Local Thermal Processes Research Articles

An improved analytical model of effective thermal conductivity for hydrate-bearing sediments during elastic-plastic deformation and local thermal stimulation

As one of the crucial thermal properties controlling the dissociation of natural gas hydrate (NGH), effective thermal conductivity (ETC) should be precisely determined to improve the efficiency of NGH exploitation. But so far, most existing analytical ETC models of hydrate-bearing sediments could not accurately characterize the evolution of ETC. In this paper, an improved analytical model is derived for quantitatively revealing physical relations between ETC and various influencing factors during elastic-plastic deformation and local thermal stimulation processes, including hydrate saturation change, complex pore structures evolution, and hydrate occurrence patterns transition. The effectiveness of the proposed model is validated against available experimental data and compared with other existing models, then effects of various critical parameters on ETC are investigated. Results show that the porosity of hydrate-bearing sediments is accurately predicted during both loading and unloading processes, and the calculated ETC values under various conditions (effective stress, hydrate saturation, and temperature) are satisfactory with the test data. Contributions of elastic deformation and plastic deformation to ETC increments are quantitatively obtained. It is noteworthy that this proposed model is significant to reveal the evolution mechanisms of ETC, helping to accurately predict gas production and offer better plans for efficient NGH exploitations.

Post-CMOS processing challenges and design developments of CMOS-MEMS microheaters for local CNT synthesis

Carbon nanotubes (CNTs) can be locally grown on custom-designed CMOS microheaters by a thermal chemical vapour deposition (CVD) process to utilize the sensing capabilities of CNTs in emerging micro- and nanotechnology applications. For such a direct CMOS-CNT integration, a key requirement is the development of necessary post-processing steps on CMOS chips for fabricating CMOS-MEMS polysilicon heaters that can locally generate the required CNT synthesis temperatures (~650–900 °C). In our post-CMOS processing, a subtractive fabrication technique is used for micromachining the polysilicon heaters, where the passivation layers in CMOS are used as masks to protect the electronics. For dielectric etching, it is necessary to achieve high selectivity, uniform etching and a good etch rate to fully expose the polysilicon layers without causing damage. We achieved successful post-CMOS processing by developing two-step reactive ion etching (RIE) of the SiO2 dielectric layer and making design improvements to a second-generation CMOS chip. After the dry etching process, CMOS-MEMS microheaters are partially suspended by SiO2 wet etching with minimum damage to the exposed aluminium layers, to obtain high thermal isolation. The fabricated microheaters are then successfully utilized for synthesizing CNTs by a local thermal CVD process. The CMOS post-processing challenges and design aspects to fabricate CMOS-MEMS polysilicon microheaters for such high-temperature applications are detailed in this article. Our developed process for heterogeneous monolithic integration of CMOS-CNT shows promise for wafer-level manufacturing of CNT-based sensors by incorporating additional steps in an already existing foundry CMOS process.

Effect of process modes on microstructure and mechanical properties of CMT wire arc additive manufactured WE43 magnesium alloy

The traditional WE43 magnesium alloy (WE43-Mg) manufacturing process faces challenges in producing large and complex structures. The cold metal transfer wire arc additive manufacturing (CMT-WAAM) offers a promising solution due to its flexibility, high deposition efficiency and low heat put. However, energy transfer and mass transfer are highly coupled in the CMT additive manufacturing process. Under different working modes, the local thermal processes are quite different for the same transition metals, which can produce different microstructures and mechanical properties. Therefore, it is necessary to study the effect of working modes on microstructure and mechanical properties. This study successfully deposited single-pass multi-layer WE43-Mg components using four CMT processes: CMT, CMT-Pulse, CMT-Advance, and CMT-Pulse + Advance. The microstructure and mechanical properties of these deposited samples were compared. Results revealed equiaxed grains with uniform sizes in the top and middle regions, with fine-grain regions between layers in the four CMT modes. Compare the microstructure characterization results, the higher the line energy, the narrower the width of the remelted fine grain zone. Four CMT modes deposited components exhibited superior mechanical properties compared to as-cast WE43-Mg. The CMT pulse mode shows the best results due to its low porosity. The average yield strength is 149.0 MPa, tensile strength is 222.9 MPa, and elongation is 6.4 %.

Application of end-face fiber optic sensor for thermooptical research

The principles of operation and implementation features of the developed fiber-optic device for pulsed thermoreflectometry based on an external Fabry-Perot interferometer are discussed. The possibility of studying local thermal processes in the near-surface layers of samples by changing the thermal reflection of probing radiation during pulsed laser heating is shown. Comparison of experimental data with modeling calculations showed the predominant influence of the thermal deformation mechanism in the case of metal samples.

