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Thermal processes affected by carbon dioxide near ground surface

This study provides penetrative investigation of the effects of carbon dioxide concentration on time-dependent temperature and energy fluxes on the ground surface subject to solar irradiation. While global warming significantly impacts human life, the factors responsible remain controversial. This work considers unsteady one-dimensional heat conduction and radiative heat transfer, including collimated and diffuse components as functions of longitude, latitude, and altitude. Diffuse radiation depends on the different absorption bands of carbon dioxide and water vapor, as functions of wavelength, temperature, concentrations or pressure. The predicted results using COMSOL computer code show that the effects of carbon dioxide concentration on ground surface temperature are negligibly small, for example, over a 5-year period. Time-dependent ground surface temperature strongly depends on the absorption or dissipation of diffuse radiation and heat conduction. Diffuse radiation has a damping effect on temperature variation. Temperature changes due to solar irradiation absorption in the atmosphere are also negligibly small, despite solar irradiation being much greater than diffuse radiation and heat conduction. The absorption or dissipation of diffuse radiation depends on the dominant absorption bands centered at 4.3 and 15 μm of carbon dioxide at different times. This study, from the viewpoint of energy conservation, identifies diffuse radiation as a critical factor influencing the rate of temperature change at the ground surface, without assuming radiative or thermal equilibrium or modeling convection. Poor management of this radiation would hinder efforts to avoid droughts, water scarcity, severe fires, rising sea levels, flooding, catastrophic storms, and biodiversity loss.

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Direct numerical simulation of turbulent heat transfer over surfaces with hemisphere protrusions

Direct numerical simulations (DNSs) of turbulent heat transfer over walls with regularly distributed hemispheric protrusions were conducted to explore how the arrangement and number density of hemispheres affect the turbulent heat transfer. For the rough walls, we considered eight rough surfaces, in which the number density, i.e., the number of hemispheres per unit area, and the distances between two neighboring hemispheres in the streamwise and spanwise directions were systematically varied. The friction Reynolds number was fixed at 660, and we considered an incompressible airflow with a Prandtl number of 0.71, neglecting the buoyancy effects. The results showed that the velocity roughness function strongly depends on the hemisphere arrangement and number density. The spanwise-aligned hemisphere array yields the larger velocity roughness function than its streamwise-aligned hemisphere counterpart, whereas the temperature roughness function depends only on number density. The Reynolds analogy factor decreases with increasing inner-scaled equivalent sand grain roughness, and the decreasing trend is weakly affected by the number density. We analyzed the momentum and heat transfer budgets and found that the pressure drag, which dominates the momentum transfer near the wall, is strongly affected by the hemisphere arrangement and number density. In contrast, the roughness-induced wall heat transfer term, which is the dominant contributor to near-wall heat transfer, depends only on the number density. This difference is the driving mechanism that causes dissimilar trends in momentum and heat transfer over walls with hemispheric protrusions.

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Unveiling Nanomechanical and Pore-Structural Evolution of Bio-Precipitate Arrays in Heterogeneous Granular Media

Biologically induced reactions in granular media (geomaterials) often rely on precipitates from enzymes or microbes to promote the formation of mineral precipitate crystals in its pores. However, there is a major knowledge gap in understanding the hypotheses behind the mechanisms of how, where, and when these biomineralization reactions influence the microbial or enzymatic precipitate growth in heterogeneous granular media, and its impact on its material properties at the pore scale. In this regard, we propose to identify the complex spatio-temporal mechanisms controlling enzymatic (EP) and microbial (MP) precipitates, the temporal distribution patterns (arrays) in heterogeneous granular media (rocks), and quantify the resultant alterations in its nanomechanical signatures due to enzymatic- or microbial-induced reactions. The specimens were incubated with enzymes and microbial species followed by quantitatively analyzing their modified nanomechanical properties (Young's modulus, E; fracture toughness, KIC; hardness, H) and pore volume in addition to characterizing the nano-to-micro-structure. Analysis of the results reveals that bio-precipitates can occlude the nano-and-micro-pores in specimens with reduced pore volume (MP: -12.4%; EP: -48.8%), thereby yielding beneficial nanomechanical alterations (MP: +21.2% H, +16% E, +41.3% KIC; EP: +38.5% H, +17% E, +22.2% KIC) depending on distinct conditions of the bio-precipitated reactions. Looking forward, this work provides a blueprint for the rational design of inherently-heterogeneous granular media with further enhanced biomimicry toward more innovative and environmentally friendly solutions in natural and built infrastructure.

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Enhancement of CO2 adsorption and oxygen transfer properties on γ-Al2O3 support through surface modification with MgO-ZrO2 for coke suppression over Ni catalyst in CO2 reforming of methane

This work focuses on employing commercial γ-Al2O3 for surface modification with MgO-ZrO2 mixed oxide to enhance the potential of CO2 adsorption and oxygen mobility. This enhancement facilitates its application as a support in catalysts for CO2 utilization such as CO2 reforming of methane (CRM). To achieve this perspective, γ-Al2O3 was modified with 10 wt.% of various MgO and ZrO2 contents (MgO:ZrO2= 10:0, 9:1,7:3, 5:5, 3:7, 1:9 and 0:10) using the impregnation method. All samples including unmodified γ-Al2O3 (Al) were characterized. Due to the increase in basicity and oxygen transfer around the surface, the improvement of the CO2 adsorption was observed on γ-Al2O3 modified with 9 wt.% MgO-1 wt.% ZrO2 (9Mg1ZrAl) and 10 wt.% MgO (10MgAl), respectively. An application of these two superior samples as a support of 10 wt.% Ni (10Ni) catalysts for CRM was investigated and compared with an unmodified γ-Al2O3. Characterization results suggest the formation of NiO-MgO solid solution at the surface due to the decrease in metal-support interaction and the increase in metal dispersion. The Ni catalysts with the surface-modified support show higher CO2 activity that raises carbon deposition resistance. The greatest coke prevention was observed on 10Ni/9Mg1ZrAl that lowers the coke deposition by 42% compared to 10Ni/Al. It indicates that the composition of this modification allowed very low ZrO2 portion to merge with MgO and MgO to form solid solution with NiO. This enables the 10Ni/9Mg1ZrAl catalyst to generate labile oxygens which can be conveyed to the Ni metal sites on the catalyst.

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