Air Mass Flux Research Articles

Flow Characteristics in an Optically Accessible Solid Fuel Scramjet

A direct connect, optically accessible combustor was used to reveal flow characteristics inside a reacting solid fuel supersonic combustor with air inlet total pressure of 12.9 atm and total temperature of 1225 K using polymethyl-methacrylate fuel grains. Flow visualization techniques such as shadowgraph, chemiluminescence, and high-speed imaging/planar pyrometry were used to characterize the flowfield, which has not been previously reported on for a solid fuel scramjet. Shadowgraphs revealed the role of the cavity flameholder geometry in defining the flowfield. Large length to depth ratios force the recirculation zone to expand into the core flow, causing flow biasing. Small length to depth ratios allow the recirculation zone to be fully contained within the flameholding cavity. CH* chemiluminescence shows that most of the heat release takes place in the cavity flameholder favoring the upstream region near the air inlet. Both the flow visualization and measured fuel regression rates indicate that the majority of the fuel that contributes to combustion pyrolyzes from the converging angle of the flameholding cavity. Fuel regression rates decrease as fuel is consumed and the cross sectional area of the flowpath increases, consistent with historical observation of solid fuel regression rate dependency on air mass flux.

Investigation of a Modular High-Pressure Heat Exchanger with Metal Foam Packing for a Pneumatic-Hydraulic Drive.

The results of the first stage of work aimed at improving a hybrid drive system in which the combustion engine is supported by a pneumatic-hydraulic motor are presented. The purpose of the described work was to show that a heat exchanger with a design adapted to the operating conditions of a pneumatic-hydraulic motor would allow sufficient air heating at the expense of waste heat from the combustion engine, thus increasing the efficiency of the drive system. It was assumed that the key component of the heat exchanger would be copper foam in order to increase the heat exchange surface. A prototype modular heat exchanger was designed and tested. An open-cell copper foam with a porosity of 0.9 and a pore density of 40PPI was placed in the heat exchanger. Experimental and numerical air heating studies were carried out under various heat exchanger operating conditions. The tests were conducted at initial air temperatures of -123 °C, -71 °C, and 22 °C and air pressures of 2.5 × 106 and 7.0 × 106 Pa. The air mass flux was in the range of 3.6-1644 kg/(m2s). It was found that the tested heat exchanger allows a reduction in air consumption in the drive system of 11% to 58% and increases the efficiency of the air expansion system by 16% to 30%. The maximum efficiency of the heat exchanger is 96%. The results of the work carried out will help to improve the pneumatic-hydraulic drive systems of work machines and vehicles.

Combustion characteristics of refuse-derived fuel pellets having varying plastic compositions.

The plastic fraction of refuse-derived fuel (RDF) pellets influences fuel's physico-chemical, and mechanical properties, which in turn might affect the combustion behavior of RDF. In the present study, the combustion behavior of different plastic fraction-simulated RDF pellets is reported. The simulated pellets were prepared based on the Indian commercial RDF composition. Initially, the plastic content varied from the existing fraction in Indian commercial RDF, i.e., 35% (RDF-1), to a lower plastic content of 5% (RDF-2). Physico-chemical characterization showed that a higher plastic fraction in RDF-1 reduces its pellet density by 25% as compared to RDF-2. The changes in RDF physico-chemical properties due to plastic variation are reflected in the RDF conversion process. Single-particle and packed-bed studies concluded that the lower density for higher plastic RDF-1 leads to lower conversion times (36%), and higher flame front speed (11%), which are desirable conditions for faster conversion. However, packed-bed studies also showed limitations regarding the utilization of high plastic RDF as RDF-1 has a narrow range of operating air mass flux due to the early advent of convective cooling of the bed. Finally, considering the constraints associated with the utilization of high plastic fraction (~ 35%) RDF and to maximize the effective utilization of plastic in RDF, a workable plastic fraction of 15% in RDF was proposed and tested for its combustion properties. RDF with 15% plastic showed faster conversion, higher flame front speed, and a wider range of operating air mass flux before the advent of convective cooling of the bed.