Dynamic Thermal Performance Analysis of PCM Products Used for Energy Efficiency and Internal Climate Control in Buildings

PCMs are attractive for the future generation of buildings, where energy efficiency targets and thermal comfort expectations are increasingly prioritized. Experimental analysis of local thermal processes in these dynamic components and whole-building energy consumption predictions are essential for the proper implementation of PCMs in buildings. This paper discusses the experimental analysis of the thermophysical characteristics of both a latent heat storage material (PCM) and a product containing this PCM. The prototype product under investigation is a panelized PCM technology containing inorganic, salt-hydrate-based PCM. The thermal analysis includes studies of melting and freezing temperatures, enthalpy changes during phase change processes, nucleation intensity, sub-cooling effects, and PCM stability. The PCM’s stability is also investigated, as is the ability of PCM products to control local temperatures and peak load transmission times. Two inorganic PCM formulations based on calcium chloride hexahydrate (CaCl2.6H2O) were prepared and tested in laboratory conditions. Material-scale testing results were compared with outcomes from the system-scale analysis, using both laboratory test methods as well as field exposure in test huts. This work demonstrates that PCM technologies used in buildings can effectively control both the magnitude of thermal storage capacity as well as the time of the peak thermal load. It was found that commonly used material-scale testing methods may not always be beneficial in assessing the dynamic thermal performance characteristics of building technologies containing PCMs.

PCBs, PCNs, and PCDD/Fs in Soil around an Industrial Park in Northwest China: Levels, Source Apportionment, and Human Health Risk.

The concentrations of polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were determined in soil samples collected around an industrial park in Northwest China, to investigate the potential impacts of park emissions on the surrounding environment. The total concentration ranges of PCBs, PCNs, and PCDD/Fs in the soil samples were in 13.2-1240, 141-832, and 3.60-156 pg/g, respectively. The spatial distribution and congener patterns of PCBs, PCNs, and PCCD/Fs indicated that there might be multiple contamination sources in the study area, so source apportionments of PCBs, PCNs, and PCCD/Fs were performed by a positive matrix factorization model based on the concentrations of all target congeners together. The results revealed that these highly chlorinated congeners (CB-209, CN-75, and OCDF) might be derived from phthalocyanine pigments, the legacy of Halowax 1051 and 2,4-D products, which together contributed nearly half of the total concentration of target compounds (44.5%). In addition to highly chlorinated congeners, the local industrial thermal processes were mainly responsible for the contamination of PCBs, PCNs, and PCDD/Fs in the surrounding soil. The total carcinogenic risk of PCBs, PCNs, and PCDD/Fs in a few soil samples (0.22 × 10-6, 0.32 × 10-6, and 0.40 × 10-6) approached the threshold of potential carcinogenic risk (1.0 × 10-6). Since these pollutants can continuously accumulate in the soil, the contamination of PCBs, PCNs, and PCDD/Fs in surrounding soil deserves continuous attention.

Spatially Resolved Temperature Distribution in a Rare-Earth-Doped Transparent Glass-Ceramic.

Knowing the temperature distribution within the conducting walls of various multilayer-type materials is crucial for a better understanding of heat-transfer processes. This applies to many engineering fields, good examples being photovoltaics and microelectronics. In this work we present a novel fluorescence technique that makes possible the non-invasive imaging of local temperature distributions within a transparent, temperature-sensitive, co-doped Er:GPF1Yb0.5Er glass-ceramic with micrometer spatial resolution. The thermal imaging was performed with a high-resolution fluorescence microscopy system, measuring different focal planes along the z-axis. This ultimately enabled a precise axial reconstruction of the temperature distribution across a 500-µm-thick glass-ceramic sample. The experimental measurements showed good agreement with computer-modeled heat simulations and suggest that the technique could be adopted for the spatial analyses of local thermal processes within optically transparent materials. For instance, the technique could be used to measure the temperature distribution of intermediate, transparent layers of novel ultra-high-efficiency solar cells at the micron and sub-micron levels.

