Search Results (482)

In this study, the possibility of using cement bypass dust as a cement additive was investigated. The utilization of cement bypass dust remains a major problem in cement production, as huge amounts of it are stored in landfills. In this study, a hydrothermal treatment is proposed to modify the properties of this dust and to expand its use. Hydrothermal treatment with pure bypass dust and quartz was carried out to achieve a CaO/SiO₂ ratio of 1 to 2. Samples were synthesized at 200 °C for 2, 4, 8, and 24 h. To examine the influence of the hydrothermal treatment on cement properties, a sample with a CaO/SiO₂ ratio of 1, hydrothermally treated for 8 h, was selected. This study employed XRD, XRF, DSC-TG, and isothermal calorimetry. Most of the target synthesis products, e.g., tobermorite and calcium silicate hydrates, formed after 8 h of sample synthesis, during which quartz was added to bypass dust and a CaO/SiO₂ ratio of 1 was achieved. An examination of the composition of the liquid medium following hydrothermal processing showed that almost all chlorine passed into the liquid medium, while some K₂O remained in the solid synthesis product. The synthesized additive is an effective catalyst for the hydration of Portland cement. After a 28-day curing period, specimens incorporating modified bypass dust replacing up to 10% of the Portland cement by weight demonstrated compressive strengths comparable to, or surpassing, those of specimens composed exclusively of Portland cement. Full article

Atmospheric climate science lacks the capacity to integrate thermodynamics with the gravitational potential of air in a classical quantum theory. To what extent can we identify Carnot’s ideal heat engine cycle in reversible isothermal and isentropic phases between dual temperatures partitioning heat flow with coupled work processes in the atmosphere? Using statistical action mechanics to describe Carnot’s cycle, the maximum rate of work possible can be integrated for the working gases as equal to variations in the absolute Gibbs energy, estimated as sustaining field quanta consistent with Carnot’s definition of heat as caloric. His treatise of 1824 even gave equations expressing work potential as a function of differences in temperature and the logarithm of the change in density and volume. Second, Carnot’s mechanical principle of cooling caused by gas dilation or warming by compression can be applied to tropospheric heat–work cycles in anticyclones and cyclones. Third, the virial theorem of Lagrange and Clausius based on least action predicts a more accurate temperature gradient with altitude near 6.5–6.9 °C per km, requiring that the Gibbs rotational quantum energies of gas molecules exchange reversibly with gravitational potential. This predicts a diminished role for the radiative transfer of energy from the atmosphere to the surface, in contrast to the Trenberth global radiative budget of ≈330 watts per square metre as downwelling radiation. The spectral absorptivity of greenhouse gas for surface radiation into the troposphere enables thermal recycling, sustaining air masses in Lagrangian action. This obviates the current paradigm of cooling with altitude by adiabatic expansion. The virial-action theorem must also control non-reversible heat–work Carnot cycles, with turbulent friction raising the surface temperature. Dissipative surface warming raises the surface pressure by heating, sustaining the weight of the atmosphere to varying altitudes according to latitude and seasonal angles of insolation. New predictions for experimental testing are now emerging from this virial-action hypothesis for climate, linking vortical energy potential with convective and turbulent exchanges of work and heat, proposed as the efficient cause setting the thermal temperature of surface materials. Full article

Underground hydrogen storage (UHS) in geological formations offers a promising solution for large-scale energy buffering, but its long-term safety and mechanical stability remain concerns, particularly in fractured rock environments. This study develops a fully coupled thermo-mechanical model to investigate the cyclic response of a dual-cavern hydrogen storage system with polymer-based sealing layers. The model incorporates non-isothermal gas behavior, rock heterogeneity via a Weibull distribution, and fracture networks represented through stochastic geometry. Two operational scenarios, single-cavern and dual-cavern cycling, are simulated to evaluate stress evolution, displacement, and inter-cavity interaction under repeated pressurization. Results reveal that simultaneous operation of adjacent caverns amplifies tensile and compressive stress concentrations, especially in inter-cavity rock bridges (i.e., the intact rock zones separating adjacent caverns) and fracture-dense zones. Polymer sealing layers remain under compressive stress but exhibit increased residual deformation under cyclic loading. Contour analyses further show that fracture orientation and spatial distribution significantly influence stress redistribution and deformation localization. The findings highlight the importance of considering thermo-mechanical coupling and rock fracture mechanics in the design and operation of multicavity UHS systems. This modeling framework provides a robust tool for evaluating storage performance and informing safe deployment in complex geological environments. Full article

