Global Thermal Model Research Articles

Global thermal niche models of two European grasses show high invasion risks in Antarctica.

The two non-native grasses that have established long-term populations in Antarctica (Poa pratensis and Poa annua) were studied from a global multidimensional thermal niche perspective to address the biological invasion risk to Antarctica. These two species exhibit contrasting introduction histories and reproductive strategies and represent two referential case studies of biological invasion processes. We used a multistep process with a range of species distribution modelling techniques (ecological niche factor analysis, multidimensional envelopes, distance/entropy algorithms) together with a suite of thermoclimatic variables, to characterize the potential ranges of these species. Their native bioclimatic thermal envelopes in Eurasia, together with the different naturalized populations across continents, were compared next. The potential niche of P.pratensis was wider at the cold extremes; however, P.annua life history attributes enable it to be a more successful colonizer. We observe that particularly cold summers are a key aspect of the unique Antarctic environment. In consequence, ruderals such as P.annua can quickly expand under such harsh conditions, whereas the more stress-tolerant P.pratensis endures and persist through steady growth. Compiled data on human pressure at the Antarctic Peninsula allowed us to provide site-specific biosecurity risk indicators. We conclude that several areas across the region are vulnerable to invasions from these and other similar species. This can only be visualized in species distribution models (SDMs) when accounting for founder populations that reveal nonanalogous conditions. Results reinforce the need for strict management practices to minimize introductions. Furthermore, our novel set of temperature-based bioclimatic GIS layers for ice-free terrestrial Antarctica provide a mechanism for regional and global species distribution models to be built for other potentially invasive species.

Analysis of the effect of symmetric/asymmetric CUSP magnetic fields on melt/crystal interface during Czochralski silicon growth

With the use of 300mm silicon wafers for industrial semiconductor device manufacturing, the Czochralski (Cz) crystal growth process has to be optimized to achieve higher quality and productivity. Numerical studies based on 2D global thermal models combined with 3D simulation of melt convection are widely used today to save time and money in the process development. Melt convection in large scale Cz Si growth is controlled by a CUSP or transversal magnetic field (MF) to suppress the melt turbulence. MF can be optimized to meet necessary characteristics of the growing crystal, in terms of point defects, as MF affects the melt/crystal interface geometry and allows adjustment of the pulling rate.Among the different knobs associated with the CUSP magnetic field, the nature of its configuration, going from symmetric to asymmetric, is also reported to be an important tool for the control of crystallization front. Using a 3D unsteady model of the CGSim software, we have studied these effects and compared with several experimental results. In addition, physical mechanisms behind these observations are explored through a detailed modeling analysis of the effect of an asymmetric CUSP MF on convection features governing the heat transport in the silicon melt.

Double acting Stirling engine: Modeling, experiments and optimization

A three phase free piston type double acting Stirling engine model is proposed and validated using experimental results. The modeling strategy is based on a combination of two sub-models: a global thermal model of the engine to deal with heat sources coupling and a detailed equivalent electrical network model which accounts for the gas and mechanical dynamic physics of the engine. Derived features, such as the amplitude, the frequency, the compression and the expansion powers are then finally obtained. The model is experimentally validated with a prototype of a free piston Stirling engine. Mean error on the amplitude, the frequency, the internal temperatures and the compression and expansion powers is 9%, so the model is considered accurate enough to predict performances.For optimization purpose, a numerical analysis is performed selecting the three following critical parameters: (i) dead volume of the chambers, (ii) natural frequency of the mechanical oscillators and (iii) thermal conduction between hot and cold sides. Smaller dead volume, large oscillating mass and high insulation are to be sought for maximizing the performances. With a pressurization of 3bar, a theoretical useful power of 18W can be reach with conservative modification of the existing prototype. Moreover, energy and exergy analyses highlight the main losses in the system: thermal leakage, gas spring hysteresis as well as heat transfer and viscous dissipation in the heat exchangers.

Experimental and numerical analysis of thermally dissipating equipment in an aircraft confined compartment

Aircraft confined compartments are subject to a wide range of boundary conditions during operation which leads to the setting up of complex internal thermal environments. These compartments require strict thermal management to ensure safe and reliable operation of installed systems. This work investigates the thermal and fluid flow fields in one such compartment – the crown area in a fuselage of a commercial aircraft which contains thermally dissipating equipment. Experimental heat transfer and PIV measurements are compared to 3D numerical simulations and are shown to be in very good agreement. There was found to be significant thermal stratification present due to the ventilation not penetrating into the bulk of the fluid. Convective heat transfer coefficients on the surfaces of the dissipating equipment varied as a function of their location, with the highest values occurring when they are placed close to the ventilation inlet. An enthalpic correction was applied to 2D simulations leading to significantly reduced solution times, and results which give a good approximation of the 3D model results.This type of detailed study of aircraft confined compartments is necessary to improve understanding of the flow regimes present in these areas, and leads to optimal positioning of installed systems in terms of thermal management, as well improving global thermal aircraft model predictions.

