scholarly journals On the Impact of Microsegregation Model on the Thermophysical and Solidification Behaviors of a Large Size Steel Ingot

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 74
Author(s):  
Chunping Zhang ◽  
Mohammad Jahazi ◽  
Paloma Isabel Gallego
Keyword(s):  
Thermophysical Properties ◽  
Steel Ingot ◽  
Solidification Process ◽  
Lever Rule ◽  
Cast Ingot ◽  
Classical Equilibrium ◽  
Large Size ◽  
Macro Scale ◽  
The Impact ◽  
Non Equilibrium

The impact of microsegregation models on thermophysical properties and solidification behaviors of a high strength steel was investigated. The examined microsegregation models include the classical equilibrium Lever rule, the extreme non-equilibrium Scheil-Gulliver, as well as other treatments in the intermediate regime proposed by Brody and Flemings, Clyne and Kurz, Kobayashi and Ohnaka. Based on the comparative analyses performed on three representative regions with varied secondary dendrite arm spacing sizes, the classical equilibrium Lever rule and non-equilibrium Scheil scheme were employed to determine the thermophysical features of the studied steel, using the experimentally verified models from literature. The evaluated thermophysical properties include effective thermal conductivity, specific heat capacity and density. The calculated thermophysical data were used for three-dimensional simulation of the casting and solidification process of a 40 metric ton steel ingot, using FEM code Thercast®. The simulations captured the full filling, the thermo-mechanical phenomena and macro-scale solute transport in the cast ingot. The results demonstrated that Lever rule turned out to be the most reasonable depiction of the physical behavior of steel in study in large-size cast ingot and appropriate for the relevant macrosegregation simulation study. The determination of the model was validated using the experimentally measured top cavity dimension, the thermal profiles on the mold outside surface by means of thermocouples, and the carbon distribution patterns via mass spectrometer analysis.

Sensitivity of the Non-Equilibrium Approach for Mixture Condensation to Heat and Mass Transfer Correlations and Thermophysical Properties

2021 ◽  
Author(s):  
Conrad Zimmermann ◽  
Cagatay N. Dagli ◽  
Zlatan Arnautovic ◽  
Stephan Kabelac
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Thermophysical Properties ◽  
Equilibrium Approach ◽  
Vle Data ◽  
The Impact ◽  
Vapor Mass ◽  
Non Equilibrium

Abstract The prediction of mixture condensation is still complex due to coupled heat and mass transfer and insufficient data of thermophysical mixture properties. This article analyzes the impact of various heat and mass transfer correlations on the non-equilibrium approach for mixture condensation in a vertical plain tube. Furthermore, the influence of thermophysical properties from different databases is investigated. The results are shown for ethanol-water, but allow conclusions to other fluid mixtures. They indicate that the liquid heat transfer coefficient in the non-equilibrium approach dominates the qualitative behavior of the condensation process, but the vapor mass transfer coefficient can only decrease or increase the quantitative level of the effective heat transfer with minor impact. More importantly, the logarithm in the vapor mass transfer term is central for the prediction of the condensation heat transfer. As this logarithm contains VLE data, it proves that there is a strong connection between VLE and overall prediction of mixture condensation. A demonstration of available data for thermophysical mixture properties of ethanol-water shows significant deviations, which affect the calculations as well. Besides, data from our own experiments are presented for mixture viscosity of ethanol-water. It is recommended to focus not only on improved heat and mass transfer correlations, but also on thermophysical properties and VLE data for a precise prediction of mixture condensation.

scholarly journals Shock interactions in inviscid air and $$\hbox {CO}_2$$–$$\hbox {N}_2$$ flows in thermochemical non-equilibrium

Shock Waves ◽  
2021 ◽  
Author(s):  
C. Garbacz ◽  
W. T. Maier ◽  
J. B. Scoggins ◽  
T. D. Economon ◽  
T. Magin ◽  
...  
Keyword(s):  
Chemical Species ◽  
High Energy ◽  
Ideal Gas ◽  
Shock Interaction ◽  
Interaction Patterns ◽  
Shock Interactions ◽  
Wave Interference ◽  
Type V ◽  
The Impact ◽  
Non Equilibrium

