Gas Transfer Research Articles

Sirolimus suppresses circulating fibrocytes in idiopathic pulmonary fibrosis in a randomized controlled crossover trial.

Fibrocytes are bone marrow-derived circulating cells that traffic to the injured lungs and contribute to fibrogenesis. The mTOR inhibitor, sirolimus, inhibits fibrocyte CXCR4 expression, reducing fibrocyte traffic and attenuating lung fibrosis in animal models. We sought to test the hypothesis that short-term treatment with sirolimus reduces the concentration of CXCR4+ circulating fibrocytes in patients with idiopathic pulmonary fibrosis (IPF). We conducted a short-term randomised double-blind placebo-controlled crossoverpilot trial to assess the safety and tolerability of sirolimus in IPF. Subjects were randomly assigned to sirolimus or placebo for approximately 6 weeks, and after a 4 week washout, assigned to the alternate treatment. Toxicity, lung function, and the concentration of circulating fibrocytes were measured before and after each treatment. In the 28 study subjects, sirolimus resulted in a statistically significant 35% decline in the concentration of total fibrocytes, 34% decline in CXCR4+ fibrocytes, and 42% decline in fibrocytes expressing ɑ-smooth muscle actin, but no significant change in these populations occurred on placebo. Respiratory adverse events occurred more frequently during treatment with placebo than sirolimus; the incidence of adverse events and drug tolerability did not otherwise differ during therapy with drug and placebo. Lung function was unaffected by either treatment with the exception of a small decline in gas transfer during treatment with placebo. As compared with placebo, short-term treatment with sirolimus resulted inreduction of circulating fibrocyte concentrations in subjects with IPF with an acceptable safety profile. gov identifier number NCT01462006FUNDING. NIH R01HL098329 and American Heart Association 18TPA34170486.

Individual Effects of Alkali Element and Wire Structure on Metal Transfer Process in Argon Metal-Cored Arc Welding.

This study aimed to clarify the effect of wire structure and alkaline elements in wire composition on metal transfer behavior in metal-cored arc welding (MCAW). A comparison of metal transfer in pure argon gas was carried out using a solid wire (wire 1), a metal-cored wire without an alkaline element (wire 2), and another metal-cored wire with 0.084 mass% of sodium (wire 3). The experiments were conducted under 280 and 320 A welding currents, observed by high-speed imaging techniques equipped with laser assistance and bandpass filters. At 280 A, wire 1 showed a streaming transfer mode, while the others showed a projected one. When the current was 320 A, the metal transfer of wire 2 changed to streaming, while wire 3 remained projected. As sodium has a lower ionization energy than iron, the mixing of sodium vapor into the iron plasma increases its electrical conductivity, raising the proportion of current flowing through metal vapor plasma. As a result, the current flows to the upper region of the molten metal on the wire tip, with the resulting electromagnetic force causing droplet detachment. Consequently, the metal transfer mode in wire 3 remained projected. Furthermore, weld bead formation is the best for wire 3.

Dimensionless Parameterizations of Air-Sea <em>CO</em><sub>2</sub> Gas Transfer Velocity on Surface Waves

Accurate quantification of air-sea gas transfer velocity is critical for our understanding of air-sea CO2 gas fluxes, global carbon budget and climate responses. CO2 transfer velocity is predominantly subject to constraints of wave-related dynamic processes at the ocean surface layer but is typically parameterized with wind speed. This study proposes and compares two parameterizations which accommodate dimensionless wave terms. The validations are conducted using both laboratory and field measurements of CO2 transfer and wave statistics. A scaling of bubble-mediated gas transfer is implemented into the formula that is linked to wave breaking probability. The improved parameterizations are capable of collapsing combined laboratory and field data sets which comprise diversified conditions of wind, wave and wave breaking.

