Numerical Study of Premixed Combustion of Methane Stabilized on Porous Medium

2016 ◽  
Author(s):  
Valerio Giovannoni ◽  
Rajnish N. Sharma ◽  
Robert R. Raine
Keyword(s):  
Porous Medium ◽  
Numerical Study ◽  
Burning Velocity ◽  
Combustion Process ◽  
Heat Losses ◽  
Low Flow ◽  
Small Scale ◽  
High Porosity ◽  
Flow Rates ◽  
Flame Holder

The present study focuses on the numerical analysis of the combustion process occurring in a small scale cylindrical combustion chamber using a commercial computational code. The chosen diameter is 18 mm, being the same as the flat flame regenerative combustor currently under experimental investigation by the author (Giovannoni), and it includes a 10 mm thick porous flame holder and a 1 mm thick stainless steel outer wall. A 17 species and 73 reactions skeletal mechanism related to methane oxidation is employed for the simulations. A parametric study is performed and results in terms of temperature profiles, major species’ concentrations and flow velocities are presented. Results show that the flame holder can considerably affect combustion and heat losses from the combustor. In particular at low flow rates, when the laminar burning velocity is much higher than the flow velocity, heat is lost mainly through the flame holder to the walls and to the surroundings. At high flow rates the flame appears to be slightly lifted from the porous medium and heat is mainly dispersed to the walls. This causes preheating of the mixture upstream of the combustion through axial conduction in the wall, achieving superadiabatic temperature. It is also clear from the simulations that employing a flame holder with low thermal conductivity and high porosity yields benefits in limiting heat losses and in widening flammability limits.

scholarly journals The new design of the wood stove based on the numerical analysis and experimental research

2020 ◽  
Vol 154 ◽  
pp. 04001
Author(s):  
Przemysław Motyl ◽  
Marcin Wikło ◽  
Julita Bukalska ◽  
Bartosz Piechnik ◽  
Rafał Kalbarczyk
Keyword(s):  
Fluid Flow ◽  
Heat Exchange ◽  
Numerical Analysis ◽  
Heat Release ◽  
Experimental Research ◽  
Numerical Study ◽  
Combustion Process ◽  
Small Scale ◽  
Wood Stove ◽  
Wood Stoves

In Europe, especially in Poland, wood-fired stoves remain one of the most popular renewable household heating. The use of wood logs in small-scale units stoves are expected to increase substantially. The work proposes a comprehensive approach to modify the design of wood stoves with heating power up to 20 kW, including design works, simulations, and experimental research. The article also presents the numerical study of a combustion process including fluid flow, chemical combustion reaction, and heat exchange in the wood stove. The retrofit enhanced a more stable heat release from the wood stove, which increased efficiency and reduction of the harmful components of combustion.

A Numerical Study on Separation Characteristics of Magnetic Particles in Magnetophoretic Chip Microchannels

2009 ◽  
Author(s):  
Xinyu Wu ◽  
Huiying Wu
Keyword(s):  
Dynamic Characteristics ◽  
Magnetic Particles ◽  
Numerical Study ◽  
Fluid Velocity ◽  
Capture Efficiency ◽  
Low Flow ◽  
Flow Rates ◽  
Soft Magnets ◽  
Design And Optimization ◽  
Capture Time

In this paper, a two-dimensional dynamic model describing the separation behaviors of magnetic particles in magnetophoretic chip microchannels integrated with double-side symmetric and asymmetric soft magnets is proposed and solved with the combining use of the finite element method and the fourth-order Runge-Kutta method. The dynamic characteristics of magnetic particles during the separation process, including the trajectories of magnetic particles, the capture time and capture efficiency are analyzed. The impacts of the geometrical configurations, fluid velocity and magnetic field intensity are also studied. The results show that the trajectories of the magnetic particles in microchannels are oscillatory because of the alternative magnetic force and this oscillation is more obvious for asymmetric positions of the soft magnets. The oscillatory motion of the particle leads to the increase of the moving distance and delay of the capture time. The capture time depends on the geometrical configurations, the initial positions and the dynamic characteristics of the particles. It is also found that under the same strength of magnetic fields there is nearly no difference on the capture efficiency for symmetric and asymmetric configurations. With the increase of fluid velocity, the capture efficiency drops drastically at low flow rates and decreases slowly at high flow rates. The distance between soft magnets and microchannel walls has the similar influence on capture efficiency. It is expected that the results presented in this paper are helpful for the design and optimization of magnetophoretic separation microsystems.