AbstractThe present study aims at providing insights into shock wave interference patterns in gas flows when a mixture different than air is considered. High-energy non-equilibrium flows of air and $$\hbox {CO}_2$$ CO 2 –$$\hbox {N}_2$$ N 2 over a double-wedge geometry are studied numerically. The impact of freestream temperature on the non-equilibrium shock interaction patterns is investigated by simulating two different sets of freestream conditions. To this purpose, the SU2 solver has been extended to account for the conservation of chemical species as well as multiple energies and coupled to the Mutation++ library (Multicomponent Thermodynamic And Transport properties for IONized gases in C++) that provides all the necessary thermochemical properties of the mixture and chemical species. An analysis of the shock interference patterns is presented with respect to the existing taxonomy of interactions. A comparison between calorically perfect ideal gas and non-equilibrium simulations confirms that non-equilibrium effects greatly influence the shock interaction patterns. When thermochemical relaxation is considered, a type VI interaction is obtained for the $$\hbox {CO}_2$$ CO 2 -dominated flow, for both freestream temperatures of 300 K and 1000 K; for air, a type V six-shock interaction and a type VI interaction are obtained, respectively. We conclude that the increase in freestream temperature has a large impact on the shock interaction pattern of the air flow, whereas for the $$\hbox {CO}_2$$ CO 2 –$$\hbox {N}_2$$ N 2 flow the pattern does not change.

Influence of Non-Equilibrium Fluid Properties During Fogging on Intake Duct and Compressor Characteristics

2017 ◽  
Author(s):  
Christoph Günther ◽  
Franz Joos
Keyword(s):  
Relative Humidity ◽  
Gas Turbine ◽  
Thermophysical Properties ◽  
Ambient Air ◽  
Compressor Stage ◽  
Compression Process ◽  
Fluid Properties ◽  
Temperature And Pressure ◽  
Gas Turbine Compressor ◽  
Non Equilibrium

This study reports on numerically calculated thermophysical properties of air passing through a gas turbine compressor after passage through an intake duct affected by wet compression. Case of reference is unaffected ambient air (referenced to as dry scenario) passing through intake duct and compressor. Furthermore, ambient air cooled down by (overspray) fogging (referenced to as wet scenarios) was considered. Acceleration at the end of intake duct causing reduction of static temperature and pressure results in supersaturated fluid properties at inlet to gas turbine compressor. These supersaturated fluid properties are non-equilibrium with saturation level above relative humidity of φ = 1. Entrance of supersaturated fluid into gas turbine compressor can result in condensation within first compressor stage. At the same time delayed impact of evaporative cooling influences compression process.

scholarly journals Empirical Investigation of Symmetric and Asymmetric Target Adjustment Models: Capital Structure of Non-Financial Firms in Jordan

2017 ◽  
Vol 9 (3) ◽  
pp. 133 ◽  
Author(s):  
Bashar K. Abu Khalaf
Keyword(s):  
Capital Structure ◽  
Stock Exchange ◽  
Interaction Model ◽  
Firm Characteristics ◽  
Leverage Ratio ◽  
Financial Firms ◽  
Large Size ◽  
Amman Stock Exchange ◽  
Target Leverage ◽  
The Impact

The different capital structure theories propose the possible asymmetric behavior of capital structure. Thus, this paper empirically investigates whether non-financial Jordanian firms follow symmetrical or asymmetrical adjustment model. Then, an interaction model with the size and profitability (firm characteristics) investigated the impact of low/high profit and small/large size on the adjustment of leverage towards the target leverage ratio. This paper covered the period of 14 years (2002-2015) for a total of 110 companies listed on Amman Stock Exchange (75 industrial and 35 services). Results indicate that although Jordanian firms seek a target leverage ratio, their adjustment towards that target is Asymmetrical and high profitable and large companies tend to adjust faster than low profitable and small size companies.

scholarly journals Beyond the bucket – Developing a global gradient-based groundwater model (G<sup>3</sup>M v1.0) for a global hydrological model from scratch