Mechanism of ion-induced mixing phenomena in Gold–Nickel bilayer on Si substrate

Gold/Nickel bilayer thin films deposited on Si(100) substrates are bombarded by 100 keV 40Ar+, 260 and 300 keV 84Kr2+ and 400 keV 132Xe3+ ions which deposit maximum energy across the Gold/Nickel interface and hence produce maximum atomic transport within two sides of the interface. However, due to the energy of the projectile ions some Si atoms have also gained energy, which, in turn, displaces the atoms. The atomic displacements caused by the projectile in the system has been analyzed using RBS, XRD, SEM/EDS and AFM/MFM techniques. The relative change in the variance of the intermixed region across the Au–Ni–Si interfaces excluding the irradiation-induced surface roughness has been calculated and it was observed that it increases linearly with ion fluence. The measured athermal mixing rates which vary between 3.7 and 6.9 nm4, have been explained by various existing phenomenological models. It shows that local or global thermal spike models are most suitable for explaining the ion beam-induced mixing of systems with strong thermochemical properties of the constituents. The mixing efficiency of this system has been calculated and found to be 1.2 nm5/keV.

Power handling of the bulk tungsten divertor row at JET: First measurements and comparison to the GTM thermal model

The design of the tile assemblies of the bulk tungsten divertor row in JET was improved in the course of several experiments as far as the power and energy performances are concerned: many prototypes were exposed to high heat fluxes in several electron and ion beam facilities during the development phase. These experiments were carried out in parallel with extensive modelling of the complete tungsten tile assembly in the so-called Global Thermal Model (GTM). The goal was to understand the heat flow from the plasma-facing surface through the supporting structure down to the base plate of the JET MkII divertor sufficiently to be able to later interpret operational data from the torus. Temperatures measured in the torus are in good agreement (−10/+15%) with the model. Some characteristic times show stronger deviations, with no incidence on the highest temperature at all times.

Eruption history of the Elysium Volcanic Province, Mars

Volcanism has played a significant role in shaping the surface of Mars. Volatiles released during eruptions profoundly altered the composition and density of the Martian atmosphere in the past. Quantifying the amounts of volcanic outgassing has been attempted regionally and globally, however, volume estimates of erupted volcanic material in time are still poorly constrained. Here we show the first eruption frequency record of a volcanic region, the Elysium Volcanic Province, which is the second largest volcanic province on Mars. Studied lava flows show model ages ranging from 3.4 Ga to 60 Ma. Together with observed resurfacing ages, the ‘visible’ record of volcanic activity extends back to 3.9 Ga. Based on our 190 model ages, continuous volcanic activity is apparent with a major peak at 2.2 Ga. In the last 1 Gyr, the activity rapidly waned. Although the majority of volcanic material (including volatiles released to the atmosphere) erupted within a short time span of less than 200 Ma, activity continued until the very recent past. Extrapolating the eruption record, it appears likely that this region of Mars is still volcanically active today. Our derivation of the eruption record has profound implications for global thermal and atmospheric modeling, indicating sustained heat production, melt generation, and magma ascent at a single location over most of the planet's geological history.

Revisiting the thermal inertia of Iapetus: Clues to the thickness of the dark material

The energy balance at the surface of an airless planetary body is strongly influenced by the bolometric Bond albedo and the surface thermal inertia. Both of these values may be calculated through the application of a thermal model to measured surface temperatures. The accuracy of either, though, increases if the value of the other is better constrained. In this study, we used the improved global bolometric Bond albedo map of Iapetus derived from Cassini VIMS and ISS and Voyager ISS data in conjunction with Cassini CIRS temperature data to reevaluate surface thermal inertia across Iapetus. Results showed the thermal inertia of the dark terrain varies between 11 and 14.8 J m −2 K −1 s −1/2 while the light material varies between 15 and 25 J m −2 K −1 s −1/2. Using an approximation to the thermal properties of the dark overburden derived from our thermal inertia results, we can implement our thermal model to provide estimates on the dark material thickness, which was found to lie between 7 cm and 16 cm. In order to develop an accurate global thermal model, a weighted function that approximates the surface thermal inertia across Iapetus was developed and verified via our measurements. The global bolometric Bond albedo map, surface thermal inertia map, and the thermal model are then used to synthesize global temperature maps that may be used to study the stability of volatiles.

