Jet Density Research Articles

Direct Assembly of Grooved Micro/Nanofibrous Aerogel for High-Performance Thermal Insulation via Electrospinning.

Maintaining human body temperature in both high and low-temperature environments is fundamental to human survival, necessitating high-performance thermal insulation materials to prevent heat exchange with the external environment. Currently, most fibrous thermal insulation materials are characterized by large weight, suboptimal thermal insulation, and inferior mechanical and waterproof performance, thereby limiting their effectiveness in providing thermal protection for the human body. In this study, lightweight, waterproof, mechanically robust, and thermal insulating polyamide-imide (PAI) grooved micro/nanofibrous aerogels were efficiently and directly assembled by electrospinning. The grooved micro/nanofibrous aerogels were directly prepared by controlling the relative humidity and solvent evaporation rate, as well as regulating the charge jet density and phase separation behavior. The prepared aerogel exhibited ultralight performance with a density of 4.4 mg cm-3, hydrophobic liquid-repelling performance with a contact angle of 137.4°, and ultralow thermal conductivity (0.02586 W m-1 k-1), making it an ideal material for maintaining thermal comfort in complex environments. This work provides valuable insights into the design and development of high-performance fiber insulation materials.

The separatrix electron density in JET, ASDEX upgrade and alcator C-Mod H-mode plasmas: A common evaluation procedure and correlation with engineering parameters

The separatrix electron density in JET, ASDEX upgrade and alcator C-Mod H-mode plasmas: A common evaluation procedure and correlation with engineering parameters

Numerical simulation of reactive jet penetrating into reinforced concrete

Abstract In order to study the damage effect of PTFE/Al/W reactive jet against reinforced concrete, AUTODYN-3D numerical simulation was used to study the formation and penetration behaviors of reactive jets with densities of 2.31g/cm3~4.12g/cm3. Simulation results show that under the same charge condition, the diameter of low-density reactive jet is larger, and there is no significant difference in the axial velocity distribution of the reactive jets with different densities. For the damage effect of reinforced concrete, the penetration hole diameter of reinforced concrete formed by low-density reactive jet is larger, moreover, the steel bars can protect the concrete and reduce the damage area of concrete surface. For the penetration ability, the reactive jets with different densities can penetrate the front layer of steel bars, and the higher density of reactive jet, the deeper penetration depth of reinforced concrete. Meanwhile, hitting position of the jet against concrete target has significant effect on penetration results. The broken steel bars in penetration hole reduce the penetration depth.

Simulation study on the jet formation of high-entropy alloy shaped charge liner

Abstract The high-entropy alloy liner has the characteristics of wide composition and performance control range, high density, high sound speed, and certain chemical activity, which makes it unique in the application of shaped charge warhead. Based on CoCrFeNiAl high-entropy alloy, the static and dynamic mechanical properties of high-entropy alloy were carried out by universal material testing machine and split Hopkinson pressure bar (SHPB). The static and dynamic stress-strain curves of high-entropy alloy were obtained, and the Johnson-Cook constitutive model parameters of high-entropy alloy were fitted. Based on the AUTODYN-2D numerical simulation platform, the jet formation behavior of CoCrFeNiAl high-entropy alloy liner was studied. The distribution characteristics of velocity field and density field in the jet formation process of high-entropy alloy liner were analyzed, and the influence of cone angle of high-entropy alloy liner on jet formation evolution, fracture, velocity field and density field was revealed. The results show that the jet head accumulation is caused by the existence of “reverse velocity gradient” in the high-entropy jet formation process. With the increase of the cone angle of the liner, the velocity of the jet head of the CoCrFeNiAl high-entropy alloy decreases, but the overall formation performance of the jet is better. Under the condition of different cone angles, the density change curve at the top axis of the high-entropy alloy liner shows the “three peaks” phenomenon. The work can provide a reference for the structural design of new high-entropy alloy liner.