Multiple upscaling procedures for gas transfer in tight shale matrix-fracture systems

Multiple upscaling schemes for gas transfer in nanoporous media, microporous matrix, core-scale matrix, and centimeter-scale matrix-fracture systems are investigated. An Open Multi-Processing (OpenMP)-based parallelized multi-scale numerical solver for micro-gaseous flow in composite microporous media is developed by coupling the pore-scale multiple-relaxation-time lattice Boltzmann method (MRT-LBM) and representative elementary volume (REV)-scale LBM model. The permeability of the microporous matrix is calculated through hundreds of pore-scale simulations for gas transfer in nanoporous media, before being imported into the REV-scale LBM to predict the core-scale matrix permeability. It is followed by the investigations of the variations of core-scale permeability with the heterogeneous spatial distribution of organic matter aggregates, mineral aggregates, interparticle pores, and microfractures. The parallel and sequential gas transfer processes in a larger shale system containing the tight matrix and hydraulic fractures are studied and analyzed. The results reveal several new insights: 1) the microscale spatial distribution of multiple constituents has relatively little effect on the core-scale permeability; 2) an ultra-large local pressure gradient occurs in a thin boundary layer of tight shale matrix, which is shown to be proportional to the square root of the permeability ratio, resulting in considerable flow characteristic velocity in the matrix; 3) the in-situ matrix-fracture transfer satisfies a sequential transport process due to a long equilibration time delay between the tight matrix and fractures; 4) the observed high production rate for tight shale may be caused by the ultra-large local pressure gradient in the matrix (and not by a large apparent permeability as commonly assumed). The results also reveal some anomalous phenomena for multiscale gas transfer in tight shale formations.

Mass transfer dynamics of single CO2 bubbles rising in monoethanolamine solutions: Experimental study and mathematical model

Carbon dioxide (CO2) absorption into amine-based absorbents is a widely used method for carbon emission reduction to deal with global warming problems. The intensification of the absorption process relies on an in-depth understanding of the mass transfer mechanisms between CO2 gas and the reaction media. However, the influence of products of a chemical reaction on mass transfer dynamics is usually underestimated. In this study, we perform research studies on the absorption process of single CO2 bubbles rising in monoethanolamine (MEA) solutions. Firstly, we perform an experimental study to visualize and measure the spatial position and the diameter of the bubbles using the high-speed camera. We observe a special phenomenon that the CO2 bubble diameter rapidly decreases to a nearly constant value in MEA solutions, and the terminal bubble diameter increases with the MEA concentration. Based on the phenomenon, we divide the absorption process into two stages. One is the mass transfer enhancement stage, where the bubble diameter decreases rapidly. The other is the mass transfer deterioration stage, where the bubble diameter remains almost constant. Furthermore, we propose an elaborate mass transfer dynamics model considering the combined effect of chemical reaction kinetics and reaction-induced bubble surface contamination. Finally, a well-predictive performance by the mass transfer dynamics model is validated by experiment. The findings of this study are of theoretical and practical significance for the mass transfer in gas–liquid reactive flow and multiphase reactor design.

Gas flow characteristics of GCL under distortions, wet-dry cycles, and hydrating fluids

Geosynthetic clay liner (GCL) is commonly used in cover system of engineered landfill to limit migration of gases and infiltration of water. In engineered landfill, gas transfer occurs by advection and diffusion, which may take place at different time frames or simultaneously depending on placement conditions. Hence, efficacy of GCL as a gas barrier under advection and diffusion needs to be assessed at various geoenvironmental settings. In the present study, the gas flow response of GCL under advection and diffusion were evaluated at various apparent degrees of saturation, distortion levels, hydrating fluids, and wet-dry cycles using custom-designed test apparatus. Gas permeability and gas diffusion coefficient of GCL were found to decrease by four and three orders of magnitude respectively with an increase in apparent degree of saturation from 7% to 80%. Gas permeability and gas diffusion coefficient were increased with an increase in distortion levels. With an increase in wet-dry cycles 1 to 5, gas permeability and gas diffusion of GCL were increased marginally when hydrated with distilled water while increased by one order of magnitude for hydrated with 0.0125 M CaCl2 solution. The obtained results were compared with published results and found to be in good agreement.

