Dry Air Conditions Research Articles

The comparative investigation of oxidation behavior and corrosion mechanisms of SiC matrix ceramics under different atmospheres

The oxidation experiments of SiC matrix ceramics were conducted at 1200 °C for 10 h under three different atmospheres: dry air, water vapor, and a mixture of H2O/air. The oxidation behaviors and corrosion mechanisms were elucidated through phase and valence bond analysis, morphology examination, as well as elemental distribution analysis of the oxidized surface and cross section. Comparing the oxidation conditions among the three atmospheres, it was found that dry air exhibited the least degree of oxidation, while water vapor showed a more pronounced increase in oxidation. Notably, the most severe oxidative corrosion occurred in the presence of H2O/air mixed gas conditions. The formation of a dense oxide layer, consisting of precipitated Y2Si2O7 crystals which result from YAG boundary phase on SiC matrix ceramics under dry air conditions, can effectively provide protection against further oxidation. However, introduction of water leads to additional corrosion on this oxide layer, particularly when combined with air.

Enhanced protonic and oxygen-ionic conductivity in Ga-doped Nd2Ce2O7 electrolytes for intermediate-temperature solid oxide fuel cell

Developing mixed oxygen-ion and proton conductors with high ionic conductivity is crucial for advancing intermediate temperature-solid oxide fuel cell (IT-SOFC). In this study, a novel Nd2-xGaxCe2O7 (NGCO, x = 0, 0.05, 0.075, 0.10 and 0.15) ceramic is synthesized by the citric acid-nitrate sol-gel combustion process. The influence of Ga doping on crystal structure, oxygen vacancy, morphology, proton transport characteristic and electrochemical performance of this materials is systematically investigated. It is found that the NGCO exhibits the fluorite-type structure and belongs to space group Fm3¯m. NGCO shows remarkable chemical stability, resisting harmful effects from CO2, water, and wet hydrogen exposure. Adding a small amount of Ga results in high-density ceramics with enlarged grain size and reduced grain boundary density. Nd1.925Ga0.075Ce2O7 (7.5NGCO) displays outstanding conductivities, exceeding Nd2Ce2O7 (NCO) by 271.4% and 248.6% in dry air and wet hydrogen conditions. Further, an anode-supported structure fuel cell with 7.5NGCO electrolyte is constructed and evaluated. The peak power density (PPD) at 700 °C reaches 702 mW/cm2, a 96% enhancement over the fuel cells with NCO electrolyte. These findings indicate that Ga-doped NCO electrolyte holds promise as a proton-conducting electrolyte suitable for IT-SOFC.

Revealing the Impact of Aging on Perovskite Solar Cells Employing Nickel Phthalocyanine-Based Hole Transporting Material.

The enhancement of the photovoltaic performance upon the aging process at particular environment is often observed in perovskite solar cells (PSCs), particularly for the devices with 2,2',7,7'-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9'-spirobifluorene (spiro-OMeTAD)as hole transporting material (HTM). In this work, for the first time the effect of aging the typical n-i-p PSCs employing nickel phthalocyanine (coded as Bis-PF-Ni) solely as dopant-free HTM is investigated and as an additive in spiro-OMeTAD solution. This study reveals that the prolong aging of these devices at dry air condition (RH= 2%, 25°C) is beneficial for the improvement of their performances. Various bulk and surface characterization techniques are utilized to understand the factors behind the spontaneous efficiency enhancement of the devices after storage. As a result, the changes in properties of the Bis-PF-Ni layer are observed and at perovskite/Bis-PF-Ni interface, which ultimately improves the charge transport and reduces non-radiative recombination. In addition, the devices with Bis-PF-Ni HTM reveal enhanced long-term ambient and thermal stability compared to the PSCs based on doped spiro-OMeTAD.

