Low Air Flow Rates Research Articles

Comprehensive analysis of emissions from wood and cow dung burning using chemometrics and two-dimensional gas chromatography

Biomass burning is a global source of climate- and health-affecting emissions. The impacts of biomass burning emissions (BBE) are tied to their complex and variable chemical makeup. For instance, the nitrogen content of BBE influences their capacity to absorb light, and therefore affect the Earth's radiative budget. Factors such as temperature, biomass type, or air flow rate during the combustion all modify the composition of BBE, making accurate characterization challenging. Herein, for the first time, principal component analysis (PCA) was applied to emissions gathered during laboratory-based combustion of wood and cow dung biomass in a tube furnace. A thermal desorption two dimensional time-of-flight gas chromatography mass spectrometry (TD-GC × GC-ToF-MS) setup was employed to separate and identify chemical species. By combining these techniques with a feature selection algorithm, we determined that low temperature and air flow rate lead to greater feature separation on PCA scores plots. Of the 729 variables used to construct the plots, 61 were identified as significant. These species - including sugars such as d-Allose and melezitose, as well as tracers such as levoglucosan and guaiacol - significantly differentiated emissions from wood versus cow dung biomass, especially at lower temperatures. In particular, combustion of either fuel at 0.2 slpm and 500 °C, lead to 20 times the variability in levoglucosan peak area over more efficient furnace parameters. Chemical species evolved only from dung burning contained on average 0.595 nitrogen atoms versus 0.515 for wood, indicating that a higher nitrogen content of the base fuel may not necessarily translate into emission of unique nitrogen containing species, potentially causing the underestimation of dung burning impacts. Overall, TD-GC × GC-ToF-MS coupled to PCA reliably separated emissions from wood and dung biomass while simultaneously identifying significant chemical features, displaying the suitability of this combination of techniques towards characterizing complex BBE matrices in the future.

Transport of microplastics treated with dielectric barrier discharge (DBD) plasma in saturated porous media

The performance of discharge plasma in treating organic pollutants and micro-organisms in water is impressive. When discharge plasma is used to treat polluted water containing organic pollutants and microorganisms, the presence of a certain amount of microplastics (MPs) in the water is unavoidable due to the complexity of the components contained in the water and the prevalence of MPs. MPs, as one of the pollutants that are difficult to be degraded by discharge plasma, undergo physical and chemical changes that increase their risk in the environment after treatment. Therefore, it is necessary to understand the fate of MPs after being treated with discharge plasma. In this study, the surface morphology of plastics before and after discharge plasma treatment was observed by scanning electron microscopy (SEM). The plastics after discharge plasma treatment were characterized by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) to determine the changes in oxygen-containing functional groups on the surface. The recovery of microplastics (MPs) in saturated porous media under different physicochemical and plasma oxidation conditions was investigated by column experiments. It has been shown that MPs exhibit increased recovery under conditions of increased flow rate and pH. A decrease in recovery was observed at elevated ionic strength and co-existing cation valence. High voltages and low air flow rates increase the oxidation of MPs by increasing the thermal effects of the dielectric barrier discharge (DBD) plasma system, the amount of reactive oxygen species (ROS) and the intensity of ultraviolet ray (UV) irradiation. The mobility of MPs is enhanced by a combination of these factors. The advection–dispersion equation (ADE) fits the transport data of MPs well. The interaction energy between quartz sand and MPs was calculated using the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. This study provides a new perspective on the potential risks of discharge plasma in water treatment.

Utilizing novel industrialized heat exchanger plate in air-based photovoltaic/thermal collectors to enhance thermal and electrical efficiency

This study aims to design a highly efficient and applicable air-based photovoltaic-thermal (PVT) collector that maximizes both electrical and thermal energy efficiencies. An innovative industrialization-ready configuration of the air-based PVT system is proposed, utilizing an industrialized heat exchanger (GRIPMetal or GM) as the absorber plate for the PVT air channel. The heat exchanger consists of spikes and cavities to enhance the heat transfer coefficient in the air channel. The proposed heat exchanger plate minimally affects the dimensions and weight of the PVT collector. A numerical model, validated against experimental results, is used to ensure the accuracy of the simulation. The study is followed by a parametric study that investigates the geometric effects of the heat exchanger and air channel, as well as the airflow rate, on the overall performance of the PVT system. It is observed that the utilization of GM plates significantly reduces the average PV panel temperature (with a maximum of 28 ℃ reduction) and enhances the convective heat transfer coefficient in the air channel, the electrical and thermal efficiencies by approximately 164%, 16.1%, and 50%, respectively, when compared to a flat plate PVT collector. The results demonstrate that the proposed PVT collector effectively compensates for the pressure drops and excess fan power consumption at low Reynolds numbers due to the GM heat exchanger, resulting in higher overall system efficiency. The optimal configuration for the proposed PVT system is achieved by employing a low airflow rate, a narrow air channel, and GM spikes of the largest size available.