Study on the 4-channel micro-monolithic design with geometry control for reversible solid oxide cell

Reversible solid oxide cell (R-SOC) has been attracting considerable attention as a technology capable of power generation and CO2 electrolysis. In addition to new material development, innovation in structural design is also a decisive factor. In this study, a 4-channel micro-monolithic design, in the form of a tear-drop inner channel structure, was successfully developed. The micro-monolith obtained includes plurality of micro-channels growing from multiple directions and spongy active regions near the exterior surface. Uniquely, the irregular tear-drop inner channels further increase the proportion of the electrochemically active region to the overall circumference, achieving more efficient utilization of the geometric surface area. Such micro-structured cells with Ni-YSZ/YSZ/YSZ-LSM materials exhibited effective performance in the reversible operation of R-SOC. A superior performance of 1.20 W·cm−2 at 800 ℃ for H2 fuel cell was demonstrated. Similarly, during the electrolysis of CO2, current density recorded by the cells reached 1.20 A·cm−2 at 1.5 V and 800 ℃, which is competitive compared with the values of the previous design investigations. Relatively low diffusion polarization shown in electrochemical impedance spectroscopy (EIS) suggests that this is due to the very gas transfer resistance in the fuel electrode. This novel multi-channel micro-monolithic structure shows a potential to substitute the conventional tubular counterpart.

Hierarchical porous metal organic framework aerogel for highly efficient CO2 adsorption

Sustainable low-carbon economy has attracted global attention, and the development of advanced CO2 capture technology has become an important undertaking. Metal organic frameworks (MOFs) featured with high specific surface area and large porosity have held the promise for CO2 adsorption, but the micron scale make them difficult to handle, leading to easily be blown away, pipeline blockage, and the decline of adsorption capacity. Here, we demonstrate a novel strategy to develop a nanoporous HKUST-1 aerogel with hierarchical pore structure by combining HKUST-1 and aramid nanofiber for promoting CO2 adsorption. The resultant HKUST-1 aerogel has a low density of 5.86 mg/cm3, high specific surface area of 636.62 m2g−1, and hierarchical porosity of 99.33 %. The meso-/macropores of HKUST-1 aerogel can act as gas transfer channels to facilitate the transport CO2 into the HKUST-1, and the micropores of HKUST-1 provide active sites for CO2 adsorption. Benefitting from the synergistic effect of the hierarchical pore structure, the HKUST-1 aerogel demonstrates high CO2 adsorption capacity of 7.29 mmol/g, and high adsorption selectivity of 39 for CO2/N2 and 42 for CO2/O2. This novel design may provide a reliable theoretical and experimental basis for the development of MOF aerogel as CO2 adsorbent candidate for environmental purification.

Sensitivity analysis of structural parameters for PEMFCs based on 1D transient model and elementary effect method

ABSTRACT To investigate the influences of structural parameters on output performances and further quantify the degree of influences, a one-dimensional transient multiphase proton exchange membrane fuel cell (PEMFC) model and a global sensitivity analysis model were established. After rigorous model validation, structural parameters such as the thickness of proton exchange membrane (MEM), catalytic layer (CL), micro-porous layer (MPL), and gas diffusion layer (GDL) as well as the porosity of CL, MPL, and GDL were studied. The ionomer volume fraction of cathode and anode were also studied. Increasing the thickness of MEM and CL decreases the membrane water content and increases the ohmic voltage loss. The increase of thickness leads to longer reaction gas transfer path and increase of transfer resistance. The increase of porosity increases the concentration of the reaction gas . However, too high porosity will reduce the effective ion conductivity . The increase of ionomer volume fraction is beneficial to electrochemical reaction. Based on quantitative sensitivity analysis, the MEM thickness and the anode ionomer volume fraction are defined as highly sensitive parameters. The MPL thickness and the GDL porosity are defined as insensitive parameters. The sensitivity of MEM thickness, CL thickness, and anode ionomer volume fraction become more prominent in large current density regions.

