Flow Residence Time Research Articles

Effect of the Radial Swirler Ellipticity on Hydrogen Flames in a Micro-Gas Turbine Combustor

ABSTRACT A radial swirler burner with an elliptic cross section has been developed for a micro-gas turbine combustor that is commissioned to accommodate hydrogen combustion in the premixed flame mode. A numerical model has been established to explore the swirling combustion performance using the partially premixed flamelet-generated manifold combustion model via employing detailed chemical kinetics. The swirler cross-section aspect ratio has been varied in the range from 1 to 2 at a vane angle of 40 degrees, while the combustion performance was investigated for both fuel conditions of pure hydrogen and 50%/50% hydrogen-methane blend at full load and 50% load. While the results demonstrated the key flow field features, the flame shape as well as the exhaust NOx and CO emissions, it was found that increasing the aspect ratio significantly increased the turbulent kinetic energy and the resultant flow strain. Increasing the aspect ratio additionally increased the peak reverse flow velocity. Inasmuch as this was associated with higher rates of excess air entrainment, the peak flame temperature and the corresponding NOx emissions were reduced on the account of increasing the total pressure drop particularly at the maximum aspect ratio. In this regard, the NOx and CO emissions, respectively, decreased by up to 33% and 46.6% at the aspect ratio of 2.0. As driven by the highly strained reactive swirling flow, the hydrogen-methane premixed flame acquired extension in the flame stability limits. This was accompanied by a consequent reduction in the flow residence time and species re-distribution for NOx formation. The elliptic cross-section radial swirler has thus been proven to be an innovative flow configuration which effectively improves the combustion performance and reduces the resultant emissions.

Initial Performance Outlook on the Sliding Particle Receiver (SlideRec)

The next generation of central receivers is expected to reach high outlet temperatures of 800 °C and above, maintain stable operation and react to a varying incoming flux magnitude caused by hourly and seasonal variations, endure high-temperature operation, and remain cost-effective. Particle-based central receivers are being considered due to their high-temperature durability and favorable thermal properties of particle materials such as bauxite particles. This paper describes a new particle-based central receiver concept and provides an initial exploration of its performance in comparison with the existing CentRec® technology. Discrete Element Method (DEM) simulations demonstrated that a stable falling and sliding particle film can be achieved inside the SlideRec. The residence time of particle flow within the SlideRec is estimated to be higher than a falling particle receiver and similar to that of an obstructed-flow receiver. The results of the thermal model (incorporating reflective, radiative, convective and conductive heat losses) indicate that the SlideRec demonstrates a higher thermal efficiency than the CentRec® under an incoming aperture flux of between 0.1 MW/m2 and 1.7 MW/m2. The concept therefore is promising and is recommended for further experimental exploration.

Performance evaluation of a scramjet engine utilizing varied cavity aft wall divergence with parallel injection in a reacting flow field

Abstract The effect of implications of the dual cavity with aft wall divergence in a parallel injection reacting flow has been numerically investigated. This research intends to emphasize the behaviour of the supersonic flow under varying divergence angles of the cavity aft wall. A two-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation and an SST k-ω turbulence model with a single-step chemical reaction for hydrogen-air are utilized for the simulation. Followed by the strut injector, the cavities are positioned symmetrically inside the combustor. The bottom cavity aft wall divergence varies, whereas the top wall is mounted with a rectangular cavity. The performance of cavity locations is compared with the baseline DLR model. From the evaluation of numerical outcomes along with different cavity configurations, it has been noted that the 15-degree cavity divergence angle enhances the recirculation zone which leads to improved mixing performance. Also, the cavity improves the combustion stability by increasing the flow residence time. From this numerical analysis, it is associated that an almost 20 % reduction in combustor length is achieved, however, an 18 % rise in the pressure loss is noted because of emanating shock waves from the cavity edges.

