Constant Temperature Conditions Research Articles

Data generation and training of surrogate models for friction factor and Nusselt number in low Reynolds number flows through pin fin geometries

Abstract The design of various biomedical, electronics cooling, and microfluidic devices relies on geometry-specific models and empirical correlations for flow and heat transfer through microscale pin fin geometries. Machine learning techniques are being used across many branches of science to develop more generalized surrogate models that can predict such transport processes. To collapse the simulation of flow and thermal properties across many different pin fin surfaces into a single predictive tool, the present study develops machine-learning-based surrogate models for the friction factor and Nusselt number (for constant wall temperature conditions) for fully developed low Reynolds number flow across pin fin geometries of differing cross-section shape (circular, square, triangular) in aligned or staggered arrangements, oriented at any angle to the incoming flow, and for a range of transverse and longitudinal pitches, with water as the working fluid. The model training data are generated using an automated workflow that allows thousands of numerical simulations to be carried out on across different geometric and flow configurations. A total of ~14,800 distinct simulation cases, for both friction factor and Nusselt number, are generated whilst varying the Reynolds number and aforementioned geometric parameters to train and test the machine learning models. The machine learning model architecture takes inputs of both image and vector data, and then outputs a scalar friction factor or Nusselt number. The trained models yield a goodness of fit (R2) value of 0.98 on unseen data.

Impact of applied and preceding pressure on performance and reversible swelling of lithium-ion pouch cells with varying microporous separators

During the compression of battery cells in battery pack production, high forces occur temporarily due to the viscoelastic behavior of the cell components. The magnitude of these forces depends on the compression speed. Shortening the production time and, thus, increasing the compression speed is desirable for cost reduction. However, it must be ensured that the cells are not negatively affected by increased forces during production. The impact of these preceding forces, acting on the cell before operation, and the applied force during operation on the performance and the reversible swelling of 5Ah NMC811/graphite lithium-ion pouch cells are investigated in this study. To this end, a universal compression testing machine was adapted to enable high-precision thickness measurements under defined constant pressure and temperature conditions. In addition, the effects of different microporous separators manufactured via dry process and wet process in an otherwise identical cell configuration were investigated. In the test procedure, the pressure was incrementally increased from 0.01MPa to 2.5MPa. Each measurement was performed at the distinct constant pressure levels, followed by a subsequent measurement at a reference pressure of 0.2MPa to evaluate the impact of the preceding step. The results revealed that elevated preceding pressures on the cell can reduce the discharge rate capability on higher C-rates by up to 11%. The discharge rate capability of the cells with the wet-processed separator was more significantly influenced by increasing applied and preceding pressure than for those with the dry-processed separator. It was found that the reversible swelling of the cell was reduced by applying higher pressures, whereas elevated preceding pressure increased the reversible swelling. The results of this study suggest that cells should not be subjected to excessive forces before operation, for instance, during battery pack production, as this can negatively affect performance and swelling behavior. Furthermore, the mechanical stability of the separator during the pack production process should also be considered when designing a cell.

Effect of PVA fibers grafted with MWCNTs on the shrinkage behaviors of engineered geopolymer composite (EGC)

Geopolymer have been considered as a promising alternative for the development of high-ductility and eco-friendly engineered materials. In this study, modified PVA fibers grafted with MWCNTs(PM) are used as additives to investigate their impact on the drying shrinkage, autogenous shrinkage and chemical shrinkage of Engineered Geopolymer Composites(EGC). Additionally, various micro-structure techniques, including X-ray Diffraction(XRD) and Scanning Electron Microscopy(SEM), are employed to examine the morphology and chemical composition of EGC. The experimental findings indicates that PVA fibers and MWCNTs both help to mitigate the drying shrinkage and autogenous shrinkage of the EGC. When the PVA fiber content is 2.0 % and the MWCNT content is 1.0 ‰, the 90-day drying shrinkage and autogenous shrinkage values of the EGC are minimized, reducing by 31.67 % and 34.16 %, respectively, in comparison to the control group. However, the incorporation of MWCNTs increases the chemical shrinkage of the geopolymer matrix, with the chemical shrinkage value reaching its maximum when the MWCNT content is 1.0 ‰. Micro-structural analysis reveals that the inclusion of PM leads to an improvement in the quantity of reaction products without affecting their type. Furthermore, the incorporation of PM refines the overall pore structure, restricts the crack development and enhances the interfacial bonding effect of EGC. Notably, a correction prediction model for drying shrinkage strain and autogenous shrinkage strain, incorporating the influence coefficients of PVA fibers and MWCNTs, is constructed under constant humidity and temperature conditions. This significantly improves the prediction accuracy of drying shrinkage and autogenous shrinkage of EGC.