320 Oxygenated Peritoneal Perfluorodecalin Improves Response to Normobaric Hypoxic Exposure in Swine

OBJECTIVES/GOALS: Patients suffering from respiratory failure have few options to support oxygenation and carbon dioxide removal aside from mechanical ventilation. Our objective was to test a novel extrapulmonary mechanism of gas exchange via peritoneal oxygenated perfluorocarbon (PFC) in a large animal model. METHODS/STUDY POPULATION: Using two 50 kg swine, hypoxia was modeled with subatmospheric oxygen and hypercarbia induced with acute hypoventilation. Through a midline laparotomy, cannulas were placed into the peritoneal space to allow for PFC infusion and circulation. After abdominal closure, these cannulas were connected to a device capable of draining, oxygenating, and infusing PFC. One animal was subjected to acute hypoxia (12% FiO2) and another animal to acute hypoventilation (4 breaths per minute). Primary outcomes were times for SpO2 to reach 75 mmHg, respectively. Trials were performed without PFC and with PFC dwelling or circulating through the peritoneal space, during which abdominal and bladder pressures were monitored and maintained under 20 mmHg by regulation of the PFC volume contained in the animal. RESULTS/ANTICIPATED RESULTS: In the animal subjected to acute hypoxia (12% FiO2), survival time improved from 5:55 to 20:00 (min:sec) after 2.5 liters of oxygenated PFC was instilled in the peritoneal space. Oxygen percent saturation of PFC before and after dwelling in the peritoneal space was measured at 100% before and 70% after dwelling in the animal during this hypoxic period corresponding with a gas transfer of 300 mL of oxygen over the 20-minute trial (i.e., 15 mL/min). Continual PFC circulation did not further extend the survival time during hypoxic conditions over PFC dwelling in the abdomen. In the animal that was acutely hypoventilated, there were no detectable differences in the rate of CO2 accumulation as measured by EtCO2 or direct blood pCO2 measurements with PFC dwelling or circulating through the peritoneal space. DISCUSSION/SIGNIFICANCE: Oxygenated PFC dwelling in the peritoneal space increased the duration of systemic arterial blood saturation remaining greater than 50% during normobaric hypoxic (12% FiO2) conditions but did not appreciably clear blood carbon dioxide during hypoventilation. Future experiments will focus on maximizing the rate of systemic oxygen uptake.

Mechanisms of gas transfer impairment utilizing nitric oxide following severe COVID-19 pneumonitis.

Reduced carbon monoxide diffusing capacity (DLCO ) is common after recovery from severe COVID-19 pneumonitis. The extent to which this relates to alveolar membrane dysfunction as opposed to vascular injury is uncertain. Simultaneous measurement of nitric oxide diffusing capacity (DLNO ) and DLCO can partition gas diffusion into its two components: alveolar-capillary membrane conductance (DmCO ) and capillary blood volume (VC ). We sought to evaluate DmCO and VC in the early and later recovery periods after severe COVID-19. Patients attended for post-COVID-19 clinical review and lung function testing including DLNO /DLCO . Repeat testing occurred when indicated and comparisons made using t-tests. Forty-nine (eight female) subjects (mean ± SD age: 58 ± 13, BMI: 34 ± 8) who had severe COVID-19 pneumonitis, WHO severity classification of 6 ± 1, and prolonged (21 ± 22 days) hospital stay, were assessed 2 months (61 ± 35 days) post discharge. DLCO adj (z-score -1.70 ± 1.49, 25/49 < lower limit of normal [LLN]) and total lung capacity (z-score -1.71 ± 1.30) were both reduced. DmCO and VC and were reduced to a similar extent (z-score -1.19 ± 1.05 and -1.41 ± 1.20, p = 0.4). Seventeen (one female) patients returned for repeat testing 4 months (122 ± 61 days) post discharge. In this subgroup with more impaired lung function, DLCO adj improved but remained below LLN (z-score -3.15 ± 0.83 vs. -2.39 ± 0.86, p = 0.01), 5/17 improved to >LNN. DmCO improved (z-score -2.05 ± 0.89 vs. -1.41 ± 0.78, p = 0.01) but VC was unchanged (z-score -2.51 ± 0.55 vs. -2.29 ± 0.59, p = 0.16). Alveolar membrane conductance is abnormal in the earlier recovery phase following severe COVID-19 but significantly improves. In contrast, reduced VC persists. These data raise the possibility that persisting effects of acute vascular injury may contribute to gas diffusion impairment long after severe COVID-19 pneumonitis.