Isotopic study for evaluating complex groundwater circulation patterns, hydrogeological zoning, and water-rock interaction in a Mediterranean coastal karst environment

In this study groundwater provenance, circulation, and rock interaction processes have been assessed by cross processing the spatial distribution of chemical and isotopic signatures in freshwater with the hydrogeological features of the coastal karst carbonate aquifer of Murgia, located in the southeastern end of Italy, along the Adriatic Sea. Thanks to widespread groundwater quality monitoring (major, minor, and trace-element analyses) and multi-isotopic measures of O, H, Sr, and B, some assumptions about complex groundwater circulation patterns, hydrogeological zoning, and water-rock interaction have been drawn. Three sectors have been distinguished into the Adriatic side of the Murgia aquifer all fed by two main recharge areas located on the most elevated, inner side of the aquifer. Each sector is characterized by different groundwater circulation patterns, residence time, and hydrogeochemical features. The water samples collected into the western sector evidence a certain degree of water-rock interaction, which allows us to assume long groundwater flow paths and residence time. On the contrary, the eastern sector of Murgia has been proven to be characterized by short residence times and a possible direct freshwater contribution even in the downstream course due to the massive presence of karst forms. Herein, the isotopic analysis of the water samples does not provide evidence of water-rock interaction. Finally, in the third, central sector, water infiltrated at different locations mixes flowing through relatively long paths even though not sufficient to allow groundwater to gain the rock's isotopic signature.

Physiochemical View of Fuel Jet Impingement and Ignition Upon Contact with a Cylindrical Hot Surface

Physiochemical View of Fuel Jet Impingement and Ignition Upon Contact with a Cylindrical Hot Surface

Computational fluid dynamics; a new diagnostic tool in giant intracerebral aneurysm treatment

Giant intracerebral aneurysms (GIA) comprise up to 5% of all intracranial aneurysms. The indirect surgical strategy, which leaves the GIA untouched but reverses the blood flow by performing a bypass in combination with proximal parent artery occlusion is a useful method to achieve spontaneous aneurysm occlusion. The goal of this study was to assess the utility of computational fluid dynamics (CFD) in preoperative GIA treatment planning. We hypothesise that CFD simulations will predict treatment results. A fluid-structure interaction (FSI) CFD investigation was performed for the entire arterial brain circulation. The analyses were performed in three patient-specific CT angiogram models. The first served as the reference geometry with a C6 internal carotid artery (ICA) GIA, the second a proximal parent artery occlusion (PAO) and virtual bypass to the frontal M2 branch of the middle cerebral artery (MCA), and the third a proximal PAO in combination with a temporal M2 branch bypass. The volume of "old blood", flow residence time (FRT), dynamic viscosity and haemodynamic changes were also analysed. The "old blood" within the aneurysm in the bypass models reached 41% after 20 cardiac cycles while in the reference model it was fully washed out. In Bypass 2 "old blood" was also observed in the main trunk of the MCA after 20 cardiac cycles. Extrapolation of the results yielded a duration of 4 years required to replace the "old blood" inside the aneurysm after bypass revascularization. In both bypass models a 7-fold increase in mean blood viscosity in the aneurysm region was noted. Bypass revascularization combined with proximal PAO favours thrombosis. Areas prone to thrombus formation, and subsequently the treatment outcomes, were accurately identified in the preoperative model. Virtual surgical operations can give a remarkable insight into haemodynamics that could support operative decision-making.

Enhancing torrefaction process efficiency for biochar production from filter cake residue in the sugar industry

