Shallow Temperature Research Articles

Assessing the Impact of a Shallow Geothermal System Operation through Multi-Layer Temperature Monitoring in a Mediterranean Climate

Shallow Geothermal Energy (SGE) exchanges heat with the ground. In continuous, long-term operation, the initial temperature field can be disturbed, and subsurface thermal changes can be developed. In this paper, the thermal impact of a SGE system under a Mediterranean climate is handled. Temperature monitoring was conducted on 15 investigation boreholes equipped with a total of 92 thermal sensors placed at specific depths. Investigation boreholes were drilled 1–2 m from SGE system borehole heat exchangers installed in a university building. The analysis handles a one-year monitoring period of SGE system operation. Temperature depth profiles, reaching up to 140 m depth, were registered with a 10 min time step, resulting in a large amount of data. Ground thermal conductivity was estimated experimentally and semi-empirically, allowing us to obtain, using a numerical model, the initial undisturbed ground temperature profiles and compare them with the monitored values. Climate data were recorded by the university meteorological station. Globally, the measured and computed data were coherent, and a non-negligible impact of the SGE system operation in the first year was observed. The building orientation as well as the nearby departments had significant impacts on the shallow ground temperature. Maximum ground temperature changes observed at depths higher than 10–20 m, ranging from 2 to 3 °C as observed in different boreholes, indicate that the system is operating efficiently.

Impacts of Land Use/Land Cover Distributions on Permafrost Simulations on Tibetan Plateau

The Tibetan Plateau (TP) is distributed with large areas of permafrost, which have received increasing attention as the climate warms. Accurately modeling the extent of permafrost and permafrost changes is now an important challenge for climate change research and climate modeling in this region. Uncertainty in land use and land cover (LULC), which is important information characterizing surface conditions, directly affects the accuracy of the simulation of permafrost changes in land surface models. In order to investigate the effect of LULC uncertainty on permafrost simulation, we conducted simulation experiments on the TP using the Community Land Model, version 5 (CLM5) with five high-resolution LULC products in this study. Firstly, we evaluated the simulation results using shallow soil temperature data and deep borehole data at several sites. The results show that the model performs well in simulating shallow soil temperatures and deep soil temperature profiles. The effect of different land use products on the shallow soil temperature and deep soil temperature contours is not obvious due to the small differences in land use products at these sites. Although there is little difference in the simulating results of different land use products when compared to the permafrost distribution map, the differences are noticeable for the simulation of the active layer. Land cover had a greater impact on soil temperature simulations in regions with greater land use inconsistency, such as at the junction of bare soil and grassland in the northwestern part of the TP, as well as in the southeast region with complex topography. The main way in which this effect occurs is that land cover affects the net surface radiation, which in turn causes differences in soil temperature simulations. In addition, we discuss other factors affecting permafrost simulation results and point out that increasing the model plant function types as well as carefully selecting LULC products is one of the most important ways to improve the simulation performance of land-surface models in permafrost regions.

High variability and exceptionally low thermal conductivities in nearshore sediments: a case study from the Eckernförde Bay

Heat flow measurements are a standard technique in Geophysics both onshore and offshore. Recently, such measurements became increasingly important in shallow waters. The increasing amount of offshore power installations makes it necessary to have a good knowledge about the subsurface heat flow and the thermal properties of the sediments to optimize the construction of the necessary powerlines. While the thermal properties are well studied for deep ocean sediments, only few published data exist for nearshore sediments. In this study, we investigate the sediment temperatures and thermal conductivities of nearshore sediments in the German part of the Baltic Sea. The shallow sediment temperatures reflect the interplay of the response to the seasonal cycle in connection with the sediments’ thermal conductivity. We find thermal conductivity values ranging from 0.67 to 3.34 W/(m*K) for the sediments down to ~ 4.2 m below seafloor. This variability exceeds that of conservative estimates widely used for coastal sediments and is also much higher than the variability found in the deep oceans. Sandy sediments show thermal conductivities larger than 1 W/(m*K) whereas organic-rich muds have lower values (< 1 W/(m*K)). Furthermore, the thermal conductivities seem to decrease with increasing free gas content in the sediment. The latter needs to be confirmed by further investigations.