Novel Size-Variable Dedicated Rodent Oxygenator for ECLS Animal Models—Introduction of the “RatOx” Oxygenator and Preliminary In Vitro Results

The overall survival rate of extracorporeal life support (ECLS) remains at 60%. Research and development has been slow, in part due to the lack of sophisticated experimental models. This publication introduces a dedicated rodent oxygenator (“RatOx”) and presents preliminary in vitro classification tests. The RatOx has an adaptable fiber module size for various rodent models. Gas transfer performances over the fiber module for different blood flows and fiber module sizes were tested according to DIN EN ISO 7199. At the maximum possible amount of effective fiber surface area and a blood flow of 100 mL/min, the oxygenator performance was tested to a maximum of 6.27 mL O2/min and 8.2 mL CO2/min, respectively. The priming volume for the largest fiber module is 5.4 mL, while the smallest possible configuration with a single fiber mat layer has a priming volume of 1.1 mL. The novel RatOx ECLS system has been evaluated in vitro and has demonstrated a high degree of compliance with all pre-defined functional criteria for rodent-sized animal models. We intend for the RatOx to become a standard testing platform for scientific studies on ECLS therapy and technology.

Cavitation Modeling Using Lumped Parameter Approach Accounting for Bubble Dynamics and Mass Transport Through the Bubble Interface

AbstractVaporous and gaseous cavitation cause several physical phenomena which are typically undesirable, such as reduction in compressibility and material damage. Therefore, the ability to capture these effects in simulation is highly valued. In the fluid power field, lumped parameter modeling technique has proven effective for analyzing components and systems, allowing for fast simulations. Past efforts in modeling cavitation using lumped parameter approach have assumed dependence of fluid properties such as bulk modulus, density, and viscosity directly to pressure and temperature. This cannot be considered as the fluid mixture is composed of different phases of matter. Some other formulations account for gaseous cavitation based on the equations that are derived from vaporous cavitation. This paper illustrates a better approach that combines the two cavitation effects by considering that both vapor and undissolved gas co-occupy a spherical bubble. The size of the spherical bubble is solved using the Rayleigh–Plesset equation, and the transfer of gas through the bubble interface is solved using Henry's law and diffusion of the dissolved gas in the liquid. These equations are coupled with a novel pressure derivative equation. To show the validity of the proposed approach, the instantaneous pressure of a closed fluid volume undergoing expansion/compression is compared with multiple experimental sources, showing an improvement in accuracy when compared to existing models. Integrating this modeling technique with current displacement chamber simulation can further improve the understanding of cavitation in hydraulic systems.

Anion‐pillared microporous material incorporated mixed‐matrix fiber adsorbents for removal of trace propyne from propylene

AbstractSeparation and purification of light hydrocarbons have been the critical processes for producing basic chemicals and polymers in petrochemical industry. Adsorbents with high performance are highly demanded for the separation of light hydrocarbons. However, the adsorbents filling in the packed bed when evaluated will inevitably induce reduced performance and increased pressure drop that considerably impede their application. Herein, mixed‐matrix fiber adsorbents with anion‐pillared hybrid microporous materials (SIFSIX‐2‐Cu‐i) embedded within poly (ether sulfone) (PES) are constructed to enable an energy‐efficient propylene/propyne separation. Owing to the sufficient binding sites and abundant channels for selective gas transfer, the fiber adsorbents achieve high C3H4 uptake capacity of 0.963 mmol g−1 in the propylene/propyne (99/1) mixture breakthrough experiments. Moreover, fiber adsorbents exhibit good tolerance toward high gas velocity and show distinctively low pressure drop, which will be advantageous in industrial applications. This work provides a strategy for fabricating high‐performance mixed‐matrix fiber adsorbents.