Power handling of a segmented bulk W tile for JET under realistic plasma scenarios

A solid tungsten divertor row has been designed for JET in the frame of the ITER-like Wall project (ILW). The plasma-facing tiles are segmented in four stacks of tungsten lamellae oriented in the toroidal direction. Earlier estimations of the expected tile performance were carried out mostly for engineering purposes, to compare the permissible heat load with the power density of 7MW/m2 originally specified for the ILW as a uniform load for 10s.The global thermal model developed for the W modules delivers results for more realistic plasma footprints: the poloidal extension of the outer strike point was reduced from the full lamella width of 62mm to ⩾15mm. Model validation is given by the experimental exposure of a 1:1 prototype stack in the ion beam facility MARION (incidence ∼6°, load E⩽66MJ/m2 on the wetted surface). Spreading the deposited energy by appropriate sweeping over one or several stacks in the torus is beneficial for the tungsten lamellae and for the support structure.

Global Simulating the Detached Solidification Growth of CdZnTe Under Microgravity and Gravity

Global thermal and flow models of detached Bridgman method applied in CdZnTe growth are established and conducted in this paper. Under a microgravity condition, two kinds of boundary conditions on the top surface of the melt (nonslip wall and free surface) are adopted with the gap width (e) ranging from 0∼1 mm, respectively. Under a gravity condition, the nonslip boundary condition on the top surface is adopted with the same range of e. The results show that under the microgravity condition, the flow is strengthened with the increase of e when the top surface is a nonslip wall. However, they show the opposite rule when the top surface is free surface. Under the gravity condition, the flow is strengthened with a larger crucible radius (ro). Velocity distributions on the meniscus show the similar rules in all conditions.

Thermal model and thermodynamic performance of molten salt cavity receiver

The design of a global steady-state thermal model of a 100 kWt molten salt cavity receiver was developed as part of the key project of the Ministry of Science and Technology of People's Republic of China (MOST). In the design process, the following factors were analyzed: receiver area, heat loss (convective, emissive, reflective and conductive), number of tubes in the receiver panel, tube diameter and receiver surface temperature. The model was also used to calculate the receiver performance of the Sandia National Laboratories' molten salt electric experiment (MSEE). In addition, the thermal performance of the designed molten salt cavity receiver is presented for a fixed outlet flow rate and a fixed output temperature.

Simulation Framework for Aircraft Power System Architecting

Today, the preliminary design process of power system architectures of civil aircraft is usually characterized by the separation into Air Transport Association chapters. However, the complexity of an aircraft energy network, the large number of influencing design parameters, and system interfaces require a common and transparent process if a meaningful evaluation of different system architectures with regard to the overall aircraft efficiency is to be achieved. The development of a dedicated methodology, a simulation framework, and adapted modeling techniques are the objectives of the presented research. This paper focuses on the dedicated modeling approaches that are developed to analyze systems at the aircraft level. Three different modeling techniques illustrate, on one hand, the effort required to develop adapted models to fit in the proposed analysis environment. On the other hand, the added value of such an integrated modeling approach is demonstrated with the examples of the electric generator sizing analysis and the link of power system simulation to a global aircraft thermal model.

Thermal model of a dish/Stirling systems

This paper presents a global thermal model of the energy conversion of the 10 kW el Eurodish dish/Stirling unit erected at the CNRS-PROMES laboratory in Odeillo. Using optical measurements made by DLR, the losses by parabola reflectivity and spillage are calculated. A nodal method is used to calculate the heat losses in the cavity by conduction, convection, reflection and thermal radiation. A thermodynamic analysis of a SOLO Stirling 161 engine is made. The Stirling engine is divided in 32 control-volumes and equations of ideal gas, mass and energy conservation are written for each control-volume. The differential equation system is resolved by an iterative method developed using Matlab ™ programming environment. Temperature, mass, density of working gas, heat transfers and the mechanical power are calculated for one Stirling engine cycle of 40 ms and for a constant direct normal irradiation (DNI). The model gives consistent results correctly fitting with experimental measurements.