Nusselt number and skin‐friction coefficients of a micropolar flow over a flat plate under constant wall temperature conditions in a porous medium

AbstractThis study examines the forced convection of a micropolar fluid (MPF) flow across a vertical permeable plate inside a porous medium. A similar solution is derived for a scenario involving a constant surface temperature. The system of transformed governing equations is addressed by employing a finite‐difference method. Notably, a parametric analysis is conducted to demonstrate how the Prandtl number, micropolar parameters, Darcy number, inertia coefficient (ξ), skin friction (Cf), and Nusselt number (Nu) impact the system. The results are then presented graphically, while the physical aspects of the issue are assessed. Although a larger Nu produced a high wall heat transfer, the Cf values are decreased as ξ increases. The ξ also reduces the local Nu. Compared with Newtonian fluids, the MPF increases Cf and reduces the heat transfer rate. The outcomes are validated by comparing the current results with other related studies. The results of this study are useful for improving the efficiency of solar panels by enhancing their cooling rate. It is also found that increasing the inertia of MPF leads to an increase in the friction coefficient (Cf) while increasing porosity, microrotation parameter n and Fs decreases (Cf).

Water temperature disturbance alters the conjugate transfer of antibiotic resistance genes via affecting ROS content and intercellular aggregation

Spread of antibiotic resistance genes (ARGs) in aquatic ecosystems poses a significant global challenge to public health. The potential effects of water temperature perturbation induced by specific water environment changes on ARGs transmission are still unclear. The conjugate transfer of plasmid-mediated ARGs under water temperature perturbation was investigated in this study. The conjugate transfer frequency (CTF) was only 7.16 × 10−7 at a constant water temperature of 5 °C, and it reached 2.18 × 10−5 at 30 °C. Interestingly, compared to the constant 5 °C, the water temperature perturbations (cooling and warming models between 5–30 °C) significantly promoted the CTF. Intracellular reactive oxygen species was a dominant factor, which not only directly affected the CTF of ARGs, but also functioned indirectly via influencing the cell membrane permeability and cell adhesion. Compared to the constant 5 °C, water temperature perturbations significantly elevated the gene expression associated with intercellular contact, cell membrane permeability, oxidative stress responses, and energy driven force for CTF. Furthermore, based on the mathematical model predictions, the stabilization times of acquiring plasmid maintenance were shortened to 184 h and 190 h under cooling and warming model, respectively, thus the water temperature perturbations promoted the ARGs transmission in natural conditions compared with the constant low temperature conditions.

Hydride induced embrittlement and fracture of non-hardening metals under hydrogen chemical equilibrium

The stress field in the hydride precipitation zone is examined, under conditions of hydrogen chemical equilibrium and constant temperature, in the case of non-hardening metals, by applying slip-line theory. It is proven that the hydride precipitation zone, in any geometry, is a constant stress area. In this area, the principal stresses are equal to the respective principal stresses, before hydride precipitation, minus the difference of hydrostatic stress before and after hydride precipitation. The general relations are applied to the case of a stationary sharp mode-I plane-strain crack and the deviations from Prandtl-field are derived, in the [-π/4, +π/4] sector ahead of the tip, where hydrides precipitate. In this case, the hydride precipitation sector is characterized by a constant hydride volume fraction. In addition, hydride precipitation is associated with the development of elastic sectors along the crack faces and the reduction of the centered fan sectors; the relation between hydride precipitation zone stress trace and the extent of the centered fan sector is presented. The mode-I plane-strain blunted crack is also considered and the deviations from the logarithmic spiral slip-lines is discussed together with the reduction of hydride volume fraction as the blunted crack-tip is approached. A general fracture criterion, based on the strength of hydride platelets, is derived, which indicates that fracture occurs, when a critical hydride precipitation zone stress trace dominates. The criterion is applied, under the condition of a dominant K-field annulus, surrounding the plastic zone, and the estimated threshold stress intensity factor of delayed hydride cracking correlates favorably with experimental measurements.

