Heat Flow Variations Research Articles

Regional estimation of Curie-point depths and succeeding geothermal parameters from recently acquired high-resolution aeromagnetic data of the entire Bida Basin, north-central Nigeria

<p><strong>Abstract.</strong> A regional estimation of Curie-point depths (CPDs) and succeeding geothermal gradients and subsurface crustal heat flow has been carried out from the spectral centroid analysis of the recently acquired high-resolution aeromagnetic (HRAM) data of the entire Bida Basin in north-central Nigeria. The HRAM data were divided into 28 overlapping blocks, and each block was analysed to obtain depths to the top, centroid, and bottom of the magnetic sources. The depth values were then used to assess the CPD, geothermal gradient, and subsurface crustal heat flow in the basin. The result shows that the CPD varies between 15.57 and 29.62<span class="thinspace"></span>km with an average of 21.65<span class="thinspace"></span>km, the geothermal gradient varies between 19.58 and 37.25<span class="thinspace"></span>°C<span class="thinspace"></span>km<sup>−1</sup> with an average of 27.25<span class="thinspace"></span>°C<span class="thinspace"></span>km<sup>−1</sup>, and the crustal heat flow varies between 48.41 and 93.12<span class="thinspace"></span>mW<span class="thinspace"></span>m<sup>−2</sup> with an average of 68.80<span class="thinspace"></span>mW<span class="thinspace"></span>m<sup>−2</sup>. Geodynamic processes are mainly controlled by the thermal structure of the Earth's crust; therefore this study is important for appraisal of the geo-processes, rheology, and understanding of the heat flow variations in the Bida Basin, north-central Nigeria.</p>

Investigating Moho depth, Curie Point, and heat flow variations of the Yozgat Batholith and its surrounding area, north central Anatolia,Turkey, using gravity and magnetic anomalies

This paper proposes an interpretation of the Bouguer gravity and magnetic anomaly map of the Yozgat Batholith and its surrounding area (north central Anatolia) for determination of crustal and geothermal structures. In the study area, the Moho and Conrad depths based on a relationship between Bouguer gravity anomaly and seismically determined crustal thickness were estimated as 34-39 km and 19.5-21.5 km, respectively. The crustal thickness of the study area increases from west to east. The estimated Curie point depths in the study area by means of spectral analysis of the magnetic data vary between 10.4 and 19.5 km. The shallow depths indicate that the magnetization is restricted to the upper crust in the study area. In addition, the heat flow values calculated for a thermal conductivity of 2.7 W m-1 K-1 range from about 80 to 150 mWm-2. The shallow velocity structures in central Anatolia are consistent with the estimated high heat flow values in the upper crust and associated with comparatively high negative Bouguer gravity anomalies.

Mathematical Modeling of Self-Oscillations in a Rijke’s Tube with Variable Heat Flow Power

In this paper the mathematical model of self - oscillation in Rijke's tube is found. We introduce the characteristic of the pressure of the heat supply. Using the energy equation in the form of the first law of thermodynamics to flow defined mechanisms of thermoacoustic instability in this problem. Using the pressure characteristic of the supply of heat and the classical Lyapunov’s theory of stability defines the conditions for self-excitation of oscillation. It was found that when the increasing combustion delay the harmonic self-oscillations of the "singing" flame are converted to the relaxation oscillations.

Heat-flow variability of suspended timber ground floors: Implications for in-situ heat-flux measuring

Reducing space heating energy demand supports the UK’s legislated carbon emission reduction targets and requires the effective characterisation of the UK’s existing housing stock to facilitate retrofitting decision-making. Approximately 6.6 million UK dwellings pre-date 1919 and are predominantly of suspended timber ground floor construction, the thermal performance of which has not been extensively investigated. This paper examines suspended timber ground floor heat-flow by presenting high resolution in-situ heat-flux measurements undertaken in a case study house at 15 point locations on the floor. The results highlight significant variability in observed heat-flow: point U-values range from 0.56±0.05 to 1.18±0.11Wm−2K−1. This highlights that observing only a few measurements is unlikely to be representative of the whole floor heat-flow and the extrapolation from such point values to whole floor U-value estimates could lead to its over- or under- estimation. Floor U-value models appear to underestimate the actual measured floor U-value in this case study. This paper highlights the care with which in-situ heat-flux measuring must be undertaken to enable comparison with models, literature and between studies and the findings support the unique, high-resolution in-situ monitoring methodology used in this study for further research in this area.