Improving the oxidation resistance by forming continuous Al2O3 protective layer in alumina-forming austenitic stainless steel

The effect of varying aluminum (Al) levels on the high-temperature oxidation resistance of Alumina-Forming Austenitic stainless steels (AFA) has been investigated under dry air conditions at 800 °C and 900 °C. Mass gain assessments indicate that AFA stainless steel containing a higher concentration of Al, with a composition of Fe-20Ni-15Cr-2.4Al-1.6Mn, demonstrates enhanced resistance to oxidation when contrasted with steel of lower Al content, characterized as Fe-23Ni-15Cr-1.9Al. This phenomenon is attributed to the development of a compact CrMn1.5O4 layer on the exterior and an Al2O3 layer on the interior. The dense oxide layers that form on the high-Al steel impede the permeation of oxygen and deter the peeling of the oxide layer, thus preserving structural stability of the material upon exposure to high temperatures. Conversely, the steel with a lower Al content undergoes considerable chipping of its oxide layer. The morphology and distribution of Al2O3 are determined by the relative rates of oxygen inward movement and aluminum outward movement. In the case of the Fe-20Ni-15Cr-2.4Al-1.6Mn steel, the tight oxide film significantly reduces the inward movement of oxygen and increases the outward movement of Al, leading to a denser Al2O3 layer underneath the Cr2O3.

2D Amino-Functionalized Black Phosphorus: A New Approach to Improve Hydrogen Gas Detection Performance.

In recent years, hydrogen has gained attention as a potential solution to replace fossil fuels, thus reducing greenhouse gas emissions. The development of ever improving hydrogen sensors is a topic that is constantly under study due to concerns about the inherent risk of leaks of this gas and potential explosions. In this work, a new, long-term, stable phosphorene-based sensor was developed for hydrogen detection. A simple functionalization of phosphorene using urea was employed to synthesize an air-stable material, subsequently used to prepare films for gas sensing applications, via the drop casting method. The material was deeply characterized by different techniques (scanning electron microscopy, X-ray diffraction, X-ray photoelectron, and Raman spectroscopy), and the stability of the material in a noninert atmosphere was evaluated. The phosphorene-based sensor exhibited high sensitivity (up to 700 ppm) and selectivity toward hydrogen at room temperature, as well as long-term stability over five months under ambient conditions. To gain further insight into the gas sensing mechanism over the surface, we employed a dedicated apparatus, namely operando diffuse reflectance infrared Fourier transform, by exposing the chemoresistive sensor to hydrogen gas under dry air conditions.

Influence of drying condition on the drying constants and activation energy for robusta coffee using heat pump drying

Abstract Heat pump drying (HPD) is a method of drying agricultural products which has great potential due to its high efficiency and energy savings. Coffee is a heat sensitive product, HPD was chosen as an alternative to existing drying methods for coffee processing. Understanding of the HPD process is important to know for optimizing the coffee drying process with HPD especially in drying characteristics. The purpose of this research is to determine the number for the drying rate constant and the energy of activation in coffee drying. The material used in this study was wet parchment Robusta coffee beans (Coffea canephora). The research was carried out experimentally for 5 h at 700 lpm air flow with varying drying air conditions by adjusting the drying temperature and specific humidity. The drying temperatures used were 60, 65, 70, 75, and 80 °C. The drying temperature is limited to 80 °C based on SNI 7467-2008. Variations in specific humidity are determined based on temperature settings in the refrigeration system of 10, 15, 20 °C and without a refrigeration system. The maximum drying rate constant was 10.69×10-3 s-1, achieved at a temperature of drying variation of 80 °C while a specific humidity of 6.16 g H2O/kg dry air, while the minimum activation energy value was 23.43 kJ/mol at the same specific humidity. The lowest drying rate constant value was 5.79×10-3 s-1, achieved at a temperature of drying variation of 60 °C and a specific humidity of 17.24 g H2O/kg dry air, while the greatest activation energy level was 26.18 kJ/mol at the same specific humidity.

On the frequency dependence of the PDIV in twisted pair magnet wire analogy in humid air

The partial discharge inception voltage (PDIV) of low-voltage induction motor turn-turn insulation analogy is investigated for variable relative humidity (RH) of the surrounding air (temperature and pressure are kept constant close to their ambient values). Three materials, perfluoralkoxy alkane, sealed and unsealed alumina (UA), are employed as the dielectric coating (insulation) of test samples. Each material’s dielectric properties change differently with RH—of these, relative permittivity is regarded as the most crucial, as it was previously proven to be, along with the coating’s thickness, the key factor in determining the PDIV in dry air conditions. To further vary the value of permittivity and thus provide larger data sets for the verification study, the frequency of the excitation voltage is also varied between 1 Hz and 50 kHz. The obtained experimental data are compared against the PDIV predictions obtained by a breakdown model based on the reduced thickness of the coating (ratio of the coating thickness to its relative permittivity). Satisfying agreement between the measured and predicted PDIV are obtained for the first two materials, whereas significant discrepancies are seen for the UA material. For this case, surface conductivity is introduced into the prediction model and much better fits to the experimental data are obtained for a suitable value of surface resistance. It is hence demonstrated that the model is able to satisfactorily predict the PDIV for three substantially different materials when the RH of the surrounding air is varied between 10% – 80% .

