Jet Inlet Research Articles

Analysis of flow-field in cuboid area with jet inlet and outlet

Analysis of flow-field in cuboid area with jet inlet and outlet

Numerical investigation of ferrofluid jet flow and convective heat transfer under the influence of magnetic sources

This work presents a numerical investigation of convective heat transfer and confined ferrofluid jet flow through a channel under the influence of six magnetic sources placed outside the system and arranged in a staggered manner. The upper and the lower walls are maintained at a constant heat flux density, while the side walls at the inlet are thermally insulated. For the ferrofluid flow, the ferrohydrodynamics (FHD) and thermophoresis effects, as well as the Brownian motion are taken into account. The governing equations are solved numerically using the finite volume method with the SIMPLE algorithm. The influence of the magnetic number (Mn), the sources position (Xi), and the jet inlet height (R) on the flow as well as on the heat transfer characteristics is analyzed. The results show that the flow structure and the thermal boundary layers development are strongly disturbed by the presence of the magnetic sources as well as the narrowing at the channel inlet. The heat transfer is enhanced with the increase of the magnetic number Mn and the reduction of the opening ratio R. It is also found that the closer the sources from the channel inlet, the higher the heat exchange, with an optimal position depending on Mn and R. Finally, the comparison between the gain in heat transfer rate and the pressure drop indicates that the case R = 1/4 and Mn = 50 leads to the most efficient system.

Numerical investigation on fluid dynamic and thermal behavior of a non-Newtonian Al2O3–water nanofluid flow in a confined impinging slot jet

A numerical investigation of hydrodynamic and heat transfer behaviors for Al2O3–water nanofluids for laminar confined slot jet impingement is presented. This study has been conducted by considering the nanofluid as Newtonian as well as non-Newtonian for a wide range of solid volume fraction (0 ≤ φ ≤ 5%) and Reynolds number range of (25–300). A single-phase fluid approach was used to model the nanofluid and the Ostwald–de Waele model described the non-Newtonian shear thinning nanofluid behavior has been adopted. A comparison with Newtonian and non-Newtonian nanofluid in terms of heat transfer coefficient, Nusselt number, streamlines and isotherms contours has been performed for the same Reynolds number, jet inlet velocity and the same aspect ratio H/W. It has been observed that the rate of heat transfer increases with Reynolds number and solid volume fraction of the nanofluid. Noting that the local Nusselt number is much higher for non-Newtonian nanofluid than Newtonian flow in the entire target surface with a particular enhancement located at the jet axis where a relative increase of 9.8% is evaluated for φ = 5% and Re = 300. However, the pumping power results showed a steep increase with the volume fraction for a Newtonian nanofluid case. In fact, the required PP is 1.32, 1.53, 1.99, 2.11 and 4 times greater than the values calculated in case of pure water at φ = 1, 2, 3, 4 and 5 respectively. At the same value of volume fraction φ, it is noted that the pumping power for a non-Newtonian nanofluid is many times higher than PP required in Newtonian nanofluid case, especially at Re ≤ 200. Lastly, the correlations for stagnation point and average Nusselt number are provided for Newtonian and non-Newtonian nanofluid.

Utilizing Modern Experimentation Method to Quantify Jet-Breaker Dimension Effects on Drop Manhole Pool Height

Drop manholes are commonly employed in sewer and drainage systems to reduce pipes slope. The operation of these structures is dominated by their flow regime. Poor hydraulic performance of them under Regime R2 was improved with the jet-breaker, which intersects the inlet jet; yet its proper dimensions were needed to be precisely determined. In this paper, effects of jet-breaker length, width, sagitta, and angle on drop manhole pool free-surface height were experimentally studied under 80% filling ratio of the inlet pipe. The modern statistical Design of Experiment (DoE) methodology and dimensional analysis were utilized to design the experiments in accordance with the 24-1IV fractional factorial design. Consequently, nine specific jet-breakers were built and examined at two different angles, and under various flow rates. The statistical analysis of the results shown that manhole pool height was significantly decreased when jet-breaker length, width, and sagitta were 1, 1.4, and 0.7 times the inlet pipe diameter, respectively, and its angle was at 70°. The use of DoE resulted in 21% reduction in experimental runs, cost, and time, while it provided comprehensive data analysis and objective conclusion.