Advanced pullulan nanofibers reinforced by cellulose fibrils as drug carriers for salicylic acid

The goal of the current work is to showcase the synthesis of homogeneous pullulan nanofibers that are strengthened by the addition of cellulose nanofibrils (CNF). One of the main difficulties this study faced was determining the ideal water/organic solvent ratio for the electrospinning process, which would allow for the maximum reduction in the amount of organic solvent (DMF or DMSO) needed. The rheological behavior of electrospinning solutions was modulated by varying both, the pullulan concentration and solvent system composition. The amount of CNF in the composition significantly affects the properties of the created nanofibers. When the CNF content increased from 1 % to 5 %, the diameter of the fibers decreases from 284 nm to 90 nm. This is attributed to the enhanced conductivity and surface charge density of the solution jet. The as prepared nanofibres can hold a variety of drugs and can be used to create novel formulations for various biomedical purposes. The nanofibres were tested for salicylic acid incorporation and release. Drug release exhibited zero-order kinetics, suggesting that the concentration remained unaffected by the rate of release. Furthermore, the nanofibres demonstrated remarkable antibacterial activity against both Gram-positive and Gram-negative bacteria.

Therapeutic Effect of Targeted Deployment Filling Coils in the Treatment of Intracranial Aneurysms.

Endovascular coil embolization is the primary therapeutic modality for intracranial aneurysms. Substantial reports have been found regarding the coil packing density and inflow jet. However, the hemodynamic effect of increasing the rate of tamponade in the inflow jet area within the aneurysm remains unclear. In this study, individualized geometries of six intracranial aneurysms were recruited: all six aneurysms were located in the internal carotid artery. Two groups were created by changing the position and orientation of the microcatheter for the release of the third segment of the filling coil. The finite element method was used to simulate coil deployment. Computational fluid dynamics was used to characterize hemodynamics in post-deployment aneurysms. The parameters evaluated included velocity reduction, wall shear stress (WSS), low WSS (LWSS), relative residence time (RRT), flow kinetic energy in the neck region of the aneurysms, and residual flow volume (RFV) in the aneurysms. At the peak time (t = 0.17 s), the targeted deployment group has similar proportion of LWSS area to conventional deployment groups: targeted 78.13% ± 34.59% versus normal 74.20% ± 36.94% (mean ± SD, p = 0.583). The targeted deployment group has a higher RRT area (targeted 16.84% ± 5.58% vs. normal 6.42% ± 5.67% [mean ± SD, p = 0.009]), smaller flow kinetic energy (targeted 9.43 ± 4.33 vs. normal 16.23 ± 5.92 [mean ± SD, p = 0.047]), and a larger RFV in the aneurysms (targeted 35.97 ± 24.35 mm3 vs. normal 25.80 ± 18.94 mm3 [mean ± SD, p = 0.44]). Inflow jets play an important role in the treatment of aneurysms, and deploying filling coils in accordance with inflow jets may result in a better hemodynamic environment.

Numerical and Experimental Simulation of Supersonic Gas Outflow into a Low-Density Medium

This study is aimed at developing methods for the experimental and numerical simulation of the outflow of underexpanded gas jets into a rarefied medium. The numerical method is based on using Navier–Stokes equations in the continuum flow regime and the direct simulation Monte Carlo method in the transitional flow regime. The experimental method includes the modeling of jet flows in the LEMPUS-2 gas-dynamic setup with electron beam diagnostics for the jet density measurements. The results of the experimental modeling for the nozzles of various diameters confirm that a key parameter determining the jet structure is the Reynolds number based on the characteristic length ReL. The results of the numerical simulations agree well with the experimental data both for the maximum values of the ReL considered (approximately 30) when a barrel jet structure with Mach disks is formed and for the minimum values (approximately 4) when no Mach disks are formed. In the entire range of parameters, significant thermal nonequilibrium is observed at all jet segments where the measurements are performed.

