Nitrogen Jet Research Articles

Pressure-equilibrium semi-implicit solver for real fluids

In this study, a semi-implicit pressure-based scheme which can suppress the spurious pressure oscillations is developed for real fluid flows. Conservation properties relevant to the proposed scheme are investigated through one-dimensional numerical simulations of the nitrogen interface advection. The efficiency and validity of this scheme are carefully examined with two- and three-dimensional numerical simulations of cryogenic nitrogen jets. From the one-dimensional simulation results, the conservation properties are well conserved as the past studies. The two-dimensional simulation results show that the developed scheme can reduce the computational cost by more than 92% (13–14 times faster) compared with the conventional density-based explicit solver employing the double flux model. It is also found that, through the three-dimensional simulation results, the developed scheme can predict the structure of the nitrogen jet under both transcritical and supercritical conditions, while taking into account the effects of real fluid properties on the mixing and spatiotemporal evolution of this jet, with excellent accuracy.

Study on the Stress Distribution Characteristics of Rock in the Bottomhole and the Influence Laws of Various Parameters Under the Impact of a Liquid Nitrogen Jet

This study presents research on the stress distribution characteristics of rock in the bottomhole and the influence laws of various parameters under the impact of liquid nitrogen jet. A multi-field coupled numerical model considering transient flow field, conjugate heat transfer, and nonlinear solid deformation was established to investigate the damage-induced fracturing mechanism of rock under liquid nitrogen jet. The study compares the impact effects of liquid nitrogen jet and water jet on rock and analyzes the variations in the stress field under different parameters. Due to its extremely low temperature, the liquid nitrogen jet creates a strong thermal stress gradient in a short time, significantly increasing the maximum principal stress and Mises stress in the rock compared to a water jet. Solid parameters, particularly the confining pressure and elastic modulus of the rock, have a more significant impact on stress distribution, while fluid parameters such as outlet pressure and fluid temperature have a smaller and more volatile effect. An increase in confining pressure inhibits tensile failure in the rock, while a higher elastic modulus enhances both tensile and shear failure. The initial rock temperature significantly affects the stress distribution, with optimal tensile failure observed at intermediate temperatures. The liquid nitrogen jet achieves a higher maximum velocity and overflow velocity than the water jet, contributing to more effective rock fracturing. The results provide a theoretical basis for the optimization of liquid nitrogen jet drilling parameters, which can help improve drilling efficiency.

On gravity-driven liquid nitrogen jets reach and horizontal spread for extinction of ground fires by aerial means

This paper describes experimental and numerical results on the reach and the spread of gravity-driven jets of liquid nitrogen (LN2) on the ground for applications to fire extinction by aerial means. A series of experiments released LN2 jets from different elevations in ambient air to measure their reach and spread distances upon the impingement. A numerical model was developed to simulate the behavior of such jets. Upon validation, the numerical model was used to further predict the LN2 pool mass and spreading distances under various release configurations. Results showed that the LN2 survivability is greatly affected by the release height of the cryogen, since the LN2 quantity reaching the ground decreases as the release height increases. Moreover, releasing larger initial LN2 quantities and, most importantly using larger nozzle diameters, both the LN2 pool mass and spreading diameter can be extended. Additional experiments were conducted where cryogen jets were released onto small (∼300 cm2) alcohol pool fires; results showed that only limited quantities of the LN2 evaporated in transit to the fire, and small amounts of the cryogen expediently snuffed the fires. A simplified model also suggested that in fire supression/extinction by LN2 the fuel cooling mechanism is of secondary importance compared to the mechanism of separating the fuel from oxygen.

Fluorescence imaging of plume-surface interaction in large-scale reduced pressure environments

Planar laser-induced fluorescence (PLIF) was applied for the first time in the 20-ft vacuum chamber at the Marshall Space Flight Center to visualize the plume-surface interaction (PSI) of a nitrogen jet seeded with nitric oxide (NO). A Mach 5.3 nozzle was used to simulate the exhaust of a landing spacecraft for two different jet stagnation pressures and one jet stagnation temperature. A flat plate was used to simulate the landing surface, and two different dimensionless altitudes were investigated. The chamber pressure was reduced such that both lunar-relevant environments at 0.01–28 Pa and Martian-relevant environments at ∼600 Pa were investigated. PLIF flow visualization was performed using a pulsed, tunable, ultraviolet laser, which entered the vacuum chamber through a window, and was directed to the test article using remote-controlled mirrors. Fluorescence at ultraviolet wavelengths was imaged using an intensified camera, which was placed inside a pressurized enclosure located inside the vacuum chamber. For the Martian-relevant condition, a Mach disk and stagnation bubble were observed at h/De = 10, whereas a pair of oblique stagnation shocks were observed at h/De = 3. Significantly complex flows, such as different stagnation shock behaviors, were observed for the lunar-relevant conditions based on the h/De and Reynolds number. The results presented here are the first NO-PLIF measurements of the PSI flowfield within rarefied environments. The unique information on jet expansion and plume structure will be useful to aid researchers in validating complex computational simulations and to inform engineering designs of extraterrestrial landing systems.

