Jet Flow Type Research Articles

Study on the gas dissolution performance and bubble generation characteristics of a jet flow type pressurized tubular microbubble generator

Microbubble generation technology has the potential to significantly enhance the separation efficiency of offshore oilfield produced water flotation treatment devices, which currently display unstable performance. In this study, we developed a jet flow type pressurized tubular microbubble generator, comprising a jet-dissolved gas tube (JDGT) and a standard ball valve. The JDGT was designed based on the principle of intensifying bubble breakup through jet nozzles and enhancing gas dissolution via up-down circulation vortex. We proposed an innovative Computational Fluid Dynamics (CFD) model that utilizes User Defined Functions (UDF) to predict the flow pattern and dissolved oxygen (DO) distribution within the tube. The relative error between numerical simulations and experimental results was 5.25 %. Under identical operating conditions, the JDGT can efficiently produce gas-dissolved water in 3.5 s, achieving a dissolved gas efficiency of 80.24 %, compared to 58.31 % for a conventional jet vertical vessel with a hydraulic retention time of 30 s. High-quality microbubbles can be generated through decompression via a standard ball valve. The oxygen volumetric mass transfer coefficient increases with the inlet water flow rate, the gas–liquid volume ratio, and increased dissolved pressure. As the inlet water flow rate increases, the Sauter mean bubble diameter initially increases before decreasing. Both the gas–liquid volume ratio and dissolved gas pressure are exponentially related to the Sauter mean bubble diameter. An engineering prototype with a treatment capacity of 35 m3/h was successfully field-tested on a platform in the South China Sea. The test results indicated that when the microbubble generator was connected to a vertical air flotation unit with a 10 % reflux flow system, the average oil concentration at the unit’s outlet was 13 mg/L. The calculated average oil removal efficiency was 72.38 %, which is 12.8 % higher than that achieved without a tubular microbubble generator.

Diffusion performance of lobed jet in the developed states consistent across temporally and spatially developing flows

This study demonstrates that temporally developing lobed jets can qualitatively reproduce the diffusion performance in the fully developed states of spatially developing lobed jets in laboratory experiments. The jet exit geometries, Reynolds number [Formula: see text], and turbulence intensity (3% of mean velocity) were set to be the same across the temporally and spatially developing jets. Four types of jet flows were tested, one being a round jet and three being lobed jets with different numbers or curvatures of lobes, referred to as 6L, 6S, and 3L, respectively. The half-width of the mean streamwise velocity distributions and centerline mean streamwise velocity of the four jets in the developed states were consistent between the numerical simulations and experiments. The round jet displayed the highest diffusion performance, followed by 3L, while 6L and 6S were the smallest and were comparable with each other. Despite such consistency in the developed states, the diffusion performance and formation of the streamwise swirling flows did not agree between the numerical and experimental results. These results suggest that unique large-scale structures corresponding to the initial conditions are reproduced in temporally developing jets, which is in good agreement with the spatially developing lobed jets. Therefore, the current study demonstrated that the temporally developing simulations can reproduce similar diffusion processes to those of the spatially developing ones.

Identification and dynamics of coherent structures in a Coanda swirling jet flow

Swirl stabilised flows are the most common technology for gas turbine combustion stabilisation. Although success on the characterisation of these flows is tangible, there are several structures that appear in such flows that are still a concern for fundamental and applied research. One of these structures is the Precessing Vortex Core (PVC), whose ambiguous characteristics make it an adequate mechanism for chemical mixing whilst being a detrimental component for thermoacoustic stabilisation. The PVC has been extensively characterised in swirling jet flows exhibiting vortex breakdown (in this study named Open Jet Flow or OJF). However this has not been the case for swirling Coanda (i.e. wall attached) Jet Flows (CoJF). Therefore, this research presents experimental work detailing the identification and visualisation of coherent structures in both types of jet flows. A generic swirl burner was fitted with a base plate in a position so that any of these two flows, OJF and CoJF, could be obtained within the same burner geometry. High speed stereo particle image velocimetry (S-PIV) was used to obtain a time-resolved flow field of each flow state at different flow rates. Two PVCs were clearly identified in both flows, one in the inner shear layer between the vortex breakdown bubble and the jet and one between the jet and the ambient. Precessing frequencies for the CoJF where ∼8.5% higher (St ∼0.9-1.0) than those of the OJF (St ∼0.8-0.9). Spectral proper orthogonal decomposition was used to identify the coherent structures in the flow. Swirl strength (λci2) analysis was conducted on the coherent modes to establish quantitative and qualitative results and to produce a 3D reconstruction of the flow field. The results indicate that precessing coherent flow structures are present in wall attached Coanda swirling flows and these are similar to the structures found in swirling jet flows undergoing vortex breakdown.