Connection between interannual variation of spring precipitation in Northeast China and preceding winter sea ice over the Barents Sea

AbstractThis study discusses the interannual variation of spring precipitation in Northeast China (NECSP) from 1980 to 2016 and its relationship with Arctic sea ice based on observation data and numerical experiments. The observed results reveal that the leading mode of NECSP mainly exhibits a homogenous pattern with a significant interannual variation. The NECSP has a significant negative correlation with the preceding winter Barents Sea ice concentration (BSIC) at the interannual scale. In the preceding winter, the decreased BSIC resulted in positive geopotential height anomalies over the polar region, which could weaken the polar vortex and westerly winds, forming a cyclonic anomaly indirectly over West Siberia. The circulation anomalies resulted in a zonal dipole pattern of preceding winter snow water equivalent (SWE) anomalies in the mid‐high latitudes of Eurasia with less SWE over Eastern Europe and more SWE over West Siberia. The SWE anomalies in winter could persist to the subsequent spring and facilitate more precipitation over Northeast China (NEC) by local thermal processes affecting circulation anomalies over Eurasia. On the other hand, the negative preceding winter BSIC anomalies can persist to spring, increasing the NECSP by strengthening the cyclonic anomalies over NEC. In this study, the response of the atmosphere to the thermal effect of SWE is further verified by using the linear baroclinic model (LBM). The response of NECSP to BSIC loss is tested by using the Community Atmosphere Model version 5.3 (CAM5.3).

Why is the November Siberian High Intensity More Predictable by NCEP-CFSv2 Model?

As a critical system of the East Asian winter monsoon, the Siberian high has an important impact on the winter weather and climate anomalies in Eurasia. Using the National Center for Environment Prediction-Climate Forecast System version 2 (NCEP-CFSv2), this study comprehensively evaluates the seasonal and monthly prediction of the Siberian high intensity during the winter time (November to February). Results show that the NCEP-CFSv2 model can skillfully predict the Siberian high intensity only in November, the reasons for which are that the local thermal process, dynamic process, and Siberian snow cover extent mainly affect the Siberian high intensity in November. In terms of the thermal process, the NCEP-CFSv2 can better reproduce the Siberian high intensity in November and its related surface soil temperature, upward long-wave radiation, and other thermal factors in Siberia. In terms of the dynamic process, the NCEP-CFSv2 can better reproduce the Siberian high strength in November, which is associated with the low-level tropospheric divergent circulation and the sinking movement of the upper and middle layers in the Siberian area. The model also reproduces the relationship between the snow cover extent over Siberia and the Siberian high intensity in November. The thermodynamic process of the Siberian high and snow cover extent in the area are predictability sources of the Siberian High intensity in November, and the NCEP-CFSv2 can reasonably reproduce these predictability sources in November.

Field investigation on the influence of periglacial processes on pile foundations on the Qinghai–Tibet plateau

AbstractPeriglacial processes can threaten the operation of engineering infrastructure. Based on field observations, the influence of four types of periglacial processes on tower foundations along the Qinghai–Tibet Engineering Corridor were investigated. These periglacial processes change the local thermal and hydraulic processes in soils around the pile foundations, thereby threatening their stability. Frost heaving‐related periglacial phenomena and fast mass wasting are major threats for the operation of pile foundations. The long‐term stability of pile foundations is also threatened by thermokarst‐related periglacial processes and slow mass wasting under the evolving climate change scenario on the Qinghai–Tibet Plateau. Frost weathering has a slight impact on the stability of concrete pile heads, and the long‐term effects of this cannot be ignored. In addition to the impacts of periglacial processes, piles are also affected by engineering problems in areas with shallow artesian ground water, where the use of thermosyphons is associated with frost jacking of the foundations. Further studies are needed on the thermal and hydraulic regimes in soils under the influence of artesian ground water and thermokarst lakes/ponds.

Welding of differentially heat-strengthened rails. Modeling of processes during welding and local thermal processing

Problem of generation of local hardened areas in weld metal d ing rails welding in production of continuous welded rails is solved by using local heat treatment of weld joint. As a result, appearance of quenching structures is excluded. However, new zones of thermal influence with reduced hardness may appear. During operation, such rails are characterized by increased wear of the rolling surface in these areas and collapse of the head at welded joint. It is the main reason for removing rails from the track earlier than time guaranteed. Application of new technology based on dependences of dispersion degree of the structural components (primarily perlite and carbide particles formed during obtaining welded butt joints of rails) on steel composition and rails cooling conditions is proposed. Cooling rate has a decisive influence on the degree of dispersion of ferritic-cementite structure formed during decomposition of austenite. When welding rails in a butt weld, generation of granular perlite is possible in the areas with temperature between Ac 1 and Ac m points. To determine these critical temperatures, thermodynamic calculations were performed using Thermo-Calc ® software (TCFE database) taking into account chemical composition of the samples obtained by spectrometry. Fe – C state diagrams for 76KhSF rail steel were modeled with the minimum and maximum content of alloying elements according to the state standard GOST R 51685 – 2013. To obtain minimal volume of sections with reduced hardness, it is possible to conduct rails welding in hard conditions by electrocontact method using pulsating reflowing. To prevent formation of defective sections with quenching structure, it is possible to control cooling of welded joint using contact heating. Measurement of the temperature distribution during welding according to the given modes and controlled cooling confirms theoretical conclusions.