Experimental investigations on a solar assisted packed bed regeneration system for building air conditioning applications

In the current study, an experimental investigation carried out on a binary liquid desiccant-based adiabatic counter flow regenerator is presented. The heat harvested from solar collector was supplied into the desiccant for desiccant regeneration. The corrosion characteristics of the binary desiccant solution on stainless steel material were studied using potentiodynamic test. Subsequently, the effects of various inlet process parameters on the performance parameters of the regenerator were studied employing structured pads as packing material. The effect of the phase change phenomena involved in a desiccant regeneration system was also assessed experimentally, along with the system performance under the inlet solution temperatures of 53, 55, 60, 65 and 70 °C at a constant desiccant solution of 50 wt%. It was observed that the corrosion rate of lithium bromide (LiBr), calcium chloride (CaCl2) and LiBr + CaCl2 (85:15) was found to be 0.0303 mm/year, 0.0144 mm/year and 0.0161 mm/year, respectively. The results showed that with the increased solution temperature and air mass flux rate, the desorption rate was increased, whereas the regeneration effectiveness was decreased. The highest desorption rate was found to be 6.8 g/m2-s at the desiccant solution temperature of 70 °C, whereas the highest regeneration effectiveness of 0.85 was obtained at the air mass flux rate of 1.1 kg/m2-s.

Interannual Variability of the Mass-Weighted Isentropic Zonal Mean Meridional Circulation in the Northern Hemisphere Winter

Abstract The atmospheric general circulation diagnosed by the mass-weighted isentropic zonal mean exhibits an extratropical direct (ETD) circulation driven by eddy momentum transport. We investigated regional atmospheric modulations associated with the year-to-year variability of ETD circulation in boreal winter using a reanalysis dataset. Composite analyses showed that the interannual variability of ETD circulation accompanies a seesaw-like variation between the Aleutian low (AL) and Icelandic low (IL), which coincides with the Pacific–North American teleconnection pattern and North Atlantic dipole anomaly. A diagnosis using isentropic airmass fluxes representing the geographical Lagrangian mean motion indicated that the significant intensification of upper-tropospheric poleward warm airflow over the eastern North Pacific is responsible for the enhanced ETD circulation, together with the intensified equatorward lower cold airflow over East Asia and eastern North America. The resulting enhanced upward propagation of the stationary planetary waves corresponds to the intensification of the divergence of the Eliassen–Palm flux, which explains the modulated ETD circulation in view of the balance between the Coriolis force and eddy momentum flux convergence. These results suggest that the AL–IL seesaw promotes variations in the global general circulation, and the anomalous ETD circulation interacts with several teleconnection patterns involving the modulation of planetary waves through anomalous meridional heat transport by the basinwide-scale eddies.

Cooling and Heating a Greenhouse in Baghdad by a Solar Assisted Desiccant System

Modeling the microclimate of a greenhouse located in Baghdad under its weather conditions to calculate the heating and cooling loads by computer simulation. Solar collectors with a V-corrugated absorber plate and an auxiliary heat source were used as a heating system. A rotary silica gel desiccant dehumidifier, a sensible heat exchanger, and an evaporative cooler were added to the collectors to form an open-cycle solar assisted desiccant cooling system. A dynamic model was adopted to predict the inside air and the soil surface temperatures of the greenhouse. These temperatures are used to predict the greenhouse heating and cooling loads through an energy balance method which takes into account the soil heat gain. This is not included in conventional methods. The results showed satisfactory agreement with published papers. Also, the results of heating and cooling loads obtained revealed good agreement with those obtained from conventional methods when the soil heat gain is included. Two identical collectors in series of total area of 5.4m2 were employed as a heating system which provides an outlet air temperature of 30 o C at air mass flux of 0.06 kg/s.m2 at midday in January. While, a 65 oC outlet air temperature was achieved for the same mass flux at midday in August. The desiccant cooling system was operated in five operating modes; the ventilation mode and four recirculation modes with 20%, 50%, 70%,and 90% recirculation. The simulation results showed that a regeneration temperature of 60-70 o C is satisfactory for a cool supply air temperature of about 19.5 o C. Also, it was noted that 20-30 % recirculation of return air would result in suitable indoor greenhouse conditions for most periods of system operation. In addition, the coefficient of performance COP of the system was high compared with the conventional vapor compression systems.