Ground-air temperature tracking from a geothermal climate-change observatory in South India

A geothermal climate-change observatory at Choutuppal (17.29 oN, 78.92°E) in south India was put into operation in July 2009 to study the inter-relationships between subsurface, ground-surface and surface-air temperature. The observatory is the first of its kind in a low latitude region with a significant monsoon season. Subsurface temperature measurements were obtained at different times of the year in two boreholes at the observatory drilled into granite to 21 m and 210 m depths respectively; a continuous record of shallow ground temperatures was acquired at six different depths to 1.2 m next to the deeper boreholes. Meteorological parameters recorded at the same site include surface air temperature (SAT), relative humidity, precipitation, solar radiation, wind speed and direction. Analysis of ground-air temperature data for the first five years (2009–2014) reveals the following. (i) Air temperature changes diffuse into the granitic subsurface with associated attenuation of high frequency components and phase lag characteristic of conductive heat transfer. (ii) Ground temperatures measured in the 1.2 m and 21 m deep holes track the diurnal and seasonal changes in SAT respectively, (iii) The ground is warmer than air on average; the difference is not constant but varies from −2.1 to +7.6 °C with a mean of 3.4 ± 1.8 (SD) oC, (iv) Ground-air temperature difference is influenced by incoming solar radiation and monsoon precipitation. On average, the ground warms by 2.5 °C for 100 Wm−2 increase in average incident solar radiation. The study highlights the importance of long-term monitoring to test ground-air temperature tracking critical to using borehole temperatures to infer climate change.

Estimating Permafrost Distribution Using Co‐Located Temperature and Electrical Resistivity Measurements

AbstractAssessing the lateral and vertical extent of permafrost is critical to understanding the fate of Arctic ecosystems under climate change. Yet, direct measurements of permafrost distribution and temperature are often limited to a small number of borehole locations. Here, we assess the use of co‐located shallow temperature and electrical resistivity tomography (ERT) measurements to estimate at high‐resolution the distribution of permafrost in three watersheds underlain by discontinuous permafrost. Synthetic modeling shows that co‐located temperature and ERT measurements allow for supervised classification schemes that provide 60% higher accuracy compared to unsupervised methods. Linking resistivity and size of the identified permafrost bodies to surface observations, we show that tall vegetation (&gt;0.5 m) and gentle slopes (&lt;15°) are related to warmer and smaller permafrost bodies, and a more frequent occurrence of taliks.

Shallow groundwater temperature patterns revealed through a regional monitoring well network

AbstractGroundwater temperature is a critical control on groundwater quality, geothermal system efficiency and ecosystem dynamics in receiving surface waters. Despite the known importance of groundwater temperature, there is a lack of dedicated aquifer thermal monitoring across spatial and temporal scales. Pressure transducers and other sensors installed in groundwater monitoring well networks often record temperature as a secondary function, but these comprehensive groundwater temperature data sets are seldom analysed. In this study, we analysed seasonal, interannual and spatial patterns of shallow groundwater temperatures from a regional groundwater monitoring network in Nova Scotia, Canada and compared these subsurface temperature data to air temperature data from nearby climate stations using linear regressions and Fourier analysis. The results showed that seasonal groundwater temperatures were damped (with seasonal amplitudes 3.6%–42% of air temperature amplitudes) and lagged (phase shifted 43–145 days) compared to air temperature, with notable year‐to‐year variations in both damping and lagging. Results also highlighted the role of snowpack thickness on the lowest mean monthly groundwater temperatures. Given potential impacts of climate change, land cover change, urbanization and geothermal energy development on groundwater temperatures, we encourage water authorities and regulators to begin or enhance aquifer thermal monitoring and provide guidance for capitalizing on existing monitoring well infrastructure to track temperature dynamics and changes.

Influences of seasonal changes of the ground temperature on the performance of ground heat exchangers embedded in diaphragm walls: A cold climate case from North China

Compared with ground heat exchangers (GHEs) in typical vertical boreholes with depth of 100–120 m, GHEs embedded in the diaphragm wall of buildings are more easily affected by periodic changes of the shallow ground temperature. Here we numerically solve the heat transfer model of the diaphragm wall with GHEs considering actual ground temperature boundary conditions in cold climate region, North China, and investigate the influences of seasonal variations of the ground temperature on heat transfer performance of GHEs. Results show that due to the above seasonal effect, the heat exchange performance of GHEs may decrease to different extent especially in relatively shallow diaphragm walls, thereby causing non-negligible design deviations. Under the present geometric and climate conditions, as the depth of GHEs increases, the maximum thermal influence distance from the diaphragm wall tends to increase during the cooling season and decrease during the heating season, respectively. The optimal spacing between GHE groups ranges from 0.5 to 0.9 m, and though a high construction cost, a smaller spacing is more favorable for improving the overall energy efficiency. The present work is expected to provide useful references for optimal design and performance prediction of GHEs embedded in diaphragm walls with similar climate conditions.