2018 ◽  
Author(s):  
Robert Reinecke ◽  
Laura Foglia ◽  
Steffen Mehl ◽  
Tim Trautmann ◽  
Denise Cáceres ◽  
...  
Keyword(s):  
Steady State ◽  
Capillary Rise ◽  
Hydrological Models ◽  
Grid Cells ◽  
Reservoir Model ◽  
Model Framework ◽  
Water Flows ◽  
Macro Scale ◽  
Gradient Based ◽  
The Impact

Abstract. To quantify water flows between groundwater (GW) and surface water (SW) as well as the impact of capillary rise on evapotranspiration by global hydrological models (GHMs), it is necessary to replace the bucket-like linear GW reservoir model typical for hydrological models with a fully integrated gradient-based GW flow model. Linear reservoir models can only simulate GW discharge to SW bodies, provide no information on the location of the GW table and assume that there is no GW flow among grid cells. A gradient-based GW model simulates not only GW storage but also hydraulic head, which together with information on SW table elevation enables the quantification of water flows from GW to SW and vice versa. In addition, hydraulic heads are the basis for calculating lateral GW flow among grid cells and capillary rise. G3M is a new global gradient-based GW model with a spatial resolution of 5' that will replace the current linear GW reservoir in the 0.5° WaterGAP Global Hydrology Model (WGHM). The newly developed model framework enables in-memory coupling to WGHM while keeping overall runtime relatively low, allowing sensitivity analyses and data assimilation. This paper presents the G3M concept and specific model design decisions together with results under steady-state naturalized conditions, i.e. neglecting GW abstractions. Cell-specific conductances of river beds, which govern GW-SW interaction, were determined based on the 30'' steady-state water table computed by Fan et al. (2013). Together with an appropriate choice for the effective elevation of the SW table within each grid cell, this enables a reasonable simulation of drainage from GW to SW such that, in contrast to the GW model of de Graaf et al. (2015, 2017), no additional drainage based on externally provided values for GW storage above the floodplain is required in G3M. Comparison of simulated hydraulic heads to observations around the world shows better agreement than de Graaf et al. (2015). In addition, G3M output is compared to the output of two established macro-scale models for the Central Valley, California, and the continental United States, respectively. As expected, depth to GW table is highest in mountainous and lowest in flat regions. A first analysis of losing and gaining rivers and lakes/wetlands indicates that GW discharge to rivers is by far the dominant flow, draining diffuse GW recharge, such that lateral flows only become a large fraction of total diffuse and focused recharge in case of losing rivers and some areas with very low GW recharge. G3M does not represent losing rivers in some dry regions. This study presents the first steps towards replacing the linear GW reservoir model in a GHM while improving on recent efforts, demonstrating the feasibility of the approach and the robustness of the newly developed framework.

scholarly journals The impact of forest regeneration on streamflow in 12 mesoscale humid tropical catchments

2013 ◽  
Vol 17 (7) ◽  
pp. 2613-2635 ◽  
Author(s):  
H. E. Beck ◽  
L. A. Bruijnzeel ◽  
A. I. J. M. van Dijk ◽  
T. R. McVicar ◽  
F. N. Scatena ◽  
...  
Keyword(s):  
Time Series ◽  
Land Cover ◽  
Forest Regeneration ◽  
Forest Cover ◽  
Impact Analysis ◽  
Forest Area ◽  
Macro Scale ◽  
Annual Time Series ◽  
The Impact ◽  
Annual Time