Experimental and Numerical Investigation for Optimization of a Hybrid Battery Thermal Management System based on PCM and Air Convection

Abstract This work presents the design and optimization of a phase change material (PCM) based hybrid battery thermal management system (HBTMS). In the first stage, experiments are performed to measure the battery cell temperatures under various charge rates with and without the usage of PCM. Thereafter, a numerical model is developed to conduct a parametric study on the effect of thickness of PCM layer around the battery cell. The maximum cell temperature (36.35°) and thermal nonuniformity are within the safe range for the PCM thicknesses of 6 to 12 mm. In the second stage, a parametric study is conducted in the 6S1P battery module to optimize the spacing between the cells at constant inlet velocity. The maximum temperature is within the optimal range when the cell spacing is 10 mm. At the constant cell spacing of 10 mm, increase in inlet velocities from 0.25 m/s to 2.5 m/s gradually improves the thermal non-uniformity. The maximum temperature and thermal non-uniformity for 6S1P battery module is found to be 42.07° and 1.17° respectively. In the third stage, 6S1P battery module is optimized for PCM thickness, cell spacing and inlet air velocity. It is found that effective thermal management is possible with PCM based HBTMS at low airflow rate of up to 1.5 m/s. The optimized PCM based HBTMS shows 46.59% and 40% reductions in PCM mass and air flow rate respectively.

Experimental comparison of aerosol transmission in displacement ventilation and mixing ventilation in a meeting scenario

The performance of displacement ventilation (DV) and mixing ventilation (MV) in aerosol contamination control was compared. The considered contamination was an aerosol emitted from a person in meeting scenarios of two and four persons. The experiments were carried out in a full-scale room measuring 4.4 m × 5.2 m × 2.9 m. Particle counting was carried out at 41 measurement points in the room to assess the concentration field of particles in the room and in the inhalation zone. The influence of the supply airflow rate and the number of activated thermal mannequins on the contaminant removal effectiveness were examined. The main conclusion is that the DV system was superior to the MV system in reducing contamination. An enhanced contaminant removal effectiveness of displacement ventilation was observed for all supply air flow rates and increased with higher airflow rates. At lower airflow rates, contamination in the inhalation zone was reduced by 40% compared to mixing ventilation, while at higher flow rates, the reduction surpassed 50%. This study highlights the advantages of displacement ventilation in terms of contamination control, infection prevention and energy efficiency, emphasising the importance of ventilation system selection for indoor environments, particularly those where airborne transmission risks are prevalent.

Application of artificial intelligence to predict energy consumption and thermal efficiency of hybrid convection-radiation dryer for garlic slices

This study aims to examine the energy-related aspects of a hybrid convection-radiation drying technique employed in the drying process of garlic slices. Several factors, including infrared radiation intensity (1500, 2000, and 3000 W/m2), air temperature (40, 50, and 60 °C), and airflow rates of the drying chamber (0.7, 1.0, and 1.5 m/s) were evaluated to optimize the responses of drying time (min), energy consumption (kJ), thermal efficiency (%), and specific energy consumption (MJ/kg). Furthermore, an Artificial Neural Network model was employed to predict the effects of the parameters above on the drying system's specific energy consumption, energy consumption, drying time, and thermal efficiency. The obtained data were analyzed using a self-organizing map and principal component analysis. Interestingly, the findings showed that increasing the air temperature and infrared radiation intensity led to shorter drying times, while higher airflow rates resulted in longer drying durations. Additionally, it was found that higher infrared intensity and air temperature, combined with lower airflow rates, improved the energy indices. Increasing the air velocity to 1.0 and 1.5 m/s at the same air temperature and radiation intensity resulted in a considerable increase in drying time by 9 and 22.7%, respectively. The lowest efficiency value of 10.1% was observed at 40 °C temperature and an air velocity of 1.5 m/s. The Artificial Neural Network model demonstrated high accuracy with a Root Mean Square Error of 0.05 and an overall accuracy of (95%) in predicting the drying parameters. Notably, the self-organizing map visualization revealed that higher air temperatures and radiation corresponded to lower drying times, energy consumption, and specific energy consumption. Conversely, higher airflow rates resulted in increased drying time and energy consumption. The present study suggested that 60 °C, 3000 W/m2 and 0.7 m/s are optimum conditions for efficiently drying garlic slices under the hybrid dryer. This investigation addresses the limitations and deficiencies of previous work on energy optimization and efficiency analysis of garlic under a hybrid dryer with infrared heating systems. Further studies on the economic feasibility of applying such a system for sample drying and the impact of drying on the thermal behaviors of the products need additional investigation.

