Thermo, Volume 2, Issue 4 (December 2022) – 8 articles

Geothermal energy storage provides opportunities to store renewable energy underground during summer for utilization in winter. Vertically oriented systems have been the standard when employing boreholes as the means to charge and discharge the underground. Horizontally oriented borehole storage systems provide an application range with specific advantages over vertically oriented systems. They are not limited to the surface requirements needed for installation with vertical systems and have the potential to limit storage losses. Horizontal systems can be incorporated into the built environment and utilize underground storage sites below existing infrastructure. An experimental study examines configurations using a mix of renewable energy (photovoltaic panels) and grid energy to charge a storage system during summer for use during winter. A comparison of five different borehole configurations at three different loading temperatures was composed using an experimentally validated numerical model. The horizontal systems studied and analyzed in this work showed improved performance with scale and charging temperature. This paper supports further exploration into specific use cases for horizontal borehole thermal energy storage systems and suggests applications which would take advantage of better performance at scale. Full article

This paper is a literature survey that focuses on the present development of thermokinetic publications. It demonstrates that in recent years pyrolysis kinetics has turned into a major application of the thermokinetics. Analysis of the respective publications suggests that too often their quality leaves much to be desired because of the poor choices of the kinetic methods and experimental conditions. It is explained that the proper choices can be made by following the recommendations of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). To help with improving the quality of the kinetic results, the ICTAC recommendations are condensed to a few easy to follow principles. These principles focus on selecting proper computational methods, collecting better experimental data, and efficiently reporting the results. The paramount computational principle is to avoid using the methods that evaluate the activation energy and other kinetic parameters from the data measured at a single heating rate. It is shown that the kinetic parameters evaluated by such methods can give rise to striking examples of failure when estimating the thermal stability at ambient temperature. Because of the vital importance of pyrolysis kinetics studies from an ecological and economical perspective, a substantial improvement of their quality is currently needed. Full article

Seasonal oscillations in the partial pressure of carbon dioxide (pCO₂) in the Earth’s atmosphere, stronger in northern latitudes, are assumed to show that terrestrial photosynthesis exceeds respiration in summer, reducing the pCO₂ in air but increasing its value in winter when respiration exceeds photosynthesis. We disagree, proposing that variation in the temperature of the surface mixing zone of seawater also reversibly regulates the pCO₂ in air as a non-equilibrium process between air and seawater. We predict by thermal modelling that carbonate (CO₃²⁻) concentration in the surface mixed layer seawater declines in winter by conversion to bicarbonate with CaCO₃ (calcite or aragonite) becoming more soluble and, proportional to the fall of temperature, calcite decalcifying more strongly, allowing more CO₂ emission to air. Paradoxically, the increasing CO₂ concentration in seawater favoring photosynthesis peaking in mid-summer declines simultaneously in autumn and early winter, forced by boundary layer fugacity into phase transfer to the atmosphere, supporting peak atmospheric pCO₂ by late winter. These physico-chemical processes reverse in late winter and spring as seawater warms favoring calcification, fugacity forcing CO₂ from the atmosphere as bicarbonate declines and carbonate increases, augmenting suspended calcite particles by several percent. Our numerical computation predicts that the larger range of thermal fluctuations in the northern hemisphere could reversibly favor absorption from air of more than one mole of CO₂ per square meter in summer with calcite formation potentially augmenting shallow limestone reefs, despite falling pH, if there is a trend for increasing seawater temperature. Another assumption we challenge is that upwelling and advection from deeper water is the sole cause of increases in dissolved inorganic carbon (DIC) and alkalinity in surface waters, even in the southern hemisphere. Instead, some calcite dissolution is favored as water temperature falls near the surface. Standard enthalpy analysis of key DIC reactions indicates why this oscillation is more obvious in the northern hemisphere with seasonal variations in water temperature (ca. 7.1 °C) being almost twice those in the southern hemisphere (ca. 4.7 °C) with a greater depth of the surface mixing zone of seawater in the southern oceans. Questions remain regarding the relative rates of biotic and abiotic inorganic precipitation and dissolution of CaCO₃ in the mixing zone. In summary, rapid biogenic calcification is favored by summer photosynthesis, but slower abiotic calcification is also more likely in warmer water. We conclude that the relative significance of terrestrial biotic and seawater abiotic processes in seawater on the seasonal oscillation in the atmosphere can only be assessed by direct seasonal measurements in seawater. Full article