High-Lift Enhancement of an Airfoil Using Arrays of Discrete Wall Jets

The circulation of a high-lift airfoil is enhanced using a spanwise array of fluidically oscillating wall jets to engender a Coanda-like effect on the suction surface near the cove between the flap and the main element. The actuation jets manipulate the interaction between the main element boundary layer and the cove jet to overcome flow separation over the flap and yield high-lift performance that is comparable to or better than conventional high-lift airfoils. The fluidic actuation enables effective operation at larger flap deflections while diminishing the sensitivity to cove characteristics. The performance of the actuator array varies with both the jet momentum coefficient and the spanwise periodic jet spacing. It is shown that the lift increment per jet, which for a sufficiently sparse jet array is invariant with jet spacing, diminishes as jet spacing is reduced due to spanwise jet interactions. Accordingly, the overall lift increment scales with the number of active jets and jet density, and a characteristic spanwise jet spacing is identified for optimal performance.

Trajectory and spreading of falling circular dense jets in shallow stagnant ambient water

This study investigates the trajectory and spreading of a horizontal circular dense jet flow discharged above the water surface, the flow of which falls into shallow stagnant ambient water. For this purpose, 27 experiments were performed using three diameters, flow rates, and falling heights to investigate jet trajectory. In addition, nine experiments with constant falling height were conducted to study jet spreading. The densimetric Froude number of the jet flow at the nozzle outlet and water surface of the present study ranged from 0.72 to 4.22 and 36.96 to 86.10, respectively. The data pertaining to this study were extracted and analyzed through image processing. The results of the experiments showed that by increasing both the momentum and falling height, the trajectory of the jet flow reached a farther distance from the discharge nozzle. The spreading of the outer boundaries of the dense circular falling jet flow tended to extend downstream of the impact point and had an elliptical motion on the bed. The relationship between radial distance from the impingement point to the outer boundary of flow and time was determined to have a power of 0.67 for flow along the flume and 0.59 for flow along the flume's width.

Prediction of Geometrical Characteristics of an Inclined Negatively Buoyant Jet Using Group Method of Data Handling (GMDH) Neural Network

A new approach to predicting the geometrical characteristics of the mixing behavior of an inclined dense jet for angles ranging from 15° to 85° is proposed in this study. This approach is called the group method of data handling (GMDH) and is based on the artificial neural network (ANN) technique. The proposed model was trained and tested using existing experimental data reported in the literature. The model was then evaluated using statistical indices, as well as being compared with analytical models from previous studies. The results of the coefficient of determination (R2) indicate the high accuracy of the proposed model, with values of 0.9719 and 0.9513 for training and testing for the dimensionless distance from the nozzle to the return point xr/D and 0.9454 and 0.9565 for training and testing for the dimensionless terminal rise height yt/D. Moreover, four previous analytical models were used to evaluate the GMDH model. The results showed the superiority of the proposed model in predicting the geometrical characteristics of the inclined dense jet for all tested angles. Finally, the standard error of the estimate (SEE) was applied to demonstrate which model performed the best in terms of approaching the actual data. The results illustrate that all fitting lines of the GMDH model performed very well for all geometrical parameter predictions and it was the best model, with an approximately 10% error, which was the lowest error value among the models. Therefore, this study confirms that the GMDH model can be used to predict the geometrical properties of the inclined negatively buoyant jet with high performance and accuracy.

Modeling and Experimental Validation of Pre-Chamber Jet Penetration Considering Jet Density and Ejection Pressure Variations

Abstract Although pre-chamber (PC) is regarded as a promising solution to enhance ignition in lean-burn gas engines, a lack of comprehensive understanding of PC jet penetration dynamics remains. This study proposed a zero-dimensional (0-D) model for PC jet penetration, considering the mixing of combustion products and unburned gases and floating ejection pressure. A combustion completion degree was defined employing fuel property and heat release to estimate varying jet density. Pressure differences between PC and the main chamber (MC) were referred to as the ejection pressure. Then, this model was validated against experiments from a constant volume chamber and a rapid compression and expansion machine with CH4-H2 blends at different equivalent ratios. Results showed that the proposed model can provide a good prediction in stationary and turbulent fields with the calibrated model coefficient. The overall jet penetration exhibits a t0.5 dependence due to its single-phase characteristic and the relative lower density compared to ambient gas in MC. The flame propagation speed and heat release in PC influence the combustion completion degree at the start of jet ejection, the mass fraction of burned gas in jet increases with the equivalent ratio. Jet penetration is primarily driven by ejection pressure, with tip dynamics barely affected by the pressure difference after the peak. Tip penetration intensity increases with increased fuel equivalent ratio and H2 addition, owing to the faster flame propagation. These findings can offer useful suggestions for model-based design and combustion model development for gas engines.