Longitudinal Lung Function Assessment of Patients Hospitalized With COVID-19 Using 1H and 129Xe Lung MRI

Microvascular abnormalities and impaired gas transfer have been observed in patients with COVID-19. The progression of pulmonary changes in these patients remains unclear. Do patients hospitalized with COVID-19 without evidence of architectural distortion on structural imaging exhibit longitudinal improvements in lung function measured by using 1H and 129Xe MRI between 6 and 52weeks following hospitalization? Patients who were hospitalized with COVID-19 pneumonia underwent a pulmonary 1H and 129Xe MRI protocol at 6, 12, 25, and 51weeks following hospital admission in a prospective cohort study between November 2020 and February 2022. The imaging protocol was as follows: 1H ultra-short echo time, contrast-enhanced lung perfusion, 129Xe ventilation, 129Xe diffusion-weighted, and 129Xe spectroscopic imaging of gas exchange. Nine patients were recruited (age 57 ± 14 [median ± interquartile range] years; six of nine patients were male). Patients underwent MRI at 6 (n= 9), 12 (n= 9), 25 (n= 6), and 51 (n= 8) weeks following hospital admission. Patients with signs of interstitial lung damage were excluded. At 6weeks, patients exhibited impaired 129Xe gas transfer (RBC to membrane fraction), but lung microstructure was not increased (apparent diffusion coefficient and mean acinar airway dimensions). Minor ventilation abnormalities present in four patients were largely resolved in the 6- to 25-week period. At 12weeks, all patients with lung perfusion data (n= 6) showed an increase in both pulmonary blood volume and flow compared with 6weeks, although this was not statistically significant. At 12weeks, significant improvements in 129Xe gas transfer were observed compared with 6-week examinations; however, 129Xe gas transfer remained abnormally low at weeks 12, 25, and51. 129Xe gas transfer was impaired up to 1 year following hospitalization in patients who were hospitalized with COVID-19 pneumonia, without evidence of architectural distortion on structural imaging, whereas lung ventilation was normal at 52weeks.

Air–sea gas exchange in a seagrass ecosystem – results from a 3He ∕ SF6 tracer release experiment

Abstract. Seagrass meadows are some of the most productive ecosystems in the world and could help to mitigate the increase of atmospheric CO2 from human activities. However, understanding the role of seagrasses in the global carbon cycle requires knowledge of air–sea CO2 fluxes and hence knowledge of the gas transfer velocity. In this study, gas transfer velocities were determined using the 3He and SF6 dual tracer technique in a seagrass ecosystem in south Florida, Florida Bay, near Bob Allen Keys (25.02663∘ N, 80.68137∘ W) between 1 and 8 April 2015. The observed gas transfer velocity, normalized for CO2 in freshwater at 20 ∘C, k(600), was 4.8 ± 1.8 cm h−1, which was lower than that calculated from published wind speed/gas exchange parameterizations. The deviation in k(600) from other coastal and offshore regions was only weakly correlated with tidal motion and air–sea temperature difference, implying that wind is the dominant factor driving gas exchange. The lower gas transfer velocity was most likely due to wave attenuation by seagrass and limited wind fetch in the study area. A new wind speed/gas exchange parameterization is proposed (k600=0.143u102), which might be applicable to other seagrass ecosystems and wind-fetch-limited environments.

Hydrodynamics and liquid–liquid mass transfer in gas–liquid–liquid three-phase flow in a cross microchannel

Gas-liquid–liquid three-phase flow in cross microchannels has been widely used in flow chemistry and process intensification. At present, the flow and mass transfer characteristics in this type of channel are not well understood. In this work, the hydrodynamics and liquid–liquid mass transfer characteristics of gas–liquid–liquid three-phase flow were systematically investigated. For the gas–liquid–liquid hydrodynamics, the general regulation laws of bubble and droplet size were obtained by considering the synergistic effect of shearing phases, and the bubble/droplet size prediction model based on the multiphase cooperative behavior was proposed, which could be used in predicting droplet/bubble size in flow systems. For the gas–liquid–liquid mass transfer process, the experimental results showed that the mass transfer coefficient first increased and then decreased with the increase of gas flow rate when the oil phase flow rate was fixed. The semi-empirical prediction formula of the mass transfer coefficient was obtained by considering the vortex strength, the interfacial area and the effective mass transfer area at the same time, which was in good agreement with the experimental results. This work could be the comprehensive study of gas–liquid–liquid three-phase flow and liquid–liquid mass transfer under gas enhancement in a cross microchannel.