Investigation of Thin-Layer Drying of Coffee Beans Using a Double-Condenser Compression Refrigeration System: Effects of Air Mass Flux, Specific Humidity and Drying Temperature

The drying process is the key to the quality of the coffee produced. The allowable moisture content of coffee beans is 12%. The air mass flux, specific humidity, and the drying temperature are varied using a bed dryer drying system combined with a double condenser refrigeration system. Robusta coffee beans are used in this research to obtain the characterization of coffee beans. The highest drying rate constant is obtained by 2.44 × 10-4 s-1 directly proportional to the increased air mass flux and drying air temperature, with a value of 1.701 kg/s m2 and 80 °C, but inversely proportional to the specific humidity, with a value of 7.01 g/kg d.a. The lowest activation energy value was 31.88 kJ/mol when the air mass flux was 1.701 kg/s m2, the drying air temperature was 80 °C, and the average specific humidity was 7.01 g/kg d.a. In this work, the developed correlation is proposed to practically predict the activation energy (EA) and the pre-exponential factor (A) with equation and respectively. Based on Ea and A correlation equation, it can be used for designing a bed dryer type coffee drying system for a larger scale.

Quantifying the Vertical Transport in Convective Storms Using Time Sequences of Radar Reflectivity Observations

AbstractA new satellite observation concept to estimate upward air mass flux in convective storms has been proposed using a convoy of small radars that measure reflectivity only. The approach is to analyze a pair of radar reflectivity profiles obtained within 30–120 s of one another, and infer the upward transport above the freezing level and at a nominal 3‐km horizontal resolution from the reflectivities and their temporal change. This paper summarizes the theoretical basis for this approach, with quantitative justification using sensitivity analyses of convection‐permitting model simulations and from ground‐based zenith profiler data. We then describe and quantify the performance of the approach to detect updrafts from the radar observations. Finally, we illustrate the expected performance of retrievals of the vertical transport and evaluate their ability to meet the objectives of the “Investigation into Convective Updrafts” mission, selected by NASA to place in orbit in 2027–2028 a convoy of three identical Ka‐band radars measuring radar reflectivity within their common swath.

Flame Dynamics in an Optically Accessible Solid Fuel Ramjet Combustor

Flow–flame interactions were investigated in an optically accessible solid fuel ramjet combustor. Experiments were performed with a single hydroxyl-terminated polybutadiene fuel slab located downstream of a backward-facing step in a rectangular chamber. To emulate flight-relevant combustor conditions, unvitiated heated air was directed through the combustion chamber with an inlet temperature of , chamber pressures of 450–690 kPa, and port Reynolds number of . To characterize the heat-release distribution and velocity field, 20 kHz -chemiluminescence and 10 kHz particle imaging velocimetry measurements were used. Comparison between the mean chemiluminescence images acquired at three flow conditions indicates reduction in flame height above the grain with increasing air mass flow rate. Dominant heat-release coherent structures in the statistically stationary flow are identified using the spectral proper orthogonal decomposition technique implemented on time series of instantaneous images. The spatial mode shapes of the chemiluminescence and velocity field measurements indicated that the flow–flame interactions were dominated by vortex shedding generated at the backward-facing step in the combustor, at Strouhal numbers of 0.06–0.10. The frequency corresponding to these modes is shown to be invariant of air mass flux, indicating that system dynamics are primarily dependent on the backward-facing step geometry and the bulk velocity in the combustor.