The influence of crustal radioactivity on mantle convection and lithospheric thickness on Mars

Orbital measurements of gravity and topography demonstrate that the crust of Mars varies in thickness by about 100 km across the surface. As a result, the heat flux due to crustal radioactivity varies laterally by nearly 15 mW m−2. In an important new paper, Plesa et al. (2016, doi:10.1002/2016JE005126) have assessed how these variations in crustal thickness and heat flow affect the spatial pattern of convection in the Martian mantle. Their results have important implications for the interpretation of the Martian heat flux that will be measured by the upcoming InSight mission to Mars.

Using DSC for the detection of diffusion-controlled phenomena in Cu-based shape memory alloys

The thermally induced reversible diffusionless martensitic transformation, that governs the mechanism of shape memory alloys (SMAs), can be conveniently illustrated, on differential scanning calorimetry (DSC) curves, by a close variation loop of heat flow with temperature. Cooling-induced direct (forward) martensitic formation causes an exothermic maximum, while martensite reversion, on heating, is associated with an endothermic peak. The occurrence of diffusion-controlled phenomena is emphasized by discontinuities of heat flow variations, such as those observed in the case of Cu–Zn–Al SMAs, experiencing thermoelastic martensitic transformation. When heating such a martensitic Cu–Zn–Al SMA, four solid-state transitions were observed on DSC curves, under the form of: (1) an endothermic minimum ascribed to martensite reversion to parent phase; (2) an endothermic minimum associated with transitory formation of bainite; (3) an exothermic maximum corresponding to the precipitation of equilibrium α-phase and (4) an endothermic peak representing the order–disorder transition of parent phase. The first transition is diffusionless, while the other three are diffusion-controlled. The DSC equipment was used to investigate the effects of: (1) heat treatment temperature, (2) number of cycles of thermomechanical treatment and (3) thermal cycling within the temperature range where diffusion-controlled solid-state transitions occur in a Cu–Zn–Al SMA, the results being corroborated with that obtained by optical (OM) and transmission (TEM) electron microscopy.

Thermal performance of solar cooker with special cover glass of low-e antimony doped indium oxide (IAO) coating

Indium, cadmium and tin based transparent conducting oxide (TCO) films have low thermal emissivity values and these are suitable for energy efficient applications where controlling of thermal effect is an important factor. Among these films antimony doped indium oxide (IAO) coated glass has been explored to have resistivity ∼2×10−2Ωcm. The film is homogeneous and good adherence to glass even in large dimensions [500mm×500mm]. This film possesses emissivity ∼0.63 and it has been taken as the standard for the calculation of solar factor (gi) and absorbed solar energy reradiated and convected indoors (Ei) of transparent conducting oxide (TCO) films of 32 types. As calculated, the gi and Ei values of a TCO films are in the ranges 0.77–0.02 and 2.9–59Wm−2 respectively. Attempt has been made to use the IAO coated glass to improve glazing system in solar cooker with the principle that lowering of gi and Ei values would correspond to significant increase of heat insulation property. The thermal performance of solar cooker box having a cover of single layer low-e IAO coated glass was compared with the solar cooker box having a cover of uncoated double glaze soda lime silicate (SLS) glass initially and finally with the same solar cooker box with evacuated glazed cover maintaining vacuum (10−3atm) in the glazing system. Thermal performance of the solar cookers at ambient condition differs due to the variation of heat flow through glass cover with different glazing systems. The performance was promising for the solar cooker box with the cover of single glazed low-e IAO coated glass. The added advantages for domestic usage are low cost of production, relatively light weight and high mechanical durability along with relatively high thermal output.