Long-Term Oxidation Studies on Porous Stainless Steel 430L Substrate Relevant to Its Application in Metal-Supported SOFC

Metal-supported solid oxide fuel cells (MS-SOFCs) can be used in portable mobile power generators due to their excellent thermal cycling performance, low cost, and strong mechanical strength. The selection and lifetime of the support material are crucial factors that affect the cell’s performance and long-term stability. The oxidizability of porous 430L stainless steel in a dry air atmosphere at 800 °C was systematically studied and reported for up to 1500 h. The aim was to investigate the lifetime of porous stainless steel as a support skeleton in a symmetric MS-SOFC. The substrates were characterized and analyzed using scanning electron microscopy, energy spectroscopy, and X-ray diffractometry after different periods of oxidation. The analysis indicated that the porous substrate’s surface oxides, under dry air conditions, consisted primarily of Fe2O3 and Cr2O3, with small amounts of Fe3O4 and MnCr2O4 spinel. The long-term oxidation process can be divided into two stages with distinct characteristics. However, the oxide flaking phenomenon occurred after 1500 h of exposure. The estimated service life of the stainless steel was consistent with the experimental results, which were around 1500 h. This estimation was based on the measured weight gain and thickness data.

Experimental and simulation study of inert gas mixture inhibiting coal spontaneous combustion

To explore the mechanism of inhibiting spontaneous combustion of coal by mixed gases, the low-temperature oxidation characteristics of coal under different components of mixed gases were analyzed. ESR and FTIR experiments were used to investigate the effects of different gas mixtures on the activity of coal during low-temperature oxidation and the oxidation reaction of coal surface functional groups. The mechanism of chemical oxygen inhibition of mixed gas was studied by density functional theory. The results show that the larger the CO2 component in the mixed gas, the higher the ability to inhibit coal oxidation. The concentration of free radicals in coal under dry air condition is higher than that under inert mixed gas condition during oxidation heating at 30–230 °C. The oxidation ability of –CH3, –OH and oxygen-containing functional groups in the mixed gas reaction is inhibited. Through quantum chemistry calculation, it is found that the mixed gas increases the activation energy of free radicals and reduces the heat release of the reaction. This study provides theoretical reference for coal mine thermal disaster.

Impact of the drying air conditions on the milling quality of a long-grain rice variety at different moisture content ranges using a lab-scale dryer

During the harvest season, rice needs to be dried immediately to prevent deterioration. Therefore, the rice industry must have the capacity to dry fast while minimizing the milling quality loss. The aim of this study was to assess the impact of drying processing variables on milling quality and drying duration, at different stages of drying. To this purpose, a thin-layer lab-scale dryer was used at different drying air temperatures, relative humidities (RH), and grain moisture content (MC) ranges. At MC up to 15%, it was possible to dry at a temperature of 47ºC and 27% RH maintaining a low milling quality loss. At lower MC, the drying air temperature should decrease to 35ºC and 50% RH to maintain the milling quality loss low. This condition increases the drying duration (compared with drying at 47ºC). Therefore, a two-stage drying program was proposed, using more severe drying conditions during the first stage (MC up to 15%) and softening the conditions during the final stage (MC from 15 to 13%). This drying program allows decreasing the drying duration, maintaining a low milling quality loss. The implementation of step-wise drying programs is expected to increase the efficiency of the commercial process.