High-Efficiency Nose-to-Lung Aerosol Delivery in an Infant: Development of a Validated Computational Fluid Dynamics Method.

Background: Computational fluid dynamics (CFD) provides a powerful tool for developing new high-efficiency aerosol delivery strategies, such as nose-to-lung (N2L) aerosol administration to infants and children using correctly sized aerosols. The objective of this study was to establish numerically efficient CFD solution methods and guidelines for simulating N2L aerosol administration to an infant based on comparisons with concurrent in vitro experiments. Materials and Methods: N2L administration of a micrometer-sized aerosol (mass median aerodynamic diameter [MMAD] = 1.4 μm) was evaluated using concurrent CFD simulations and in vitro experiments. Aerosol transport and deposition was assessed in a new nasal airway geometry of a 6-month-old infant with a streamlined nasal cannula interface, which was constructed as a CFD mesh and three-dimensionally printed to form an identical physical prototype. CFD meshes explored were a conventional tetrahedral approach with near-wall (NW) prism elements and a new polyhedral mesh style with an equally refined NW layer. The presence of turbulence in the model was evaluated using a highly efficient low-Reynolds number (LRN) k-ω turbulence model, with previously established NW corrections that accounted for anisotropic wall-normal turbulence as well as improved NW velocity interpolations and hydrodynamic particle damping. Results: Use of the new polyhedral mesh was found to improve numerical efficiency by providing more rapid convergence and requiring fewer control volumes. Turbulent flow was found in the nasal geometry, generated by the inlet jets from the nasal cannula interface. However, due to the small particle size, turbulent dispersion was shown to have little effect on deposition. Good agreement was established between the CFD predictions using the numerically efficient LRN k-ω model with appropriate NW corrections and in vitro deposition data. Aerosol transmission efficiencies through the delivery tube, nasal cannula, and infant nasal model, based on experimental and CFD predictions, were 93.0% and 91.5%, respectively. Conclusions: A numerically efficient CFD approach was established to develop transnasal aerosol administration to infants and children. Small particle aerosols with aerodynamic diameters of ∼1.5 μm were confirmed to have low inertial depositional loss, and have low deposition from turbulent dispersion, making them ideal for high-efficiency lung delivery through an infant nasal cannula interface.

The influence of aspect ratio on the iso-thermal flow characteristics of multiple confined jets

We report a systematic study of the interaction between four rotationally symmetric jets within a cylindrical chamber obtained with particle image velocimetry, under conditions relevant to a wide range of practical applications including the hybrid solar receiver combustor. The geometry consists of a cylindrical cavity with four inlet jets (representing four burners), which are configured in an annular arrangement and aligned at an inclination angle (αj) to the axis with a tangential component (azimuthal angle θj) to generate a swirl in the chamber. The configurations of αj = 25° were assessed with two azimuthal angles θj = 5° and 15°, a range of chamber aspect ratios (Lc/Dc), and a fixed nozzle Reynolds number of ReD = 10 500. The experimental results reveal a significant dependence of the mean and turbulent flow-fields on the aspect ratio Lc/Dc for the values of αj and θj considered here. Three different flow regimes and their controlling parameters were identified within the range 1 ≤ Lc/Dc ≤ 3. The dependence of the flow characteristics on the chamber length Lc was weak within 1.5 < Lc/Dc ≤ 3, but significant for 1 ≤ Lc/Dc ≤ 1.5. It was also found that the value of Lc/Dc has a controlling influence on the position and strength of large-scale recirculation regions, together with the extent of flow unsteadiness, although this influence is reduced as θj is increased.