Early evolution of Mars with mantle compositional stratification or hydrothermal crustal cooling

Analysis of Martian gravity and topography implies that crustal thickness variations created in the earliest evolution of planet have persisted to the present day. Relaxation of crustal thickness variations due to lower crustal flow by thermally activated creep is strongly temperature‐dependent and so, for particular crustal rheology and thickness, provides a constraint on thermal evolution. Previous models have assumed that the heat flux from the mantle, which controls lower crustal temperatures, simply reflects radiogenic heat production. However, global thermal evolution models in which the mantle cools by solid‐state thermal convection indicate that the additional contribution to near‐surface heat flux due to secular cooling significant increases lower crustal temperatures. With, a 50‐km‐thick crust, and a wet diabase rheology, these higher temperatures allow crustal rock to flow fast enough to relax crustal thickness variations during the first ∼750 Myr of evolution. Previous studies have not considered the presence of an impact‐brecciated crustal layer that would almost certainly be present on early Mars and could have a significant influence on crustal temperatures. The presence of a dry brecciated crustal layer several kilometers thick would significantly increase the temperature of the lower crust resulting in more rapid relaxation of crustal thickness variations. If the porosity of a brecciated crust is water saturated, then the effect of such a layer is greatly reduced. However, if water is present, cooling of the upper crust by groundwater convection in a deeper impact‐fractured crustal layer with modest permeabilities could reduce lower crustal temperatures enough to explain the preservation of ancient crustal thickness variations. A cooler lower crust is also possible if solid‐state thermal convection in the mantle is inhibited by a stable compositional stratification resulting from the fractional solidification of an early magma ocean.

Global 1° × 1° thermal model TC1 for the continental lithosphere: Implications for lithosphere secular evolution

This paper reports a new 1° × 1° global thermal model for the continental lithosphere (TC1). Geotherms for continental terranes of different ages (> 3.6 Ga to present) constrained by reliable data on borehole heat flow measurements (Artemieva, I.M., Mooney, W.D. 2001. Thermal structure and evolution of Precambrian lithosphere: a global study. J. Geophys. Res 106, 16387–16414.), are statistically analyzed as a function of age and are used to estimate lithospheric temperatures in continental regions with no or low-quality heat flow data (ca. 60% of the continents). These data are supplemented by cratonic geotherms based on electromagnetic and xenolith data; the latter indicate the existence of Archean cratons with two characteristic thicknesses, ca. 200 and > 250 km. A map of tectono-thermal ages of lithospheric terranes complied for the continents on a 1° × 1° grid and combined with the statistical age relationship of continental geotherms ( z = 0.04 ⁎ t + 93.6, where z is lithospheric thermal thickness in km and t is age in Ma) formed the basis for a new global thermal model of the continental lithosphere (TC1). The TC1 model is presented by a set of maps, which show significant thermal heterogeneity within continental upper mantle, with the strongest lateral temperature variations (as large as 800 °C) in the shallow mantle. A map of the depth to a 550 °C isotherm (Curie isotherm for magnetite) in continental upper mantle is presented as a proxy to the thickness of the magnetic crust; the same map provides a rough estimate of elastic thickness of old (> 200 Ma) continental lithosphere, in which flexural rigidity is dominated by olivine rheology of the mantle. Statistical analysis of continental geotherms reveals that thick (> 250 km) lithosphere is restricted solely to young Archean terranes (3.0–2.6 Ga), while in old Archean cratons (3.6–3.0 Ga) lithospheric roots do not extend deeper than 200–220 km. It is proposed that the former were formed by tectonic stacking and underplating during paleocollision of continental nuclei; it is likely that such exceptionally thick lithospheric roots have a limited lateral extent and are restricted to paleoterrane boundaries. This conclusion is supported by an analysis of the growth rate of the lithosphere since the Archean, which does not reveal a peak in lithospheric volume at 2.7–2.6 Ga as expected from growth curves for juvenile crust. A pronounced peak in the rate of lithospheric growth (10–18 km 3/year) at 2.1–1.7 Ga (as compared to 5–8 km 3/year in the Archean) well correlates with a peak in the growth of juvenile crust and with a consequent global extraction of massif-type anorthosites. It is proposed that large-scale variations in lithospheric thickness at cratonic margins and at paleoterrane boundaries controlled anorogenic magmatism. In particular, mid-Proterozoic anorogenic magmatism at the cratonic margins was caused by edge-driven convection triggered by a fast growth of the lithospheric mantle at 2.1–1.7 Ga. Belts of anorogenic magmatism within cratonic interiors can be caused by a deflection of mantle heat by a locally thickened lithosphere at paleosutures and, thus, can be surface manifestations of exceptionally thick lithospheric roots. The present volume of continental lithosphere as estimated from the new global map of lithospheric thermal thickness is 27.8 (± 7.0) × 10 9 km 3 (excluding submerged terranes with continental crust); preserved continental crust comprises ca. 7.7 × 10 9 km 3. About 50% of the present continental lithosphere existed by 1.8 Ga.