A new non‐equilibrium modification of the k−ω$$ k-\omega $$ turbulence model for supersonic turbulent flows with transverse jet

AbstractThe goal of this research is to propose a new modification of a non‐equilibrium effect in the turbulence model to better predict high‐speed turbulent flows. For that, the two local compressibility coefficients are included in the balance production/dissipation terms in a specific dissipation rate equation. The specific dissipation rate reacts to changes in the local Mach number and density through these local coefficients. The developed model is applied to the numerical simulation of the spatial supersonic turbulent airflow with round hydrogen injection. In that, the effects of the proposed turbulence model on the flow field behavior (shock wave and vortex formations, shock wave/boundary layer interaction, and mixture layer) are studied via the solution of three‐dimensional Favre‐averaged Navier–Stokes equations with a third‐order Essentially Non‐Oscillatory scheme. A series of numerical experiments are performed, in which an allowable range of local constants by comparing results with experimental data is obtained. The non‐equilibrium modification by simultaneous decrease of the turbulence kinetic energy and increase of the specific dissipation rate gives a good agreement of the hydrogen depth penetration with experimental data. Also, the numerical experiment of the supersonic airflow with a nitrogen jet shows wall pressure distribution is consistent well with experimental data.

Comparison with the effect of the cyclic liquid nitrogen jet and liquid nitrogen immersion cooling on the deterioration of mechanical properties of high temperature rocks

In order to study the effect of liquid nitrogen jet cooling on the deterioration of mechanical properties of high temperature rocks, the cyclic liquid nitrogen jet (LNJ) cooling and liquid nitrogen immersion (LNI) cooling were carried out on 200 °C and 400 °C granite. The variations of ultrasonic velocity, tensile strength, acoustic emission and energy evolution were analyzed. The results showed that with the increase of rock temperature and cooling cycles, the deterioration of mechanical properties of high temperature rock was enhanced by cyclic LNJ and LNI cooling. Differently, the deterioration effect of LNI cooling on mechanical properties was weakened with the increase of cycles. On the contrary, the deterioration effect caused by LNJ cooling was significantly enhanced with the increase of cycles. For example, when the LNI cooling cycles exceeded 5 times for 200 °C sample and 3 times for 400 °C sample, the tensile strength and absorbed energy at failure decreased limitedly with the growth of cooling cycles. However, the deterioration degree of rock mechanical properties at 400 °C showed a linear decline trend with the increase of LNJ cooling cycles. The temperature and the number of cycles had significant effects on mechanical properties, with temperature having the greatest influence. The difference between LNJ and LNI cooling became more pronounced with increasing cycles. LNJ cooling, by creating localized high thermal stresses and non-uniform heat transfer, led to continuous deterioration of mechanical properties with each cycle. In contrast, LNI cooling's effect saturated after initial cycles. The multi-cycle LNJ cooling method could improve the fracture degree of high temperature rock under low load level, so as to improve the efficiency of high temperature hard rock formation drilling.

Influence of thermodynamic conditions on the mixing characteristics of a supercritical nitrogen jet under mode excitation

Fuel injection mixing is one of the critical factors affecting the energy conversion efficiency and emission level of thermal engines. The effect of thermodynamic conditions on mixing characteristics of supercritical cryogenic nitrogen jet under varicose mode excitation is investigated using the unsteady Reynolds-averaged Navier-Stokes method combined with real-gas thermodynamics and transport properties of nitrogen in NIST database. The ambient-to-jet density ratio is defined to represent different thermodynamic conditions and is found to affect the jet mixing enhancement directly. As the density ratio increases from 0.098 to 0.432, the density gradient reduces in the jet shear layer, mitigating flow stratification. Jet mixing is enhanced with a reduction of density potential core length by 24 % and a tripled density spreading angle. Under varicose mode excitation, large vortices are formatted close to the jet orifice, especially for higher density ratio cases. The peak of the jet turbulent kinetic energy is higher and shifts upstream as density ratio increasing. The jet mixing enhancement is further achieved, with the spreading angle increment growing from 1° to 4° and the velocity decay rate increasing from 0.03 to 0.15. As the excitation amplitude rising from 5 % to 15 %, the growth of jet momentum instability in the jet potential core breaks the velocity gradients inhibition on jet mixing. The supercritical jet enters self-similar region earlier, with density potential core length shortened by 51 % and spreading angle increased by 28 % at a middle density ratio of 0.275.