Geomorphology of the central Red Sea Rift: Determining spreading processes

Continental rifting and ocean basin formation is occurring today in the Red Sea, providing a possible modern analogue for the creation of mid-ocean ridges. Yet many of the seafloor features observed along the axis of the Red Sea appear anomalous compared to ancient and modern examples of mid-ocean ridges in other parts of the world, making it unclear, until recently, whether the Red Sea is truly analogous. Recent work suggests that the main morphological differences between the Red Sea Rift (RSR) and other mid-ocean ridges are due to the presence and movement of giant, submarine salt flows, which blanket large portions of the rift valley and thereby the oceanic crust. Using ship-based, high-resolution multibeam bathymetry of the central RSR between 16.5°N and 23°N we focus here on the RSR volcanic terrains not covered by salt and sediments and compare their morphologies to those observed along slow and ultra-slow spreading ridges elsewhere. Regional variations in style and intensity of volcanism can be related to variations in volcanic activity and mantle heat flow. The Red Sea oceanic seafloor shows typical features of mature (ultra)slow-spreading mid-ocean ridges, such as 2nd order discontinuities (overlapping spreading centres) and magma focussing in the segment centres (forming spreading-perpendicular volcanic ridges of thick oceanic crust). The occurrence of melt-salt interaction at locations where salt glaciers blanket the neovolcanic zone, and the absence of large detachment faults are unique features of the central RSR. These features can be related to the young character of the Red Sea and may be applicable to all young oceanic rifts, associated with plumes and/or evaporites. Thus, the RSR falls in line with (ultra)slow-spreading mid-ocean ridges globally, which makes the Red Sea a unique but highly important type example for initiation of slow rifting and seafloor spreading and one of the most interesting targets for future ocean research.

Thermal performance evaluation of a mineral-based cement tile as roofing material

In tropical climates like India, solar radiation is the major source of heat gain through roofs as they are exposed to the sun throughout the day. As the ambient conditions are dynamic, it is important to look at periodic variation of heat flow through roofs. In this context, apart from U-values that the Energy Conservation Building Code of India (ECBC-2007) prescribes for envelopes, more specific performance indicators should be considered for designing energy efficient buildings. The study presented in this paper evaluates thermal performance of Cement Tile as roofing material and compares it with the performance of two other typical roof insulation materials monitored in hot and dry climate of India. The results are supported with physical structures using Scanning Electron Microscope (SEM) images and energy simulations. Despite having higher overall U-value (over six times), Model 1 (with Cement Tile) shows better thermal performance and negligible energy savings than Model 2 (with extruded polystyrene as insulation material) and Model 3 (with POP false ceiling). Therefore, the overall U-values calculated from the layer wise thermal conductivity along with Discomfort Degree Hour, Building Index, and Average heat flux would provide a better understanding of thermal performance of the roof as was demonstrated by our experiments.