An investigation into the reliability of newly proposed MoSi2N4/WSi2N4 field-effect transistors: A Monte Carlo study

Recently, the two dimensional complex MA2Z4 structures have been suggested as suitable replacements for silicon channels in field-effect transistors (FETs). Specifically, two materials of MoSi2N4 and WSi2N4 due to their very desirable electrical and thermal properties are noticed. On the other hand, the reliability of transistors, which is determined by the maximum temperature they obtain during the performance, specifies the usefulness of the newly proposed channels for thermal management solution. In this work, the FETs, including MoSi2N4 and WSi2N4 channels, are investigated using Monte Carlo simulation of the phonon Boltzmann equation. In particular, the phonon analysis has been carried out to investigate the peak temperature rise. Our calculations confirm that MoSi2N4 and WSi2N4 present lower maximum temperature than the previously suggested candidate, the blue phosphorene (BP) which itself reaches a shallow temperature. Concretely, the phonon exploration shows that the competition between the dominant heat carrier velocity, and its related frequency settles the maximum temperature value. The material WSi2N4 with much more phonons in TA mode, with almost high velocity and relatively low-frequency, shows adequate thermal condition, and its peak temperature is very low, say 110 K, less than that of BP. The material MoSi2N4 attains the maximum temperature of only 10 K less than BP peak temperature. This behavior attributes to the dominant LA phonons which are fast but also have high frequency and consequently make the temperature get larger than that of the WSi2N4. In summary, WSi2N4, with very low peak temperature, and in the next step MoSi2N4, both with beneficial electrical/thermal properties, are suggested as very suitable candidates for producing more reliable FETs, fulfilling the thermal management.

Measurement and modeling of the evaporation rate of loess under high temperature

The high-temperature dewatering method has a broad application prospect in loess reinforcement, and the evaporation boundary is a crucial factor in determining the dewatering effect. This study conducts evaporation tests on unsaturated loess columns at high temperatures using a self-made high-temperature evaporation test apparatus to reveal the laws of water and heat transfer and surface evaporation in unsaturated loess under high temperatures. Based on the study's results, high temperatures have a significant driving effect on water. Under high temperatures, the portion of soil near the hot end is rapidly dewatered, forming a drying zone. The presence of an evaporation boundary intensifies the high-temperature dewatering effect. Under hot-end dewatering and surface evaporation, soil water content presents the distribution laws of high at both ends and low in the middle. High temperatures greatly increase surface evaporation. The water content and temperature of surface soil significantly affect evaporation intensity, as do the water gradient and temperature gradient of shallow soil. The evaporation coefficient, defined as the ratio of evaporation intensity to saturated evaporation intensity (potential evaporation intensity), is employed to characterize soil evaporation efficiency. The evaporation coefficient measured under high temperatures is found to be higher than that calculated by the existing models for the evaporation coefficient. A new evaporation coefficient model is built using modifying existing models. The new model comprehensively considers surface and shallow soil temperatures and water contents. Validation results showed that the model can more precisely calculate the evaporation rate of surface soil under the influence of a high-temperature heat source. The research results of this paper reveal the evaporation characteristics of the surface and water migration characteristics inside loess under high temperature, which is helpful for promoting the application of thermal dewatering method in the reinforcement engineering of loess pit slopes.

Reservoir Temperature Calculation and Modeling for Convective Geothermal Systems: Case Study of Five Major Hot Springs in Lushan, Henan, China