Thermal behavior of biomass under thermochemical treatment at different air fluxes in an updraft reactor

Thermochemical treatment was investigated experimentally at different air fluxes in an updraft reactor. The test rig was equipped with a special attached door that will open at a specific time step. This unique feature allows investigators to obtain information on the packed bed color variation along the different heights of the reactor that evolves at different points in time. The analysis focused on the temperature dynamics obtained from installed thermocouples with the packed bed color variation at each time step. The investigation was conducted for three different supply air mass fluxes, which were 670, 480, and 190 kg/m2h. The general thermal behavior is addressed in the first part of the paper because it is similar for all different input air mass fluxes. Next, the distinctive operation parameters among different air mass fluxes are discussed; these included the hot spot zone, fuel conversion characteristic, temperature distribution, heat transfer, and kinetic activities along the height of the reactor.

Effects of carbonization on the combustion of rice husks briquettes in a fixed bed

Carbonization of raw materials for making briquettes has been identified as a possible way of improving calorific values and fixed carbon contents of briquettes. In spite of these benefits, the main challenges of carbonization are increased percentage of ash content and energy required to process the fuel. In this study, fuels with mixtures of carbonized and raw rice husks were combusted in a fixed bed to examine the effect of carbonization on their combustion properties with an aim of establishing an optimum ratio. Bed temperature distribution, ignition, flame propagation speed, combustion rates and reaction zone thickness were investigated. All experiments were performed in a fixed bed operated in a reverse counter-current flame propagation mode. Four mixtures consisting of different ratios of carbonized rice husks were used to process briquettes; namely, 25 wt%, 50 wt%, 75 wt% and 100 wt% biochar. Air-mass flux for combustion of each mixture was varied between 0.02 and 0.6 kg/m2s. It was established that carbonization increases ignition time and peak bed temperature but lowers flame propagation speed, reaction zone thickness, and combustion rates. Briquettes with lower percentage of biochar had higher volatiles and higher devolatilization rate that shortened combustion period. Briquettes with carbonized rice husk of between 50 wt% and 75 wt% were found to have optimum combustion properties. Processing of briquettes should be done within these carbonization ratios in order to achieve desirable combustion properties.

Air horizontal jets into quiescent water

Gas submerged jet is an outstanding thermohydraulic phenomenon in pool scrubbing of fission products during a severe nuclear accident. Experiments were performed on the hydraulic characteristics in the ranges of air mass flux 0.1–1400 kg/m2s and nozzle diameter 10–80 mm. The results showed that the dependence of inlet pressure on the mass flux follows a power law in subsonic jets and a linear law in sonic jets. The effect of nozzle submerged depth was negligible. The isolated bubbling regime, continuous bubbling regime, transition regime, and jetting regime were observed in turn, as the mass flux increased. In the bubbling regime and jetting regime, the air volume fraction distribution was approximately symmetric in space. Themelis model could capture the jet trajectory well. In the transition regime, the air volume fraction distribution loses symmetry due to the bifurcated secondary plume. The Li correlation and Themelis model showed sufficient accuracy for the prediction of jet penetration length.

Numerical study on the heat and mass transfer in charging and discharging processes of a triangular honeycomb thermochemical energy storage reactor

• A triangular honeycomb reactor has been designed and experimentally investigated. • A 3-D numerical model of this reactor has been developed and validated. • Relationships between heat transfer and mass diffusion are determined. • The thermal efficiency of triangular honeycomb reactor can achieve around 20% Adsorption heat storage based on porous adsorbents attracts considerable attention for the high energy storage density and long storage duration compared to sensible and latent heat storage methods. However, one of the critical challenges is the poor heat and mass transfer performance of thermochemical reactors. This study presents a triangular honeycomb reactor using zeolite 13X-H 2 O working pair and investigates the heat and mass transfer performance. To do this, a three-dimensional transient heat and mass transfer model has been built in COMSOL to simulate the adsorption and desorption processes of the new reactor. A detailed numerical model and the corresponding modelling methods are critical to the investigation while most of the recent studies are based on one-dimensional and two-dimensional models. The model has been experimentally validated thoroughly to a close agreement in both adsorption and desorption processes (mean sum of percent errors of 0.6% to 8.91% for air temperature and relative humidity). The reactor thermal efficiency from the simulation and experiment are 19.57% and 21.93%, respectively, which are achieved by the fast and controllable charging and discharging performance along with the reduced air pressure drop benefited from the reactor design. To add value of the charging and discharging details, this study also presents the contour diagrams with detail discussions for the air velocity, temperature, water concentration, and heat and mass flux variations of the triangular honeycomb channel during desorption and adsorption processes. The results show that the side of triangle channel has larger and stronger moisture desorption in a charging process and stronger moisture adsorption in a discharging process than that of the triangle corner areas.