Case Study on the design optimization of the positive pressure operating room

Ventilation systems of operating rooms (ORs) are significantly important in preventing postoperative wound infections that can cause morbidity and mortality after surgery in or out of the hospital. This study aims to identify the optimum overpressure for efficient operation while reducing the risk of surgical site infections (SSIs) based on the actual OR with the help of computational fluid dynamics. The species transport model, Lagrangian discrete phase model, and turbulent standard k-ε\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upvarepsilon $$\\end{document} model are mainly used for the transient numerical study to improve the performance of the OR and reduce SSI cases. Four OR schemes were initially calculated for the best location of the patient on the surgical table. The results revealed that the modified position 90˚ is the best location with the minimum CO2 and BCP concentrations. The investigated operating room could host up to ten surgical members with the optimum overpressure of 5.89 Pa and 0.56 m/s of supply velocity under the standard cleanliness level. Modifying the supply surface area will enhance the performance of the operating room by providing a cleaner zone and maintaining the desired room pressure, even with a low airflow rate. This optimization scheme could guide practical applications in all positively pressurized operating rooms to address issues related to overpressure effects.

Nasal High-Flow Oxygen Therapy in Chronic Respiratory Failure for Homecare Applications-A Feasibility Study.

Background: While high-flow nasal cannulas (HFNCs) represent the standard of care in the intensive care unit for patients with severe hypoxemia, its use in homecare settings is uncommon despite its potential. The potential benefits and challenges of the high-flow nasal cannula (HFNC) in homecare settings compared to standard long-term oxygen via nasal low-flow therapy are unclear. Methods: We conducted a prospective monocentric feasibility study at the Department of Respiratory Medicine, University Hospital, Goethe University Frankfurt, Germany. Patients with interstitial lung disease or severe bronchiectasis (including cystic fibrosis) were enrolled into the study. The HFNC was introduced during hospitalization. The patients' compliance with home use advice and arterial blood gas results were evaluated at a 4-6-week follow-up. Results: A total of 12 patients were analyzed. HFNC initiation did not result in a significant improvement of the pO2/fiO2 (p/f) ratio. Only 8 out of 12 (66.6%) patients used the HFNC at home after the initial in-hospital initiation. Only 7 of the total 12 patients were using the therapy at a follow-up 3-6 weeks after HFNC onset. Two patients died during the observation, resulting in a surveillance mortality rate of 16.7%. Conclusions: The feasibility data showed low adherence to the HFNC at home. The lack of any positive effect on the p/f ratio may be due to low airflow rates and overall mild hypoxemia compared to patients with severe respiratory failure in the ICU.

Low reaction threshold of ambient temperature oxidation of coal: Perspective from oxygen concentration and airflow rate

Coal spontaneous combustion remains a significant hazard in mining operations. In this study, the temperature rise characteristics of sub-bituminous coal were investigated using an air stream of varying concentration and airflow rate. The chemical structure changes under various oxygen contents were analyzed using the FTIR technique. The findings demonstrate that ambient temperature oxidation can occur even under low oxygen and airflow rate conditions, emphasizing the need for vigilance. Although oxygen enrichment in the atmosphere promotes the coal-oxygen complex and increases the total temperature rise (TTR), TTR can still reach 0.31 °C with 6 vol% oxygen. There exists an optimum ventilation rate to maximize the TTR. TTR at the flow rate of 25 mL/min is 47 %, 36 %, 165 % and 308 % higher than at the 10, 50, 75 and 100 mL/min. Moreover, FTIR experiments indicated the difference of active groups under different oxygen concentrations is slight. The low reaction threshold for ambient temperature oxidation complicates the prevention of coal spontaneous combustion during latency periods.