Scenario-Based Robustness Analysis of Optimized I.D.E.-Style Treadle Pump Designs

2016 ◽  
Author(s):  
Christopher McComb ◽  
Nathan G. Johnson ◽  
Brandon T. Gorman
Keyword(s):  
Developing Countries ◽  
Service Providers ◽  
Operating Cost ◽  
Robustness Analysis ◽  
Development Aid ◽  
Low Flow ◽  
Entrepreneurial Activity ◽  
Small Scale ◽  
Pareto Optimal ◽  
Flow Rates

Poverty affects hundreds of millions of people globally. Market-based strategies can help alleviate poverty in developing countries by encouraging entrepreneurial activity and have the potential to be more effective than traditional approaches, such as development aid from countries or non-governmental organizations. Development organizations often target the agricultural sector because of the prevalence of subsistence and small-scale farming, particularly in rural regions of developing countries. Improving the reliability of irrigation techniques can help farmers expand out of primarily subsistence farming and begin to sell a portion of their crop, thus achieving the objectives of market-based poverty alleviation. Human-powered pumps are a popular tool used in irrigation because they require low capital cost and negligible operating cost. Previous work provided a model for finding Pareto-optimal IDE-style treadle pump designs. This work utilizes that model to produce a dense set of Pareto-optimal designs, and then investigates the robustness of the designs by simulating their performance in a variety of modified use scenarios. Our results show that pumps optimized for low flow rates (less than 3.0 L/s) are highly robust, particularly with respect to age-related changes in the operator’s stature or mobility. In addition, these pumps can operate with near-optimal efficiency across a variety of target flow rates and well depths. These pumps are ideal for single family use or for shared use amongst multiple families in a village. Pumps optimized for flow rates greater than 3.0 L/s are less robust with respect to changes of operator stature (experiencing decreases in flow rate of up to 60%) but may be suitable for use on farms or by service providers.

Numerical study on the combustion characteristics in a porous-free flame burner for lean mixtures

2019 ◽  
Vol 234 (4) ◽  
pp. 935-945 ◽  
Author(s):  
Seyed Amin Ghorashi ◽  
Seyed Mohammad Hashemi ◽  
Seyed Abdolmehdi Hashemi ◽  
Mahdi Mollamahdi
Keyword(s):  
Porous Medium ◽  
Numerical Study ◽  
Combustion Process ◽  
Experimental Tests ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Numerical Results ◽  
Flame Stability ◽  
Porous Burner ◽  
Flame Burner

The present work implements a numerical simulation to investigate the combustion process in a porous-free flame burner. The non-equilibrium thermal condition is performed, and discretization and solving of the governing equations are conducted in a two-dimensional axisymmetric model. In order to simulate the combustion process, a reduced chemical kinetic mechanism of GRI 3.0, which includes 16 species and 41 reactions, is used. In order to prove the precision of the numerical method, some experimental tests are carried out and the numerical results are in a good agreement with the experimental measurements. The numerical results demonstrate that the porous-free flame burner has a higher flame stability compared to the conventional porous burner and the radiative efficiency of the porous-free flame burner is less than the porous burner. In addition, an increase in thermal conduction of the porous medium leads to an extension in the flame stability. In addition, the results show that with decreasing the pore density of porous medium, the flame stability is extended.

Numerical Study on Flame Mesoscopic-Characteristics of Oxy-Coal Mild Combustion

2016 ◽  
Author(s):  
Ruochen Liu ◽  
Enke An ◽  
Kun Wu
Keyword(s):  
Flame Front ◽  
High Velocity ◽  
Numerical Study ◽  
Combustion Process ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Small Scale ◽  
Turbulent Regime ◽  
Mild Combustion ◽  
Global Regime

For achieving efficient oxy-coal combustion in a MILD (Moderate or Intense Low Oxygen Dilution) state, the optimum operating conditions with high-velocity jets in a lab-scale cylindrical furnace (Φ200mm×2000mm) was determined. The mesoscopic characteristics of turbulent and flame behavior under different jet design and jet spacing were simulated and compared. The results show that L=30∼60mm(O2 side) and L=60mm(O2 center) conditions are recommended as oxy-coal MILD combustion as well as IFRF furnace condition, the flame front locates in distributed regime, the global regime was depict as 1 < l/lF < 4, 60 < ReT < 150 and 50 < Ka < 500 ; for flaming conditions, the flame front locates in small-scale turbulent regime or thin reaction zone, the global regime was depicted as 0.5 < l/lF < 4, 40 < ReT < 110 and 30 < Ka < 900 ; with high-velocity oxygen jet technology, the combustion process is in slow chemistry regime (Da << 1), governed by chemical-kinetic mechanism; large spacing (L=75mm) is not favored for co-flow burners due to poor radial mixing as well as the restriction of wall.

