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This experimental study aimed to investigate the potential control of microstructural-mineralogical characteristics on thermal properties and its relation with the deformational behaviour in mild to high temperature (25°–800°C) regime of coal-bearing sandstone from an underground coal mine fire region. Barakar sandstone from Jharia Coalfield, India, one of the world's largest underground coal mine fire regions, was chosen. The thermal parameters and their relations to the mineralogical, microstructural, and damage characteristics of Barakar sandstone have been discussed. Thermal conductivity (λ), thermal diffusivity (κ), and specific heat capacity (Cp) of heat-treated samples were determined using the transient plane source method. Additionally, detailed petrography, scanning electron microscopy, and electron probe micro-analyser were used to understand the thermal effect on mineralogy and microstructures. The deformational behaviour with elevated temperature was investigated through the universal testing machine. The obtained results suggest three characteristic temperature regimes: mild temperature regime (25°–300°C), transitional temperature regime (300º–500°C) and high temperature regime (500º–800°C). Moreover, prediction models for thermal properties have also been developed using multi-gene genetic programming (MGGP), considering physical properties as input parameters. In view of experimental constraints to determine the thermos-elastic properties of a rock due to tedious experimental processes, the proposed prediction models shall be very useful to indirectly estimate the thermal properties of sandstone rocks using easily determined physical parameters. The outcome of the present study may be useful to understand the subsidence induced by underground coalmine fire, which is a distressing issue in the Jharia region due to persistent coalmine fire. [ABSTRACT FROM AUTHOR]

In spite of the fact that rhyolite constitute a vital part of the key tectonic environments, such as continental rift-arc systems and oceanic islands, the data on the thermal and physical properties are scarce, which hinders the exact thermal modelling of these regions. Here, we have investigated the thermal conductivity from room temperature (25 °C) to elevated temperatures (up to 300 °C) for 11 massive rhyolite samples, collected from the greenstone belt of the Bundelkhand Craton, central India. The petrographical, geochemical (major oxide and trace elements) and physical (density and porosity) properties have been studied to characterize the samples before measurement of thermal conductivity at elevated temperatures. Geochemical results indicate that these rhyolites are high-K (K2O: 3.6–5.4 wt. per cent), calc-alkaline in nature with enriched REE signatures {(La/Yb)N: 9.4–22.3, (Gd/Yb)N: 1.2–1.9} and are similar to FI-type Archaean rhyolites. The density of these rhyolites depicts a narrow range between 2590 and 2690 kg m−3, with an average of 2637 kg m−3 and negligible porosity. Their thermal conductivity at room temperature varies between 2.5 and 3.3 W m−1 K−1, with an average of 2.8 W m−1 K−1; the decrease in thermal conductivity from room temperature to 300 °C ranges between 16 and 32 per cent, with an average of 23 per cent; and the temperature coefficient of thermal conductivity b , in the expression λ T = λRT (1 +  bT)−1, varies between 0.7 × 10−3 and 1.7 × 10−3 K−1 with an average of 1.1 × 10−3 K−1. Our study reveals that the massive rhyolites have an almost similar density as their intrusive equivalent like Bundelkhand granitoids, but their thermal properties, such as thermal conductivity at room temperature (λRT), decrease in thermal conductivity with temperatures (Δλ) and the temperature coefficient of thermal conductivity (b), lies between the two extreme variety of the granitoids, that is (i) alkali feldspar granite to monzogranite and (ii) granodiorite to tonalite to quartz diorite. We suggest that the temperature coefficient of the massive rhyolite can be expressed as b  = 0.81 × λRT–1.21, which will be useful in determining the thermal conductivity of such rhyolites at elevated temperatures from their thermal conductivity at room temperature (λRT). Thermal and physical parameters reported for rhyolites will provide important constraints in various geophysical and thermo-mechanical modelling for the rhyolitic terrains. [ABSTRACT FROM AUTHOR]