Heat transfer within a multi-package: Assessing the impact of package design on the cooling of strawberries

Perishable horticultural products may necessitate multi-packaging for preservation. The optimized primary and secondary packaging designs allow to reduce cooling time and ensure uniform product temperature, thereby enhancing fruit quality. This study examined how the secondary package design impacts the cooling of strawberries in airtight clamshells (AC) during precooling. The AC design simulates heat transfer within Modified Atmosphere Package (MAP) where there is no direct interaction between the external cooling air and the internal environment of the clamshell. Laboratory experiments were conducted to simulate one level of a pallet, using artificial material instead of real strawberries in order to have a better control of thermophysical properties and thus to better investigate heat transfer mechanisms. The thermal performance of an existing tray design was compared to three new alternative designs. The effect of air headspace, vent holes area and inlet airflow rate on the cooling efficiency was investigated.Experimental results revealed significant cooling heterogeneities among different AC positions, with the largest observed disparities being 1.8 h for half cooling time (HCT) and 3.7 h for seven-eight cooling time (SECT) in the current tray design. Incorporating vent holes into the current commercialized tray design demonstrated superior cooling performance, with 8% improvement of the overall average HCT. Analysis showed increasing the thickness of the air headspace above the AC increased 91% and 113% the overall average HCT and SECT, respectively. The research found that airflow distribution in a tray has a critical effect on the heat transfer between the AC walls and the surrounding air temperature. Thus, the packaging design is crucial in ensuring proper ventilation around the ACs.The alternative designs or operating under a lower airflow rate revealed a potential to cut down on energy use for ventilation. Specifically, when the airflow rate was reduced by one-quarter, there was a remarkable 94% decrease in energy usage. However, this benefit is counterbalanced by a 100% increase in the overall average HCT, which might adversely affect the product quality. Hence, optimizing the packaging design is essential to ensure the right balance between energy efficiency and product quality.The HCT exhibited a linear correlation with the external resistance, which is influenced by the airflow behavior, whatever the AC positions and tray designs.

Enhancing control disorder and implementing V2X-Based suppression methods for electric vehicle CO2 thermal management systems

In recent years, the development of electric vehicles (EVs) thermal management systems has underscored the crucial role in ensuring driving safety and optimizing driving range has become increasingly prominent. However, the inherent dynamic complexity of EV operation coupled with automatic control systems, can sometimes lead to unstable behavior, resulting in performance degradation and safety risks for compressors and batteries. To effectively address this issue, an evaluation was conducted on the dynamic control characteristics of an EV thermal management system utilizing CO2 as the refrigerant in this study. Through mathematical modeling and experimental analysis, the erratic nature of the dynamic thermal process was first identified. The underlying reasons were elucidated, focusing on system control characteristics and intrinsic mechanisms. It was found that control disorder could induce abnormal actions in thermal management system components like compressors and expansion valve, leading to significant performance decline and issues such as liquid carryover in compressor suction. Furthermore, specific control disorder regions of CO2 heat pumps for EVs were delineated, providing a framework for assessing the likelihood of system control disorder. Notably, control disorder was more likely to occur under conditions of low indoor air flow rate, high ambient temperature, and low supply air temperature. Given the widespread nature of this issue and the lack of suitable solutions, two control disorder suppression schemes were developed using V2X technology and validated through simulation. Results showed that adoption of V2X communication technology prevented an average of 70.1 % COP degradation, ensuring stability and safety of compressors and batteries under various operating conditions. The research provides useful information for exploring the dynamic characteristics of CO2 thermal management systems, offering a novel approach to enhance the system stability and efficiency.

