Flame Propagation Through Atmospheres Involving Concentration Gradients Formed by Mass Transfer Phenomena

1975 ◽  
Vol 97 (4) ◽  
pp. 615-617 ◽  
Author(s):  
G. A. Karim ◽  
P. Tsang
Keyword(s):  
Mass Transfer ◽  
Flame Propagation ◽  
Concentration Gradient ◽  
Fire Spread ◽  
Local Concentration ◽  
Concentration Gradients ◽  
Lean Mixtures

The purpose of the present work is to establish experimentally the nature of the phenomena and the rate of fire spread through explosive media involving concentration gradients in a fuel-air mixture. Most of the work reported has been limited to upward flame propagation using methane as a fuel. Wide deviations from the quasi-steady approach were observed when a flame propagates along a negative concentration gradient in lean methane-air mixtures. It appears that the observed rate of fire spread in stratified lean mixtures can be correlated directly in terms of local concentration gradients and the corresponding propagation rates under homogeneous conditions.

Hydrogen-Air Deflagration in the Presence of Longitudinal Concentration Gradients

2013 ◽  
Author(s):  
S. Kudriakov ◽  
M. Kuznetsov ◽  
E. Studer ◽  
J. Grune
Keyword(s):  
Flame Propagation ◽  
Hydrogen Concentration ◽  
Concentration Gradient ◽  
Nuclear Reactor ◽  
Combustion Process ◽  
Pressure Sensors ◽  
Severe Accident ◽  
Critical Conditions ◽  
Local Concentration ◽  
Concentration Gradients

Hydrogen gathering at the top of the containment or reactor building may occur due to an interaction of molten corium and water followed by a severe accident of a nuclear reactor (like TMI, Chernobyl, Fukushima accidents). It accumulates usually in a containment of nuclear reactor as a stratified semi-confined layer of hydrogen-air mixture. Depending on the local concentration and/or presence and activation of mitigation devices, hydrogen may burn following different combustion regimes. Thus, there is a need to estimate the severity of a combustion process under given geometrical configuration, scale, ignition position, and uniformity and composition of combustible mixture. A series of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the LACOMECO European project is devoted to flame propagation in an obstructed large scale cylinder vessel with vertical hydrogen concentration gradients. A 33 m3 volume divided in two sub-compartments, lower (21.6 m3) and upper (11.2 m3), separated by round duplex door of 1 m diameter with a metal structure with 6 layers of wooden plates reproduce real geometry of obstructions with a blockage ratio of 0.33–0.43. A sampling probes method is used to control real distribution of hydrogen. Practically linear positive and negative vertical concentration gradients in the range from 4 % to 13 % are created prior to ignition. Pressure sensors (PCB type), ion probes and thermocouples are used in the experiments to monitor dynamics of hydrogen combustion. The process of flame propagation is investigated depending on hydrogen concentration gradient and ignition positions. Critical conditions for flame acceleration-deceleration and quenching of the flame due to hydrogen concentration gradient are the main scopes of the work. The experimental data obtained during the project will be used for safety analysis, risk assessment and as benchmark experiments for CFD numerical codes validation.

scholarly journals Mass Transfer and Flow Characterization of Novel Algae Based Nutrient Removal System

2021 ◽  
Author(s):  
Andreas Heyland ◽  
Jeremy Chau ◽  
Kevin Chai ◽  
Andrew Eaton ◽  
Kathleen Nolan ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Nutrient Removal ◽  
Concentration Gradient ◽  
Mass Transfer Rate ◽  
Algal Growth ◽  
Mixing Efficiency ◽  
Concentration Gradients ◽  
Recirculating Aquaculture Systems ◽  
Removal System

Abstract Background: Recirculating aquaculture systems (RAS) are an essential component of sustainable inland seafood production. Still, nutrient removal from these systems can result in substantial environmental problems, or present a major cost factor with few added value options. In this study, an innovative and energy-efficient algae based nutrient removal system (NRS) was developed that has the potential to generate revenue through algal commercialization. We optimized mass transfer in our NRS design using novel aeration and mixing technology, using air lift pumps and developed an original membrane cartridge for the continuous operation of nutrient removal and algae production. Specifically, we designed, manufactured and tested a 60-liter NRS prototype. Based on specific airlift mixing conditions as well as concentration gradients, we assessed NRS nutrient removal capacity. We then examined the effects of different internal bioreactor geometries and radial orientations on the mixing efficiency. Results: Using the start-up dynamic method, the overall mass transfer coefficient was found to be in the range of 0.00164-0.0074s-1, depending on flow parameters and we confirmed a scaling relationship of mass transfer across concentration gradients. We found the optimal Reynolds number to be 500 for optimal mass transfer, as higher higher Reynolds numbers resulted in a relatively reduced increase of mass transfer. This relationship between mass transfer and Reynolds number is critical to assess scalability of our system. Our results demonstrate an even distribution of dissolved oxygen levels across the reactor core, demonstrating adequate mixing by the airlift pump, a critical consideration for optimal algal growth. Distribution of dissolved gases in the reactor was further assessed using flow visualization in order to relate the bubble distribution to the mass transfer capabilities of the reactor. Conclusions: Manipulation of the concentration gradient across the membrane demonstrates a more prominent role of airlift mixing at higher concentration gradients. Specifically, the mass transfer rate increased 3-fold when the concentration gradient was increased 2.5-fold. Our findings provide support for scalibilty of the design and support the use of this novel NRS for nutrient removal in aquaculture and potentially other applications.