The thermal storage temperature and water-rock interaction process of the Lushan convective geothermal system (Qinling stratigraphic zonation fracture zone in China) are clarified by using surface cold water and geothermal fluid as the research objects. In this study, a conceptual model of the temperature profile of the geothermal system in the study area was developed using surface temperature inversion, the cation temperature scale, the SiO2 temperature scale method, the mineral equilibrium phase method, the silicon-enthalpy model, the FixAl method, and the Cl-enthalpy model. The inversion temperature at the surface is in the range of 33-39°C, and the temperature difference indicates the direction of the Checun-Lushan fracture. The study area is recharged from atmospheric precipitation, and the temperature of the recharge area is approximately 5.8–7.7°C (the temperature of the alkali field is approximately 10°C), and the recharge elevation is approximately 1200 m. The thermal storage pattern in the study area is near-surface hydrothermal thermal storage transferred to shallow thermal storage and then to deep thermal storage. The near-surface hydrothermal thermal storage temperature is at a constant temperature of 60°C, and the shallow thermal storage temperature is calculated by K-Mg and Li-Mg geothermometers to be between 99 and 112°C. The thermal storage temperature is simulated using the FixAl method, with deviation values ranging from 2.9% to 15.0%. The silicon-enthalpy model calculates the deep thermal storage temperature to be between 181 and 230°C. The mixing ratio of geothermal water in the study area is extremely high, with a cold water mixing ratio of 85.4–94.8%. The home ground fluid temperature was estimated to be approximately 282°C using the Cl-enthalpy model. The main thermally controlled conductivity channel in the study area is the Checun-Lushan fracture zone. The water vapor formed by convection at depth moves upward to approximately 5 km to form a deep thermal reservoir, and this convection and upward movement cause it to mix with cold water from the fracture zone to form a shallow thermal reservoir, which moves to the near-surface, forming a hydrothermal-type reservoir, which is later discharged in the form of a spring. The conceptual model of geothermal system temperature established in this study provides a basis for further development and utilization of Lushan hot springs and provides guidance for future thermal storage temperature calculations of convection-type geothermal systems in uplifted mountains.

An Improved Shallow Water Temperature Model for An Australian Tidal Wetland Environment Using Publicly Available Data

Larval mosquito development is directly impacted by environmental water temperature. Shallow water less than 1 m deep is a common larval mosquito habitat. Existing mathematical models estimate water temperature using meteorological variables, and they range in complexity. We developed a modification of an existing one-layer heat balance model for estimating hourly water temperature and compared its performance with that of a model that uses only air temperature and water volume as inputs and that uses air temperature itself as an indicator of water temperature. These models were assessed against field measurements from a shallow tidal wetland—a known larval habitat—in southwest Western Australia. We also analysed publicly available measurements of air temperature and river height to determine whether they could be used in lieu of field measurements to allow cost-effective long-term monitoring. The average error of the modified version of the heat balance equation was −0.5 °C per hour. Air temperature was the second-best performing method (x¯ error = −2.82 °C). The public data sources accurately represented the onsite water temperature measurements. The original heat balance model, which incorporates a parameterisation of evaporative heat flux, performed poorly in hot, dry, windy conditions. The modified model can be used as an input to larval mosquito development models, assisting Local Government Environmental Health officers to determine optimal mosquito development periods and the timing of mosquito monitoring activities to enhance mosquito control.

Evaluation of high-tensile steel using nonlinear analysis: Experiment-FE materials benchmarking of LNG carrier structures under low-temperature conditions

Natural gas is the cleanest energy source compared to other fossil fuels. When the temperature is between −160 ºC to −164 ºC at atmospheric pressure, natural gas will be in liquid form, commonly called Liquefied Natural Gas (LNG). Currently, the demand for the availability of natural gas is increasing rapidly. However, not all countries have natural gas reserves. In this case, ships transport Liquefied Natural Gas (LNG) between continents and oceans to meet global needs. Since the Northern Sea Route (NSR) was opened, the route has become an alternative route where ships can save fuel because the distance is closer than the standard route (through the Suez Canal). However, because this route is in the Arctic region, which has a harsh environment, the ship may experience a structural failure, resulting in an accident and possibly causing material, human or other casualties. This paper employed the finite element method to observe the materials used as raw materials for the structure of natural gas shipping vessels. High tensile steel grade AH 32 was tested for tensile using numerical analysis. The temperature varied from room to shallow temperature (−160 ºC). Besides that, the mesh sizes used were 1 mm, 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm to produce outcomes that are most similar to earlier research assessed via experimental testing. The result obtained was that the mechanical properties of AH 32 steel will change significantly at shallow temperatures, which can be observed from the engineering stress–strain graph. High tensile steel grade AH 32 becomes very brittle at −160 ºC. Besides that, the necking phenomenon, as in the experimental test, can also be observed through numerical analysis.