Numerical Simulations of Heat and Mass Transfer Process of a Direct Evaporative Cooler From a Porous Layer

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Karima Sellami ◽  
M'barek Feddaoui ◽  
Nabila Labsi ◽  
Monssif Najim ◽  
Youb Khaled Benkahla
Keyword(s):  
Porous Medium ◽  
Porous Layer ◽  
Numerical Study ◽  
Simple Algorithm ◽  
Mass Transfer Process ◽  
High Porosity ◽  
Ambient Conditions ◽  
Cooling Performance ◽  
Evaporative Cooler ◽  
Direct Evaporative Cooler

This paper deals with the numerical study of the combined heat and mass exchanges in the process of direct evaporative cooler, from a porous media of laminar air flow between two parallel insulated walls. The numerical model implements momentum, energy, and mass conservation equations of humid air and water flow incorporating non-Darcian model in the porous region. The finite volume method is used for the mathematical model resolution, and the velocity–pressure coupling is treated with the SIMPLE algorithm. The main objective of this study is to examine the influences of ambient conditions and the porous medium properties (porosity and porous layer thickness) on the direct evaporative cooling performance from a porous layer. The major results of this study demonstrate that the porous evaporative wall could, in a satisfying manner, reduce the bulk air temperature. The better cooling performance can be achieved for lower air mass flow at the entrance and relative humidity. Additionally, the evaporative cooler is more effective for a high porosity and a thick porous medium, with an improvement achieving 23% for high porosity.

Numerical Study of a Small-Scale Micro Gas Turbine-ORC Power Plant Integrated With a Biomass Gasifier

2020 ◽  
Author(s):  
Fabrizio Reale ◽  
Raniero Sannino ◽  
Raffaela Calabria ◽  
Patrizio Massoli
Keyword(s):  
Power Plant ◽  
Gas Turbine ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Combustion Process ◽  
Combustion Stability ◽  
Small Scale ◽  
High Hydrogen ◽  
Micro Gas Turbine ◽  
Fuel Blends

Abstract The paper is focused on coupling a small-scale power plant, based on a micro gas turbine (mGT) and a bottoming Organic Rankine Cycle (ORC), with a biomass gasifier. The aim of this study is to define the optimal strategies to maximize the benefits related to distributed generation and to promote the organic solid waste gasification, in terms of energy efficiency and renewable sources exploitation. In particular, they were investigated the energetic performances of the system when the micro gas turbine was fed with several fuel blends, made by specific volume concentration of syngas and biogas. The low heating value of both considered fuels implies the necessity of operating the mGT in peculiar conditions as determined by the performance maps of compressor and turbine. Then, the thermodynamic analyses of the whole energy system have been carried out to evaluate the performance for each fuel. The high hydrogen content of syngas and the different thermodynamic properties of the studied fuel blends required a deeper investigation of the combustion process. In order to analyze the combustion stability and the fluid dynamic aspects, an accurate investigation of combustion chamber has been performed through a CFD solver. Finally, a comparison of the plant performances for each fuel blend have been reported, along with opportunities and critical aspects related to power plant integration.

An Experimental Investigation of a Temperature Controlled Vapor Supply System

2013 ◽  
Author(s):  
Robert G. Ryan ◽  
Jeffrey Bunting
Keyword(s):  
Constant Pressure ◽  
Heat Transfer Process ◽  
Supply System ◽  
Low Flow ◽  
Small Scale ◽  
Mechanical Pressure ◽  
Vapor Source ◽  
Flow Rates ◽  
Supply Tank ◽  
Temperature Levels

A variety of applications require a constant pressure vapor supply for processes such as purging fluid systems. A typical design would use a high pressure tank of gas (e.g. helium) along with a mechanical pressure regulator to deliver a constant pressure flow. An alternative concept for the vapor source is to use a tank containing a saturated liquid-vapor mixture. As the vapor is drawn off of the top of the tank, the temperature of the mixture is controlled to maintain the desired vapor delivery pressure. The potential advantage of this approach is that the vapor supply system can be designed to be lighter, more compact, and safer. An experiment was designed to test the practicality of this concept in a small scale system. Carbon dioxide was chosen for the saturated mixture due to its availability, safety, and desirable operating pressures near ambient temperature levels. The apparatus was designed to allow for the measurement of relevant temperatures and pressures over a range of vapor delivery flow rates. Temperature control of the supply tank was accomplished by submergence in an ice bath. The experimental results confirm that this type of system can produce a well regulated vapor supply at low flow rates, but fails to produce steady pressures at higher delivery flows due to limitations of the heat transfer process in the supply tank.