Attention to photovoltaic (PV) cells to convert solar irradiation into electricity is significantly growing for domestic usage and large-scale projects such as solar farms. However, PV efficiency decreases on hot days. This paper proposes an effective cooling technique consisting of a 2% nano encapsulated phase change material (NEPCM) slurry and impinging jets (IJs) in a PV system. The impact of five influencing parameters on PV efficiency is studied using a multi-phase volume of fluid (VOF) model encompassing the effects of solar irradiation, latent heat, mass flow rate, number of nozzles, and jet-to-surface distance. The maximum efficiency of 15.82% is achieved under irradiation of 600 W/m². The latent heat shows a slight improvement at the low particle concentration. Increasing the mass flow rate to 0.12 kg/s enhances the PV output power by 17.32%. While the PV performance is shown to be improved over the increment of the number of nozzles, the jet-to-surface spacing of 5.1 mm records a remarkable PV surface temperature reduction to 33.8 °C, which is the ideal operating temperature for the PV panel. Full article

Lead–Bismuth Eutectic (LBE) is a heavy metal liquid alloy used as a coolant for compact high temperature reactors (CHTRs), fast breeder reactor (FBRs) and as a spallation target for ADS. In spite of many advantages due to its thermophysical properties, corrosion towards structural materials remains one of the major issues of LBE. In absence of any oxygen impurity, corrosion in LBE is driven by dissolution processes and the solubility of the main elements of the structural material alloys. Using the CALPHAD method, Thermo-Calc software, a thermodynamic database was developed to assess the interaction between Ni and LBE coolant. The solubilities of Ni in LBE, Bi and Pb liquids have been calculated at different temperatures. Full article

The potential regarding the indicated efficiency of an alternative piston trajectory for a spark ignited methane combustion engine has been investigated in this study. A physics-based cylinder model including a predictive combustion model was used to account for the interaction of the thermodynamics with altered kinematics. Using a genetic optimization algorithm on an adjustable spline, piston trajectories for different piston acceleration limits have been found for both full and part load operating points. All optimization processes led to increased indicated efficiencies up to a maximum of 52%. The increase in efficiency of the optimized piston trajectory is analyzed based on the results of the numeric simulation and can be explained by the following effects: deeper expansion of the working gas, reduced pumping losses, reduced wall heat losses, shorter heat release, and increased trapped air mass. Full article

Foresight of geothermal energy installation is valuable for energy decision-makers, allowing them to readily identify new capacity units, improve existing energy policies and plans, expand future infrastructure, and fulfill consumer load needs. Therefore, in this paper, an improved grey prediction model (IGM (1,1)) was applied to perform the annual geothermal energy installation capacity prediction for the top 10 countries based on installed power generation capacity evaluated at the end of 2021, namely the United States, Indonesia, Philippines, Turkey, New Zealand, Mexico, Italy, Kenya, Iceland, and Japan, for the next nine years for the period from 2022 through 2030. These data can be used by future researchers in the field. Separately, datasets from 2000 to 2021 were collected for each country’s geothermal energy installation capacity to build a model which can accurately predict the annually geothermal energy installation capacity by 2030. The IGM (1,1) model used a small dataset of 22 data points, with one point denoting one year (i.e., 22 years), to predict the capacity of geothermal energy installations for the next nine years. Following that, the model was implemented for each dataset in MATLAB, where appropriate, and the model accuracy was evaluated. Ten separate geothermal energy installation capacity datasets were used to validate the improved model, and these datasets further demonstrated the overall improved model’s accuracy. The results prove that the prediction accuracy of the IGM (1,1) model outperforms the benchmark conventional GM (1,1) model, thereby enhancing the overall accuracy of the GM (1,1) model. The IGM (1,1) model ensures error reduction, suggesting that it is an effective and promising tool for accurate short-term prediction. The results reveal the 2030 geothermal energy installation capacity rankings. Full article