The dynamic processes in second generation HTS tapes under the pulsed current and magnetic impact

This paper presents the results of complex multiphysical modelling of non-equilibrium states arising in high-temperature superconducting composites under current, magnetic, and combined control switching impacts types. The simulation and analysis of the dynamics of electrophysical and thermal processes occurring in the HTS composites layered structure taking into account the influence of local thermal processes in the composite structure, in particular, heat generation bursts during a pulse, has been performed. The HTS composite switching times from the superconducting to the normal state have been investigated for various current pulses amplitudes in homogeneous magnetic fields. An experimental verification of the numerical model has been carried out.

Probing the thermal runaway triggering process within a lithium-ion battery cell with local heating

Thermal runaway is the most important safety problem of the lithium ion battery. A thermal model combined five side reactions is established to analyze the high temperature distribution change of the separator during the local thermal runaway process of a lithium-ion battery cell with local heating terminals in this paper. The results show that thermal runaway will not be triggered inside a battery cell if a balance of the heat convection between the battery cell and the air forms when a single terminal is heated with 423.15 K. And local thermal runaway can be triggered when the both terminals of the battery cell are heated with 473.15 K and 423.15 K. In addition, the temperature distribution of the separator layer shows an extension trend along the horizontal direction firstly and then along the vertical direction, and local heating makes a big temperature difference inside a battery cell.

Temperature mapping of operating nanoscale devices by scanning probe thermometry.

Imaging temperature fields at the nanoscale is a central challenge in various areas of science and technology. Nanoscopic hotspots, such as those observed in integrated circuits or plasmonic nanostructures, can be used to modify the local properties of matter, govern physical processes, activate chemical reactions and trigger biological mechanisms in living organisms. The development of high-resolution thermometry techniques is essential for understanding local thermal non-equilibrium processes during the operation of numerous nanoscale devices. Here we present a technique to map temperature fields using a scanning thermal microscope. Our method permits the elimination of tip–sample contact-related artefacts, a major hurdle that so far has limited the use of scanning probe microscopy for nanoscale thermometry. We map local Peltier effects at the metal–semiconductor contacts to an indium arsenide nanowire and self-heating of a metal interconnect with 7 mK and sub-10 nm spatial temperature resolution.

Diffusion flames in condensed-phase energetic materials: Application to Titanium–Boron combustion

The characteristics of a steady diffusion flame that arises at the interfaces of two condensed phase reactant streams that form an opposed counterflow are discussed. We assume that the flow is due to deformation from compaction or local heating and thermal expansion processes in the microscale environment of composite energetic materials. As a representative example of high temperature combustion of metal/intermetallic reactants, the overall reaction of titanium and boron to create titanium diboride products is considered under near isobaric conditions. The multi-component diffusion description uses a generalized Fick formulation with coefficients related to the binary diffusivities defined in the Maxwell–Stefan relations. A fairly simple depletion form with Arrhenius temperature dependent coefficients is used to describe the reaction rate. Several types of analyses are carried out at increasing levels of complexities: an asymptotic analysis valid in the limit of low strain rates (high residence time in the reaction zone), a constant mixture density assumption that simplifies the flow description, diffusion models with equal and unequal molecular weights for the various species, and a full numerical study for finite rate chemistry, composition-dependent density and strain rates extending from low to moderate values. All are found to agree remarkably well in describing the flame structure, the flame temperature and the degree of incomplete combustion. Of particular importance is the determination of a critical strain rate beyond which steady burning may no longer be observed. The analysis has a general character and can be applied to other condensed phase energetic material systems, where reaction and diffusion occur in the presence of flow and material deformation.

Numerical Evaluation and Optimization of Depth-oriented Temperature Measurement for the Investigation of Thermal Influences on Groundwater Resources

High-resolution depth-oriented temperature measurements have been introduced to investigate a groundwater body in the urban area of Basel. In total, four devices were installed with up to 16 sensors - located in both the saturated and unsaturated zone. Measurements were performed over a period of 4 years and provide sufficient data to set up and calibrate high-resolution numerical local heat-transport models. Calibration was performed for the saturated and unsaturated zone, respectively.Model results show that although depth-oriented measurements provide valuable insights into local thermal processes, the identification of governing and impacting factors strongly depends on appropriate positioning of the measurement device.