Application of Jets and Vortex Generators to Improve Air-Cooling and Temperature Uniformity in a Simple Battery Pack

Abstract In this paper, the problem of air cooling and temperature nonuniformity at the cell and pack level is addressed. Passive techniques are developed by integrating jet inlets and vortex generators (VGs) in a simple battery pack with the goal to achieve an effective cooling, and the desired temperature uniformity at the cell and pack level to less than 5 °C, without an increase in the required mass flow and power requirements. Moreover, various configurations of the developed techniques are assessed and compared. In order to achieve the objectives, computational fluid dynamics (CFD) is used to conduct numerical studies on the battery packs. The results concluded that by adding both the delta winglet (DW) vortex generator arrays and jet inlet arrays in the same configuration, improvements in temperature reduction and uniformity can be achieved. The results showed that the maximum temperature of the battery pack was reduced by ∼6% and the temperature uniformity at the pack level was increased by 24%. Additionally, a ∼37% improvement in the temperature uniformity at cell level was achieved.

Effect of Jet Flow between Electrodes on the Cathode Quality in Copper Electrorefining with High Current Density

Increasing current density is one of the main methods for improving the productivity of copper electrorefining. However, in the conventional bottom-inlet/top-outlet mode, an increase in current density leads to a deterioration of the surface quality of the cathode copper. This paper describes an experimental study of the influence of the jet flow between electrodes on the cathode quality. The surface roughness and the standard deviation of the cathode copper were used to evaluate the cathode quality. The results showed that in the single-side jet inlet mode, the electrolyte circulation rate has great influence on the surface roughness of the cathode copper, which is inversely correlated. However, when the electrolyte circulation rate is small, the surface roughness of the cathode copper is not uniform. The farther the position at the surface of the cathode copper is to the jet region, the coarser the cathode copper surface, and vice versa.

Distributor performance in a bubbling fluidized bed: Effects of multiple gas inlet jet and bubble generation

This study considers the role of the distributor effect during the bubble generation, growth and interaction within a bubbling fluidized bed. To characterize this effect, short-term and long-term dynamics are explored in time and frequency domains. Controversy occurs when inspecting what is actually known of the gas distribution mechanism in bubbling fluidized beds. To sustain discussion, classical and innovative techniques, such as Digital Image Analysis, DIA, and Wavelet Analysis WA, are used. As a result, the conclusion is that the distributor not only has no effect in the averaged long-term dynamics but also has no effect on the general bubble generation characteristic frequencies. The analysis performed on the bubble generation region concludes that the distributor design has a great influence at the short-term scale such as during the bubble generation process controlling the spatial distribution of the bubble nucleation sites over the distributor plate.

Numerical and experimental investigation of impinging turbulent flow of twin jets against a wall

In the present study, impinging of vertical twin jet against a horizontal plate is numerically and experimentally investigated. Four two equation RANS based turbulence models are used and their capabilities to simulate such complicated turbulent flow were examined. The two fluid jets are separated by a thin membrane. The inlet jet hydraulic diameters are the same and the Reynolds number of external flows of jets is 13500. The ratio of width of nozzles (e) to nozzle-to-plate distance (H) considered as 1:10. The turbulent models used in this work are k-e, k-e RNG, k-ω and k-ω SST. The results obtained by the models were compared with each other as well as two-dimensional PIV data to evaluate the capabilities of such models for this kind of flows. By comparing the numerical and experimental results, it is concluded that all of the models can predict acceptable results in the free jet area, but in the near wall region none of the models can predict flow characteristics with reasonable accuracy. It was observed that, at low nozzle-to-plate distances, the prediction results of the turbulence models are approximately in accordance with the experimental data, particularly for a zone near the midline separating the two jets.

Heat transfer and pressure loss characteristics in a swirl cooling tube with dimples on the tube inner surface

This paper presents a numerical study of heat transfer and pressure loss characteristics in a swirl cooling tube with five tangential inlet jets and with dimples on the tube inner surface. The swirl tube has a length of 20 times the tube diameter, and the Reynolds number based on the tube diameter ranges from 10,000 to 40,000. Polyhedral meshes as well as the SST k-ω turbulence model were chosen for the numerical calculations. A swirl cooling system with a smooth tube was investigated as baseline, and comparatively with dimples on the tube inner surface. The results showed different swirling flow and heat transfer patterns in the swirl tubes. Dimples on the tube inner surface can reduce the wetted-area averaged heat transfer coefficient on the tube inner surface. However, the total heat transferred in the dimpled swirl cooling tubes can be increased by up to 7.2% due to the increased heat transfer area and the interactions between the swirling flow and the dimpled wall. On the other hand, the pressure loss in the dimpled tube can be appreciably reduced by up to 17.6% compared with that of the smooth swirl tube. Detailed flow interactions between the jets, the tube wall and the dimples are illustrated to explain the heat transfer change and pressure loss reduction mechanisms.