A computational‐experimental investigation of thermal vapor compressor as an energy saving tool for the crystallization of sugar in a sugar processing plant

AbstractEnergy saving in the food industry is of a great deal of importance. Thermal vapor compressors (TVCs) do not have moving parts which offer advantages including simplicity, low construction capital, and low maintenance costs. In this study, a TVC is designed, and simulated to recover waste vapor streams and reuse the recovered streams in the crystallization of sugar. Computational fluid dynamics is employed to simulate the flows. The effect of motive steam pressure on the entrainment ratio and compressor ratio is simulated. Thermodynamics parameters such as static pressure, temperature, velocity, Mach number, and mass ratios of motive steam and suction are assessed. As the flow is of jet flow type, the realizable k‐e turbulent model is used to model the turbulence. The results show that by applying the motive steam at a pressure of 28 bars (boiler outlet), the pressure and temperature of discharge vapor reach the values of 0.65 bar and 511 K, respectively. The average mass ratios of motive and suction flow at the output of the designed TVC diffuser are 0.59 and 0.41, respectively. As the crystallization pressure demand is 0.6 bar, the findings reveal that the discharged vapor from TVC has sufficient enthalpy to be consumed in the crystallization section, hence making the whole process more efficient.Practical applicationEquipping the crystallization section of the sugar factory with a thermal vapor compressor, beside the recovery of low‐pressure vapor with motive steam, can reduce energy consumption and play a key role in decreasing fossil pollution. Computational Fluid Dynamics is a validated tool in the simulation of the food processing phenomenon. In terms of TVC optimization, the results obtained from this research serve to designers and process managers to get a detailed perception of energy reduction scenarios and recovery of low enthalpy streams.

Experimental investigation on the flow and rock breaking characteristics of supercritical carbon dioxide jets

Supercritical carbon dioxide (SC-CO2) jets are of increasing interest in drilling and completion engineering due to their superiority over water jets. To understand the nature of SC-CO2 jets and improve performance, the flow characteristics of SC-CO2 jets were experimentally investigated, followed by rock breaking tests. Flow images of the jet under various operating conditions were captured by a high speed CCD camera. A comparative analysis of an SC-CO2 jet flow with classical theories and other types of jet flows was performed. The results show that the submerged environment can greatly affect the characteristics of SC-CO2 jets. When injecting into a gaseous CO2 environment, the saturation curve is crossed and intense phase transition occurs in the jet flow. The jet appears as a classical single-phase gas/gas turbulent shear layer. Whereas, under an SC-CO2 submerged environment, shock waves can be found in the jet flow. The initial instability and spreading rate reduce with the increase in inlet pressure. The jet behaves as a typical compressible jet. These features are different from water jets and are most likely the reason for the better rock breaking performance of SC-CO2 jets. Further, SC-CO2 jets under a gaseous CO2 submerged environment are prone to result in large and shallow breaking pits, while the jets under an SC-CO2 environment tends to cause small and deep breaking pits.