The Coral Bleaching Automated Stress System (CBASS): A low‐cost, portable system for standardized empirical assessments of coral thermal limits

AbstractOcean warming is increasingly affecting marine ecosystems across the globe. Reef‐building corals are particularly affected by warming, with mass bleaching events increasing in frequency and leading to widespread coral mortality. Yet, some corals can resist or recover from bleaching better than others. Such variability in thermal resilience could be critical to reef persistence; however, the scientific community lacks standardized diagnostic approaches to rapidly and comparatively assess coral thermal vulnerability prior to bleaching events. We present the Coral Bleaching Automated Stress System (CBASS) as a low‐cost, open‐source, field‐portable experimental system for rapid empirical assessment of coral thermal thresholds using standardized temperature stress profiles and diagnostics. The CBASS consists of four or eight flow‐through experimental aquaria with independent water masses, lighting, and individual automated temperature controls capable of delivering custom modulating thermal profiles. The CBASS is used to conduct daily thermal stress exposures that typically include 3‐h temperature ramps to multiple target temperatures, a 3‐h hold period at the target temperatures, and a 1‐h ramp back down to ambient temperature, followed by an overnight recovery period. This mimics shallow water temperature profiles observed in coral reefs and prompts a rapid acute heat stress response that can serve as a diagnostic tool to identify putative thermotolerant corals for in‐depth assessments of adaptation mechanisms, targeted conservation, and possible use in restoration efforts. The CBASS is deployable within hours and can assay up to 40 coral fragments/aquaria/day, enabling high‐throughput, rapid determination of thermal thresholds for individual genotypes, populations, species, and sites using a standardized experimental framework.

Hydrochemical, D–O–Sr isotopic and electromagnetic characteristics of geothermal waters from the Erdaoqiao area, SW China: Insights into genetic mechanism and scaling potential

The Erdaoqiao area has been the hot area of geothermal resource prospecting in southwestern China. Significance difference of scaling potential has been found between left and right riverbanks of the Erdaoqiao area. However, there still has no interpretation for the scaling difference since the genetic mechanism of geothermal waters remains unclear. In this study, hydrochemical, D–O–Sr isotopic and electromagnetic (EM) approaches were integrated to clarify the genetic mechanism and quantitively evaluate scaling potential of geothermal waters. All geothermal waters belonged to Ca–Na–HCO3 type and were determined by the weathering and/or dissolution of carbonates (66.87%) and silicates (31.53%) with cation exchange based on hydrochemical and Sr isotopic analyses. Na–K–Mg triangle diagram indicated they were immature water mixed by shallow cold water. Quartz geothermometer indicated the shallow reservoir temperatures (after cold–water mixing) of left riverbank (88.46 °C–90.51 °C) were higher than those of right riverbank (61.20 °C–87.89 °C). Silica – Enthalpy methods revealed the initial geothermal reservoir temperatures and cold-water mixing ratio were 102.03 °C–138.93 °C and 65.24%–85.87% in the right riverbank, 144.11 °C–146.76 °C and 73.08%–74.79% in the left riverbank of the Erdaoqiao area. D-O isotopes proposed the geothermal waters were recharged by atmospheric precipitation in the elevation of 4957 m to 5118 m. Therefore, the genetic model of geothermal waters in the Erdaoqiao area can be constructed. Stronger calcite scaling in left riverbank was attributed to deeper circulation identified by higher reservoir temperature and electromagnetic exploration. Quantitively evaluation demonstrated that the weight of scaling during 48 h in left riverbank (2968 kg) was four times higher than that in right riverbank (748 kg). The achievements of this study contribute to geothermal exploration in the Erdaoqiao and other similar areas worldwide.

Influence of wildfire on the rapidly changing features of patchy permafrost, Northeast China

AbstractAs an active ecological agent in the boreal forest, wildfires have many important impacts on the underlying permafrost. However, investigations of post‐fire changes in the features of ecosystem‐protected permafrost are extremely limited in the patchy permafrost regions, Northeast China. Additionally, the impacts of wildfires on patchy permafrost are complicated in this region. In this paper, based on field surveys and observations, permafrost features and their influencing factors were analyzed in the area burned in 2006. The results showed notably lower soil temperatures in shrub‐wetland (NWH1, unburned and NWH2, light burn) in comparison with those in the birch‐larch forest (NWH3, light burn and NWH4, moderate burn). Changes in shallow ground temperatures (0–4 m in depth) were significant. Mean annual soil temperatures (MAST) and annual maximum soil temperature at the light‐burn NWH2 site were 0.3–5.2°C higher than those of unburned NWH1, but annual minimum soil temperatures, 0.3–2.1°C lower. MASTs at the moderately burned NWH4 were 0.6–1.6°C higher than those at the light‐burn NWH3. The active layer thickness (ALT) was greater at burned sites, and; at the moderately burned site, only seasonal frost was found when 13 years after the burn. The contents of soil organic carbon and total nitrogen were the highest at the unburned NWH1 from 0.0 to 0.4 m in depth, followed by those at the lightly‐burned NWH2 and NWH3, and the lowest at the moderately‐burned NWH4. Climate warming, forest fires, and changing local factors (e.g., soil moisture contents, snow cover, soil texture and drainage conditions) worked together to increase ground temperature and ALT. These research results could provide important scientific basis for the protection of boreal forest and wetlands and the ecosystem‐protected permafrost under a warming climate.