Improved advection, resolution, performance, and community access in the new generation (version 13) of the high-performance GEOS-Chem global atmospheric chemistry model (GCHP)

Abstract. We describe a new generation of the high-performance GEOS-Chem (GCHP) global model of atmospheric composition developed as part of the GEOS-Chem version 13 series. GEOS-Chem is an open-source grid-independent model that can be used online within a meteorological simulation or offline using archived meteorological data. GCHP is an offline implementation of GEOS-Chem driven by NASA Goddard Earth Observing System (GEOS) meteorological data for massively parallel simulations. Version 13 offers major advances in GCHP for ease of use, computational performance, versatility, resolution, and accuracy. Specific improvements include (i) stretched-grid capability for higher resolution in user-selected regions, (ii) more accurate transport with new native cubed-sphere GEOS meteorological archives including air mass fluxes at hourly temporal resolution with spatial resolution up to C720 (∼ 12 km), (iii) easier build with a build system generator (CMake) and a package manager (Spack), (iv) software containers to enable immediate model download and configuration on local computing clusters, (v) better parallelization to enable simulation on thousands of cores, and (vi) multi-node cloud capability. The C720 data are now part of the operational GEOS forward processing (GEOS-FP) output stream, and a C180 (∼ 50 km) consistent archive for 1998–present is now being generated as part of a new GEOS-IT data stream. Both of these data streams are continuously being archived by the GEOS-Chem Support Team for access by GCHP users. Directly using horizontal air mass fluxes rather than inferring from wind data significantly reduces global mean error in calculated surface pressure and vertical advection. A technical performance demonstration at C720 illustrates an attribute of high resolution with population-weighted tropospheric NO2 columns nearly twice those at a common resolution of 2∘ × 2.5∘.

Design and development of solar assisted fluidized bed dryer integrated with liquid desiccant dehumidifier: Theoretical analysis and experimental investigation

Higher energy demand for ventilating higher mass flux of hot air in fluidized bed drying (FBD) and SDG-7 of the UN has been actuated the researchers towards solar energy intervention in FBD. However, the thumb rules and systematic design calculation of the solar system for FBD have not been reported in the literature. In view of that, a novel solar thermal system was designed and developed by thermo-hydrodynamic analysis, considering the variable physical properties of bioproducts and fluctuating weather. The key design parameters were fresh and desired dried product's moisture content, physical properties of products, dryer capacity, desired drying temperature, ambient conditions, etc. In order to enhance the drying effectiveness, state-of-the-art technology for air dehumidification was integrated by using an aqueous blend of LiCl (35 %) + CaCl (5 %) desiccant. A solar photovoltaic system was also estimated for recirculating the moisture-saturated desiccant over an unglazed solar absorber to regenerate it. From the experiment of ginger drying, it was explicitly found that the developed solar FBD could supply sufficient heat energy (173.06–604.12 W/hr.) compared to the required heat load (124.65 W/hr.), which justifies the operational flexibility. The obtained solar heat fraction (∼1) and solar fraction (0.52–0.64) imply that the solar energy could fulfill the heat energy demand by 100 % and total energy demand (heat + electrical) up to 64 %. The energy efficiency, exergy efficiency, and sustainability index of the solar thermal system were obtained up to 48 %, 2.96 %, and 1.03, respectively. Aiming for effective energy utilization, an intermittent heat supply strategy was associated. Compared to continuous drying, intermittent drying reduced the active drying time (2–2.5 hrs.) and specific energy consumption (33.47–43.83 %) and fortified the dried ginger by reducing shrinkage (11–12 %) and increasing the rehydratability (up to 22.15 %).