Flow and heat transfer measurements in swirl tubes with one and multiple tangential inlet jets for internal gas turbine blade cooling

In this paper, we present a detailed experimental and numerical study of the flow phenomena and the heat transfer in swirl tubes with one and multiple tangential inlet jets. Such tangential jets induce a highly 3D swirling flow and an enhanced turbulence in the tube, increasing the convective heat transfer. Thus, a swirl tube is considered as an effective cooling method for technical applications with high thermal loaded components like gas turbine blades.The flow field, the heat transfer and the pressure loss are examined in a swirl tube with three different inlet jet configurations with one (MI1), three (MI3) or five (MI5) tangential inlet jets in axial direction. For this purpose, we measured the flow field via stereo-PIV (Particle Image Velocimetry) and the heat transfer by applying a transient technique using thermochromic liquid crystals for several Reynolds numbers. The numerical simulations are performed via Detached Eddy Simulation.The PIV results reveal a complex axial velocity changing after each inlet due to the additional mass flow. Two main structures occur in the swirl tube with five inlet jets: a vortex in the tube center in a wave-like form and large spiral vortices around the tube axis especially near the inlet jets. In the inlet region(s) the highest heat transfer occurs and decreases continuously until the next inlet or towards the tube outlet for the swirl tube with one inlet. The swirl tubes with multiple inlets show lower maximum heat transfer rates compared to the swirl tube with only one inlet due to lower inlet jet velocities. However, the heat transfer distribution is more homogeneous over the entire tube length at a much lower pressure loss. The homogeneous heat transfer can be explained by two mechanisms. At the inlets, the tangential jets impinge onto the concave wall and cause an enhanced convective heat transfer correlating with large spiral vortices. Secondly, the axial velocity becomes stronger further downstream after each inlet jet and causes an enhanced heat transfer between the inlet jets.The thermal performance parameter for all investigated swirl tube configurations is in the same order of magnitude. Thus, all swirl tube configurations are suitable for cooling. If one is interested in a maximum heat transfer paid by a high pressure loss, the swirl tube with one inlet is the best choice. If a lower but more homogeneous heat transfer with a low pressure loss is desired, one should choose the swirl tube with multiple inlets.

Numerical investigation of jet agitation in a nuclear liquid waste storage tank

Radioactive liquid waste is often stored in a large capacity (150 m3) horizontal cylindrical tanks. It is necessary to keep the contents of the tank agitated to prevent the settling of fine solids in the tank. In extreme cases, solids settled at the tank base may invoke the system malfunction. This paper deals with the Computational Fluid Dynamic (CFD) modeling of the agitation mechanism considering the turbulent dispersion effects. The simulations are conducted on a standard tank geometry to arrive the optimum jet velocity required to suspend the settled solid particles thoroughly. The distribution of volume phase fraction, velocity magnitude, turbulence kinetic energy (TKE) and eddy dissipation of each phase for different inlet jet velocities (v = 10–25 m/s) have been presented. The spatial variation of these quantities are measured at three different planes in the vessel mainly in the vicinity of the nozzle exit. The results indicate that the jet velocity is a significant parameter that influences the particle suspension. Parametric studies have also been carried out for four different particle sizes, viz. dp = 5, 10, 50 and 100 μm. The present study revealed that, for the range of parameters covered, the smallest (dp = 5 μm) and the largest (dp = 100 μm) particle sizes has least effect in terms of solids suspension.