Direct CO2 capture from simulated and Ambient Air over aminosilane-modified hierarchical silica

Aminosilane-modified Hierarchical silica, HSA and HST-based adsorbents were synthesized by aminosilanization using Hierarchical silica (HS) with 3-aminopropyltriethoxysilane (APS) and N1-(3-trimethoxysilylpropyl)diethylenetriamine (TMPTA), respectively, and characterized to establish their physicochemical, structural, morphological, and porosity properties. Their CO2 adsorption performance was evaluated under direct air capture (DAC) conditions: 1) simulated air with CO2 concentration of 400 ppm in helium (He) at 30 °C and 2) indoor air with CO2 concentration ≥400 ppm at 30 °C, where HSA and HST modified with 70 wt% of respective aminosilanes outperformed others. The modified HS adsorbents showed an increase in kinetics, CO2 uptake under dry and humid conditions, stable cyclic adsorption-desorption performance, moderate enthalpy of desorption indicating a dominant chemisorption mechanism. Under dry and humid simulated air conditions (400 ppm CO2 in He), HSA-70 displayed a CO2 uptake of 0.82 mmol/g and 1.70 mmol/g, respectively, while HST-70 exhibited enhanced CO2 uptake of 1.54 mmol/g and 2.08 mmol/g, respectively. Cyclic stability of HSA-70 and HST-70 was confirmed through five thermal swing adsorption (TSA) cycles. In addition to this, their use for indoor air CO2 capture was also explored through ten short TSA cycles. Developed HSA-70 and HST-70 adsorbents exhibited more selectivity for CO2 over water, demonstrating their usage in practical direct air CO2 capture application.

Preparation and NH3 gas-sensing properties of Ag/β-AgVO3 nanorods.

NH3 gas sensors operating at room temperature, consisting of Ag nanoparticles decorated β-AgVO3 nanorods (Ag/β-AgVO3 NRs), were fabricated via a facile hydrothermal method without the need for a template. The surface characteristics and compositions of Ag/β-AgVO3 NRs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Ag nanoparticles, ranging in diameter from approximately 20 to 40 nm, were dispersed on the surface of monoclinic β-AgVO3 NRs with diameters ranging from 50 to 105 nm and lengths from 0.3 to 1.3 μm. The NH3 gas sensing properties of Ag/β-AgVO3 NRs were studied under both dry air and humid conditions at room temperature. Comparative analysis demonstrated that the Ag/β-AgVO3 NRs exhibited a strong response to NH3 gas under 70% relative humidity (RH) at room temperature compared to α-AgVO3 NRs. Specifically, the response of the Ag/β-AgVO3 NRs to 5 ppm NH3 increased by 2.25 times as the RH varied from 20% to 80% at room temperature. This enhanced response was attributed to the effects of formation of nanoheterojunctions, nano-metallic Ag activity and the conductivity of NH4+ and OH- ions induced by the presence of humidity. The room temperature NH3 gas sensors based on Ag/β-AgVO3 NRs demonstrated strong responses to low NH3 concentrations, high selectivity, good reproducibility, and long-term stability, and show promise for the development of low-power and cost-effective NH3 gas sensors for practical applications even under high humidity.

The effect of environmental variations on the production of the principal agricultural products in Colombia.

The agricultural sector of Colombia supports the national economy and food security due to the rich lands for cultivation. Although Colombia has a vast hydrological basin, climate change can impact agricultural productivity, generating economic and social adverse effects. For this, we evaluated the impact of some environmental variables on the production of the most sold crops using production, climatic, and hydrological data of the 1121 municipalities from 2007 to 2020. We modeled the production of coffee, rice, palm oil, sugarcane, and corn, adopting a Bayesian spatio-temporal model that involved a set of environmental variables: average temperature, minimum temperature, maximum temperature, evapotranspiration, precipitation, runoff, soil moisture, vapor pressure, radiation, and wind speed. We found that increases in the average temperatures can affect coffee (-0.2% per °C), rice (-3.76% per °C), and sugarcane (-0.19% per °C) production, meanwhile, these increases can boost palm oil (+2.55% per °C) and corn (+1.28% per °C) production in Colombia. This statement implies that the agricultural sector needs to substitute land use, promoting the production of palm oil and corn. Although our results did not find a significant effect of hydrological variables in any crop, suggesting that the abundance of water in Colombia might balance the impact of these variables. The increases in vapor pressure impact all the crops negatively (between -11.2% to -0.43% per kPa), except rice, evidencing that dry air conditions affect agricultural production. Colombia must manage the production location of the traditional products and implement agro-industrial technologies to avoid the climate change impact on crops.