scholarly journals Bacterial Chemotaxis to Naphthalene Desorbing from a Nonaqueous Liquid

2003 ◽  
Vol 69 (10) ◽  
pp. 5968-5973 ◽  
Author(s):  
Aaron M. J. Law ◽  
Michael D. Aitken
Keyword(s):  
Mass Transfer ◽  
Pseudomonas Putida ◽  
Aqueous Phase ◽  
Concentration Gradient ◽  
Bacterial Chemotaxis ◽  
Wild Type ◽  
Concentration Gradients ◽  
Mutant Strains ◽  
Hydrophobic Pollutants ◽  
Phase Liquid

ABSTRACT Bacterial chemotaxis has the potential to increase the rate of degradation of chemoattractants, but its influence on degradation of hydrophobic attractants initially dissolved in a non-aqueous-phase liquid (NAPL) has not been examined. We studied the effect of chemotaxis by Pseudomonas putida G7 on naphthalene mass transfer and degradation in a system in which the naphthalene was dissolved in a model NAPL. Chemotaxis by wild-type P. putida G7 increased the rates of naphthalene desorption and degradation relative to rates observed with nonchemotactic and nonmotile mutant strains. While biodegradation alone influenced the rate of substrate desorption by increasing the concentration gradient against which desorption occurred, chemotaxis created an even steeper gradient as the cells accumulated near the NAPL source. The extent to which chemotaxis affected naphthalene desorption and degradation depended on the initial bacterial and naphthalene concentrations, reflecting the influences of these variables on concentration gradients and on the relative rates of mass transfer and biodegradation. The results of this study suggest that chemotaxis can substantially increase the rates of mass transfer and degradation of NAPL-associated hydrophobic pollutants.

scholarly journals Mass transfer and flow characterization of novel algae-based nutrient removal system

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Andreas Heyland ◽  
Jordan Roszell ◽  
Jeremy Chau ◽  
Kevin Chai ◽  
Andrew Eaton ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Nutrient Removal ◽  
Concentration Gradient ◽  
Mass Transfer Rate ◽  
Algal Growth ◽  
Mixing Efficiency ◽  
Concentration Gradients ◽  
Recirculating Aquaculture Systems ◽  
Removal System

Abstract Background Recirculating aquaculture systems (RAS) are an essential component of sustainable inland seafood production. Still, nutrient removal from these systems can result in substantial environmental problems, or present a major cost factor with few added value options. In this study, an innovative and energy-efficient algae based nutrient removal system (NRS) was developed that has the potential to generate revenue through algal commercialization. We optimized mass transfer in our NRS design using novel aeration and mixing technology, using air lift pumps and developed an original membrane cartridge for the continuous operation of nutrient removal and algae production. Specifically, we designed, manufactured and tested a 60-L NRS prototype. Based on specific airlift mixing conditions as well as concentration gradients, we assessed NRS nutrient removal capacity. We then examined the effects of different internal bioreactor geometries and radial orientations on the mixing efficiency. Results Using the start-up dynamic method, the overall mass transfer coefficient was found to be in the range of 0.00164–0.0074 $${\mathrm{s}}^{-1}$$ s - 1 , depending on flow parameters and we confirmed a scaling relationship of mass transfer across concentration gradients. We found the optimal Reynolds number to be 500 for optimal mass transfer, as higher Reynolds numbers resulted in a relatively reduced increase of mass transfer. This relationship between mass transfer and Reynolds number is critical to assess scalability of our system. Our results demonstrate an even distribution of dissolved oxygen levels across the reactor core, demonstrating adequate mixing by the airlift pump, a critical consideration for optimal algal growth. Distribution of dissolved gases in the reactor was further assessed using flow visualization in order to relate the bubble distribution to the mass transfer capabilities of the reactor. We run a successful proof of principle trial using the green alga Dunaliella tertiolecta to assess mass transfer of nutrients across the membrane and biomass production. Conclusions Manipulation of the concentration gradient across the membrane demonstrates a more prominent role of airlift mixing at higher concentration gradients. Specifically, the mass transfer rate increased threefold when the concentration gradient was increased 2.5-fold. We found that we can grow algae in the reactor chamber at rates comparable to those of other production systems and that the membrane scaffolds effectively remove nutrients form the wastewater. Our findings provide support for scalability of the design and support the use of this novel NRS for nutrient removal in aquaculture and potentially other applications.

