down ◽  
Current State ◽  
Study Results ◽  
Extreme High Temperature ◽  
Design Guide ◽  
Pavement Temperature

Top-down fatigue cracking (TDFC) is now recognized as a common type of distress occurring in all types of environments on heavy-duty hotmix asphalt (HMA) pavements, but TDFC modeling is still limited in current state-of-the-practice tools. Despite significant recent advances in TDFC modeling, for regions with high-temperature seasons an extreme high-temperature profile with depth is a potentially important factor that deserves further consideration. This paper explores the potential of temperature gradients caused by high pavement surface temperatures to induce TDFC. Although, for the Hawaii environment, the Mechanistic–Empirical Pavement Design Guide (MEPDG) always predicts that the HMA modulus decreases with depth after some aging of the pavement, the study results indicate that for some plausible high-temperature profiles the HMA modulus increases with depth even when frequencies are computed with the MEPDG procedure. This increase results in the greatest tensile strains, maximum shear strains, and estimated damage occurring near the top of the HMA layer at the edge of the load. The apparent inconsistency is attributed to the coarse modeling of temperatures within a season in the MEPDG; this coarse modeling may result in such high-temperature profiles not being modeled. A modification of the MEPDG procedure to refine the modeling of environmental effects at high temperatures (e.g., including the 95th and 98th pavement temperature percentiles) is recommended. This modification would allow better modeling of TDFC with the traditional approach.

Passive Auto-Focus Algorithm for Correcting Image Distortions Caused by Gas Flow in High-Temperature Measurements of Surface Phenomena

2012 ◽  
Vol 17 (4) ◽  
pp. 379-384 ◽  
Author(s):  
Krzysztof Strzecha ◽  
Tomasz Koszmider ◽  
Damian Zarębski ◽  
Wojciech Łobodziński
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Temperature Measurements ◽  
Surface Phenomena ◽  
Auto Focus ◽  
High Temperature Measurements

Abstract In this paper, a case-study of the auto-focus algorithm for correcting image distortions caused by gas flow in high-temperature measurements of surface phenomena is presented. This article shows results of proposed algorithm and methods for increasing its accuracy.

scholarly journals Performance Evaluation of Asphalt Rubber Mixture with Additives

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1200 ◽  
Author(s):  
Cheng ◽  
Liu ◽  
Ren ◽  
Huang
Keyword(s):  
High Temperature ◽  
Fatigue Cracking ◽  
Crumb Rubber ◽  
Good Choice ◽  
Environmental Benefits ◽  
Fatigue Properties ◽  
Control Group ◽  
Rubber Mixture ◽  
Asphalt Rubber ◽  
Temperature Performance

Crumb rubber, as a recycled material used in asphalt mixture, has gained more attention in recent years due to environmental benefits and the advantages of its pavement, such as excellent resistance to cracking, improved durability, less road maintenance, lower road noise, etc. However, the high-temperature performance of mixture with crumb rubber does not perform well. In order to improve the performance, this paper examined the effect of additives on the laboratory performance of asphalt rubber Stone Matrix Asphalt (AR-SMA) with additives. Three groups of AR-SMA: no additives, Styrene–Butadiene–Styrene (SBS) and Granular Polymer Durable additive (GPDa) were included, with no additives as a control group. Each group was investigated at three asphalt rubber content (ARC): 6.4%, 6.9%, 7.4% with regard to high-temperature and fatigue properties. The results show that with increasing ARC, the high-temperature performance of mixture without additive decreases, and the high-temperature performance increases first and then decreases for SBS and GPDa. Moreover, the rutting resistance of AR-SMA with GPDa at 6.9% ARC performs best. Under the condition of mixtures with appropriate ARC, AR-SMA with GPDa has higher fatigue life and sensitivity to fatigue cracking than the control group. Simultaneously, the fatigue performance of AR-SMA with GPDa is not as significant as that without additive with increasing ARC. In a word, GPDa is a good choice to improve the performance of AR-SMA. However, it should be noted that optimal asphalt content of AR-SMA mixtures with GPDa is higher than that of traditional mixtures.

scholarly journals Diurnal variations in the UV albedo of arctic snow

2008 ◽  
Vol 8 (21) ◽  
pp. 6551-6563 ◽  
Author(s):  
O. Meinander ◽  
A. Kontu ◽  
K. Lakkala ◽  
A. Heikkilä ◽  
L. Ylianttila ◽  
...  
Keyword(s):  
High Surface ◽  
Measured Temperature ◽  
Snow Melt ◽  
Clear Sky ◽  
Different Types ◽  
Essential Parameter ◽  
Surface Reflectivity ◽  
Climate Studies ◽  
Radiative Transfer Modeling ◽  
Surface Layer Thickness