The torrefaction process is a promising technique for enhancing the quality of solid biomass fuels. This study investigates the effects of torrefaction on biochar produced from filter cake residue, a byproduct of the sugar industry. The primary objectives were to evaluate the impact of process parameters on biochar properties and identify optimal conditions for maximizing the higher heating value (HHV). Filter cake residue was subjected to torrefaction at temperatures ranging from 220-340°C under an inert atmosphere. The influence of particle size (20, 60, and 100 mesh), nitrogen flow rate (20-30 ml/min), temperature (220-340°C), and residence time (30-90 min) on biochar properties was examined using response surface methodology. Proximate analysis revealed that torrefaction significantly reduced moisture, volatile matter, and ash content while increasing fixed carbon content. The maximum HHV of 21.9571 MJ/kg was achieved at a particle size of 20 mesh, nitrogen flow rate of 25 ml/min, temperature of 340°C, and residence time of 60 min. The experimental results agreed with predicted values from the developed models, with an average error of 3.64%. Optimal torrefaction conditions were determined to be a particle size of 21.77 mesh, nitrogen flow rate of 22.50 ml/min, temperature of 311.13°C, and residence time of 42.58 min, yielding a maximum HHV of 18.4853 MJ/kg. These findings demonstrate the potential of torrefaction for upgrading filter cake residue into a high-quality solid biofuel, providing a sustainable solution for waste utilization in the sugar industry.

Identifying manning roughness coefficient using automatic calibration method and simulation of pollution incidents in the Nile River, Egypt

Identifying manning roughness coefficient using automatic calibration method and simulation of pollution incidents in the Nile River, Egypt

Investigation of a dual-spiral flat plate solar water heater under natural convection: an experimental study

In residential and industrial areas, a flat plate solar collector (FPSC) is an important technology that allows for direct solar energy utilisation for heating water. Conventional FPSCs have relatively low efficiency. More study is needed to increase the efficiency of FPSC by using novel designs. Modifications to the design of solar collectors are always a viable option for improving thermal efficiency significantly. In this study, dual spiral-shaped flow tubes were constructed instead of the usual flat plate solar collector's number of riser tubes and headers and tested with three different mass flow rates (0.0058, 0.0083, and 0.0117 kg/s). The optimum instantaneous efficiency achieved is 70.8% at a flow rate of 0.0117 kg/s, representing a 13.7% improvement in efficiency compared to the conventional collector. The modified collector achieves its highest instantaneous efficiency when the outlet water temperature is measured at 53.4°C. The modified collector improves heat transfer by increasing surface contact area of water and increasing the flow residence time. This results in a higher absorption of heat by the water, leading to a significant enhancement in the efficiency. When all other parameters are kept the same as in a conventional design, highly encouraging results in modified solar collector have been recorded.

Rough ice cover modified hyporheic exchange: A numerical study on the mechanical effect propagating from the ice-water interface to the sediment–water interface

Rough ice cover modified hyporheic exchange: A numerical study on the mechanical effect propagating from the ice-water interface to the sediment–water interface

Multiphase Numerical CFD Simulation of the Hydrothermal Liquefaction Process (HTL) of Sewage Sludge in a Tubular Reactor

This article presents multiphase numerical computational fluid dynamics (CFD) for simulating hydrothermal liquefaction of sewage sludge in a continuous plug-flow reactor. The discrete particle method (DPM) was used to analyze the solid particles’ interaction in liquid–solid high shear flows to investigate coupling computational fluid dynamics (CFD). Increasing solid particles’ interactions were observed with the increasing liquid velocity. The study examined the influence of parameters such as flow rate, temperature, and residence time on the efficiency of bio-oil production. An increase in temperature from 500 to 800 K caused an increase in the amount of biocrude oil produced from 12.4 to 32.9% within 60 min. In turn, an increase in the flow rate of the suspension from 10 to 60 mL/min caused a decrease in the amount of biocrude oil produced from 38.9 to 12.9%. This study offers insights into optimizing the flow channel of tubular reactors to enhance the HTL conversion efficiency of sewage sludge into biocrude oil. A parametric study was performed to investigate the effect of the slurry flow rate, temperature, and the external heat transfer coefficient on the biocrude oil production performance. The simulation data will be used in the future to design and scale up a large-scale HTL reactor.