Planetary heat flow from shallow subsurface measurements: Mars

Planetary heat flow probes measure heat flow (depth-resolved temperature and thermal conductivity) to provide insight into the internal state of a planet. The probes have been utilized extensively on Earth, twice on the Moon, and once on the Surface of comet 67P-CG. Mars is an important target for heat flow measurement as heat flow is a critical parameter in Martian thermal history models. Earlier studies indicate that Martian planetary heat flow can be accessed at 5m below the surface in dry regolith monitored over at least one Martian year. A one Martian year monitoring period is necessary because, in the shallow subsurface, heat flow from the interior is superposed with time varying heat flow contributions, primarily due to insolation. Given that a heat flow probe may not achieve its target depth or monitoring period, this study investigates how the depth (2–5m), duration (0–1 Martian year) and quality of measurements influence the accuracy of planetary heat flow. An inverse model is used to show that, in the preceding scenarios, the accuracy of planetary heat flow directly estimated from depth-dependent thermal conductivity with 10–20% precision errors, temperatures with 50–100mK precision errors and modelling uncertainties up to 500mK, can, on average, be improved by a factor of 27 with optimization to 13%. Accuracies increase with sensor penetration depth and regolith monitoring period. Heat flow optimized from instantaneous measurements or those with the shortest regolith monitoring periods have increased accuracy where the frequency and amplitude of the temperature variation are lowest. The inverse model is based on the Function Specification Inversion method. This study demonstrates that a solution subspace can be identified within a space of uncertainties modelled for the temperature measurements and planetary heat flow: the subspace is defined by a constant log-ratio of their respective standard deviations. Optimized heat flow estimates display reduced correlation with increasing temperature precision and systematic conductivity errors, with the constraint of other known model parameters. Consequently, the model permits upper bounds to be placed on the conductivity estimate without conductivity optimization, as heat flows are optimized to a limiting value with increasing systematic conductivity errors for any given parameter set. Overall, the results demonstrate a 52% chance of achieving a direct heat flow estimate accurate to within 40%, with the same being 82% after optimization.

Geothermal Gradients and Heat Flow Variations in Parts of the Eastern Niger Delta, Nigeria

Abstract: Geothermal gradients and present day heat flow values were evaluated for about seventy one wells in parts of the eastern Niger delta, using reservoir and corrected bottom – hole temperatures data and other data collected from the wells. The results showed that the geothermal gradients in the shallow/continental sections in the Niger delta vary between 10 - 18° C/km onshore, increasing to about 24° C/km seawards, southwards and eastwards. In the deeper (marine/paralic) section, geothermal gradients vary between 18 - 45° C/km. Heat flow values computed using Petromod 1–D modeling software and calibrated against corrected BHT and reservoir temperatures suggests that heat flow variations in this part of the Niger delta range from 29 – 55 mW/m2 (0.69 – 1.31 HFU) with an average value of 42.5 mW/m2 (1.00 HFU). Heat flow variations in the eastern Niger delta correspond closely to variations in geothermal gradients. Geothermal gradients increase eastwards, northwards and seawards from the coastal swamp. Vertically, thermal gradients in the Niger delta show a continuous and non-linear relationship with depth, increasing with diminishing sand percentages. As sand percentages decrease eastwards and seawards, thermal gradient increases. Lower heat flow values (< 40 mW/m2) occur in the western and north central parts of the study area. Higher heat flow values (40 - 55 mW/m2) occur in the eastern and northwestern parts of the study area. A significant regional trend of eastward increase in heat flow is observed in the area. Other regional heat flow trends includes; an eastwards and westwards increase in heat flow from the central parts of the central swamp and an increase in heat flow from the western parts of the coastal swamp to the shallow offshore. Vertical and lateral variations in thermal gradients and heat flow values in parts of the eastern Niger delta are influenced by certain mechanisms and geological factors which include lithological variations, variations in basement heat flow, temporal changes in thermal gradients and heat flow, related to thicker sedmentary sequence, prior to erosion and evidenced by unconformities, fluid redistribution by migration of fluids and different scales of fluid migration in the sub-surface and overpressures.

Heat flow–heat production relationship not found: what drives heat flow variability of the Western Canadian foreland basin?

Heat flow high −80 ± 10 mW/m2 in the northern western parts of the Western Canadian foreland basin is in large contrast to low heat flow to the south and east (50 ± 7 mW/m2) of the same basin with the same old 2E09 year’s Precambrian basement and some 200-km-thick lithosphere. Over-thrusted and flat-laying sedimentary units are heated from below by heat flow from the old craton’ crust and low 15 ± 5 mW/m2 mantle contribution. The heat flow vs. radiogenic heat production statistical relationship is not found for this area. To account for this large heat flow contrast and to have 200-km-thick lithosphere, we would need to assume that high heat production layer of the upper crust varies in thickness as much as factor of 2 and/or that the measured heat production at top of Precambrian basement is not representative for deeper rocks. The other explanation proposed before that heat in the basin is redistributed by the regional fluid flow systems driven from high hydraulic head areas close to the foothills of the Rocky Mountains toward low elevation areas to the east and north cannot be explained by observed low Darcy fluid velocities and the geometry of the basin.