Effectiveness of potato late blight (Phytophthora infestans) forecast by meteorological estimation in mountainous terrain based on CARAH rules

Potato late blight (PLB) caused by Phytophthora infestans (Mont.) de Bary, its incidence and development are highly dependent on meteorological conditions. To solve the problem of PLB in mountainous terrain under the condition of limited meteorological monitoring capability, the air temperature and humidity was estimated based on the basic meteorological datasets, the forecast effect of the onset period and infection cycle of PLB based on CARAH rules was evaluated. The average MAE, RMSE and CI of the estimated air temperature and observations were 1.17 °C, 1.52 °C and 0.95, respectively. The average MAE, RMSE and CI of the estimated relative humidity and observations were 8.0 %, 10.7 % and 0.53, respectively. The curve of the infection cycle of PLB at different locations were estimated from the basic meteorological datasets based on the CARAH rules, and the false alarm and missing ratios were 8.8 % and 4.6 % respectively. It may be delayed by 1 or 2 fungal generations compared to the observations, and then the protective fungicide should be adjusted to a systemic fungicide. The false alarm of the infection cycle of PLB may increase in dry air conditions, and the missing report may occur in humid condition.

Effect of water spray on tip leakage flow in a inlet stage of high-speed compressor

Water spray can reduce the inlet air temperature of the compressor inlet stage of the high-altitude high-speed turbine engine. In this paper, the Euler-Lagrange method is used to simulate the gas-liquid two-phase flow with droplet evaporation in NASA Stage 35. The effects of water spray on the heat and mass transfer characteristics of the stage, the tip leakage vortex structure, the unsteady characteristics of tip leakage flow and compressor performance are analyzed. The results show that the water spray increases the inlet mass flow and tip leakage flow rate of the stage, decreases the tip temperature. The inlet mass flow and tip leakage flow rate increase with the growth of inject mass flow rate and the decrease of droplet size. Water spray increases the scale of the main tip leakage vortex, and deflects the secondary leakage flow in the flow direction. Water spray increases the amplitude of pressure fluctuation at the blade tip. The frequency of pressure fluctuation at dry air condition is 0.2BPF, which decreases to 0.15BPF after water spraying. The leakage vortex weakens the strength of shock wave which causes a decline in the diffusing ability of blade; the leakage vortex is mixed with the main stream, resulting in a large aerodynamic loss. Although the injection of droplets increases the loss of tip leakage flow, it optimizes the performance of NASA stage 35 significantly. Spray increases the total pressure ratio of the R domain from 1.835 to 1.9; the total temperature ratio of the stage reduces from 1.225 to 1.203 and decreases the rotor loss coefficient from 0.12 to 0.08.

Vacuum ultraviolet-induced surface modification of polyoxymethylene plates for photo-activation bonding

The surface photoactivation technique using vacuum ultra-violet (VUV) light at 172 nm in wavelength has been applied for adhesive-free bonding of polyoxymethylene (POM) plates. The POM surfaces were photochemically modified via VUV light irradiation in dry air conditions, resulting in the formation of oxygen-containing functionalities. The POM plates were successfully bonded with a practical bonding strength below the melting point. The maximum bonding strength was obtained at an irradiation time of 60 min, while a longer irradiation time resulted in lower bonding strength. Surface morphologies of the photoactivated and fractured POM surfaces were observed by a laser scanning microscope. Due to the VUV irradiation, numerous cracks were formed on the POM surfaces. The fractured surface shows that a cohesive failure occurs at the bonding interface. Atomic force microscopy was used to observe the cross-sectional images of the bonding samples. Around 10 μm width, significant phase contrast between the bonding interface and bulk POM indicates the different mechanical properties, due to VUV irradiation. The modified POM surfaces adhered through thermocompression, and the mechanical interlocking and entanglement of POM molecules can result in successful bonding.