A numerical study of EGS heat extraction process based on a thermal non-equilibrium model for heat transfer in subsurface porous heat reservoir

With a previously developed numerical model, we perform a detailed study of the heat extraction process in enhanced or engineered geothermal system (EGS). This model takes the EGS subsurface heat reservoir as an equivalent porous medium while it considers local thermal non-equilibrium between the rock matrix and the fluid flowing in the fractured rock mass. The application of local thermal non-equilibrium model highlights the temperature-difference heat exchange process occurring in EGS reservoirs, enabling a better understanding of the involved heat extraction process. The simulation results unravel the mechanism of preferential flow or short-circuit flow forming in homogeneously fractured reservoirs of different permeability values. EGS performance, e.g. production temperature and lifetime, is found to be tightly related to the flow pattern in the reservoir. Thermal compensation from rocks surrounding the reservoir contributes little heat to the heat transmission fluid if the operation time of an EGS is shorter than 15 years. We find as well the local thermal equilibrium model generally overestimates EGS performance and for an EGS with better heat exchange conditions in the heat reservoir, the heat extraction process acts more like the local thermal equilibrium process.

Nucleosynthetic strontium isotope anomalies in carbonaceous chondrites

Precise Sr isotopic compositions in samples from sequential acid leaching experiments have been determined for three carbonaceous chondrites, Allende, Murchison, and Tagish Lake, together with those in the bulk aliquots of these meteorites. The chondritic acid leachates and residues were characterized by Sr isotope anomalies with variable μ84Sr values (106 relative deviation from a standard material) ranging from +120 to −4700 ppm, documenting multiple nucleosynthetic sources within a single meteorite. In addition, the μ84Sr patterns across leaching samples for individual chondrites differed from one another. The highest μ84Sr values were observed for leaching Step 3 (HCl+H2O, 75 °C) for Allende and Murchison likely because of the incorporation of calcium and aluminum-rich inclusions (CAIs). In contrast, extremely low μ84Sr values were observed in the later fractions (Steps 6 and 7) for Murchison and Tagish Lake, suggesting the existence of s-process-enriched presolar SiC grains derived from AGB stars.A μ84Sr–ϵ54Cr diagram was prepared with the CAIs and bulk aliquots of carbonaceous chondrites and other meteorites (noncarbonaceous) that were plotted separately; however, they still formed a global positive correlation. CAIs presented the highest μ84Sr and ϵ54Cr values, whereas carbonaceous chondrites and noncarbonaceous meteorites had intermediate and the lowest μ84Sr and ϵ54Cr values, respectively. The positive trend was interpreted as resulting from global thermal processing in which sublimation of high μ84Sr and ϵ54Cr carriers generated the excess μ84Sr and ϵ54Cr signatures in CAIs, while noncarbonaceous planetesimals accreted from materials that underwent significant thermal processing and thus had relatively low μ84Sr and ϵ54Cr values. Apart from the global trend, the carbonaceous chondrites and noncarbonaceous meteorites both exhibited intrinsic variations that highlight an isotopic dichotomy similar to that observed in other isotope combinations (e.g., ϵ54Cr–ϵ50Ti, ϵ54Cr–Δ17O). A plausible scenario for creation of the intrinsic variations involves local thermal processing (e.g., flash heating for chondrule formation) caused by additional selective destruction of presolar grains differently than that caused by global thermal processing. The existence of such a global positive trend and local variations for two meteorite groups suggests a complicated dynamic history for the dust grains with respect to thermal processing, material transportation, and mixing in the protoplanetary disk prior to planetesimal formation.

Use of phase transition to obtain gradient materials

Metal-physical principles of fabricating a gradient material—a material with a given distribution of regions with different physical and mechanical properties—are described. The possibility of the preparation of such material is demonstrated by the example of alloys of the iron-chromium-nickel system of the austenite-martensite class. A structure consisting of macroscopic regions of austenite and martensite of given form is prepared in these alloys using the methods of plastic deformation and local thermal processing.

Study on Diffusive Wear and Hardness of Driller of Machining Deep Hole in Sheet

The processing technology of machining deep hole in thin sheet is a kind of process using friction between driller and workpiece and plasticity of workpiece to form hole. The process is a kind of green mechanical processing technology. Studying green processing process in mechanical is becoming a development direction. In this paper, the new technological process to form deep hole on relative thin panel by friction heat not only saves material, but also saves man-hours, and the workpiece has a good piece of assembly. Because the processing technic is belong to local thermal processing, the diffusive wear and hardness of cemented carbide driller are studied by energy dispersive spectrum analysis energy dispersive spectrum analysis in this paper. The study results are useful to improve the life of driller and look for more appropriate machining parameters, and laid a foundation for further research on forming deep holes process on thin sheet metal by friction heat.