Diels–Alder Reaction of Biofuran Derivatives and Cycloolefin for Directional Synthesis of Fused Ring Hydrocarbon High Density Jet Fuel

Diels–Alder Reaction of Biofuran Derivatives and Cycloolefin for Directional Synthesis of Fused Ring Hydrocarbon High Density Jet Fuel

Combustion Behavior of Supersonic Jet for Single‐Flow Postcombustion Oxygen Lance with Various Secondary Nozzle Parameters

A 3D model is established to discuss the influence of combustion reaction on jet characteristics. Based on this, combustion behaviors of supersonic jet for single‐flow postcombustion oxygen lance with various secondary nozzle parameters (diameter, inclination angle, and number) are analyzed. The results indicate that after activating combustion reaction, the jet velocity, dynamic pressure, density, and temperature of primary jet at H = 1.45 m are 1.27, 1.15, 0.56, and 1.97 times than those of without considering the combustion, respectively. Enlarging secondary nozzle diameter is helpful to extend the flame core lengths of primary and secondary jets (the axial distance from lance tip to isotherm of 1773 K) as well as the combustion region. With the increase of secondary nozzle angle, the two flame core lengths both decrease, while the combustion zone increases. Increasing the number of secondary nozzles, the flame core length of primary jet increases while that of the secondary jet decreases, and the combustion region first increases and then decreases. As for the influences of the above parameters on flame core lengths of primary and secondary jets as well as the combustion region, the number is the greatest, followed by the inner diameter, and the inclination angle is the smallest.

Interactions of laser-driven tin ejecta microjets over phase transition boundaries

Ejecta microjets offer an experimental methodology to study high-speed particle laden-flow interactions, as microjets consist of millions of particulates traveling at velocities of several kilometers per second and are easily generated by most common shock drives. Previous experiments on the OMEGA Extended Performance laser found that collisions between two counter-propagating laser-driven tin ejecta microjets varied as a function of drive pressure; jets generated near shock pressures of 10 GPa passed through each other without interacting, whereas jets generated at shock pressures of over 100 GPa interacted strongly, forming a cloud around the center interaction point. In this paper, we present a more systematic scan of tin ejecta microjet collisions over intermediate pressure regimes to identify how and at what shock pressure interaction behavior onsets. Radiographs of interacting microjets at five different laser drive energies qualitatively demonstrate that interaction behavior onsets slowly as a function of laser drive energy. Quantitative mass and density metrics from each radiograph provide trends on jet characteristics and collisional mass dispersion. It is observed that jetting mass, jet densities, and mass dispersion increase with increasing drive pressures and that the increased jet density at the higher drive energies may account for the increased mass dispersion. This work provides an important step in the understanding of tin ejecta microjet collisions and paves the way for future studies on the physics dominating high-speed particle-laden flow interactions.

Mixing and spreading of inclined dense jets with submerged aquatic canopies

Mixing and spreading of inclined dense jets with submerged aquatic canopies

Direct numerical simulation of shock wave/boundary layer interaction controlled by steady microjet in a compression ramp

Shock wave/boundary layer interaction in a 24° turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation. Three different jet spacings which are termed as sparse, moderate and dense are considered, and the induced vortex system and shock structures are compared. A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation, reducing the separation region. The dense jet spacing configuration creates a larger momentum deficit region, reducing the friction downstream of the corner. Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock. The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation. Furthermore, the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods, revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.