Analysis of the shear-driven flow in a scale model of a phase separator: Validation of a coupled CFD approach using experimental data from a physical model

The effect of shear stress at the interface between a flowing gaseous phase and a liquid-filled cavity, a scenario commonly found in flue gas/slag phase separators, is investigated in this study. This effect is frequently disregarded in computational fluid dynamics (CFD) simulations within metallurgy, primarily due to its limited influence on the motion of liquids (e.g., slag, liquid metal) when compared to other factors such as stirring by natural convection or bubbling. This study was undertaken to investigate shear-driven flow in a 1:4 scale model of a phase separator in which a flue gas stream coming from a furnace is mobilizing the flow of a slag melt. To cover a wide range of operating conditions, silicone oil with varying viscosities (20, 50, and 70 cSt) was considered for mimicking viscous slag. Additionally, different volumetric airflow rates (18, 27, and 36 m3/h) were considered to simulate the flue gas flow. Particle image velocimetry (PIV) measurements were conducted on the model. The experimental results were utilized to validate computationally efficient, coupled steady-state simulations of the system. Notably, the steady-state simulations, requiring approximately one hour of CPU time, demonstrated a computation time decrease of two magnitudes compared to conventional Volume of Fluid (VOF) modeling. A stable, laminar flow pattern of the liquid phase with surface velocities of up to approximately 30 mm/s was observed for the case with the lowest oil viscosity and the highest airflow rate, while a steady, turbulent flow was observed in the gas phase. Conversely, the lowest surface velocities, measuring around 5 mm/s, were recorded and calculated for the scenario with the highest oil viscosity and the lowest airflow rate. It was noted that velocities increased proportionally with the airflow rate but exhibited a disproportionate relationship with oil viscosity. The prediction of velocity magnitudes by the steady-state CFD model was highly accurate, with only minor discrepancies observed between the measured and calculated flow patterns. In summary, valuable insights into the often-overlooked shear stress effects at the phase boundary in gaseous-liquid flow over a cavity are provided by our study.

Experimental investigation of simultaneous nitrification-denitrification and phosphorus removal in pilot-scale sequencing batch moving bed biofilm reactors (SB-MBBRs)

Sequencing batch moving bed biofilm reactors have been widely used in commercial wastewater treatment facilities for organic carbon and nitrogen removal. However, these reactors can remove low phosphorus (P) levels. Therefore, this study investigated the potential of SB-MBBRs for maximizing simultaneous nitrification-denitrification and P removal (SNDPR) potential from P-rich municipal wastewater impacted by industrial discharges. A series of experiments were carried out to investigate the effect of external volatile fatty acid (VFA) dosing, airflow rate, and temperature on SNDPR using pilot-scale SBMBBRs. Stable and robust SNDPR was achieved with an optimum acetic acid supply of 150 mg SCOD/L, at 20 oC and 2.5 L air/min. A low airflow rate (AFR) and high-temperature conditions affected P release and uptake kinetics. Efficient PHA storage, dissolved oxygen (DO) transfer (outer layer), DO diffusion limitation (inner layer) of biofilm, and conversion of NH4-N to NO2-N/NO3-N enhanced SNDPR in the two pilot SB-MBBRs.

A GPU-accelerated computational fluid dynamics solver for assessing shear-driven indoor airflow and virus transmission by scale-resolved simulations

We explore the applicability of MATLAB for 3D computational fluid dynamics (CFD) of shear-driven indoor airflows. A new scale-resolving, large-eddy simulation (LES) solver titled DNSLABIB is proposed for MATLAB utilizing graphics processing units (GPUs). In DNSLABIB, the finite difference method is applied for the convection and diffusion terms while a Poisson equation solver based on the fast Fourier transform (FFT) is employed for the pressure. The immersed boundary method (IBM) for Cartesian grids is proposed to model solid walls and objects, doorways, and air ducts by binary masking of the solid/fluid domains. The solver is validated in two canonical reference cases and against experimental data. Then, we demonstrate the validity of DNSLABIB in a room geometry by comparing the results against another CFD software (OpenFOAM). Next, we demonstrate the solver performance in several isothermal indoor ventilation configurations and the implications of the results are discussed in the context of airborne transmission of COVID-19. The novel numerical findings using the new CFD solver are as follows. First, a linear scaling of DNSLABIB is demonstrated and a speed-up by a factor of 3-4 is also noted in comparison to similar OpenFOAM simulations. Second, ventilation in three different indoor geometries are studied at both low (0.1 m/s) and high (1 m/s) airflow rates corresponding to Re=5000 and Re=50000. An analysis of the indoor CO2 concentration is carried out as the room is emptied from stale, high CO2 content air. We estimate the air changes per hour (ACH) values for three different room geometries and show that the numerical estimates from 3D CFD simulations differ by 80%–150% (Re=50000) and 75%–140% (Re=5000) from the theoretical ACH value based on the perfect mixing assumption. Third, the analysis of the CO2 probability distributions (PDFs) indicates a relatively non-uniform distribution of fresh air indoors. Fourth, utilizing a time-dependent Wells-Riley analysis, an example is provided on the growth of the cumulative infection risk which is shown to reduce rapidly after the ventilation is started. The average infection risk is shown to reduce by a factor of 2 for lower ventilation rates (ACH=3.4-6.3) and 10 for the higher ventilation rates (ACH=37-64). Finally, we utilize the new solver to comment on respiratory particle transport indoors. A key contribution of the paper is to provide an efficient, GPU compatible CFD solver environment enabling scale-resolved simulations (LES/DNS) of airflow in large indoor geometries on a single GPU designed for high-performance computing. The demonstrated efficacy of MATLAB for GPU computing indicates a high potential of DNSLABIB for various future developments on airflow prediction.