Physicochemical properties and performance of non-woody derived biochars for the sustainable removal of aquatic pollutants: A systematic review

Biochar is a carbon-rich material produced from the partial combustion of different biomass residues. It can be used as a promising material for adsorbing pollutants from soil and water and promoting environmental sustainability. Extensive research has been conducted on biochars prepared from different feedstocks used for pollutant removal. However, a comprehensive review of biochar derived from non-woody feedstocks (NWF) and its physiochemical attributes, adsorption capacities, and performance in removing heavy metals, antibiotics, and organic pollutants from water systems needs to be included. This review revealed that the biochars derived from NWF and their adsorption efficiency varied greatly according to pyrolysis temperatures. However, biochars (NWF) pyrolyzed at higher temperatures (400-800°C) manifested excellent physiochemical and structural attributes as well as significant removal effectiveness against antibiotics, heavy metals, and organic compounds from contaminated water. This review further highlighted why biochars prepared from NWF are most valuable/beneficial for water treatment. What preparatory conditions (pyrolysis temperature, residence time, heating rate, and gas flow rate) are necessary to design a desirable biochar containing superior physiochemical and structural properties, and adsorption efficiency for aquatic pollutants? The findings of this review will provide new research directions in the field of water decontamination through the application of NWF-derived adsorbents.

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

Design expert based optimization of the pyrolysis process for the production of cattle dung bio-oil and properties characterization

This study aimed to optimize pyrolysis conditions to maximize bio-oil yield from cattle dung, a waste product of livestock practices. Pyrolysis of cattle dung was carried out in batch type reactor. The pyrolysis process was optimized using a central composite design in response surface methodology, with conversion parameters such as pyrolysis temperature, vapor cooling temperature, residence time, and gas flow rate taken into account. The cattle dung bio-oil was analyzed using gas chromatography/mass spectroscopy (GC/MS), an elemental analyzer, a pH probe, and a bomb calorimeter. Furthermore, the ASTM standard procedures were used to determine the bio-fuel characteristics. The optimized conditions were found to be a pyrolysis temperature of 402 °C, a vapor cooling temperature of 2.25 °C, a residence time of 30.72 min, and a gas flow rate of 1.81 l min−1, resulting in a maximum bio-oil yield of 18.9%. According to the findings, the yield of bio-oil was predominantly affected by pyrolysis temperature and vapor cooling temperature. Moreover, the bio-oil that was retrieved was discovered to be similar to conventional liquid fuels in numerous ways.

The effect of fluid viscoelasticity in soft lubrication

The effect of fluid viscoelasticity in soft lubrication

A Comprehensive Study of Biochar Yield and Quality Concerning Pyrolysis Conditions: A Multifaceted Approach

In this research, we investigated the yields of biochar, bio-oil, and synthesis gas under various pyrolysis conditions, as well as their impact on the elemental composition, FTIR, EDX, SEM, and HCV values of biochar. This study utilized three different pyrolysis temperatures (400 °C, 500 °C, 600 °C), two holding times (30 and 60 min), and two N2 gas flow rates (0.2 and 0.5 L min−1). We observed that an increase in pyrolysis temperature led to a decrease in the yields of biochar and bio-oil, while synthesis gas yield increased, as expected. Additionally, a higher gas flow rate resulted in a reduction of biochar yield from 34.07% to 32.72%. A longer residence time diminished the bio-oil yield but increased the synthesis gas yield. The FTIR, EDX, and elemental analysis of biochar produced at a pyrolysis temperature of 600 °C, with a 60-min holding time and a 0.2 L min−1 N2 gas flow rate, indicated maximized carbon content. Moreover, a more porous structure was observed at higher pyrolysis temperatures. The research also revealed that increases in pyrolysis temperature, residence time, and gas flow rate enhanced the energy content of the biochar.