Comparative extinction of pine needle fires by gravity-fed release of inert cryogen or water

Dead needle debris accumulates in pine forest floors and poses wildfire hazards. This manuscript reports on laboratory-scale research, where gravity-fed liquid nitrogen (LN2) jets were used to suppress and extinguish pine needle fires. Minimum quantities of LN2 needed for fire extinction were determined, and similar quantities of gravity-fed water jets or water sprays were also used to illustrate differences in the underlying extinction mechanisms. LN2 snuffed the fires instantaneously, as its massive flash-vaporization and volumetric expansion displaced the surrounding air and starved the fires for oxygen. Concomitant cooling of the flame zone and the fuel bed also occurred by the vaporizing cryogen. To the contrary, water suppressed the fire by wetting and cooling accessible fuel surfaces. However, fuel bed surfaces which were not wetted continued to pyrolyze and smolder, and eventually reignited. In these experiments, a portion of the volatile LN2 jet vaporized in transit, a portion vaporized while traversing the hot gases of the flame, a portion vaporized in the pine needle pile, and some reached the ground and was absorbed therein. Application of LN2 to fires in confined spaces was most effective for fire extinction. Application of the cryogen to hot spots facilitated flash vaporization for maximum volumetric expansion.

Analysis of the interaction of a shock with two square bubbles containing different gases

The shock–bubble interaction problem remains of interest to researchers to study shock accelerated in-homogeneous flows and the Richtmyer–Meshkov instability. In the present work, simulations have been performed using the high-order Direct Flux Reconstruction scheme to study such interactions when a Mach 1.22 shock is incident on two configurations: one in which a helium bubble is in front of SF6, and, the other in which SF6 is in front of helium; in both cases, the ambient gas is nitrogen. High-order schemes are often preferred for such cases since these interactions usually involve small-scale flow features that are better resolved using high-order methods. When helium is in front of SF6, the helium bubble traverses along the initial horizontal surface of the SF6 and nitrogen, and with time, moves ahead of SF6. There are no regions of pure helium for this case at later stages. When SF6 is placed in front of helium, a separation of helium takes place in two parts, one of which mixes with SF6 while the other remains mostly pure even at later stages. A jet of nitrogen can also be seen moving at very high speeds, penetrating the region of pure helium.

Risk Assessment and Analysis of Rock Burst under High-Temperature Liquid Nitrogen Cooling

Rock burst, an important kind of geological disaster, often occurs in underground construction. Rock burst risk assessment, as an important part of engineering risk assessment, cannot be ignored. Liquid nitrogen fracturing is a new technology used in the geological, oil, and gas industries to enhance productivity. It involves injecting liquid nitrogen into reservoir rocks to induce fractures and increase permeability, effectively reducing rock burst occurrences and facilitating the flow of oil or gas toward the wellbore. The research on rock burst risk assessment technology is the basis of reducing rock burst geological disasters, which has important theoretical and practical significance. This article examines the temperature treatment of two types of rocks at 25 °C, 100 °C, 200 °C, 300 °C, and 400 °C, followed by immersion in a liquid nitrogen tank. The temperature difference between the liquid nitrogen and the rocks may trigger rock bursting. The research focused on analyzing various characteristics of rock samples when exposed to liquid nitrogen. This included studying the stress–strain curve, elastic modulus, strength, cross-section analysis, wave velocity, and other relevant aspects. Under the influence of high temperature and a liquid nitrogen jet, the wave velocity of rocks often changes. The structural characteristics and possible hidden dangers of rocks can be understood more comprehensively through section scanning analysis. The stress–strain curve describes the deformation and failure behavior of rocks under different stress levels, which can help to evaluate their stability and structural performance. The investigation specifically focused on the behavior of rocks subjected to high temperatures and liquid nitrogen. By analyzing the stress–strain curves, researchers were able to identify the precursors and deformation processes that occur before significant deformation or failure. These findings have implications for the mechanical properties and stability of the rocks.