Autogenous shrinkage of high-performance concrete subjected to different curing temperatures

High-performance concrete (HPC) shows obvious autogenous shrinkage in the early stage. In actual engineering, the interior of HPC undergoes a variable temperature evolution, and the impact of variable temperature conditions on the autogenous shrinkage of HPC is unclear. This paper examines the impact of different curing temperatures on the material properties of HPC, as well as the evolution of HPC autogenous shrinkage. Three measured temperature histories and four constant temperatures were used as curing conditions. Additionally, an HPC autogenous shrinkage prediction model was established considering the impact of curing temperature. The test results indicate that the compressive strength and elastic modulus of HPC increase with increasing curing temperature. Furthermore, there is a significant increase in the autogenous shrinkage rate of HPC as the curing temperature increases. Existing maturity methods overestimate the impact of temperature on the autogenous shrinkage process of HPC. The proposed autogenous shrinkage prediction model enhances the accuracy in predicting the autogenous shrinkage of HPC under constant and variable curing temperature conditions.

Radon and water geochemistry at the active Campi Flegrei volcano (Italy): The role of pore-water phenomena

This study provides new 222Rn measurements performed by RAD7 on 31 thermal waters from the Campi Flegrei caldera, the active volcanic-geothermal field close to Naples (Southern Italy). Waters sampled between 2021 and 2023 are characterized for physical parameters, major ions geochemistry and radium content. Rn contents from Somma-Vesuvius, Ischia and Vulcano volcanoes, together with the river plain north to the Campi Flegrei, were obtained for comparison. The Campi Flegrei caldera reaches the highest Rn concentrations respect to the other sites, varying from 0.03 ± 0.02 to ca. 1887 ± 13 Bq/L, although mostly are below 60 Bq/L. We detect a steady-state condition of constant temperature, facies and radon activity that characterizes most sites, with only minor impacts from seasonalilty and Weigel's effects. Just a small fraction of 222Rn derives from its 226Ra parent in solution, while radon activity in local waters is mainly due to emanation from the radium-containing rock reservoir. Our dataset proofs that radon couples with temperature, sulfate and CO2 in relations to rock-leaching and pore-water phenomena that proceed in the reservoir as it warms up and degasses. Rn and CO2 are decoupled in deeply and timely equilibrated geothermal fluids.Two main end-members, i.e., a low radioactive cold diluted and the Rn-richest hypersaline water from the deep geothermal reservoir are recognized; seawater contamination and heating over 70 °C play a major role in radon decrease.Related radium contents, physical parameters and major ions geochemistry are also presented for a comparison with published data.

Effects of Temperature Regulation on the Physiological Characteristics and Platycodin Synthesis of Platycodon grandiflorum

Platycodon grandiflorum, a dual-purpose herb for food and medicine, is widely distributed in Asia. Although P. grandiflorum has relatively low requirements for its growing environment, temperature remains an important ecological factor affecting its growth, development, and quality formation. In order to explore the effect of different temperatures on P. grandiflorum during their growth period, the diversity in growth physiology, platycodin contents, and gene expression of key enzymes were investigated under constant (8 °C, 18 °C, and 28 °C) and variable (8–18 °C, 8–28 °C, and 18–28 °C) temperature conditions at each of the three levels. The results suggested that both constant and variable temperatures at high levels significantly increased the aboveground fresh weight of P. grandiflorum. However, the low–variable temperature was beneficial for the accumulation of dry and fresh weight in the roots. Regardless of whether temperatures were constant or variable at low levels, this increased the content of soluble sugars, proline, and peroxidase in P. grandiflorum, while upregulating the expression levels of key enzyme genes involved in platycodin synthesis. Meanwhile, a low–constant temperature inhibited the photosynthetic rate of P. grandiflorum. Furthermore, medium–constant and large-scale variable temperatures were conducive to the accumulation of platycodins in the roots. This research provides a theoretical basis and data support for the influence of temperature variations on P. grandiflorum quality formation.

Temperature-Dependent Oviposition Models for Monochamus saltuarius (Coleoptera: Cerambycidae).