Reynolds Number Dependence of Higher Order Statistics for Round Turbulent Jets Using Large Eddy Simulations

Despite the large repository of experimental and computational studies on the topic of turbulent jets, inconclusive and conflicting estimates prevail in regard to certain terms in the turbulence energy budget and the dependence (or lack of dependence) of these and other flow physics on the jet Reynolds number. No comprehensive study exists which adequately addresses these inconsistencies. The purpose of this study is to resolve these contradictions and ascertain the true dependence of the flow statistics on the jet Reynolds number. This is accomplished through high fidelity Large Eddy Simulations (LES), which are performed for a single isothermal round jet at three different Reynolds numbers, encompassing nearly two orders of magnitude. In each case, results are compared to well-accepted experimental and computational studies, and excellent agreement is found with experimental quantities either directly acquired or computed directly from raw data. A separate discrete eddy simulation of the flow in the nozzle upstream of the jet inlet is performed and is found to be crucial in quantifying the flow physics in the near field (e.g., virtual origin). Results show a definite Reynolds number dependence for nearly all third order terms and this is non-negligible especially for the mean convection and production terms in the turbulent kinetic energy budget.

Analysis of the turbulent flow structure in a jet stirred reactor using proper orthogonal decomposition

The accuracy of the experimental measurement of gas phase chemical kinetics related quantities using Jet Stirred Reactors (JSR) depends to a large degree on the homogeneity of the mixture inside the reactor. It is well-established that the mixing process in fluids is dominated by turbulent motions. Coherent turbulent structures are identified by applying the technique of Proper Orthogonal Decomposition (POD) based on previously performed highly-resolved large-eddy simulations. The structures of the highest energies are generated by the jets which inject fresh gases and in the wakes of the pipes leading to the injection nozzles. Furthermore, lower energetic regions were observed in the proximity of the impingement areas of the inlet jets on the surface of the spherical reactor chamber. The data provided herein contributes to the understanding of the flow dynamics in JSRs and aims to guide their future development in order to increase measurement accuracy.

Heat transfer analysis of slot jet impingement using Nano fluid on convex surface

Numerical simulation is performed for investigating the heat transfer performance using nanofluids in a confined slot jet impingement on a convex surface. The impinging jet is water - alumina nanofluids (40 nm average particle size). The aim of this numerical study is to evaluate the augmentation of heat transfer with suspended nanoparticles (in this case Al2O3 - water) using temperature independent nanofluids properties. Different parameters such as various Reynolds numbers, distance between jet to target plate have been considered to investigate the flow behaviour and convective heat transfer performance of the system. Results in the form of distribution of average Nusselt number and convective heat transfer coefficients at the curved surface are shown to elucidate the heat transfer and flow behaviour process. In addition, qualitative analysis of both stream function and isotherm contours is carried out to perceive the flow pattern and heat transfer mechanism due to addition of nanofluids. The results reveal that average Nusselt number and heat transfer coefficient significantly rises with rise in jet inlet Reynolds number. It is also proved that heat transfer is augmented when nano particles are added to a base fluid.

Effect of the particle size of pulverized olive cake on combustion parameters in Stirling engine in Morocco

Morocco is one of the richest countries with olive tree. Annually, about 675,000 t of Olive Cake are produced and injected which leads to damaging the environment especially the groundwater as well as the water table itself. To remedy this problem, and because olive cake has a high caloric value, the idea of this paper comes to valorize this waste through the Stirling engine in order to produce clean energy with low greenhouse emissions.To fulfill this purpose, the impact of the particle size of pulverized olive cake (OC) on the flow behavior and combustion parameters in a 3D vertical chamber was investigated. The spherical OC particles are injected through two injectors perpendicularly to the air inlet jets. Two particle sizes are chosen to conduct this study (PS1, PS2). The numerical approach is based on Reynolds averaged Navier–Stokes (RANS) method using the realizable k–ε turbulence model. For gas phase a non-premixed combustion model is used, and for the discrete second phase a Lagrangian approach is chosen. Temperature distribution, flow topology, velocity contours, and species concentrations profiles in the burner are obtained for the two cases. Results show that the first case particle size gives optimal results and is more suitable for this study.