Low-frequency oscillation flow in nitrogen jet condensation

Jet condensation is a complicated two-phase flow phenomenon that occurs in pipe flow, especially in cryogenic fluids. In this study, the condensation flow dynamics of a stream of nitrogen (N2) injected into a subcooled liquid nitrogen (LN2) flow was photographically investigated using a high-speed camera. The pulsating pressure was measured at different observation points using dynamic pressure transducers. Three typical condensation flow patterns were observed and measured under different nitrogen volume fluxes: suck-back flow, transition flow, and oscillation flow. Suck-back flow occurs at a smaller N2 volume flux, where the LN2 is periodically sucked back into the gas chamber. Oscillation flow is encountered at larger N2 volume flux, along with intense pressure fluctuations. Using fast Fourier transform analysis, the frequency of these pressure oscillations was found to be in the range 16–18 Hz with a maximum amplitude of about 10 kPa. An image-processing method was developed to track the fluid motion in the dynamic photographs recorded by the high-speed camera according to the local changes of pixels. The results show the presence of a periodic shrinking of the vapor-plume trail with the same frequency as the pressure oscillation. The mechanism for the low-frequency oscillation flow is, therefore, identified as periodic interfacial condensation. The findings of this study provide strong evidence for the origin of the low-frequency pressure oscillations observed in cryogenic liquid rocket engines. This information can be used to improve the design and operation of such propulsion systems.

Hexamethyldisiloxane pyrolysis: Probing H-atom initiation by femtosecond two-photon LIF

Previous experiments have led to the hypothesis that pyrolysis of silica nanoparticle precursors carried in an inert central gas jet surrounded by a laminar flame is initiated not by thermal decomposition (the measured jet temperatures are too low for pyrolysis), but by reactions with H-atoms diffusing from the surrounding flame into the jet. The current work tests this hypothesis using femtosecond two-photon laser-induced fluorescence (fs-TPLIF) to image H-atom concentrations in the same flame configuration as the previous experiments. Methane flames (ϕ = 0.83, 1.01 and 1.13) were generated using a multi-element diffusion (Hencken) burner equipped with a central tube through which the N2 jet was introduced. The fs-TPLIF line imaging showed significant concentrations of H-atoms in the nitrogen jets at heights above the burner (HAB) close to the methane flame front. The measurements indicate radial diffusion of the H atoms from the flame to the jet is significant. The H-atom concentrations in the jet increased with increasing stoichiometry of the methane flame. Additional experiments were performed with hexamethyldisiloxane entrained in the central jet flow. In each case, a diffusion flame producing silica nanoparticles was established at the boundaries between the central jet and the methane flames. The 2D H-atom images showed a transition from over-ventilated diffusion flames to under-ventilated diffusion flames with increasing equivalence ratio. Furthermore, the fs-TPLIF profiles show a significant production of H-atoms within the jet when the surrounding flame is lean. This knowledge contributes to a deeper understanding of the underlying mechanisms governing these synthesis flame systems and opens avenues for advancing silica nanoparticle synthesis techniques.

Downhole heterogeneous heat transfer characteristics and rock stress distributions induced by liquid nitrogen jet

Downhole heterogeneous heat transfer characteristics and rock stress distributions induced by liquid nitrogen jet

The influence of gas heating on the calculated supersonic parameters of gas-powder flow at slag blower in the converter. Message 1

The article shows that one of the priority tasks in steel production technology is to increase the durability of the lining of oxygen converters. It is shown that the slag blower is a radical way to increase the durability of the lining of oxygen converters. When blowing the melt with oxygen, the MgO content in the slag is 6-8%. To increase the chemical affinity of the slag and the lining, it is proposed to blow the converter slag with jets of nitrogen or powder gas. To achieve optimal chemical affinity of the lining and slag, it is recommended to modify the latter by increasing the content of magnesium oxide in it to 12-14%. Increased durability of the lining makes it possible to solve the problem of replacing wasteful wastes of coal slag and changing environmental concerns on the excess media. It is shown that an attempt to increase the efficiency of modeling very complex processes of interaction of supersonic jets with converter slag has not yet been solved a. A critical analysis of existing methods for constructing mathematical models based on the use of known gas-dynamic laws of interaction of free turbulent jets with the melt is carried out. It has been established that only supersonic jets with their characteristic shock-wave structure always enter the slag melt. An integral method for calculating the parameters of a gas-powder flow in a supersonic nozzle taking into account the powder concentration is presented. It is determined how heating of the gas suspension affects the required pressure in front of the nozzle block, the speed and flow density in the outlet section of the supersonic nozzle. The gas dynamics system is connected to the heat exchange of the flowing gas-dispersed mixture in the Laval expansion nozzles to establish the heating effect in front of the nozzle block of the two-phase gas suspension to a temperature that will ensure The increase in the fluidity of the gas flow is doubled and its kinetic energy is increased threefold. The method of expanding the parameters of the gas-powder flow between the Laval expansion nozzle involves the infusion of 10 physical effects into 14 parameters of the gas-powder flow. It is shown that numerical expansions allow the tuyere body to be used as a heat exchanger for heating the gas suspension, as well as for increasing the pressure of the gas-powder jet that flows from the nozzles