Comparison of flow dynamics of Perimount Magna and Magna Ease aortic valve prostheses

The aim of the present study was to evaluate and compare the in vitro and flow dynamics of the Magna (MB) and the Magna Ease aortic valve bioprosthesis (MEB) within the ascending aorta. A 2D-particle-image-velocimetry (2D-PIV) study was performed to compare the flow dynamics induced by each pericardial Carpentier-Edwards Magna and Magna Ease aortic valve prosthesis in the aortic flow field directly behind the valve. Both prostheses (diameter 23 mm) were placed inside an artificial aorta under pulsatile flow conditions (70 Hz and 70 ml stroke volume). The flow field was evaluated according to velocity, shear strength, and vorticity. Both prostheses showed a jet flow type profile with a maximum velocity of 0.97±0.09 m/s for MB and 0.83±1.8 m/s for MEB. Flow fields of both valves were similar in acceleration, peak flow deceleration and leakage phase. Maximum shear strength was 20,285±11,774 l/s2 for MB and 17,006±8453 l/s2 for MEB. Vorticity was nearly similar for counterclockwise and clockwise rotation in both prostheses, but slightly higher with MB (251±41 l/s and -250±39 l/s vs. 225±48 l/s and -232±48 l/s). The point-of-interest (POI)-analysis revealed a higher velocity for left-sided aortic wall compared to right-sided at MB (0.12±0.09 m/s vs. 0.18±0.10 m/s, p<0.001), but was consistent at MEB (0.09±0.05 m/s vs. 0.08±0.04 m/s, p=0.508), respectively. Velocity, shear strength and vorticity in an in vitro test set-up are lower with MEB compared to MB, thus resulting in improved flow dynamics with a similar flow field, which might have a positive influence on blood rheology and potential valve degeneration.

Fluid Dynamic Investigation of the ATS 3F Enable Sutureless Heart Valve

: Currently, sutureless heart valves (SHV) reveal good clinical results during aortic valve replacement. The aim of this study was to evaluate the fluid dynamics of the ATS 3F Enable SHV in the ascending aorta and their influence on the aortic wall in an in vitro setup. : A two-dimensional particle image velocimetry study with an image rate of 15 Hz was conducted to evaluate the fluid dynamics of the SHV in the aortic flow field. The prosthesis (diameter, 23 mm) was placed inside a silicone mock aorta under pulsatile flow conditions. Velocities, vorticity, and strain rate were obtained and calculated with a fixed frequency (70 Hz) at constant stroke volume (70 mL). : 3F Enable showed a jet flow type profile with a maximum velocity of 1.01 ± 0.13 m/s during peak flow phase (PFP). The jet flow was surrounded by ambilateral vortices with a slightly higher percentage of clockwise than counterclockwise vorticity (377 ± 57/s vs 389 ± 76/s), strain rate (370 ± 79/s for elongation vs -370 ± 102/s for contraction) was nearly similar. The point-of-interest analysis revealed a higher velocity for bottom compared with upper aortic wall (0.28 ± 0.07 m/s vs 0.31 ± 0.06 m/s, P = 0.024). All values were lower during acceleration and deceleration phase compared with PFP. : The peak flow of the 3F Enable SHV seems to be little higher compared with native aortic valves, thus simulating nearly physiologic conditions. Vorticity and strain rate are high during PFP and low during other phases and might have an influence on the aortic wall as well.

Environmental fluid dynamics-jet flow

Jet flow is a very important research subject in both fundamental fluid dynamics and engineering applications. Jet flow has the essences of fluid dynamics, such as free and wall-bounded shear flows, turbulent flow, eddy and large vortical structures and their stability and control, and so forth. This article serves as an overview of our past and ongoing research activities on various types of jet flow, with particular reference to their application in the field of environmental fluid dynamics. The research objectives, approach, results and their engineering implications of each topic will be presented.