A consistent model for fluid distribution, viscosity distribution, and flow‐thermal structure in subduction zone

AbstractWater plays crucial roles in the subduction zone dynamics affecting the thermal‐flow structure through the fluid processes. We aim to understand what controls the dynamics and construct a model to solve consistently fluid generation, fluid transport, its reaction with the solid and resultant viscosity, and thermal‐flow structure. We highlight the effect of mechanical weakening of rocks associated with hydration. The viscosity of serpentinite (ηserp) in subduction zones critically controls the flow‐thermal structure via extent of mechanical coupling between the subducting slab and overlying mantle wedge. When ηserp is greater than 1021 Pa s, the thermal‐flow structure reaches a steady state beneath the volcanic zone, and the melting region expands until Cin (initial water content in the subducting oceanic crust) reaches 3 wt %, and it does not expand from 3 wt %. On the other hand, when ηserp is less than 1019 Pa s, the greater water dependence of viscosity (expressed by a larger fv) confines a hot material to a narrower channel intruding into the wedge corner from a deeper part of the back‐arc region. Consequently, the overall heat flux becomes less for a larger fv. When ageba (age of back‐arc basin as a rifted lithosphere) = 7.5 Ma, the increase in fv weakens but shifts the melting region toward the trench side because of the narrow channel flow intruding into the wedge corner, where as it shuts down melting when ageba=20 Ma. Several model cases (particularly those with ηserp=1020 to 1021 Pa s and a relatively large fv for Cin=2 to 3 wt %) broadly account for the observations in the Northeast Japan arc (i.e., location and width of volcanic chain, extent of serpentinite, surface heat flow, and seismic tomography), although the large variability of surface heat flow and seismic tomographic images does not allow us to constrain the parameter range tightly.

Improving the temperature predictions of subsurface thermal models by using high-quality input data. Part 2: A case study from the Danish-German border region

We present a 3D numerical crustal temperature model and analyse the present-day conductive thermal field of the Danish-German border region. The model region covers the northernmost part of the North German Basin, a transition zone between the deep-reaching sedimentary rocks of the Glückstadt Graben (including complex salt structures) and the shallow crystalline basement of the Ringkøbing-Fyn High. The modelling approach is novel as it implements for the first time a comprehensive analysis of well-log data on a regional modelling scale. Those logs were used both to derive the spatial distribution of rock thermal conductivity across the study area, and to calculate heat flow values. New values of terrestrial surface heat flow are reported for eight deep boreholes in the North German Basin ranging from 72 to 84mW/m2 with a mean of 80±5mW/m2. The values are computed from continuous temperature logs, carefully corrected BHT values, drill-stem tests and well-log derived rock thermal properties (thermal conductivity, radiogenic heat production) and were included in the setup of the numerical lower boundary conditions. New surface heat flow is up to 20mW/m2 higher than low values reported in some previous studies for this region. Heat flow from the mantle is 33–40mW/m2.The model temperature predictions are validated against 59 temperature observations from 24 wells. The prediction uncertainties between observed and modelled temperatures at deep borehole sites are small (rms=3.5°C, ame=2.1°C). Pronounced lateral temperature variations are predicted and found to be caused mainly by complex geological structures, including a large amount of salt structures and marked lateral variations in the thickness of basin sediments. The associated variations in rock thermal conductivity generate significant variations in model heat flow and large variations in temperature gradients.With regard to the utilization of geothermal energy, the Rhaetian and the Middle Buntsandstein sandstone reservoirs are found with temperatures within the range of 40–80°C, suitable for low enthalpy heating purposes, in most of the area and locally also with higher temperatures. Temperatures above 120°C, of interest for the production of electricity, are observed only in the very southeastern part of the study area.