Abstract. The relevance of snow for climate studies is based on its physical properties, such as high surface reflectivity. Surface ultraviolet (UV) albedo is an essential parameter for various applications based on radiative transfer modeling. Here, new continuous measurements of the local UV albedo of natural Arctic snow were made at Sodankylä (67°22'N, 26°39'E, 179 m a.s.l.) during the spring of 2007. The data were logged at 1-min intervals. The accumulation of snow was up to 68 cm. The surface layer thickness varied from 0.5 to 35 cm with the snow grain size between 0.2 and 2.5 mm. The midday erythemally weighted UV albedo ranged from 0.6 to 0.8 in the accumulation period, and from 0.5 to 0.7 during melting. During the snow melt period, under cases of an almost clear sky and variable cloudiness, an unexpected diurnal decrease of 0.05 in albedo soon after midday, and recovery thereafter, was detected. This diurnal decrease in albedo was found to be asymmetric with respect to solar midday, thus indicating a change in the properties of the snow. Independent UV albedo results with two different types of instruments confirm these findings. The measured temperature of the snow surface was below 0°C on the following mornings. Hence, the reversible diurnal change, evident for ~1–2 h, could be explained by the daily metamorphosis of the surface of the snowpack, in which the temperature of the surface increases, melting some of the snow to liquid water, after which the surface freezes again.

Rapid Synthesis of Bi Substituted Ca3Co4O9 by a Polyacrylamide Gel Method and its High-Temperature Thermoelectric Power Factor

2010 ◽  
Vol 434-435 ◽  
pp. 393-396 ◽  
Author(s):  
Ying Song ◽  
Qiu Sun ◽  
Li Rong Zhao ◽  
Fu Ping Wang
Keyword(s):  
High Temperature ◽  
Thermoelectric Power ◽  
Power Factor ◽  
Solid State Reaction Method ◽  
Polyacrylamide Gel ◽  
Measured Temperature ◽  
Thermoelectric Power Factor ◽  
Gel Method ◽  
Plasma Sintering ◽  
Polyacrylamide Gel Method

A series of polycrystalline (Ca1-xBix)3Co4O9 ( x = 0.0 ~ 0.075 ) powders were synthesized rapidly by a polyacrylamide gel method. The dense ceramics were fabricated using the spark plasma sintering ( SPS ) technique. Effects of Bi substitution on high temperature thermoelectric properties of Ca3Co4O9 were evaluated. Both the electrical conductivity and Seebeck coefficient increased with increasing Bi content up to x = 0.05, thus leading to an enhanced thermoelectric power factor. The Bi substituted sample with x = 0.05 obtained in this study has the highest thermoelectric power factor in the measured temperature range. It reaches 4.810-4 Wm-1K-2 at 700 °C, which is 26 % higher than that of Ca3Co4O9 without Bi substitution, and is by up to 15 % larger as compared to the Bi substituted sample synthesized by the solid state reaction method and the SPS technique due to the high chemical homogeneous powder prepared by the polyacrylamide gel method.

598 Temperature profiles of sunlight-exposed surfaces in a desert climate: Determining the risks for pavement burns.

2021 ◽  
Vol 42 (Supplement_1) ◽  
pp. S150-S151
Author(s):  
Paul J Chestovich ◽  
Richard Z Saroukhanoff ◽  
Syed F Saquib ◽  
Joseph T Carroll ◽  
Carmen E Flores ◽  
...  
Keyword(s):  
Ambient Temperature ◽  
Solar Irradiance ◽  
Time Of Day ◽  
Temperature Measurements ◽  
Solar Irradiation ◽  
Porous Rock ◽  
Solid Materials ◽  
Contour Plots ◽  
Desert Climate ◽  
Sunlight Intensity

Abstract Introduction In the desert climates of the United States, plentiful sunlight and high summer temperatures cause significant burn injuries from hot pavement and other surfaces. Although it is well known that surfaces reach temperatures sufficient to cause full-thickness burns, the peak temperature, time of day, and highest risk materials is not well described. This work measured continuous temperature measurements of six materials in a desert climate over a five-month period. Methods Six different solid materials common in an urban environment were utilized for measurement. Asphalt, brick, concrete, sand, porous rock, and galvanized metal were equipped with thermocouples attached to a data acquisition module. All solid materials except metal were placed in a 2’x2’x3.5” form, and identical samples were placed in both shade and direct sunlight. Ambient temperature was recorded, and sunlight intensity was measured using a pyranometer. Measurement time interval was set at three minutes. A computational fluid dynamics (CFD) model was created using Star CCM+ to validate the data. Contour plots of temperature, solar irradiance, and time of day were created using MiniTab for all surfaces tested. Results 75,000 temperature measurements were obtained from March through August 2020. Maximum recorded temperatures for sunlight-exposed samples of porous rock was 170 F, asphalt 166 F, brick 152 F, concrete 144 F, metal 144 F, and sand 143 F. Peak temperatures were recorded on August 6, 2020 at 2:10 pm, when ambient temperature was 120 F and sunlight intensity 940 W/m2 (Table). Temperatures ranged from 36 F - 56 F higher than identical materials in the shade at the same time. The highest daily temperatures were achieved between 2:00 pm to 4:00 pm due to maximum solar irradiance. Contour plots of surface temperature as function of solar irradiation and time of day were created for all surfaces tested. Nearly identical results obtained from the CFD models to the experimentally collected data, which validated the experimental data. Conclusions Surfaces exposed to direct, continuous sunlight in a desert climate achieve temperatures from 143 F to 170 F in the early afternoon and are high enough to cause significant injury with sufficient exposure. Porous rock reached the highest temperature, followed closely by asphalt. This information is useful to inform the public of the dangers of exposed surfaces in a desert climate.

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