As autogenous and thermal strains are significantly high in alkali-activated pastes, it becomes necessary to investigate ways to reduce these. This research studies how the volume changes of pastes made from slag activated by alkalis can be mitigated by substituting part of the slag with limestone filler and how this impacts the properties of the material, including autogenous strains, thermal strains, heat flow, compressive strength, and workability. The first part investigates how the different substitution rates impact the compressive strength and workability. The substitution rates of 15% and 30% emerged as the most optimal with a maximal reduction in the compressive strength of 23%. Five compositions were consequently investigated in the second part of the study. Isothermal calorimetry revealed that the limestone filler was probably not entirely inert and showed the effect of dilution, which is linked to the increase in the solution-to-binder ratio when the substitution rate increases. The autogenous shrinkage decreased when substituting 15% of the slag, while higher autogenous shrinkage was obtained when 30% was substituted. In addition, its rate of development was reduced. Finally, the coefficient of thermal expansion was generally slightly reduced and delayed when slag was substituted. Full article

The transition toward a renewable-based energy structure has significantly accelerated the advancement of energy storage technologies. Compressed air energy storage (CAES) is regarded as a highly promising long-duration energy storage solution due to the advantages of its large scale and long service life. However, the efficiency of conventional compressed air energy storage (CAES) systems remains limited due to the inadequate utilization of thermal energy. Isothermal compressed CAES (ICAES) technology, based on liquid pistons, can overcome the efficiency bottleneck by enabling temperature control during air compression. However, the operation of liquid pistons under high-pressure storage conditions remains a challenge because of the high compression ratio. To enhance the utilization rate of the two-stage liquid piston unit by using the synchronous operations of compression and discharge processes, this paper proposes a coordinated operation scheme. Then, a multi-stage ICAES system under constant-pressure air storage is proposed. Mathematical models and energy efficiency analysis methods of the multi-stage ICAES system are also established. Finally, the operational characteristics are analyzed in combination with the ICAES at 200 kWh. The results show that the proposed system can achieve an overall efficiency of 68.0%, under 85% and 90% efficiencies for low-pressure and linear equipment, respectively. The coordinated operation of the two-stage liquid piston unit can be further extended to multi-stage operations, demonstrating broad application prospects in ICAES systems. Full article

Compressed air energy storage (CAES) systems represent a critical technological solution for addressing power grid load fluctuations by generating electrical power during peak load periods and storing energy during low load periods. As a prominent branch of CAES, isothermal compressed air energy storage (ICAES) systems have attracted significant research attention due to their elimination of requirements for high-temperature storage chambers and high-temperature compressors. Implementing constant-pressure operation in air storage reservoirs not only enhances energy storage density but also improves system safety. However, existing constant-pressure air storage methodologies necessitate supplementary infrastructure, such as high-pressure water reservoirs or elevated hydraulic columns, thereby escalating capital expenditures. This study introduces a novel constant-pressure air storage strategy for ICAES systems utilizing a linear-driven liquid piston mechanism. The proposed approach achieves constant-pressure air storage through the dual-mode operation strategies of buffer tanks (CBA and CBP modes) and hydraulic cylinders (CPP and CPW modes), eliminating the requirement for an auxiliary high-pressure apparatus or extensive civil engineering modifications. A prototype two-stage constant-pressure ICAES architecture was proposed, integrating low-pressure equipment with liquid pistons and providing detailed operational processes for preconditioning, energy storage, and power generation. A comprehensive mathematical model of the system is developed and validated through process simulation and performance characterization of a 100 kWh capacity system. It demonstrates that under operational conditions of 1 MPa of low pressure and 5 MPa of storage pressure, the system achieves an efficiency of 74.0% when the low-pressure equipment and liquid piston exhibit efficiencies of 85% and 90%, respectively. Furthermore, parametric analysis reveals a negative correlation between system efficiency and low-pressure parameters. Full article