Variations in Moho and Curie depths and heat flow in Eastern and Southeastern Asia

The Eastern and Southeastern Asian regions witness the strongest land–ocean and lithosphere–asthenosphere interactions. The extreme diversity of geological features warrants a unified study for a better understanding of their geodynamic uniqueness and/or ubiquity from a regional perspective. In this paper we have explored a large coverage of potential field data and have detected high resolution Moho and Curie depths in the aforementioned regions. The oldest continental and oceanic domains, i.e. the North China craton and the Pacific and Indian Ocean have been found thermally perturbed by events probably linked to small-scale convection or serpentinization in the mantle and to numerous volcanic seamounts and ridges. The thermal perturbation has also been observed in proximity of the fossil ridge of the western Philippine Sea Basin, which shows anomalously small Curie depths. The western Pacific marginal seas have the lowest Moho temperature, with Curie depths generally larger than Moho depths. The contrary is true in most parts of easternmost Eurasian continent. Magmatic processes feeding the Permian Emeishan large igneous province could have also been genetically linked to deep mantle/crustal processes beneath the Sichuan Basin. The regionally elongated magnetic features and small Curie depths along the Triassic Yangtze-Indochina plate boundary suggest that the igneous province could be caused by tectonic processes along plate margins, rather than by a deep mantle plume. At the same time, we interpret the Caroline Ridge, the boundary between the Pacific and the Caroline Sea, as a structure having a continental origin, rather than as hotspot or arc volcanism. The surface heat flow is primarily modulated by a deep isotherm through thermal conduction. This concordance is emphasized along many subduction trenches, where zones of large Curie depths often correspond with low heat flow. Local or regional surface heat flow variations cannot be faithfully used in inferring deep thermal structures, which can be better constrained overall through Curie depths detected from surface magnetic anomalies.

Geothermal gradients of the northern continental shelf of the Gulf of Mexico

A wide, systematic variation of sedimentary geothermal gradients has been previously observed along the northern continental shelf of the Gulf of Mexico. From east to west, geothermal gradients change from 25 to 30 °C/km off Alabama to lower values (15–25 °C/km) off eastern Louisiana and to higher values (30–60 °C/km) off Texas. In order to assess the mechanism responsible for this variation, the present study first compiled an extensive bottom-hole temperature database from over 6000 wells in the northern continental shelf and constructed a more detailed geothermal gradient map than those published previously. Second, basin models were then constructed for three areas within the continental shelf (off Texas, Louisiana, and Alabama) that show differing geothermal gradients. A basin model is a mathematical model that simulates the heat transport through the crust and the sediments of a basin in the context of its geologic evolution. Previous researchers proposed two possible causes for the observed geothermal gradient variation in the northern continental shelf. The first was the thermal effect of sedimentation: areas with faster sediment accumulation result in low geothermal gradients, and vice versa. The second was that basal heat flow (heat flow that enters from the igneous crust to the bottom of the sediments) varied across the continental shelf. The present study finds that sedimentary geothermal gradients in these areas are primarily impacted by two competing mechanisms associated with sediment accumulation. One is the radiogenic heat production within the sediment that adds to the total heat budget upward through the sedimentary column. The other is the transient effect of fast sediment accumulation, which results in reduction in the upward heat flow. Off Louisiana, the transient effect prevails, and hence the area shows the lowest geothermal gradients. Off Texas, due to slower sedimentation, the positive contribution by radiogenic heat is most significant. Off Alabama, because the sediments there are not as thick, the overall contribution of radiogenic heat is less. The models show that the thermal effects of sedimentation are large enough to explain the observed variation in geothermal gradients. Therefore, corresponding variation in basal heat flow is not required.