The influence of gas heating on the calculated supersonic parameters of gas-powder flow at slag blower in the converter. Message 2

The article presents the results of numerical modeling of the interaction of a supersonic non-calculated gas-powder jet with the surrounding strongly heated environment of the converter cavity, including slag particles ejected by the jet. The method of determining the depth of penetration of the jet into the melt is the subject of many years of discussion, but it has not been solved analytically. A new approach to solving this problem is proposed, which consists in the fact that in this work the structure is considered not according to the laws of subsonic turbulent flow, but as supersonic, not calculated. In this paper, there is a task - to increase the stability of the slag crust, nitrogen supply of MgO powder is provided, which, in turn, enters the jet and slows it down. To solve this problem, the solution of many parametric equations is proposed to establish the effect of heating on the qualitative characteristics of the slag crust on the surface linings. A physical model has been created that predicts the outflow of a gas-powder jet (N2 + powder) from a Laval nozzle. The formation outside the jet nozzle is established, which becomes a supersonic non-computational structure with a shock wave. The most important hydro-gas-dynamic characteristic of the gas jet flow is its momentum, which depends on a number of factors and physical effects. The scheme for solving a fairly high-tech problem involves the following: calculation of the parameters of the gas-powder flow at the exit from the nozzle; calculation of the amount of added gas mass from the environment; temperature: pulse speed; jet power, etc. It was established that in some cases, when a chemical connection between the slag and the lining is ensured (when there is an optimal value of MgO and CaO in the slag), it is possible to stop the supply of refractory powder and then the slag will be inflated only with a nitrogen jet. Using the law of constancy of momentum in different cross-sections of the jet (for example, in the outlet cross-section of the nozzle and in the fixed cross-section of the XX stream), it is possible to calculate: total momentum, average mass velocity of the nitrogen-powder jet, average mass temperature of the jet. It is shown that the power of the gas-powder jet flowing into the melt is most significantly affected by the heating of the gas-dispersed flow to the temperature before the nozzles. It was established that an increase in temperature from 50°C to 600°C leads to an increase in momentum by almost 2.75 times. The joint solution of almost 50 equations (messages 1 and 2) makes it possible to visually present the picture of the interaction of the supersonic jet with shock waves and melt, as well as to develop recommendations for improving the energy efficiency of slag-blowing technology. Since conducting an experiment in the converter cavity is difficult, the results of numerical calculations are verified by the method of special cases

Experimental and Numerical Simulation of the Heat Transfer of the UHTC Surface in Underexpanded Dissociated Nitrogen Jets

Experimental and Numerical Simulation of the Heat Transfer of the UHTC Surface in Underexpanded Dissociated Nitrogen Jets

Experimental investigation of hydrogen jet flame inhibition by nitrogen jet

With the rapid development of hydrogen energy and the increase of the risk of hydrogen jet fires, a reliable fire protection technology is required to extinguish hydrogen jet flame efficiently. An experimental investigation was carried out to study the inhibition of a hydrogen jet flame by a nitrogen jet. The impact angle, nozzle diameter and nozzle position of the nitrogen jet were the variables. The flame characteristic parameters were analyzed, including the flame length, deflection height and deflection angle. The results show that the inhibited flame length was always positively correlated with the vertical distance between the nozzles. The increase of the impact angle had a significant inhibitory effect on the flame length. Besides, the explanatory factor was used to describe the influence of various initial release conditions on flame inhibition and was calculated by the combination of the explanatory variables, such as impact angle, impact stroke and impact height. The flame length reduction ratio, deflection height reduction ratio and dimensionless deflection angle are positively correlated with the explanatory factor. It means that the jet flame is more easily extinguished under a larger explanatory factor. The critical parameter of the explanatory factor for extinguishing the hydrogen jet flame was verified experimentally.