Particle agglomeration via resonant acoustic mixer for dry powder inhalation

The work presented in this paper employed a resonant acoustic mixing (RAM) process to optimize the fine particle agglomeration process for dry powder inhalation to achieve efficient pulmonary delivery of melatonin. The formulation prepared by acoustic mixing with the double layer grids demonstrated superior agglomerate particle size distribution and approximately 90% of the metered dose in the dosing chamber was emitted from Turbuhaler® (90% emitted dose). Acceleration force during acoustic mixing significantly affected the packing fraction of mixtures and mechanical strength of agglomerates resulting in improved fine particle fraction. The particle agglomeration via RAM can improve the efficiency of agglomerate production by utilizing the internal space of the mixer to induce more particle collision. The agglomerates formulation exhibited ideal fine particle fraction of 47.65 ± 1.46% and 56.02 ± 2.55% at flow rates of 30 and 60 L/min, respectively. The fine particle deposition was only slightly affected at the lower air-flow rate, suggesting a reliable inhalation performance in vivo.

Experimental investigation of a desalination system using porous carbon tube as a humidification media with swirl flow

Humidification-dehumidification (HDH) technology is a technique for small-scale water desalination applications based on carrier gas humidification motivated by thermal energy. The present work introduces an experimental investigation of a desalination unit based on HDH method. The main objective of this study is to evaluate the heat and mass transport properties of porous carbon tubes (PCT) as a humidification medium with swirl flow for HDH unit. Processes for transferring heat and mass are investigated at varied the temperatures of water and air, water-to-air mass ratios (MR), and helical flow channel pitch (HCP). The performance analysis is investigated based on some of performance metrics such as gained output ratio (GOR), humidification efficiency (ηH), exergy efficiency (ηex), sustainability indicator (SI), and water cost (WC). Results indicate that the increase in MR and HCP increases all of performance parameters. High values of MR based on low air flow rate decrease the entropy generation and enhance the exergy efficiency. The humidity efficiency and GOR improve with the rise in the MR based on the water flow rate. The study of sustainability indicator shows that the proposed system has possibilities of doing business. It still has room for energy improvement and losses, though. The system's usability will increase after these modifications are made. When the process temperature associated with heating the feed water or/and input air rises, more freshwater is produced. The proposed system's maximum hourly yield reaches about 0.225 L with cost 0.078 cent. The best value of GOR, exergy efficiency, humidification efficiency and suitability indicator performed by the current system are about 3, 51.67 %, 48.72 % and 2.07 respectively.

Impact of Preheating on Flame Stabilization and NOx Emissions From a Dual Swirl Hydrogen Injector

Abstract Flame stabilization, flame structure, and pollutant emissions are investigated experimentally on a swirled injection system operating with globally lean air/hydrogen mixtures at atmospheric conditions and moderate Reynolds numbers. This injector consists of two coaxial ducts with separate injection of hydrogen into a central channel and of air into an annular channel. Both streams are swirled. The resulting flames exhibit two stabilization modes. In one case, the flame takes an M-shape and is anchored to the hydrogen injector lips. In the second case, the flame is aerodynamically stabilized above the injector and takes a V-shape. Regions of existence of each stabilization mode are determined according to the operating conditions. For low air flow rates, the flame can be either anchored or lifted above the hydrogen injector lips depending on the path followed to reach the operating condition. At high air flow rates, the flame is always lifted regardless of the trajectory followed. The impact of air inlet temperature on these stabilization regimes is then evaluated from T= 300 K up to 770 K. Flame re-attachment is shown to be controlled by edge flame propagation and the impact of preheating is well reproduced by the model. Unburnt hydrogen and NOx emissions are finally evaluated. Unburnt hydrogen is only observed for global equivalence ratios below 0.4 and at ambient inlet temperature. NOx emissions decrease when the global equivalence ratio is reduced. Furthermore, at fixed global equivalence ratio, NOx emissions decrease as the thermal power increases, regardless of air preheating and the flame stabilization regime. At high power, NOx emissions reach an asymptotic value that is independent of the thermal power. The impact of flame shape, air preheating, and combustion chamber wall heat losses on NOx production is also evaluated. NOx emissions are shown to scale with the adiabatic flame temperature Tad at the global equivalence ratio and the residence time inside the combustor.