We have investigated 78 core samples of basaltic trap and Neoarchean basement in the laboratory from a 981 m deep scientific borehole KBH‐05, in the Koyna−Warna seismic zone, in order to characterize their thermal and physical properties and present a probable crustal thermal model. The Koyna−Warna, located in the Deccan Volcanic Province (DVP), is globally one of the most prominent Reservoir Triggered Seismicity (RTS) regions. Thermal conductivity, density, and porosity vary widely (1.0–1.7 Wm−1K−1, 2,400–3,000 kg m−3, 0.2%–10%) for the basalt due to their lithological heterogeneities, i.e., massive/amygdaloidal/vesicular. In comparison, the basement, which dominantly consists of gneiss/migmatite gneiss (granodiorite to tonalite to quartz monzodiorite in composition) and amphibolite, have shown a wider range in thermal conductivity (2.2–3.4 Wm−1K−1) but constricted range in density and porosity (2,600–2,800 kg m−3, 0.01%–0.15%). Based on gamma and sonic logs, as well as radioelements (Th, U, K), the 499 m thick basaltic trap can be divided into two thick layers (325, 174 m) and five sub‐layers, which can be correlated with different basaltic formations. Similarly, the underlying basement can also be divided into two layers (93, 384 m). The upper basement layer has two times higher concentrations of Th and U than the lower layer, with heat production of 2.0, 0.8 μWm−3. Further, the study provides a robust temperature estimate of 165°C–250°C at 10 km depth, considerably higher than reported earlier for the DVP, and reveals that in addition to thermal parameters, RTS also plays an important role in the seismogenesis of the region. Plain Language Summary: The Koyna‐Warna region, located in the western part of Deccan Volcanic Province, India, is one of the finest examples of Reservoir Triggered Seismicity in the world. Scientific deep drilling provides a rare opportunity to study thermal and physical properties of a one‐km thick drilled column consisting of a half‐km basaltic trap and another half‐km concealed basement. Study also provides a robust upper crustal thermal model for this region and provides an insight into the causes of seismogenesis. Before laboratory measurements, studied core samples have been characterized by petrology, geochemistry, and geophysical logs. Significant variations in thermal conductivity and density in the basaltic trap could be attributed to the lithological heterogeneities from massive to amygdaloidal/vesicular basalts, while the basement to the compositional variations from granodiorites to tonalites to quartz monzodiorites. Based on gamma and sonic logs, as well as radioelements, the basaltic trap can be divided into two layers and five sub‐layers, which can be correlated to basalt flows. Similarly, the underlying basement can be divided into two layers, with two times higher radioelements in the upper‐layer. Further, the study reveals that in addition to thermal parameters, Reservoir Triggered Seismicity also plays an important role in the seismogenesis of the region. Key Points: Basalt trap & basement beneath Koyna‐Warna show variations in thermal/physical properties that have been correlated to lithology/compositionBased on gamma and sonic logs as well as radioelements, the basalt trap can be divided into five sub‐layers which can be correlated with basalt flowsRobust temperature estimate at 10‐km depth revealed that seismicity is not entirely controlled by temperature, but also by reservoir‐induced [ABSTRACT FROM AUTHOR]

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Polyolester (POE) oil and mineral (Min) oil are widely used in household refrigerators as compressors lubricants in India. An experimental calculation on the thermal, chemical, corrosion, and nature‐friendly properties of POE oil and Min oil suspended with silica nanoparticles is conducted for confirming its practicality to adopt in refrigeration compressors as nanolubricant. No surfactants were used for synthesizing the nanolubricants. The mass fractions from 0.01% to 0.2% and temperatures from 25°C to 85°C are considered. The thermal conductivity and fire point increased as SiO2 mass proportions increased. The pour and cloud points decreased, and in the corrosive nature, apparently little effect was observed by adding SiO2 nanoparticles. The total acid number (TAN) and saponification number increased with the increase in SiO2 nanoparticle concentration. All the synthesized nanolubricants were biodegradable and a little toxic. Refrigerant compressors with long life, with smooth and safe working are expected using POE oil and Min oil with up to 0.2% SiO2 (without surfactants) because of augmented thermal properties and less influenced corrosive, chemical, and eco‐friendly properties. [ABSTRACT FROM AUTHOR]

We measured the thermal constants (including conductivity, specific heat, and thermal diffusivity) of methane hydrate (MH)–bearing sediment samples recovered in 2015 from the Krishna–Godavari Basin, in India. These samples were recovered through the National Gas Hydrate Program Expedition 02 (NGHP-02). The measurements were performed using the single-sided Transient Plane Source (TPS) method. To investigate the influence of the sediment composition on the thermal properties of MH-bearing sediments, the thermal constants of MH-bearing sediments were measured at 5 °C and 10 MPa over a porosity (ϕ) range of 41% ≤ ϕ ≤ 51% and MH saturation (S h) range of 17% ≤ S h ≤ 74%. In addition, density and mineral compositional measurements of the dry sediment grain samples were conducted. The measured thermal conductivity slightly decreases with increasing ϕ and is independent of S h. The measured specific heat increased with increasing ϕ , whereas it decreased with increasing S h. The measured thermal diffusivity decreased with increasing ϕ , whereas it increased with increasing S h. Various models were used to estimate the thermal constants to examine the applicability of these models to natural MH-bearing sediments. The distribution model (using a geometric mean model) is valid from the low to high MH saturations; however, the thermal properties of clay-rich layers are not likely reproducible by the distribution model from the mineral compositions. This indicates that the low value of the observed thermal conductivity in the clay-rich samples is likely a product of the sediment's small grain size. • Thermal properties of sediments from the Krishna–Godavari Basin were measured. • Highly saturated methane hydrate-bearing sediments thermal constants were reported. • The measurements were performed using the single-sided TPS method. • The distribution model is valid from the low to high MH saturation range. • The measured thermal conductivity is independent of the MH saturation. [ABSTRACT FROM AUTHOR]

Abstract: Thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and Computational Fluid Dynamics modeling. Effects of time duration of continuous operation, thermal conductivity of soil pipe diameter and flow velocity on thermal performance of EATHE under transient conditions have been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of EATHE. Study reveals that the effect of pipe diameter due to prolonged use of EATHE system on its thermal performance is least in case of soil with higher value of thermal conductivity. Results show that the increase in flow velocity leads to deterioration in thermal performance of EATHE system. Under steady state condition, drop of 18.8°C in air temperature is obtained, whereas, under transient conditions cooling of air reduces from 18.7°C to 16.6°C for soil thermal conductivity of 0.52Wm−1 K−1, after 24h of continuous operation. [Copyright &y& Elsevier]