Effect of Methane Co-Injection in SAGD--Analytical and Simulation Study

SPE Journal ◽  
2012 ◽  
Vol 17 (03) ◽  
pp. 687-704 ◽  
Author(s):  
Jyotsna Sharma ◽  
R. Gordon Moore ◽  
Sudarshan A. Mehta
Keyword(s):  
Fluid Flow ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Heat Losses ◽  
Steam Quality ◽  
Fine Grid ◽  
Recovery Method ◽  
Flow Rates ◽  
Noncondensable Gas ◽  
Phase Mobility

Summary Steam-assisted gravity drainage (SAGD) is a commercially viable recovery method for oil sands of Athabasca used where other methods have been unsuccessful. In one variation of SAGD, a small amount of a noncondensable gas is added to the injected steam to maintain pressure in the chamber while using the energy in place, reducing steam consumption and providing thermal insulation from overburden heat losses. The role of gas during steam-gas co-injection processes, in terms of its effects on chamber development, bitumen flow rates, and heat losses, is not fully understood, and therefore is the main focus of this work. A new analytical model for gas injection in SAGD is derived, taking into account the three-phase flow of gas, oil, and water in the reservoir. The analytical theory is used to predict the fluid flow rates as well as phase mobility, relative permeability, and saturation profiles in the mobile oil region. The theoretical results are replicated by fine-grid numerical simulations. Methane was used as the noncondensable gas for the purpose of this study because it is the main solution gas in most reservoirs. It is, however, believed that the findings of this study are equally applicable to other noncondensable gases such as nitrogen, air, helium, and others. Fine-grid numerical simulations were performed to gain a visual understanding of gas distribution in a SAGD chamber and its effect on in-situ steam quality, overburden heat losses, phase saturations, and fluid-flow rates. The simulation results support the predictions of the mathematical theory. The results of the analytical and numerical study reveal that methane co-injection with steam is in general unfavorable in a SAGD operation. The injected methane tends to accumulate at the steam condensation front, which lowers the heat transfer rate of steam to the adjacent oil, resulting in lower oil production rates and slower growth of the chamber.

Optimizing the Design of Unbonded Flexible Pipelines With More Realistic Predictions of pH and H2S Content in the Annulus

2017 ◽  
Author(s):  
Li Ke ◽  
Carol Taravel-Condat ◽  
Jean Kittel ◽  
Rémy Mingant ◽  
Claude Duret-Thual ◽  
...  
Keyword(s):  
Ph Monitoring ◽  
Stationary Phases ◽  
Oil Field ◽  
Low Flow ◽  
Small Scale ◽  
Flow Rates ◽  
Dissolved Iron ◽  
Flexible Pipes ◽  
Steel Grades

Due to its high metallic confinement, the annulus of unbonded flexible pipelines is a specific and mild corrosive medium for carbon steel armour wires. This environment presents high supersaturation levels of dissolved iron, leading to pH values far above thermodynamic equilibrium. Furthermore, the permeation of acidic gases (such as CO2 and H2S) through the polymer pressure sheath occurs at very low flow rates. Since the annulus is supersaturated with dissolved iron, part of the H2S is consumed as it slowly arrives into the annulus. Therefore, the annular medium contains low levels of gas far below those predicted by standard thermodynamic models, and less H2S is available to trigger sour cracking. The recent development of harsher oil field conditions (higher water depths, increased CO2 content, presence of H2S...) induced the need to refine the design of flexible pipes to propose more cost effective solutions. As pH and H2S content are key parameters for the selection of steel grades, taking into account the supersaturation and the H2S consumption in the annulus allows major optimization of flexible pipes by using for instance steel grades with higher strength. Therefore, extensive experimental work was conducted over the past years to better characterize the annulus and predict more realistic pH and H2S levels. In this paper, the following developments are presented: – A kinetic corrosion model named FlexCor was derived from numerous corrosion tests done at various CO2 pressures in confined configuration, with in-situ pH monitoring. These tests were performed over long durations (3 months) in order to capture the effective long term supersaturated pH. The kinetic model is able to simulate the transient and stationary phases of the supersaturated pH evolution up to 45 bara of CO2, providing a good fit with the experimental data. The tests also demonstrated that the annulus environment remains supersaturated even at high CO2 partial pressures. – A methodology taking into account the H2S consumption was developed based on extensive long-term small scale and full scale testing (> 2 years), where low flow rates of H2S were imposed. The experimental results show that H2S consumption is far from negligible, even when the annulus is not fully flooded. This H2S consumption methodology was certified by an Independent Verification Agency and is now being applied on commercial projects.

Sign in / Sign up

Export Citation Format

Share Document