Successive reactivation of older structures under variable heat flow conditions evidenced by K–Ar fault gouge dating in Sierra de Ambato, northern Argentine broken foreland

The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of N–S reverse faults that disrupted a W–E Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ∼9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ∼477−470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the K–Ar dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 °C). K–Ar ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (∼360–220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of ∼360 Ma and a last clay minerals forming event at ∼220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (∼360−311 Ma for 2−1 μm grain size fraction, ∼326−286 Ma for 1–0.2 μm and ∼291−219 Ma of <0.2 μm), we modeled discrete deformation events at ∼417 Ma (ending of the Famatinian cycle), ∼317–326 Ma (end of Gondwanic orogeny), and ∼194–279 Ma (Early Permian - Jurassic deformation). According to our data, the Neogene reactivation would not have affected the K–Ar system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data.

Geothermal energy characterization in the Appalachian Basin of New York and Pennsylvania

Analysis of geothermal energy resources in the Appalachian Basin of the eastern United States is of interest, given the region’s population- and climate-driven demand for thermal energy. This study provides a fuller picture of geothermal resources across New York and Pennsylvania than previous studies by providing a rigorous statistical analysis of temperature-depth data using records from nearly 8000 locations. The compilation of thousands of temperature-depth data enables a significant increase in the spatial resolution of geothermal resource assessment maps for this region. In addition, this project has contributed to the compilation of geothermal data at a national level through the National Geothermal Data System. These temperature-depth measurements are byproducts of historical and recent drilling for petroleum and natural gas in the sedimentary basin. Bottom hole temperatures (BHTs) were recorded before the wells reached thermal equilibrium and at a wide range of depths. To extract a comprehensive description of the thermal state of the Appalachian Basin strata required application of both a BHT correction scheme and a simple thermal model. The model results for individual wells were combined with geostatistical interpolation employing kriging to produce maps that reveal significant variations in subsurface thermal gradient and surface heat flow with markedly improved spatial resolution. An area in south-central New York State displays favorable geothermal resource potential, with heat flow estimates of 50–60 mW/m 2 . There are 2 elongate, 200–300 km long, northeast-trending bands of favorable geothermal resource potential in central and western Pennsylvania, with heat flow of 55–90 mW/m 2 .

Multiple‐scale hydrothermal circulation in 135 Ma oceanic crust of the Japan Trench outer rise: Numerical models constrained with heat flow observations

AbstractAnomalous high heat flow is observed within 150 km seaward of the trench axis at the Japan Trench offshore of Sanriku, where the old Pacific Plate (∼135 Ma) is subducting. Individual heat flow values range between 42 and 114 mW m−2, with an average of ∼70 mW m−2. These values are higher than those expected from the seafloor age based on thermal models of the oceanic plate, i.e., ∼50 mW m−2. The heat flow exhibits spatial variations at multiple scales: regional high average heat flow (∼100 km) and smaller‐scale heat flow peaks (∼1 km). We found that hydrothermal mining of heat from depth due to gradual thickening of an aquifer in the oceanic crust toward the trench axis can yield elevated heat flow of the spatial scale of ∼100 km. Topographic effects combined with hydrothermal circulation may account for the observed smaller‐scale heat flow variations. Hydrothermal circulation in high‐permeability faults may result in heat flow peaks of a subkilometer spatial scale. Volcanic intrusions are unlikely to be a major source of heat flow variations at any scale because of limited occurrence of young volcanoes in the study area. Hydrothermal heat transport may work at various scales on outer rises of other subduction zones as well, since fractures and faults have been well developed due to bending of the incoming plate.

Enhancing energy recovery in the steel industry: Matching continuous charge with off-gas variability smoothing

In order to allow an efficient energy recovery from off-gas in the steel industry, the high variability of heat flow should be managed. A temperature smoothing device based on phase change materials at high temperatures is inserted into the off-gas line of a continuous charge electric arc furnace process with scrap preheating. To address overheating issues, a heat transfer fluid flowing through containers is introduced and selected by developing an analytical model. The performance of the smoothing system is analyzed by thermo-fluid dynamic simulations. The reduced maximum temperature of off-gas allows to reduce the size and investment cost of the downstream energy recovery system, while the increased minimum temperature enhances the steam turbine load factor, thus increasing its utilization. Benefits on environmental issues due to dioxins generation are also gained.