Complex Flow Mechanism and Pressurization Effect of Liquid Nitrogen Jet Fracturing Formation Perforation Tunnel

As an anhydrous fracturing method, liquid nitrogen jet fracturing technology is expected to become an efficient development method for shale gas resources. In order to explore the influence of the pressurization effect in the liquid nitrogen jet channel, the flow field in the perforation tunnel during the liquid nitrogen jet fracturing process was simulated by computational fluid dynamics, and the complex flow mechanism of liquid nitrogen in the perforation tunnel was analyzed. The pressurization effect of liquid nitrogen jet and water jet fracturing was compared, and the influence of various parameters on the pressurization effect of liquid nitrogen jet fracturing was studied. The research results indicate that under the same conditions, liquid nitrogen jets have a pressurization effect comparable to water jets, and the difference between the pressurization values of the liquid nitrogen jet and the water jet in the perforation tunnel is not more than 0.4 MPa under different nozzle pressure drop conditions. The larger the nozzle pressure drop and nozzle diameter, the greater the pressure increase value in the perforation tunnel of liquid nitrogen jet fracturing, which decreases with the increase in casing hole diameter. Further analysis shows that the pressurization effect is most affected by the two parameters of casing hole diameter and nozzle diameter. The essential reason for its influence on the pressurization value is the squeezing effect of the jet on the perforation tunnel fluid and the sealing effect of the shrinking part of the perforation tunnel on the backflow. The ambient pressure, the temperature of liquid nitrogen, and the diameter of the wellbore have no obvious effect on the pressurization effect. Therefore, through the reasonable combination of casing hole diameter and nozzle diameter, the sealing effect of the contraction part of the perforation tunnel on the fluid and the squeezing effect on the fluid in the perforation tunnel will be affected, which will significantly improve the pressurization effect of the liquid nitrogen jet in the perforation tunnel.

Experiments and modelling of liquid nitrogen jet release and dispersion for fire-related applications

Cryogenic liquid nitrogen (LN2) is proposed as an effective fire suppressant/extinguisher for challenging fires. Upon reaching a fire source, this inert cryogen vaporizes expediently and separates the fuel from the air. Additionally, it cools the burning fuel and slows down its pyrolysis/gasification reactions. A prior investigation concentrated on the survivability of single LN2 droplets, following breakup of the jet exiting the nozzle, and the predicted the droplet size that reaches a target. This investigation addresses the application of a liquid nitrogen jet for the extinction of fires with a combination of experiments and theoretical analysis. Small scale laboratory experiments were conducted with a sprayer and larger scale experiments were conducted with a cryogenic hose and nozzle. In these experiments the reach of the liquid nitrogen jets was measured, and their fire extinction capabilities were assessed. Numerical simulations were performed with the ADREA-HF CFD code using the mixture approach and explicit modelling of LN2 evaporation using the Lee model. Numerical results on the reach of a liquid nitrogen jet qualitatively matched the experimental observations for release of a liquid nitrogen jet in open atmosphere. The Lee model coefficient was found to depend strongly on the nozzle diameter. An integral model was also constructed to explore the effects of relevant parameters, such as the LN2 storage tank pressure, the initial jet vapor quality, the jet velocity at the nozzle exit and the effects of the ambient air entrainment. Based on experiments and theoretical analysis, it became evident that for effective extinction of a fire with liquid nitrogen a commercial nozzle should have a large diameter and should be brought close to the burning target, i.e., within a few meters. As this action can pose potential safety risks to firefighters, the advancement of the nozzle towards the fire should be operated remotely.

Locally Resolved Simulation of Gas Mixing and Combustion Inside Static and Moving Particle Assemblies

AbstractResolving the flow field within the voids between particles of reacting granular assemblies is essential to obtain correct conversion rates. Due to the associated computational cost, a high spatial resolution cannot be employed on the device‐scale. A combination of a locally resolving and an averaging method is suggested. Namely, the so‐called blocked‐off method is used to resolve the voids between particles within prescribed regions, while the volume‐averaged method is applied in the remaining domain. For a nitrogen jet injected into a regular simple cubic packing of spherical particles passed by a cross‐flow of air, the jet dispersion is too low when applying the volume‐averaged method for the whole computational domain. The same is also observed in a reacting methane jet flowing into a bed of arbitrarily packed particles with air cross‐flow, where the locally resolved approach predicts significantly larger local reaction rates.