The role of smoldering in the ignition of Pinus palustris needles

The pyrolysis process and the critical ignition conditions of dead Pinus palustris needles were studied experimentally to understand the role of smoldering in the onset of flaming combustion. The results obtained show that methane (CH4), carbon monoxide (CO), carbon dioxide (CO2), and water vapor (H2O) are the main constituents of the pyrolysis gases generated. The predominance of these compounds was found to be independent of the external heat flux, while their concentrations were sensitive to it. The heat of combustion of the pyrolysis gas and the pyrolysis reaction rate increased with increasing external heat fluxes. Visual observations and parameter measurements during testing hinted at the significance of smoldering to flaming ignition under forced flow conditions. The contribution of smoldering to flaming ignition was quantitively analyzed by combining the measured parameters during testing with the characterized pyrolysis process. The quantification results suggested a significant contribution of smoldering combustion to the flaming ignition under low heat fluxes and high airflow rate conditions.

Membrane bubble aeration unit: Experimental study of the performance in lab scale and full-scale systems

The transfer of oxygen is limited at the gas/liquid interface by the low solubility of oxygen in water. Fine bubble diffusers have a standard oxygen transfer efficiency (SOTE) lower than 30% in a full-scale system. Porous membranes can be employed as diffusor to improve the efficiencies taking the advantage of the high exchange interfacial area and the low volume of equipment. The aim of this work is to study the feasibility of membrane systems for aeration in a full-scale system. Several membrane modules were prepared using hollow fibers hydrophobic membranes and compared with the traditional disk diffusor currently employed in wastewater treatment. The mass transfer coefficient (KLa) and SOTE were assessed by carrying out the aeration tests in both lab-scale and full-scale systems exploring different operating parameters such as system flow rate, the geometry of the module and the surface of the device. The advantage and disadvantages of employing membranes in the aeration process were highlighted. The membrane unit showed better overall mass transfer efficiency increasing from 28% at the lab-scale to 34% in the full-scale system. Unlike the conventional disk diffusers, it has been found that the membrane aerator can operate with significantly lower air flow rates, which leads to a doubling of the efficiency. Moreover, the membrane surface generating the bubbles can be easily increased while maintaining the same module footprint, which in turn allowing a further increase of efficiency from 9% to 24%. However, important phenomena of scaling were observed on the membrane surface.

Automated fault detection and diagnosis of airflow and refrigerant charge faults in residential HVAC systems using IoT-enabled measurements

While automated fault detection and diagnosis (AFDD) in residential heating, ventilation, and air-conditioning (HVAC) using smart thermostat data is gaining increasing attention in recent times, it still requires in-depth investigation for market adoption, especially with real-life data. This paper proposes an Internet of Things (IoT) - based approach that adds a smart sensor to the smart thermostat data to carry out AFDD. The approach uses a model which predicts enthalpy change across the evaporator and compares the prediction to the measured enthalpy change. Deviations which exceed analytically determined thresholds then signal faults in the HVAC system. The faults detected are either installation related or degradation related. Experimental tests were carried out in four homes located in Norman, Oklahoma. From the tests, installation issues like indoor/outdoor mismatch were detected in two homes, while a 30% low charge and low indoor airflow rate were detected in one home. The results show that the proposed AFDD algorithm was able to successfully detect two prevalent faults, namely low indoor airflow and low refrigerant charge. Unlike most of the smart thermostat-based approaches, the proposed IoT-based approach can detect and diagnose both faults but only require one additional sensor which is provided by smart thermostat manufacturers.