Monochamus saltuarius Gebler is a serious insect pest in Europe and East Asia regions, including Portugal, Spain, China, Japan, and Korea. It transfers the pine wood nematode Bursaphelenchus xylophilus to conifer trees, resulting in pine wilt disease (PWD). As temperature is a key factor influencing insect population dynamics, temperature-dependent models describing M. saltuarius oviposition could estimate population growth potential and evaluate outbreak risks. In this study, the longevity and fecundity of M. saltuarius females were measured under constant temperature conditions ranging from 20 to 32 °C, and temperature-dependent models were constructed. The longevity of M. saltuarius females ranged from 83.36 days to 22.92 days, with a total fecundity of 141 eggs and 52.77 eggs at 20 °C and 32 °C, respectively. To describe oviposition, we used a single-phase simulation describing oviposition as a single model and a two-phase simulation describing sexual maturation and oviposition as two separate models. These models effectively described M. saltuarius oviposition (r2 > 0.96) under constant temperature conditions, with the two-phase simulation demonstrating greater accuracy overall. Such models could facilitate assessments of PWD risks. The modeling framework of this study shows potential for predicting threats from various forestry and agricultural pests.

Release of contaminants from polymer surfaces under condition of organized fluid flows

The use of polymers for water storage or distribution is closely monitored, especially with regard to the possible contamination with substances coming from the material's surfaces. Different standards are practiced across countries according to type of applied materials and such test methods are prevalently based on constant temperature conditions. However, these polymers systems could be located in diverse environment which does not necessarily provide constant conditions. Experimental findings show that exposure of liquid inside polymeric materials to specific temperature gradients, and consequently to emerging organized flows, can result in an accelerated leaching of undesirable substances from the solid surface. In presented work model steady-state and organized flow conditions are used to compare release of contaminates from polyethylene by measuring of surface tension, UV–Vis spectroscopy, FTIR, scanning electron microscopy and elemental analysis of polymer surfaces and water leachates. The pilot study shows that convective flow generated via temperature gradient significantly affects contaminant release in comparison to a steady state and mixing flow conditions.

Frequency-Dependent Fatigue Properties of Additively Manufactured PLA.

Vibration-fatigue failure occurs when a structure is dynamically excited within its natural frequency range. Unlike metals, which have constant fatigue parameters, polymers can exhibit frequency-dependent fatigue parameters, significantly affecting the vibration resilience of 3D-printed polymer structures. This manuscript presents a study utilizing a novel vibration-fatigue testing methodology to characterize the frequency dependence of polymer material fatigue parameters under constant temperature conditions. In this investigation, 3D-printed PLA samples with frequency-tunable geometry were experimentally tested on an electro-dynamical shaker with a random vibration profile. Using the validated numerical models, the estimation of vibration-fatigue life was obtained and compared to the experimental results. Performing the numerical minimization of estimated and actual fatigue lives, the frequency-dependent fatigue parameters were assessed. In particular, the results indicate that the tested samples exhibit varying fatigue parameters within the loading frequency range of 250-750 Hz. Specifically, as the loading frequency increases, the fatigue exponent increases and fatigue strength decreases. These findings confirm the frequency dependence of fatigue parameters for 3D-printed polymer structures, underscoring the necessity of experimental characterization to reliably estimate the vibration-fatigue life of 3D-printed polymer structures. The utilization of the introduced approach therefore enhances the vibration resilience of the 3D-printed polymer mechanical component.

Calcium carbonate crystallization process analysis on a heat transfer surface

This paper explores the growth process of calcium carbonate crystallization fouling on a heat surface using finite element methods to solve physical equations such as momentum, energy, and concentration diffusion, incorporating the impact of bulk crystallization on the concentration of scaling ions. The simulation uses deformation geometry, moving grids, and automatic re-meshing methods to study the dynamic growth of fouling layers and the spatiotemporal changes in fluid velocity, temperature, and concentration field-related parameters caused by it. Results indicate that the deposition interface temperature increases along the flow direction under constant heat flux conditions, leading to an increase in deposition rate. When the interface temperature exceeds 340 K, the fouling deposition rate becomes highly sensitive to temperature changes. The fouling thickness also increases along the flow direction, causing the heat transfer surface near the outlet to face a more severe heat transfer deterioration caused by scaling. Under constant temperature conditions, the deposition rate increases rapidly near the inlet and varies less along the flow direction. When the wall temperature remains constant, scaling is more likely to occur at the fluid inlet as the fluid temperature increases. This model also examines the effects of changes in the porosity of the fouling layer and ion interactions in composite salt solutions on the growth characteristics of the fouling layer.