This study analyzed the compression isotherms of 7β-alkyl cholic acid derivatives and compared them to those of cholic and deoxycholic acids to elucidate their orientation and molecular interactions (acidic aqueous substrate—pH 2; NaCl concentration—3 M; temperature—T = 298.15 K). It was found that the compression isotherm of the 7β-octyl derivative of cholic acid in the monomolecular layer is most similar to the compression isotherm of deoxycholic acid. In 7β-alkyl derivatives of cholic acid, the hydrophobic interaction energy in their aggregates from a monomolecular film increased with the length of the alkyl chain. However, this energy did not increase linearly with C atoms, suggesting the existence of a conformational equilibrium. In binary mixtures of the tested bile acids and lecithin, only the 7β-octyl derivatives of cholic acid and deoxycholic acid had orientations in which the steroid skeleton had a “vertical” position, i.e., only the C3 OH group was immersed in the aqueous substrate, which resulted in the maximum hydrophobic interaction with lecithin. In 7β-octyl derivatives, part of the octyl chain probably also participated in the interaction with lecithin. In 7β-propyl and 7β-butyl derivatives, C7 alkyl groups sterically shielded the C7 α-axial OH group. However, in the 7β-ethyl derivative the C7 OH group was not additionally sterically shielded, so this derivative, similarly to cholic acid, partially dissolved in the aqueous substrate after the collapse point. Full article

High-volume fly ash cement exhibits drawbacks such as delayed hydration and reduced early-age compressive strength due to the replacement of large amounts of cement with fly ash. In recent years, various studies have been conducted to overcome these limitations by incorporating nanomaterials, such as nano-silica, to promote the hydration of cementitious systems. This study aims to investigate the effect of colloidal nano-silica on the hydration behavior of cement. Cement paste specimens were prepared with varying dosages of colloidal nano-silica to evaluate its influence. To examine the hydration characteristics and mechanical performance, compressive strength tests, isothermal calorimetry, and thermo-gravimetric analyses were conducted. Furthermore, the effect of colloidal nano-silica on the hydration of cement blended with fly ash was also examined. The experimental results revealed that the incorporation of colloidal nano-silica accelerated the hydration reactions in both ordinary and fly ash-blended cement pastes and significantly improved early-age compressive strength. In particular, the 7-day compressive strength of fly ash-blended cement mortar improved by 22.2% compared to the control specimen when 2% colloidal nano-silica was incorporated. The use of colloidal nano-silica appears to be a practical approach for enhancing the early strength of high-volume fly ash concrete, and its broader application and target expansion could contribute to the advancement of a low-carbon construction industry. Full article

Circulating fluidized bed combustion (CFBC) ash, a byproduct typically generated from coal-fired CFBC power plant boilers, contains high content of free lime and anhydrite. Due to its chemical composition, CFBC ash exhibits self-cementing properties; however, its performance is limited. One approach to enhancing the self-cementing properties of CFBC ash is through the incorporation of mineral admixtures such as gypsum. This study investigated the influence of desulfurization gypsum (DG) on the self-cementing behavior of CFBC ash. To this end, paste and mortar specimens were prepared and evaluated for their hydration and mechanical characteristics. The hydration behavior was analyzed using isothermal calorimetry, thermogravimetric analysis (TGA), setting time measurements, and X-ray diffraction (XRD) analysis. Mechanical properties were assessed by measuring the compressive strength at various curing ages. Additionally, changes in microstructure were examined by evaluating the pore size distribution through mercury intrusion porosimetry (MIP). The experimental results indicate that the appropriate incorporation of DG enhances the hydraulic reactivity of CFBC ash and significantly improves the compressive strength. Full article