Supersonic combustion diagnostics with dual comb spectroscopy

Supersonic engine development requires accurate and detailed measurements of fluidic and thermodynamic parameters to optimize engine designs and benchmark computational fluid dynamic (CFD) simulations. Here, we demonstrate that dual frequency comb spectroscopy (DCS) with mode-locked frequency combs can provide simultaneous absolute measurements of several flow parameters with low uncertainty across a range of conditions owing to the broadband and ultrastable optical frequency output of the lasers. We perform DCS measurements across a 6800–7200 cm−1 bandwidth covering hundreds of H2O absorption features resolved with a spectral point spacing of 0.0067 cm−1 and point spacing precision of 1.68 × 10−10 cm−1. We demonstrate 2D profiles of velocity, temperature, pressure, water mole fraction, and air mass flux in a ground-test dual-mode ramjet at Wright-Patterson Air Force Base. The narrow angles of the measurement beams offer sufficient spatial resolution to resolve properties across an oblique shock train in the isolator and the thermal throat of the combustor. We determine that the total measurement uncertainties for the various parameters range from 1% for temperature to 9% for water vapor mole fraction, with the absorption database/model that is used to interpret the data typically contributing the most uncertainty (leaving the door open for even lower uncertainty in the future). CFD at the various measurement locations show good agreement, largely falling within the DCS measurement uncertainty for most profiles and parameters.

Relationship Between Convective Storm Properties and Lightning Over the Western Ghats

AbstractX‐band radar observations are integrated with lightning location network observations to investigate the relationship between convective storm properties and lightning over the Western Ghats during a monsoon season (June–September 2014). Convective storms (cells) were identified using an objective‐tracking method and instantaneous lightning strikes within the radar domain were then linked with observed storms. This spatio‐temporal sampling of individual convective cells and lightning has facilitated process‐based study of electrified convection over the Ghats for the first time. Storm and lightning occurrences are typically high during monsoon onset and withdrawal months of June and September, respectively. A spatial correspondence between deep‐intense storms, lightning, and intense convective cores indicated presence of large hydrometeors in the mixed‐phase region of storm supported by strong updrafts and is essential for lightning. The large‐scale instability that peaked during afternoon hours was a key factor in the formation of deep‐intense storms and lightning. Results show that majority of lightning‐producing storms are located on the leeward side as opposed to the windward side. These storms have deeper top‐heights, larger areas and vertically integrated liquid, and an enhanced hail probability than those devoid of lightning. Warm season convection in the study area is accompanied by the preponderance of negative Cloud to Ground (−CG) flashes over positive Cloud to Ground (+CG) lightning. Storms with +CG features exhibited much higher (>2 times) vertical airmass flux in the mid‐troposphere (6–9 km) than storms without +CG features. Furthermore, for majority of +CG storms, intracloud flash occurrences increased significantly above the freezing level.

Optimization of combustion parameters of carbonized rice husk briquettes in a fixed bed using RSM technique

This study investigates the combustion of carbonized rice husk briquettes in a fixed bed to establish the optimum briquetting and combustion conditions. The combustion properties, namely, the average flame propagation speed, the average burning rates, the reaction zone thickness, maximum flame temperature and the ignition time, were optimized with respect to air-flow rate, binder ratio and particle size using response surface methodology (RSM). Seventeen experiments with different combinations of air-flow rate, binder ratio, and particle sizes, each at three levels set according to Box-Behnken Design (BBD), an RSM technique, were performed. Mathematical models for predicting the responses were developed by fitting experimental data. It was established that the binder and air-mass flux predominantly affected all fuel samples during processing and combustion. Optimal values of the ignition time and reaction zone thickness were established to be 249.08 s and 102.43 mm when air-mass flux, binder ratio and particle size were 0.31 kg/m2.s, 25% and 2.6 mm, respectively. On the other hand, the optimal peak bed temperature was 1226.25 °C when air-mass flux, binder ratio and particle size were 0.31 kg/m2.s, 25% and 0.3 mm, respectively.