Wildfire-induced shifts in groundwater discharge to streams identified with paired air and stream water temperature analyses

Within the western United States, increasingly severe and frequent wildfires may alter the magnitude, timing, and quality of water exported from burned areas by streams. Post-fire hydrologic studies often focus on peak stream flow responses to shifts in runoff generation or on annual streamflow yield response to changes in evapotranspiration following fire. However, the magnitude and duration of wildfire effects on groundwater recharge, changes in subsurface routing, and consequences for stream low flows sourced predominately by baseflow are poorly understood. Here, we demonstrate an approach using the amplitude and phase of paired annual air and stream water temperature signals to broadly identify changes in watershed subsurface flow contributions after fire. Watersheds were classified using pre-fire temperature data, as having air-coupled (i.e., reduced apparent groundwater signature), deep groundwater, or shallow groundwater stream temperature signals. Changes in pre- and post-fire paired air and stream water temperature metrics were compared for locations (n = 17) spanning a large range of physiographic and climatic conditions across the western United States. Pre- and post-fire comparisons were computed by quantile using bootstrapped confidence intervals (ci = 95), as well as in aggregate using Kruskal-Wallis and post-hoc Dunn tests. Statistical comparisons of pre- and post-fire temperature metrics suggest that overall, watersheds classified as having minimal groundwater influence are the most likely to experience fire-induced subsurface hydrologic change. More specifically, watersheds classified as having air-coupled or shallow groundwater signals experienced increases in the magnitude of groundwater discharge, with more stable annual thermal regimes post-fire that are less-coupled to ambient air temperature. These findings form the basis of a conceptual framework for watershed resistance to subsurface hydrologic change following fire that can be broadly applied as a first approximation for water management, impacts on aquatic habitat, and post-wildfire response planning.

Thermoelectric generator for high temperature geothermal anomalies: Experimental development and field operation

In the current climate and energy context, it is important to develop technologies that permit increase the use of renewable sources such as geothermal energy. Enhancing the use of this renewable source is particularly important in some places, due to its availability and the enormous dependence on fossil fuels, as is the case of the Canary Islands. This work proposes the use of thermoelectric generators with heat exchangers working by phase change to transform the heat from the shallow high temperature geothermal anomalies on the island of Lanzarote directly into electricity, since the use of conventional geothermal power plants would not be possible because they would damage the protected environment. To bring this proposal to reality, this work has succeeded in developing and field-installing a geothermal thermoelectric generator that operates without moving parts thanks to its phase-change heat exchangers. This robust generator do not require maintenance nor auxiliary consumption, and produces a minimal environmental impact, it is noiseless, and the use of water as working fluid makes it completely harmless.The developed device consists of a thermosyphon as hot side heat exchanger, thermoelectric modules and cold side heat exchangers also based in phase change. Tests were carried out in the laboratory at various heat source temperatures and varying the number of thermoelectric modules. It was determined that installing more modules decreases the efficiency per module (from 4.83% with 4 modules to 4.59% with 8 modules at a temperature difference between sources of 235 °C), but for the number of modules tested the total power increases, so the field installation was carried out with 8 modules. After the good results in the laboratory, it was satisfactorily installed at Timanfaya National Park (Lanzarote, Spain) in a borehole with gases at 465 °C. This generator presents a maximum output power of 36 W (4.5 W per module), and is generating 286.94 kWh per year, demonstrating the great potential of the developed thermoelectric generators to build a larger-scale renewable installation.