This research investigates whether metakaolin can be used as a partial substitution for slag to mitigate significant volume changes in alkali-activated slags. Its effect on compressive strength and workability (as well as on isothermal calorimetry, autogenous strain, and coefficient of thermal expansion (CTE)) were found to depend on both the type and concentration of the alkaline activator. When using 8 M and 10 M sodium hydroxide (NaOH), increasing the substitution rate increased the compressive strength. With sodium silicate (Na₂SiO₃), compressive strength decreased as the substitution increased. Isothermal calorimetry revealed metakaolin’s dilution effect at 10% substitution. With 8 M NaOH, a third reaction peak appeared, whose magnitude increased with the substitution rate, while the second peak decreased. The swelling was increased at 10% substitution, followed by constant shrinkage in case of NaOH-activation. Shrinkage was mitigated with Na₂SiO₃-activation. Higher substitutions with 8 M NaOH resulted in a significant increase in the shrinkage rate and CTE, occurring when the third reaction peak appeared. A 10% substitution delayed the CTE increase but resulted in higher later-age values (dilution effect). The 20% substitution led to a similar final CTE value at 300 h, while 30% substitution resulted in a decrease in CTE after the initial increase. Full article

The fineness of the raw material is the essential factor affecting the burnability of raw meal, with the fineness of the siliceous material being of the utmost importance. In this paper, Portland clinker was prepared from sandstones with four different particle sizes. The effects of sandstone fineness on calcination, crystal structure, phase assemblage, and hydration of the clinker were investigated by means of thermomechanical analysis (TMA), X-ray diffraction analysis (XRD), isothermal conduction calorimetry (ICC), and thermogravimetric analysis (TGA). The results show that as sandstone fineness decreases, the clinkers undergo a gradual decrease in shrinkage during calcination, alongside a consistent rise in free lime (f-CaO) content. The decrease in sandstone fineness has been shown to have a significant effect on the size of C₃S and C₂S, but no obvious effect on their crystal structure. The f-CaO rapidly reacts with water to form Ca(OH)₂ in the initial stage of cement hydration, resulting in the shortening of the hydration induction period and the advance of the hydration of C₃S. Furthermore, the compressive strength of Portland cement increases with the increase in sandstone fineness at every age, and the increase in age compensates for the differences in strength among samples. Full article

This study presents a comprehensive dynamic model of a small-scale, solar-powered hydraulic gas compression energy storage system tailored for renewable energy applications. Addressing the intermittency of renewable energy sources, the model incorporates mass, momentum, and energy conservation principles and is implemented using GT-Suite simulation software v2025.0. The system, based on a liquid piston mechanism, was analyzed under both adiabatic and isothermal compression scenarios. Validation against experimental data showed maximum deviations under 10% for pressure and 5 °C for temperature. Under ideal isothermal conditions, the system stored up to 8 MJ and recovered 6.1 MJ of energy, achieving a round-trip efficiency of 76.3%. In contrast, adiabatic operation yielded 52.6% efficiency due to thermal losses. Sensitivity analyses revealed the importance of heat transfer enhancement, with performance varying by over 15% depending on spray cooling intensity. These findings underscore the potential of thermally integrated hydraulic systems for efficient, scalable, and cost-effective energy storage in distributed renewable energy networks. Full article