Application of CFD-DSMC coupling method in H2 flow and heat transfer in microtube

In the research of porous media and the interior of microelectronic devices, fluids frequently shuttle among pores and wall cracks, therefore it is of great significance to explore the influence of media wall on fluid flow and heat transfer. In this paper, CFD-DSMC coupled iterative algorithm is first used in the research of the flow and heat transfer of gas near the wall in the porous media, which simplified into the flow and heat transfer in micron-scale tube with smooth and rough wall conditions. It is found that compared with the pure CFD method, the velocity field obtained by the coupled method is quite different in the region close to the wall, and this will affect the flow field in the mainstream region, that is, with the higher roughness of the wall, the velocity in the central region will be smaller. There is no significant difference in the temperature distribution in the microtube before and after coupling, but the temperature in the mainstream decreases with the increase of the roughness of the wall. In addition, the temperature jump was found from some of the coupling results close to the wall. The results will contribute to a deeper understanding of the influence of rough surfaces on gas flow and heat transfer near the wall, and provide guidance for the regulation of flow and heat transfer in porous media.

Andean headwater and piedmont streams are hot spots of carbon dioxide and methane emissions in the Amazon basin

Rivers substantially contribute to global greenhouse gas emissions, yet emissions from headwater streams are poorly constrained. Here, we report dissolved concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in Andean headwater and piedmont streams in the Napo River basin in Ecuador, part of the Amazon River catchment. Concentrations increased exponentially with elevation decrease between 3990 and 175 m above sea level. Concentration changes scaled with catchment slope, and were attributed to variations in gas transfer velocity, forest cover, inundation extent, and water temperature. We estimate river emissions across the whole Amazon basin using existing data for the lowland Central Amazon. We find that Andean mountainous headwater and piedmont streams are hotspots of CO2 and CH4 emission, with respective areal fluxes being 1.7 and 4.5 higher in headwater streams, and 1.2 and 6.6 higher in piedmont streams than in lowland streams. Together, Andean mountainous headwater and piedmont streams and rivers represented 35% CO2 and 72% CH4 of basin scale integrated fluvial diffusive emissions. Conversely, N2O emissions from headwater and piedmont streams were low compared to lowland streams.

Simulation of Internal Manifold-Type Molten Carbonate Fuel Cells (MCFCs) with Different Operating Conditions

Molten carbonate fuel cells (MCFCs) use molten carbonate as an electrolyte. MCFCs operate at high temperatures and have the advantage of using methane as a fuel because they can use nickel-based catalysts. We analyzed the performance of an internal manifold-type MCFC, according to operating conditions, using computational fluid dynamics. Different conditions were used for the external and internal reforming-type MCFCs. Flow directions, gas utilization, and operating temperatures were used as the conditions for the external reforming-type MCFCs. The S/C ratio and reforming area were used as the conditions for internal reforming-type MCFCs. A simulation model was developed, considering gas transfer, reforming reaction, and heat transfer. The simulation results of external reforming-type MCFCs showed similar pressure drops in all flow directions. As the gas utilization decreased, the temperature decreased, but the performance increased. The performance improved with increasing operating temperatures. The simulation results for the internal reforming-type MCFCs showed that more hydrogen was produced as the S/C ratio decreased, and the performance increased accordingly. More hydrogen was produced as the reforming area increased. However, similar performance was obtained when the reforming area contained the same active area. The external and internal reforming-type MCFCs were compared under the same conditions. The efficiency of the external reforming-type MCFCs is higher than that of the internal reforming-type MCFCs.