Combustion and NOx formation characteristics from a 330 MWe retrofitted anthracite-fired utility boiler with swirl burner under deeply-staged-combustion

In order to achieve peak carbon dioxide emissions and carbon neutrality goals, a higher requirement is put forward for coal type adaptability medium, load stable combustion performance, and pollutant emission for wall-fired boiler with swirl burners. In this work, through industry experiments, the combustion characteristics of a retrofitted wall-firing mode 330 MWe power unit feed with anthracite were investigated. The combustion system was retrofitted employing the centrally fuel-rich (CFR) swirl burner and deeply-staged combustion technology. The experiment data were measured, including flue gas temperature and composition, furnace temperature, and the main operational parameter under high-load (300 MWe), medium-load (230 MWe), and low-load (150 MWe) conditions. The stable combustion of anthracite is achieved at various loads. With the excessive air coefficients of the main combustion region increase, the corresponding second air damper opening increase under high-load condition or over-fire-air damper opening decrease, both the flue gas temperature and heating rate of pulverized coal increase advance the ignition and promote the stable combustion and burn-out of anthracite coal. In the initial combustion stage, the O2 given into the chamber increase, both O2 consumption rate and CO concentration decrease, but NOx concentration increases. While in the later stage, both the O2 and CO concentration tend to become flat. Meanwhile, the O2 concentration is lower than 2.1%, the CO concentration maintains a relatively high level, and NOx production is inhibited effectively and becomes flat gradually. With the excess air coefficient increase, the temperature in the main combustion region increases, and the difference in furnace temperature between the burn-out region and the main combustion region diminishes. The unburned carbon content in fly ash and exhaust gas temperature decreases, while NOx emission increases. There is little difference for the flue gas temperature distribution in the side-wall region, and the measured O2 concentration is always higher than 3.5% with the different mass flux of secondary air and over-air-fire. With decreasing load, the NOx emission decreases from the highest 1392.66 to the lowest 958.38 mg/m3 (O2 6%), and the boiler efficiency improves. Compared with high-load and medium-load, the slagging tendency of the water wall is lower under low-load condition.

Stratosphere‐Troposphere Exchanges of Air Mass and Ozone Concentration in the Last Glacial Maximum

AbstractStratosphere‐troposphere exchange (STE) of ozone represents a significant source term in the tropospheric ozone budget and can impact surface ozone concentrations, tropospheric oxidation capacity, and methane lifetime. Using the Whole Atmosphere Community Climate Model 6, changes in the air mass and ozone STEs in the Last Glacial Maximum (LGM) as compared with preindustrial (PI) climate are investigated. We use dynamic isentropic surfaces that are determined by fitting to the tropical tropopauses as the upper boundary of the lowermost stratosphere in a mass budget approach, a method particularly suitable for estimating air mass and ozone STEs across different climates. Relative to the PI, the magnitude of ozone STE in the LGM is decreased by 14%–19%, 18%–24%, 18%–23%, 16%–21%, and 15%–21% over the Northern hemisphere extratropics, Southern hemisphere extratropics, the tropics, the extratropics, and the globe, respectively. The extratropical and global decreases are mainly caused by decreased ozone in the extratropical lower stratosphere associated with a weakening of Brewer‐Dobson circulation, while changes in air mass fluxes play a minor role because the effects of weakening Brewer‐Dobson circulation and increased isentropic density partly cancel each other. Analysis of the modeled tropospheric ozone budget indicates that the ozone STE in the LGM is 28% of the tropospheric ozone production rate, as compared to about 9% in the modern climate (year 2000) and 19% in the PI.