Ti-2Al-9.2Mo-2Fe (2A2F) alloy is a low-cost β-Ti alloy in which the expensive β-stabilizing elements (Ta, Nb, W, Ni) are replaced with relatively inexpensive Mo and Fe for use in low-cost applications in various industries. The 2A2F alloy exhibits excellent mechanical properties such as high specific strength and low elastic modulus compared to conventional steel alloys but is prone to brittleness owing to the formation of the ω phase when heat-treated at relatively low temperatures. Therefore, an appropriate aging treatment should be performed to control the precipitation of the isothermal ω phase and secondary α phase. This study aims to derive the appropriate aging-treatment conditions following a solution treatment at 790 °C for 1 h, which is below the β-transus temperature of 815 °C. The aging treatments are conducted at holding temperatures in the range of 450–600 °C and holding times between 1 and 18 h. At relatively low aging temperatures of 450 °C and 500 °C, the precipitation of the isothermal ω phase resulted in significantly high hardness and compressive strength. As the aging temperature and holding time increased, the ω phase gradually transformed into the secondary α phase, leading to a balanced combination of strength and ductility. However, at excessively high aging temperatures and prolonged durations, excessive precipitation and growth of secondary α phases occurred, which caused a reduction in hardness and compressive strength, accompanied by an increase in ductility. In this study, the effects of precipitation evolution on mechanical properties such as tensile strength and hardness under various heat treatment conditions were comparatively analyzed. Full article

Density and viscosity are fundamental properties necessary for processing of red palm oil (RPO). The main fatty acid constituents of RPO were determined to be palmitic acid (C_16:0), oleic acid (C_18:1), and linoleic acid (C_18:2). Rheology measurements confirmed that RPO behaved as a Newtonian fluid. Viscosities and atmospheric densities of RPO were measured at 0.1 MPa and (293 K to 413) K and correlated with the Rodenbush model (0.05% deviation). Dynamic viscosities of RPO were correlated with the Vogel–Fulcher–Tammann model (0.06% deviation) and Doolittle free volume model (0.04% deviation). High-pressure densities of RPO were measured at (10 to 150) MPa and (312 to 352) K. The Tait equation could correlate the high-pressure densities of RPO to within 0.021% deviation and was used to estimate the thermal expansion as 5.1 × 10⁻⁴ K⁻¹ (at 312 K, 150 MPa) to 4.8 × 10⁻⁴ K⁻¹ (at 352 K, 150 MPa) and isothermal compressibility as 7.3 × 10⁻⁴ MPa⁻¹ (at 352 K, 0.1 MPa) to 3.5 × 10⁻⁴ MPa⁻¹ (at 352 K, 150 MPa). Parameters for the perturbed-chain statistical associating fluid theory equation of state were determined and gave an average of 0.143% deviation in density. The data and equations developed should be useful in high-pressure food processing as well as in applications considering vegetable oils as heat transfer fluids or as lubricants. Full article

This study investigates the correlation between the hydrophilic–lipophilic balance (HLB) values and the π–A isotherm parameters of surfactant monolayers composed of sorbitan esters, specifically sorbitan monopalmitate, sorbitan tristearate, sorbitan monooleate, and sorbitan sesquioleate. The surfactant mixtures were prepared, and their π-A isotherms were recorded. The HLB values calculated for each mixture were in the range 2.10–6.70. The HLB values were compared to compression parameters, including the ratios of the slopes and the ratios of the intercepts, which were between 0.19 and 4.00 and between 0.64 and 1.77, respectively, across the monolayer compression stages. The findings indicate a significant relationship between HLB values and isotherm parameters, particularly for systems with sorbitan monooleate and sorbitan sesquioleate. A value of determination coefficient of 0.95 was found for the linear equation representing the slope ratios as a function of HLB, whereas the intercept ratios, as a linear function of HLB, gave a lower value of 0.71. The results allow for the use of the π–A Langmuir isotherm to experimentally estimate the value of the HLB in mixtures of the sorbitol esters of fatty acids, whose value is an important parameter in the selection of optimized topical and transdermal formulations, highlighting the specific formulations that enhance active substance delivery while minimizing skin irritation potential. Full article