Fast heavy ion induced interface mixing in thin-film systems

Thin layer systems (Fe 2O 3/SiO 2, NiO/SiO 2, Cu 2O/SiO 2, ZnO/SiO 2, Fe/SiO 2, Ni/SiO 2, Cu/SiO 2, Ni 3N/SiO 2, Ni 3N/Si 3N 4, Ni 3N/SiO 2, Ni 3N/SiC and Ni 3N/Si) have been irradiated with Ar, Kr, Xe and Au ions in the energy range from 90 up to 350 MeV. Interface mixing was observed above a threshold value ( S ec) of the electronic stopping power, which is determined by the less sensitive component with respect to electronic energy deposition. The estimation of an effective diffusion constant supports the assumption that efficient mixing occurs by transient interdiffusion in a molten track as soon as the electronic energy loss in both layers exceeds the respective track formation threshold. Above the threshold mixing scales with the square of the electronic stopping power ( S e). This result again indicates that, according to the global thermal spike model, the one-dimensional energy deposition along the ion path results in a molten track across the interface.

Investigation and modeling of plasma-wall interactions in inductively coupled fluorocarbon plasmas

Plasma-wall interactions in fluorocarbon based feedgas chemistries, namely CF4, are examined in a standard inductively coupled Gaseous Electronics Conference reference cell using in situ Fourier-transform infrared spectroscopy and microwave interferometry. Measurements show the dissociation of the CF4 feedgas into radical CFx species, as has been observed elsewhere [M. J. Goeckner and R. A. Breun, J. Vac. Sci. Technol. A 11, 3 (1993)], and qualitatively reveal a decrease in plasma-wall interactions as wall temperature is increased. Experimental results such as plasma density, 1011 cm−3, and CF4 density 1013 cm−3, are further compared to results from the hybrid plasma equipment model [R. Kinder and M. J. Kushner, J. Vac. Sci. Technol. A 19, 76 (2001)] to better elucidate the influence of wall temperature on plasma exposed surfaces and sticking coefficients. Last, CF4 vibrational temperatures were also measured, revealing that the line-averaged vibrational temperature remains at a constant 40–60 K above the chamber wall temperature while the vibrational temperature in the center of the discharge is significantly higher. Moreover, the vibrational temperatures are further compared to results from a global thermal model and are in good agreement.

Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests

Recent high-power laser deposition experiments on octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) produced ignition times from milliseconds to seconds. Global chemical kinetic thermal decomposition models for HMX and TATB developed to predict thermal explosion experiments lasting seconds to days are applied to these laser ignition experimental data. Excellent agreement was obtained for TATB, while the calculated ignition times were longer than experiment for HMX at lower laser fluxes. Inclusion of HMX melting and faster reaction for liquid HMX in the HMX decomposition model improved the agreement with experiment at lower laser energies.

Numerical study on directional solidification of AlSi alloys with rotating magnetic fields under microgravity conditions

A global thermal model of the ARTEX facility, developed with the modeling tool CrysVUn, is presented. The model is validated with experimental data obtained under microgravity conditions during the TEXUS39 mission. Numerical studies are then reported, in which the effects of a rotating magnetic field are investigated during directional solidification of binary AlSi7 alloys. It appears that beyond a certain magnetic field strength a macrosegregation effect is resulting, leading to the development of a liquid channel inside the mushy zone.

Atomic transport in ceramics induced by electronic energy deposition (invited)

In the present paper an overview over the results of a systematic study on swift heavy ion beam mixing of ceramic thin layer packages will be presented. It will be shown that interface mixing due to electronic energy deposition in these systems is a threshold process and can be regarded as transient interdiffusion in the molten ion track. The mixing threshold is given by the track formation threshold in the less sensitive of the interface forming materials with respect to beam induced damage. The mixing rate shows a square scaling with the electronic stopping power, in agreement with the global thermal spike model. The mixing efficiencies (except for NiO samples) do not vary much for different materials, and no influence of the solid state properties on the mixing effect can deduced. NiO seems to take an exceptional position within the investigated materials since it shows an extraordinary high mixing effect, which furthermore exhibits a spatial anisotropy. The latter is not yet fully understood.