Laboratory study on inclined desalination discharges in perpendicular cross-flow

To mitigate the ecological impact of dense effluents discharged from diffusers, understanding the influence of ambient currents and discharge characteristics on desalination outfall performance is crucial. For this purpose, a series of laser-induced fluorescence (LIF) experimental tests were conducted to address the combined effects of the flowing current strength and nozzle inclination in the discharge region for dense jets issuing into a plane perpendicular to the cross-flows. Various nozzle discharge angles (30°, 45°, and 60°) and cross-flow Froude numbers (urF=uau0×u0g0′D) are studied to assess 3D jet trajectory and concentration distribution. Empirical equations describing the dilution and geometrical characteristics of the jets are also derived. The findings indicate that deploying the 60° jet can achieve dilutions of over 50 % and 20 % compared to the 30° and 45° jets, respectively, due to its longer trajectory and greater expansion. Thus, the previously reported insensitivity of dilution to the nozzle angles in the range of 40°-70° for stationary ambient water is questioned herein when dealing with flowing currents. Moreover, the 60° jet is more sensitive to the changes in urF compared to the two other shallower angles. The presented outcomes provide valuable insights for safeguarding coastal water bodies through the efficient design of inclined dense outfall discharges.

Ar(1s5) density in a co-axial argon plasma jet with N2–O2 shielding

Atmospheric-pressure microplasma jets (µAPPJs) are versatile sources of reactive species with diverse applications. However, understanding the plasma chemistry in these jets is challenging due to plasma-flow interactions in heterogeneous gas mixtures. Spatial metastable density profiles help to understand these physical and chemical mechanisms. This work focuses on controlling the shielding gas around a µAPPJ. We use a dielectric barrier discharge co-axial reactor where a co-flow shields the pure argon jet with different N2–O2 gas mixtures. A voltage pulse (4 kV, 1 µs, 20 kHz) generates a first discharge at the pulse’s rising edge and a second discharge at the falling edge. Tunable diode laser absorption spectroscopy measures the local Ar(1s5) density. A pure N2 (100%N2–0%O2) co-flow leads to less reproducible and lower peak Ar(1s5) density ( 5.8×1013cm−3 ). Increasing the O2 admixture in the co-flow yields narrower Ar(1s5) absorbance profiles and increases the Ar(1s5) density ( 6.9×1013 to 9.1×1013cm−3 ). The position of the peak density is closer to the reactor for higher O2 fractions. Absence of N2 results in comparable Ar(1s5) densities between the first and second discharges (maxima of 9.1×1013 and 9.3×1013cm−3 , respectively). Local Ar(1s5) density profiles from pure N2 to pure O2 shielding provide insights into physical and chemical processes. The spatially-resolved data may contribute to optimising argon µAPPJ reactors across the various applications and to validate numerical models.

Efficient energy transport throughout conical implosions.

The double-cone ignition (DCI) scheme has been proposed as one of the alternative approaches to inertial confinement fusion, based on direct-drive and fast-ignition, in order to reduce the requirement for the driver energy. To evaluate the conical implosion energetics from the laser beams to the plasma flows, a series of experiments have been systematically conducted. The results indicate that 89%-96% of the laser energy was absorbed by the target, with moderate stimulated Raman scatterings. Here 2%-6% of the laser energy was coupled into the plasma jets ejected from the cone tips, which was mainly restricted by the mass reductions during the implosions inside the cones. The supersonic dense jets with a Mach number of 4 were obtained, which is favorable for forming a high-density, nondegenerated plasma core after the head-on collisions. These findings show encouraging results in terms of energy transport of the conical implosions in the DCI scheme.

Heat transfer effect on the modeling of jets under supercritical and transcritical conditions

The injection of nitrogen under supercritical and transcritical conditions, where the injection temperature is below nitrogen’s critical point, but the pressure is above it, is considered in this paper. While the scientific community recognizes that the sharp gradients of the different thermophysical parameters make it inappropriate to employ a two-phase flow modeling at conditions above the critical point, the issue is not restrained to the mere representation of turbulence for a mono-phase flow. Instead, a quantitative similarity with gas-jet-like behavior led to proposing an incompressible but variable density hypothesis suitable for describing supercritical and sub/near-critical conditions. Presently, such an approach is extended and assessed for a configuration including injector heat transfer. As such, axial density and temperature decay rates and jet spreading rates of density and temperature are evaluated, indicating a higher mixing efficiency in the supercritical regime and an overall dominance of heat propagation over momentum transport, with a greater preponderance in the supercritical regime.