High length-to-width aspect ratio lead bromide microwires via perovskite-induced local concentration gradient for X-ray detection

CrystEngComm ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 2215-2221
Author(s):  
Emma Dennis ◽  
Soumya Kundu ◽  
Deepak Thrithamarassery Gangadharan ◽  
Jingjun Huang ◽  
Victor M. Burlakov ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Concentration Gradient ◽  
Width Ratio ◽  
Local Concentration ◽  
X Ray ◽  
Lead Bromide ◽  
High Length

Well-oriented PbBr2 microwires with a length-to-width ratio of up to 5000 were grown using a concentration gradient in co-crystallization with perovskite. Planar-integrated microwires showed a response to X-ray photons.

Experimental Study on Horizontal Fire Spread Characteristics of Transformer Oil

2021 ◽  
pp. 1-11
Author(s):  
Liyang Li ◽  
Xincheng GUO ◽  
Rongsheng Lu ◽  
Peng Chen ◽  
Congling Shi
Keyword(s):  
Heat Transfer ◽  
Liquid Phase ◽  
Convective Heat Transfer ◽  
Flame Propagation ◽  
Convective Heat ◽  
Fire Spread ◽  
Surface Flow ◽  
Transformer Oil ◽  
Total Heat Flow ◽  
Flame Radiation

Abstract In order to study the horizontal fire spread characteristics of transformer oil, a series of experiments were carried out on the experimental platform developed, the influence of the initial temperature and the width of the oil pool on the flame propagation, including the propagation speed, flame morphology and the temperature field distribution of the gas-liquid two-phase, was analyzed to reveal the flame propagation characteristics and the oil surface temperature rise law in the process of transformer oil fire propagation, and a theoretical model of coupled liquid-phase convective heat transfer and flame radiation heat transfer was established by combining thermodynamic theory to quantitatively calculate the heat transfer process of surface flow in flame propagation process. Through the theoretical analysis and quantitative calculation of gas-liquid heat transfer, it is proved that the surface flow is mainly driven by surface tension and the flame spreads in the form of pulsation. Combined with the experimental data for verification, it is found that the proportion of liquid-phase convective heat transfer to the total heat flow is much larger than that of flame radiation to the total heat flow, which proves that liquid-phase convective heat transfer is the main mode of surface flow heat transfer.

Direct Microprobe Evidence of Local Concentration Gradients and Recycling of Electrolytes During Fluid Absorption in the Rectal Papillae of Calliphora

1980 ◽  
Vol 88 (1) ◽  
pp. 21-48 ◽  
Author(s):  
BRIJ L. GUPTA ◽  
BETTY J. WALL ◽  
JAMES L. OSCHMAN ◽  
T. A. HALL
Keyword(s):  
Extracellular Fluid ◽  
Sodium Concentration ◽  
Dry Mass ◽  
Local Concentration ◽  
Concentration Gradients ◽  
Sodium Potassium ◽  
Local Osmosis ◽  
Intercellular Channels ◽  
Tissue Compartments ◽  
Micro Analysis

1. The concentrations of sodium, potassium and chloride and dry mass were measured by electron-probe X-ray micro-analysis in 1 μm thick frozen-hydrated sections from Calliphora rectum in 5 different states of absorptive function. 2. In all cases the average concentrations of sodium + potassium + chloride was consistently higher in the fluid in the lateral intercellular spaces than in the cytoplasm, the average ratio being 2:1 in water-fed flies and higher in water-deprived flies. 3. The highest concentration of electrolytes was found in the extracellular channel of complex lateral membrane stacks, which is consistent with the histochemical localization of major cation pumps at these sites (Berridge & Gupta, 1968). This concentration exceeded the electrolyte concentration in other tissue compartments by some 80 m-equiv/1 H2O in water-fed flies and about 700 m-equiv/1 H2O in water-deprived flies. The potassium and sodium concentration ratio of this extracellular fluid was nearly 1:1 in water-fed flies, 3:1 in water-deprived flies with KC1 in the rectal lumen, and 0·5:1 with NaCl in the rectal lumen. 4. Results suggest that the extracellular fluid is generated in membrane infoldings along the intercellular channels, and that this fluid gains water and sodium, but loses a variable amount of potassium and chloride, as it passes to the haemolymph, thus supporting the idea of local osmosis and ion recycling.

Experimental and Numerical Investigation of H2-Air Deflagration in the Presence of Concentration Gradients

2013 ◽  
Author(s):  
S. Kudriakov ◽  
E. Studer ◽  
M. Kuznetsov ◽  
J. Grune
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Hydrogen Concentration ◽  
Concentration Gradient ◽  
Large Scale ◽  
Gravity Concentration ◽  
Concentration Gradients ◽  
Flame Acceleration ◽  
Institute Of Technology ◽  
Karlsruhe Institute

A set of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the LACOMECO European project is devoted to flame propagation in an obstructed large scale facility A3 (of 8 m height and 33 m3 volume) with initially vertical hydrogen concentration gradients. Almost linear positive and negative (relative to gravity) concentration gradients are created prior to ignition in the range from 4% to 13%, and the process of flame acceleration is investigated depending on hydrogen concentration gradient and ignition positions. In this paper we describe the A3 facility and analyse the experimental data obtained during the project. The results of numerical simulation performed using Europlexus code are presented together with the critical discussions and conclusions.

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