Abstract. Although regenerating forests make up an increasingly large portion of humid tropical landscapes, little is known of their water use and effects on streamflow (Q). Since the 1950s the island of Puerto Rico has experienced widespread abandonment of pastures and agricultural lands, followed by forest regeneration. This paper examines the possible impacts of these secondary forests on several Q characteristics for 12 mesoscale catchments (23–346 km2; mean precipitation 1720–3422 mm yr−1) with long (33–51 yr) and simultaneous records for Q, precipitation (P), potential evaporation (PET), and land cover. A simple spatially-lumped, conceptual rainfall–runoff model that uses daily P and PET time series as inputs (HBV-light) was used to simulate Q for each catchment. Annual time series of observed and simulated values of four Q characteristics were calculated. A least-squares trend was fitted through annual time series of the residual difference between observed and simulated time series of each Q characteristic. From this the total cumulative change (Â) was calculated, representing the change in each Q characteristic after controlling for climate variability and water storage carry-over effects between years. Negative values of  were found for most catchments and Q characteristics, suggesting enhanced actual evaporation overall following forest regeneration. However, correlations between changes in urban or forest area and values of  were insignificant (p &amp;geq; 0.389) for all Q characteristics. This suggests there is no convincing evidence that changes in the chosen Q characteristics in these Puerto Rican catchments can be ascribed to changes in urban or forest area. The present results are in line with previous studies of meso- and macro-scale (sub-)tropical catchments, which generally found no significant change in Q that can be attributed to changes in forest cover. Possible explanations for the lack of a clear signal may include errors in the land cover, climate, Q, and/or catchment boundary data; changes in forest area occurring mainly in the less rainy lowlands; and heterogeneity in catchment response. Different results were obtained for different catchments, and using a smaller subset of catchments could have led to very different conclusions. This highlights the importance of including multiple catchments in land-cover impact analysis at the mesoscale.

scholarly journals Applications of nanotechnology with hybrid Photovoltaic/Thermal systems

2020 ◽  
pp. 1-15
Author(s):  
Mohammed Alktranee
Keyword(s):  
Thermophysical Properties ◽  
Base Fluid ◽  
Volume Fraction ◽  
Working Fluid ◽  
Spectral Filter ◽  
Thermal Systems ◽  
Cooling Fluid ◽  
Numerical Studies ◽  
The Impact ◽  
T System

This paper appears potential of use nanofluids as a working fluid with the photovoltaic/thermal (PV/T) systems as an alternative of the conventional liquids in improves the efficiency of the hybrid PV/T system. The review highlights the impact of some parameters (base fluid, volume fraction, the concentration of nanoparticles, surfactants, shape, and size of nanoparticles) on nanofluids' thermophysical properties and their effect on the PV/T system's efficiencies. Hence, it discusses the PV/T behavior, which uses different nanofluids based on previous experimental, analytical, and numerical studies. The review concluded that using nanofluid as a cooling fluid or spectral filter contributes by enhancing the performance and increasing the PV/T system's efficiency. Thus, each type of nanofluids has certain features that contribute to removing the PV cells' excess heat by cooling it, contributing to its work's stability, and increasing its productivity. Nanofluids thermophysical properties play an intrinsic role by enhancing nanofluids' performance, thus positively reflecting on the PV/T system's performance. Despite the variation in the values of thermal and electrical efficiency, Most of the studies that used nanofluids have achieved encouraging results that appeared by improving the performance of PV/T systems.

scholarly journals 15. Clicker Lessons: Assessing and Addressing Student Responses to Audience Response Systems

2011 ◽  
Vol 1 ◽  
pp. 85
Author(s):  
Tim Pelton ◽  
Leslee Francis Pelton ◽  
Mary Sanseverino
Keyword(s):  
Audience Response ◽  
Evaluation Tool ◽  
Audience Response Systems ◽  
Self Evaluation ◽  
Perceived Need ◽  
Large Size ◽  
Response Systems ◽  
Support Teacher ◽  
The University ◽  
The Impact

This project began in response to a perceived need to assess students’ perceptions with respect to the emerging use of audience response systems (clickers) in several mid- to large-size undergraduate courses at the University of Victoria. We developed and validated a “Clicker Use Survey” to gather students’ opinions with respect to clicker utility and the impact of clicker use on their learning. With the collected data we generated a set of baseline distributions to support assessment of various clicker use protocols and created a self-evaluation tool to share with instructors to support teacher reflection on the efficacy of their clicker practices. We also provided a sample self-evaluation to model the use of the tool. Links to the survey instrument, baseline data and self-evaluation tool, and sample self-evaluation are provided.

scholarly journals Hydrazine-nitrate combustion synthesis of BaCeO3 preceramic powders: structure, morphology and thermophysical properties

2021 ◽  
Author(s):  
Maksim Tenevich ◽  
Andrey Pavlovich Shevchik ◽  
Vadim Igorevich Popkov
Keyword(s):  
Thermophysical Properties ◽  
Simultaneous Thermal Analysis ◽  
Combustion Method ◽  
Sintered Sample ◽  
Combustion Products ◽  
Laser Flash ◽  
Barium Cerate ◽  
Hydrazine Nitrate ◽  
Average Size ◽  
The Impact