Research on ventilation cooling design driven by human thermal response in high geothermal temperature tunnel construction

Constant high temperature conditions in tunnel not only significantly reduced the labor efficiency of workers but also affected their physical and mental health. However, the traditional design of ventilation and cooling for high geothermal tunnel construction only considers the control of environment temperature and ignores the thermal comfort state of the workers, which will increase the potential risk of tunnel safety accidents. Therefore, this paper adopted the methods of scene testing, theoretical analysis and numerical simulation to establish a modified evaluation model applicable to the thermal comfort of workers in high geothermal tunnels. By analyzing the temperature distribution pattern of heat-sensitive parts of workers engaged in different labor intensity under different air supply parameters, the design strategy for ventilation and cooling of high-temperature tunnels was refined on the basis of ensuring that the environment temperature and thermal comfort meet the requirements. The results show that ventilation design parameters that satisfy the environmental temperature control criteria are equally adequate for worker thermal comfort at light-intensity work. However, when the ambient temperature is higher than 40 °C, the thermal comfort of workers engaged in medium-intensity work still does not meet the requirements, even if the ambient temperature already meets the criteria. It is recommended that the wind speed be increased by at least 8.3 %, 15.6%and 28.6 % for ambient temperatures of 40 °C, 45 °C and 50 °C, respectively. More effective cooling techniques should be tried to further enhance thermal comfort for workers engaged in heavy workloads especially in hot environments exceeding 40 °C.

Research on Ozone-Enhanced Oxidation of Industrial Zinc Sulfite from Flue Gas Desulfurization

ABSTRACT This study investigates the air oxidation and ozone-enhanced oxidation of zinc sulfite. Zinc sulfite was prepared by reacting pure or industrial zinc oxide with SO2 in water. The oxidation experiments were conducted under constant temperature conditions, with slurry, oxygen, and ozone concentrations in the ranges of 0.5–4%, 10–60%, and 1100–1920 ppm, respectively. The experiments involved determining the zinc ion concentration, sulfite concentration, dissolved oxygen, ozone concentration in the exhaust gas, and total organic carbon value for analysis of the oxidation process. The findings revealed that the mass transfer rate of O2 and/or O3 determined the reaction rate in the main stage of the oxidation process, while ozone affected the non-mass transfer control stage, resulting in an average enhancement of 15% in the oxidation rate. Furthermore, ozone causes organic matter attached to industrial zinc sulfite particles to fall off into the solution, significantly improving the oxidation ratio of industrial zinc sulfite.

Performance analysis and optimization of the Gyroid-type triply periodic minimal surface heat sink incorporated with fin structures

The Triply Periodic Minimal Surface (TPMS) structures demonstrate substantial value and development potential in applications and research concerning heat sinks and heat exchangers. To further enhance the convective heat transfer performance of TPMS, this study proposes a novel method of incorporating fin structures into TPMS. This method is applicable to various types of TPMS, and the new structure constructed using this method is termed “TPMS with Fin Structures (TFS).” Subsequently, a TFS-Gyroid heat sink based on the Gyroid-type TPMS was constructed. This study presents a calculation method for the fin height in TFS-Gyroid (HTFS-Gyroid). Numerical simulation methods were employed to investigate the influence and mechanism of HTFS-Gyroid on the convective heat transfer performance and flow resistance of the TFS-Gyroid heat sink model, with air as the working fluid and under constant wall temperature (100 °C) conditions. The results indicate that within the flow range of 24–120 L/min, as HTFS-Gyroid increases from 0 to 1.6 mm, the average surface convective heat transfer coefficient (h̅) of the TFS-Gyroid heat sink model increases by 27.4 %-34.6 %, and the inlet–outlet pressure drop (ΔP) increases by 42.5–632.8 Pa. As HTFS-Gyroid increases, the PEC of the TFS-Gyroid heat sink model gradually decreases, whereas j/f gradually increases. The primary mechanisms by which the fin structures enhance the convective heat transfer performance of the TFS-Gyroid heat sink are: 1) increased heat exchange area, 2) the fin structures induce a large number of longitudinal vortices and secondary flows within the flow channels, and 3) the formation of “Fins Occupying the Perforated Structure (FOPS)” within the flow channels.