A novel ray method for the coking of n-decane in circular tubes with flexible cross-section area

Coking of endothermic hydrocarbon fuels significantly deteriorates the efficiency of regenerative cooling for hypersonic airbreathing vehicles. A novel ray method based on dynamic mesh techniques is proposed to describe the coking behavior in a circular tube with a flexible cross-section area. This method can be used to identify metal and deposit coke efficiently, which promotes the applicability of the dynamic mesh method in flexible structures. The cooling performance of n-decane before and after coking is numerically simulated and compared. The deposition brings higher thermal risks by elevating the solid temperature. However, the deposition reduces the channel’s cross-sectional area and increases the flow speed, leading to decreased flow residence time. Because the suppressing effect from lower flow residence time outweighs the promotion effect from increased temperature, the n-decane conversion decreased after coking.

A tractable methodology for assessing the pressure scaling of sooting processes in a counterflow diffusion flame from 1 to 6 bar

A tractable methodology for assessing the pressure scaling of sooting processes in a counterflow diffusion flame from 1 to 6 bar

Characteristics of a Heat Exchanger in a Liquid Rocket Engine Using Conjugate Heat Transfer Coupling with Open-Source Tools

Since a heat exchanger used in a gas generator of an open-cycle liquid rocket engine was operated in a high-temperature environment, the coupled analysis for heat transfer characteristics and structural integrity should be performed simultaneously. For these reasons, a numerical analysis of the heat exchanger in a liquid rocket engine was performed to elucidate the effects of heat transfer and structural deformation simultaneously using conjugate heat transfer (CHT) analysis and open-source tools. For the baseline heat exchanger, which had an inner helically coiled tube with nine turns (), the heat transfer characteristics were investigated and findings showed that the heat transfer performance was reduced from the sixth turn. Further analysis was performed to examine the effect of the number of turns in terms of heat flux and the corresponding pressure drop and the weight of the structure. The results indicated that the heat exchanger with had a significantly reduced outlet temperature due to an excessively shortened flow residence time. The heat exchanger with showed an outlet temperature similar to that of the baseline; it also presented advantages in terms of the pressure drop and structure weight. In addition, the thermal deformation and stress caused by temperature changes were numerically investigated to consider the structural integrity of the heat exchanger with . Further numerical analyses were performed at various flow rates. As the flow rate of helium increased, the amount of heat received from the high-temperature exhaust gas from the gas generator increased but the outlet temperature of helium decreased gradually. Finally, the temperature difference between the outer and inner walls increased due to the high heat flux in the region around the inlet, resulting in an increase in thermal stress. Based on these results, the optimal shape and flow rate of the system were identified. Furthermore, the heat transfer performance was found to correlate with the flow characteristics of the coiled tube.

Modelling droplet size distribution in inline electrostatic coalescers for improved crude oil processing

Water-in-oil emulsions pose significant challenges in the petroleum and chemical industrial processes, necessitating the coalescence enhancement of dispersed water droplets in emulsified oils. This study develops a mathematical model to predict the evolution of water droplet size distribution in inline electrostatic coalescers (IEC) as a promising means to improve the water separation efficiency of current oil processing systems. The proposed model utilizes the population balance modelling approach to effectively simulate the dynamic and complex processes of coalescence and breakage of droplets in crude oil which directly influence the separation efficiency of the process. The method of classes as an effective mathematical technique is selected to solve the population balance equation (PBE). The accuracy of the model and considered assumptions agree well with experimental data collected from the literature. The results demonstrate the model's ability to accurately simulate droplet coalescence and breakage in emulsified oil while predicting droplet size distribution and water removal efficiency. The electric field strength, residence time, and fluid flow rate significantly influence the coalescence of droplets. At 4 kV and 5 m3/h after 4 s the mean diameter of droplets (D50) and separation efficiency reach the maximum of 94.3% and 432 µm, respectively. The model enables the optimization of operational conditions, resulting in increased performance and reliability of oil-processing systems while reducing the energy consumption and use of chemical demulsifiers. Additionally, utilization of the device in optimized conditions significantly reduces the size and weight of downstream separation equipment, which is particularly advantageous for heavy oils and offshore fields.