Abstract In the present work, preceramic nanocrystallite barium cerate (BaCeO3) was successfully synthesized using the hydrazine-nitrate combustion method. Using carbon-free hydrazine (N2H4) as fuel significantly reduced the formation of carbon by-products. Characterization of the as-received powders was performed by XRD, energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), simultaneous thermal analysis (DTA-TGA) and adsorption-structural analysis (N2, 77 K). Thermophysical properties of the sample annealed at 1000 °С were investigated using laser flash analysis (LFA) in the temperature interval of 1000 °С. As a result of a comprehensive study, the sequence of chemical and phase transformations that lead to the formation of BaCeO3 with a rhombic structure (Pnma, a = 6.2145 Å, b = 8.7776 Å, c = 6.2337 Å) during the thermal processing of combustion products was investigated. It was established that the average size of the obtained nanocrystals is 38 ± 3 nm and that they form micron-sized agglomerates with a specific surface area of the powder of 4.8 m2/g. It was shown that the sintered sample of BaCeO3 is characterized by thermal diffusivity values of 0.28 to 0.20 mm2/s and thermal conductivity values of 0.41 to 0.35 W/mK, depending on temperature. These results, given the impact of porosity on the sample (~ 40%), show very good agreement with the thermophysical characteristics of densely sintered ceramics based on BaCeO3 – a solid oxide electrolyte SOFC. Consequently, the proposed method of hydrazine-nitrate synthesis of BaCeO3 presents itself as a promising approach to obtaining preceramic powders and ceramics in the area of SOFC.

scholarly journals Effectiveness of Flexible Dam Operation and Sediment Replenishment at Managawa Dam, Japan

2018 ◽  
Vol 13 (4) ◽  
pp. 691-701 ◽  
Author(s):  
Katsumi Matsushima ◽  
Makoto Hyodo ◽  
Noriyuki Shibata ◽  
Yoshihiro Shimizu ◽  
◽  
...  
Keyword(s):  
Flood Pulse ◽  
Demonstration Project ◽  
Scale Analysis ◽  
Management Options ◽  
Ecological Processes ◽  
Fluvial Systems ◽  
Macro Scale ◽  
Dam Operation ◽  
The Impact ◽  
The Relationship

A field demonstration project on flexible dam operation at the Managawa dam in the Kuzuryu River Basin has been implemented since 2000. The goal is to restore flow and sediment regimes in the Managawa River, which flows along the Ono-city and is located below the dam. Flexible dam operation stores inflow discharge into a reservoir, which generally uses part of the flood control capacity and appropriately discharges the stored water to the river, also known as the “flood pulse,” for restoring dynamic fluvial systems and the resulting ecological processes. In addition, other options have been carried out in combination with flexible dam operation, for example, sediment replenishment since 2003 and channel rehabilitation since 2007. This article reveals the positive impacts and effectiveness of flexible dam operation, sediment replenishment, and channel rehabilitation, and discusses challenges and future prospects toward translating the field demonstration project into dam management on the ground level. First, we classified reach types to identify the impact of various management options, e.g., flexible dam operation, sediment replenishment, and channel rehabilitation. These management options can influence respected reaches. We conducted a macro-scale analysis to understand the relationship between the aforementioned management options and dynamic fluvial systems, addressing changes in gravel riverbed, vegetation, and habitat types (riffles and pools). Second, a micro-scale analysis was conducted to understand the relationship between the management option and changes in attached algae to sediment and macro-invertebrates, etc. The results show the effectiveness of the middle-scale flood pulse to restore dynamic fluvial systems, increase habitat diversity, and sustain ecological processes. Furthermore, we discussed the impacts of such options on the flow and sediment regimes in Managawa River and revealed that flexible dam operation reduces the occurrence of low flow and midscale floods. It was also revealed methods such as sediment replenishment and channel rehabilitation play an important role in increasing the effectiveness of the middle-scale flood pulse and restoring dynamic fluvial systems, even though sediment replenishment is not sufficient to restore sediment regimes (i.e., bring then back to pre-dam conditions).

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