Research on the enhancement material and culture method of soil aggregates composed of feldspathic sandstone and sand

The Mu Us Sandy Land is a region characterized by wind-blown sand and soil erosion in northern China. To enhance the soil quality of this area, various organic materials were incorporated into the mixed soil at a volume ratio of 1:2 for feldspathic sandstone to sand. Culture was conducted in the field and under constant temperature conditions in laboratory culture chambers. Four treatments were established in the experiment, each calculated based on weight ratio and controlled (with no organic material added, CK); single application of straw (5% straw, P1); single application of biochar (5% biochar, P2); combined application of biochar and straw (5% biochar + 5% straw, P3). After 90 days of culture, soil samples were collected for analysis of various indicators such as soil aggregate particle size distribution, water stability of soil aggregates, mean weight diameter, mean geometric diameter, and fractal dimension using dry sieving and wet sieving methods. The objective is to establish a scientific basis and provide technical support for addressing the challenges associated with compound soil and implementing rational fertilization measures. The research results indicate that: (1) The quantity of aggregates > 0.25 mm under different treatments follows the order CK < P1 < P2 < P3, and the differences between treatments are significant (P < 0.05); (2) Soil water stability, mean weight diameter (MWD), mean geometric diameter (GMD), and fractal dimension of soil aggregates in compound soil with different organic material additions are superior to the control, and the effect of biochar on improving soil aggregates is better than that of corn straw. The combined application of both significantly improves the effect compared to single applications. In both culture modes, under wet sieving, the P3 treatment shows the highest MWD and GMD of soil aggregates, with an increase ranging from 3.45% to 85% and 4.55% to 38.46%, respectively, compared to other treatments. (3) The trend of fractal dimension among treatments is consistent: P3 < P2 < P1 < CK, and the differences between treatments are significant (P < 0.05). Moreover, there is a good negative correlation linear equation relationship between the fractal dimension (y) and WR > 0.25 (x) of compound soil, with a correlation coefficient of up to 0.9851. In conclusion, the incorporation of organic materials can effectively enhance the proportion of macroaggregates in compound soil consisting of Feldspathic sandstone and sand, thereby improving soil stability and erosion resistance. The optimal outcome is achieved through the combined application of biochar and straw. Indoor culture proves to be more effective than field culture, while wet sieving accurately reflects the structural characteristics of compound soil under both dry and wet sieving treatments.

Roles of soil minerals in the degradation of chlorpyrifos and its intermediate by microwave activated peroxymonosulfate

Soil mineral is one of the important factors that affecting oxidant decomposition and pollutants degradation in soil remediation. In this study, the effects of iron minerals, manganese minerals and clay minerals on the degradation of chlorpyrifos (CPF) and its intermediate product 3,5,6-trichloro-2-pyridinol (TCP) by microwave (MW) activated peroxymonosulfate (PMS) were investigated. As a result, the addition of minerals had slight inhibitory effect on the degradation efficiency of CPF by MW/PMS, but the degradation efficiency of TCP was improved by the addition of some specific minerals, including ferrihydrite, birnessite, and random symbiotic mineral of pyrolusite and ramsdellite (Pyr-Ram). The stronger MW absorption ability of minerals is beneficial for PMS decomposition, but the MW absorption ability of minerals cannot be fully utilized because of the weaker MW radiation intensity under constant temperature conditions. Through electron spin resonance test, quenching experiment and electrochemical experiment, electron transfer, SO4− and OH, SO4− dominated TCP degradation by MW/PMS with the addition of birnessite, Pyr-Ram and ferrihydrite, respectively. Besides, the adsorption effect of ferrihydrite also enhanced the removal of TCP. The redox of Mn (III)/Mn (IV) or Fe (II)/Fe (III) in manganese/iron minerals participated in the generation of reactive species. In addition, the addition of minerals not only increased the variety of alkyl hydroxylation products of CPF, causing different degradation pathways from CPF to TCP, but also further degraded TCP to dechlorination or hydroxylation products. This study demonstrated the synergistic effect of minerals and MW for PMS activation, provided new insights for the effects of soil properties on soil remediation by MW activated PMS technology.