Experiment and Improvement Mechanism Analysis on the Mechanical Properties of Improved Chlorine Saline Soil

Chlorine saline soil has adverse engineering geology such as dissolution, collapse, and pulping, the recycling of saline soil in subgrade treatment is of great research significance. First, the unconfined compressive strength (UCS) test was conducted using an orthogonal test design, and the optimal ratios of salt content, cement content, lime content, fiber content, and fiber length were determined. Second, the cyclic loading (CL) test was conducted using an orthogonal test design, and the influence of five factors, including freeze–thaw (FT) times, CL times, stress level (SL), amplitude, and frequency, on peak intensity, peak strain, and cumulative strain under FT cycles and natural air-drying (A-D) conditions were determined. Finally, the improvement mechanism of the above inorganic materials was microscopically analyzed by scanning electron microscope-energy dispersive spectrometer and X-ray diffraction tests. The UCS test results show that the improving effect of the optimal ratio for chlorine saline soil was best when the optimal ratio values were 3% (salt content), 8% (cement content), 12% (lime content), 0.2% (fiber content), and 18 mm (fiber length). CL test results show that with the increase in natural A-D time, it was found that the FT number and SL have significant effects on the strength, the number of FT times and cycle times have significant effects on the deformation, and the frequency and cycle times have significant effects on the cumulative deformation. From the microstructure analysis, the improvement mechanism is mainly the filling of pores and linking particles by water-hard gels and gas rigid gels to make the microstructure dense, effectively reduce pores, and effectively improve the engineering characteristics of chlorine saline soil. The results of this study provide a scientific basis for the engineering design of subgrade in arid areas and the in situ recycling of saline soil.

Quality and safety aspects of traditionally air-dried and nitrite-free meat product with reduced salt level

This paper studies the effect of reduced sodium chloride amounts (3%, 5% and 7%) on the quality aspects and safety elements of traditionally salted ham without any nitrates and nitrites added, dried and ripened under natural air-drying conditions. The physicochemical and textural properties, the degree of proteolysis, the microbiological characteristics and sensory profile of dry-cured ham were analysed at different production stages. A salting degree above 3% in the manufacture of this traditional dried product had a key role in the development of the desired microbiological and sensory characteristics in the absence of nitrites. Salting of the pork hams with 5% and 7% sodium chloride for 45 days at a temperature of 2±2 °С ensured a salt concentration and water activity that would guarantee the product safety with regard to the microbiological risks during the subsequent drying and ripening under natural air-drying conditions. The Elena ham samples salted with 5% sodium chloride and ripened for a period of 12 months in natural air-drying chambers were characterized as having the most balanced flavor.

Estimation of effective water vapour diffusion and mass transfer during quinoa (Chenopodium quinoa Willd.) drying

This study shows the modeling of the convective drying operation of quinoa (Chenopodium quinoa Willd. var. Hualhuas) grains implemented in the General Algebraic Modeling System (GAMS) software. The proposed model was based on Fick’s second law. The drying experiences were carried out using a pilot-scale oven. The drying air conditions were: 40, 60, and 80°C and 0.2 and 0.7 m s-1. The mathematical modeling was employed to describe the behavior of the drying operation according to variations of the average moisture over time. The effective diffusivity of moisture and mass transfer were studied for the different operating conditions. The model was validated by experimental data. It was possible to model the quinoa grains drying process, obtaining a high precision between the experimental and estimated values. Quinoa drying curves can be represented properly by the studied model. In the operating ranges tested, the effective diffusivity values of moisture were between 2.52 10-10 and 1 10-9 m2 s-1 and the mass transfer values were between 7.20 and 11.47 cm s-1. The effective diffusivity (Deff) showed significant differences (P<0.05) with the speed of the drying air, while the mass transfer coefficient (k) was significantly affected (P<0.05) by the temperature of the drying air.

Convective drying of iron ore fines: A CFD model validated for different air temperatures and air velocities

In this research, a granular Eulerian multiphase model coupled with heat and mass transfer was used to simulate the convective drying process of iron ore fines. The CFD model was validated with experimental data for different air temperatures and air velocities. Convective drying experiments were performed using laboratory-scale equipment in order to obtain drying kinetics data for iron ore fines at air temperatures up to 140 °C and air velocities up to 15 m/s. The drying system had combined characteristics of fluidized bed and pneumatic transport. Numerical results showed good agreement with experimental data (average RMSE of 3.9 × 10−3) for the moisture content for nine drying air conditions. Since the coupled momentum, heat and mass transfer model could accurately and validly estimate the drying rate for iron ore fines according to the local conditions of the drying air in laboratory-scale equipment, it has potential for application in CFD simulations of industrial-scale equipment.