Spatiotemporal Variations of Soil Temperature at 10 and 50 cm Depths in Permafrost Regions along the Qinghai-Tibet Engineering Corridor

Soil temperature plays an essential role in the permafrost thermal state and degradation process. Especially the soil temperatures at 10 cm and 50 cm depths in the active layer, which are much easier to be observed in situ, have great effects on the surface water cycles and vegetation, and could be used as the upper boundary for permafrost models to simulate the thermal state of the permafrost and active layer thicknesses. However, due to the limitations of the observation data, there are still large uncertainties in the soil temperature data, including at these two depths, in the permafrost region of Qinghai–Tibet Plateau (QTP). In this study, we evaluated and calibrated the applicability of four daily shallow soil temperature datasets (i.e., MERRA-2, GLDAS-Noah, ERA5-Land, and CFSR) by using the in situ soil temperature data from eight observation sites from 2004 to 2018 in the permafrost region along the Qinghai–Tibet Engineering Corridor. The results revealed that there were different uncertainties for all four sets of reanalysis data, which were the largest (Bias = −2.44 °C) in CFSR and smallest (Bias= −0.43 °C) in GLDAS-Noah at depths of 10 cm and 50 cm. Overall, the reanalysis datasets reflect the trends of soil temperature, and the applicability of reanalysis data at 50 cm depth is better than at 10 cm depth. Furthermore, the GLDAS-Noah soil temperatures were recalibrated based on our observations using multiple linear regression and random forest models. The accuracy of the corrected daily soil temperature was significantly improved, and the RMSE was reduced by 1.49 °C and 1.28 °C at the depth of 10 cm and 50 cm, respectively. The random forest model performed better in the calibration of soil temperature data from GLDAS-Noah. Finally, the warming rates of soil temperature were analyzed, which were 0.0994 °C/a and 0.1005 °C/a at 10 cm and 50 cm depth from 2004 to 2018, respectively.

Designing Gadolinium-doped ceria electrolyte for low temperature electrochemical energy conversion

Reducing the operational temperature of solid oxide fuel cells (SOFC) is vital to improving their durability and lifetime. However, a traditional SOFC suffers from high ohmic and polarization losses at low temperatures, leading to poor performance. Gadolinium-doped ceria is the best ionic conductor for SOFC at lower temperatures. The present work envisages the GDC as an electrolyte for applying low-temperature solid oxide fuel cells (LT-SOFCs). So, in this regard, herein, GDC is synthesized through a wet chemical co-precipitation technique as a functional electrolyte layer fixed between two symmetrical porous electrodes NCAL (Ni0.8Co0.15Al0.05LiO2). Due to the improved surface properties of the synthesized GDC, particles perform better than commercially available GDC. The synthesized GDC electrolyte shows an impressive fuel cell performance of 569 mW/cm2 and a high ionic conductivity of 0.1 S/cm at a shallow temperature of 450 °C. Moreover, the fuel cell device utilizing the synthesized GDC remained stable for 150 h of operation at a high current density of 110 mA/cm2 at 450 °C. The high conduction mechanism has been proposed in detail. The results show that excellent fuel cell performance, high ionic conductivity, and better stability can be achieved at exceptionally low enough temperatures. Also, the proposed work suggests that new electrolytes can be designed for developing advanced low-temperature fuel cell technology.

Pyrolytic biochar from plastic film waste addition on farmland for maize growth improvement: Process and effect study

Pyrolyzing and returning to farmland is one of the potential methods for farmland plastic film waste. This study explored both pyrolyzation and activation optimum conditions of a mixture of plastic film (polyethylene) and maize straw (MPS) in a 1:5 ratio to produce MPS-char, investigated the action of the char on the maize seedling stage (for 30 days). The results showed that the char promoted the root to be more advanced than aboveground part, therefore, this study experimentally clarified the role MPS-char played when added to the soil. The functional groups of the char were varied by the participation of polyethylene. Carbon-based groups were observed, such as carbonyl or carboxyl groups, which could constitute an NH4+ absorption release system to increase the existence of urea in soil, therefore the average nitrogen concentration was improved by 16.18 %. However, the shallow soil temperature increased by 2.03 °C, and the deep soil temperature slightly decreased with the effect of MPS-char. While, the soil moisture content was slightly reduced in the second half of the experiment, and the soil oxygen content increased by 7.64 % throughout the whole experiment. Overall, returning MPS-char to farmland showed a positive effect on maize growth, which was caused by the variation of both chemical and physical properties. This variation provides opportunities for further promotion of rhizosphere development.