Effects of Straw Addition on N2O and CO2 Emissions from Red Soil Subjected to Different Long-Term Fertilization

Straw return, as an important measure for soil fertility improvement in farmland, significantly affects the emissions of greenhouse gases N2O and CO2. Thus, the collected soil samples from five long-term (30-year) fertilization treatments (no fertilization, CK; recommended chemical fertilizer, F; 200 % of recommended chemical fertilizer, 2F; pig manure, M; and chemical fertilizer combined with pig manure, FM) were amended with and without straw and incubated under constant temperature and humidity conditions (25 ℃ and 65 % maximum field water holding capacity) for 20 days so as to investigate the key factors influencing N2O and CO2 emissions in response to straw addition in long-term fertilization treatments. The results showed that fertilization significantly increased N2O emissions. Compared to those under the unfertilized treatment[(22.05 ±2.09) μg·kg-1, calculated as nitrogen, the same as below], cumulative N2O emissions from the chemical fertilizer treatments significantly increased by 119 %-195 %[(48.38 ±20.81) μg·kg-1 and (65.13 ±12.55) μg·kg-1 from the F and 2F treatments, respectively], and those from the manure treatments increased by 275 %-399 %[(82.72 ±12.73) μg·kg-1 and (1 101.99 ±425.71) μg·kg-1 from the M and FM treatments, respectively]. Soil NO3--N, DOC, and DTN were the main factors influencing N2O emissions from fertilized treatments in the absence of straw addition. Straw addition significantly increased cumulative N2O emissions by 345 % and 247 % in the 2F and M treatments, respectively, compared to those in the corresponding fertilized treatments without straw addition, with no significant effect on N2O emissions in the CK, F, and FM treatments. Straw addition increased DOC content and microbial activity and decreased soil NO3--N and DTN contents, thereby increasing N2O emissions. Fertilization also significantly increased CO2 emissions. Compared to those from the unfertilized treatment, cumulative CO2 emissions from the manure treatments significantly increased by 120 %-130 %[(122.11 ±4.3) mg·kg-1 (calculated as carbon, the same as below) and (116.47 ±4.55) mg·kg-1 from the M and FM treatments, respectively], and those in the 2F treatment increased by 28 %[(65.13 ±12.55) mg·kg-1]. In the absence of straw addition, soil MBC, DOC, and DTN were the main factors influencing CO2 emissions. Compared to those in the treatments without straw addition, straw addition significantly increased cumulative CO2 emissions by 660 %-1132 % among fertilization treatments, due to increased DOC and MBC contents and enhanced microbial activity. In conclusion, straw addition significantly increased N2O and CO2 emissions through increased soil DTN consumption and DOC content among fertilization treatments. In soils treated with manure amendment, straw return should be rationally considered for the purpose of balancing the comprehensive trade-offs between fertility improvement and greenhouse gas emissions.

Numerical analysis of magnetohydrodynamic free stream and radiative heat transfer flow of nanofluid in a permeable medium over a linearly stretched cylinder with Arrhenius activation energy

This research article explores the transport characteristics of magnetohydrodynamic Newtonian nanofluid flowing past a stretching cylinder in a permeable medium, considering the activation energy effects using Buongiornos mathematical model. Unlike conventional studies employing constant temperature, concentration and density boundary conditions, convective boundary conditions are utilized in this investigation. The analysis incorporates various significant parameters such as magnetic field, joule heating, viscous dissipation, thermophoresis, Brownian motion, Arrhenius activation energy, and chemical reaction. The governing equations in the form of ODEs are obtained by employing similarity variables.The MATLAB built-in solver bvp4c is employed for obtaining the solutions. The impacts of these parameters on the velocity profile, temperature profile, concentration profile, density profile, skin friction coefficient, Sherwood number, and Nusselt number are elucidated through graphical and tabular representations. The results indicate that an increase in the chemical reaction parameter leads to higher nanoparticle concentration distributions, while the activation energy parameter exhibits the opposite trend. This study holds relevance for various practical applications in applied sciences, including nuclear reactor cooling, geothermal reservoirs, chemical engineering, and thermal oil recovery.