Mathematical modelling of the indoor ice arena with two control volumes for calculation of the air exchange

The existing methods of calculation of ventilation and air conditioning systems in the indoor ice skating arenas specify the audience stand area zone separately of the ice rink space. They do not take into account interaction of the zones, which have different temperature and moisture parameters. Calculation of the required air exchange of the ice field area is represented herein through mathematical modelling, which reasonably divide the space volume in two distinctive control areas. A mathematical model of the physical process, which takes place in the indoor ice arena space, enables determination of the air exchange to get the required normative parameters of the air in separate space KOs. The suggested method proposes a procedure of the microclimate parameter calculation of separate control volumes of the indoor ice arena space, when the air is distributed according to an “up-to-down” scheme. It will permit to determine the parameters and the operation modes of supply and exhaust ventilation equipment. The method takes into account the processes of heat- and mass transfers in two distinctive control volumes of the ventilated area under permanent conditions. Methodical bases are developed for physically reasonable way of calculating the required air exchange, bearing maximal consideration of the factors influencing heat-air processes in the ventilated volume as a whole and according to two separate typical control volumes of the indoor ice arena ventilated space. The dependence of changes of the relative air consumption in an axis-symmetric jet from the sectional area of the hole, the height of location and the dynamic coefficient of the diffuser are given herein. The method allows determination of the location height and the type of the air diffuser, as well as the air parameters at the jet outlet from the diffuser to provide the design air parameters at the jet inlet into the skating-rink area. There are presented the air jet temperature changes at the jet inlet in the serviced area, as well as the air jet temperature changes at the outlet of the diffuser depending on the amount of the inflow air and the location height of the diffusers. The submitted I-d diagram shows the changes of the air inflow jet settings in the indoor skating-rink space with two control volumes, when the air exchange is made according to the “top-to-down” scheme. The graph-analytical method of the air parameter calculations in the skating-rink area on the basis of I-d-chart, allows to consider the process of mixing air of two control volumes and to clarify the air parameters at the diffuser jet outlet, taking into account the type of the jet, the height of the diffuser location and the characteristics of the diffuser. If the air exchange of the ice rank zone is performed according to the “top-to-down” scheme, the availability of heat and humidity emissions in II KO (stands zone) makes reasonable provision of the inflow air supply by the smallest possible number of the air diffusers, as well as determination of the height of the air diffuser location closer to the served area of the ice rink.

Heat Transfer Augmenation Using Nanofluid of a Confined Slot Impingement Jet on Concave Surface

Numerical investigation of heat transfer process using A12O3-water nanofluid in a confined slot jet impingement on concave surface is performed. The simulation is conducted on a two-dimensional turbulent flow with k –ω SST model for the turbulence computation. A constant heat flux is considered on concave surface. Different parameters such as various Reynolds numbers, and nozzle-to-surface spacing have been considered to study the flow field and convective heat transfer performance of the system. Results in form of distribution of local and average Nusselt number and Convective heat transfer coefficients at the curved surface are shown to elucidate the heat transfer and fluid flow process. In addition, qualitative analysis of both stream function and isotherm contours is carried out to perceive the flow pattern and heat transfer mechanism due to addition of nanofluids. The results reveal that average Nusselt number as well as heat transfer coefficient significantly rises with jet inlet Reynolds number. It is also proved that heat transfer is augmented when nanoparticles are added to a base fluid.

Reducing greenhouse gas emissions in Sandia methane-air flame by using a biofuel

Abstract This article aims to study suitability and merits of employing a biofuel in methane-air jet flames for energy security and environmental sustainability purposes. A special biofuel (methyl decanoate, methyl 9-decenoate, and n-heptane) oxidation with 118 species reduced/skeletal mechanism and 837 reactions is combusted instead of methane. The biofuel was fed in the main jet inlet of the well-known Sandia flame D (SFD) while the hot pilot jet is still responsible for ignition. The open-source software OpenFOAM was used for simulating turbulent biofuel-air combustion. To check the accuracy of computational results, the system was initially validated with SFD experimental results and good agreements were found. After ignition, mean temperature distribution and species mean mass fraction at different distances in axial and radial directions were investigated. Results showed that the biofuel can be effectively used as an alternative to SFD not only for generating a reasonable temperature as methane does, but also for significantly reduction in principal greenhouse gas emissions.