Modeling Study on the Entrainment of Ambient Air into Subsonic Laminar and Turbulent Argon Plasma Jets

Modeling study is performed to reveal the special features of the entrainment of ambient air into subsonic laminar and turbulent argon plasma jets. Two different types of jet flows are considered, i.e., the argon plasma jet is impinging normally upon a flat substrate located in atmospheric air surroundings or is freely issuing into the ambient air. It is found that the existence of the substrate not only changes the plasma temperature, velocity and species concentration distributions in the near-substrate region, but also significantly enhances the mass flow rate of the ambient air entrained into the jet due to the additional contribution to the gas entrainment of the wall jet formed along the substrate surface. The fraction of the additional entrainment of the wall jet in the total entrained-air flow rate is especially high for the laminar impinging plasma jet and for the case with shorter substrate standoff distances. Similarly to the case of cold-gas free jets, the maximum mass flow-rate of ambient gas entrained into the turbulent impinging or free plasma jet is approximately directly proportional to the mass flow rate at the jet inlet. The maximum mass flow-rate of ambient gas entrained into the laminar impinging plasma jet slightly increases with increasing jet-inlet velocity but decreases with increasing jet-inlet temperature.

CO 2-dispersion studies in an operation theatre under transient conditions

Maintaining air quality and thermal comfort inside an operation theatre equipped with horizontal jet flow type air-conditioning units, has been a challenge to engineers. The objective of this study is to analyze the airflow pattern in such operation theatres and the influence of location of the air-conditioners. The outcome of this study is expected to reduce the post-operation problems faced due to excess concentration of contaminants. Experimental studies were conducted in 10 different hospital operation theatres. Parameters such as air temperature and carbondioxide concentration were measured at discrete points chosen in the theatre. A 3D time-dependent numerical model was developed to simulate the airflow in terms of parameters such as velocity, temperature and CO 2 distributions in an operation theatre under transient conditions. The Eulerian approach using the volume fraction of the mixture of air and CO 2 was used to solve the numerical model. Finite volume approach was attempted in this work with PISO (pressure implicit with split operators) algorithm for the pressure correction equations. The simulated results were compared with the experimental results for validity. The locations of the air-conditioners were changed in the numerical model to analyze the airflow patterns and the contaminant distribution.

Bulk Amorphous Formation and Magnetic Properties of Nd-Fe-Co-Al Alloys by the New Gas Jet Flow Type Levitating Process

The amorphous formation ability and the magnetic properties of Nd 60 Fe 30-x Co x Al 10 (x = 10, 15, 20 or 30) alloys in the containerless process were studied by the new gas jet flow type levitating process. The gas jet flow type levitating process enables solidification without any container wall by the inert gas jet. The samples were solidified at the cooling rate of around 100 K/s. Then, the undercooling of samples exhibits high values (AT = 60-150 K). From X-ray diffraction measurements, the Nd 60 Fe 30-x Co x Al 10 samples exhibit a typical broad diffraction pattern for an amorphous structure. The DTA curves of x = 10, 15 and 20 showed an exothermic peak due to the crystallization. That is, it was revealed that the Nd 60 Fe 30-x Co x Al 10 samples formed bulk amorphous. Also, the coercivity is 1.6, 3.3 and 3.6kOe for the Nd 60 Fe 20 Co 10 Al 10 , Nd 60 Fe 15 Co 15 Al 10 and Nd 60 Fe 10 Co 20 Al 10 , respectively. From the thermomagnetic curves, the Curie temperature is determined to be 463, 482 and 482 K for the Nd 60 Fe 20 Co 10 Al 10 , Nd 60 Fe 15 Co 15 Al 10 and Nd 60 Fe 10 Co 20 Al 10 , respectively. In the M-H loops and the thermomagnetic curves, this difference between x = 10 and x = 15, 20 may depend on the microstructure.

ガスジェット浮遊型電磁溶融プロセスによって作製したLa-Cu-Ni-Co-AlおよびNd-Fe-Co-Al系バルク状近似アモルファス合金

For Rare Earth-Transition Metal-Al with high undercooled liquid formability and glass-forming ability, bulk alloys have been produced with gas jet flow type electromagnetic levitation process, which is a new containerless process. A series of alloys of La80-xCu10Ni5Co5Alx (x=15, 20, 25 at%) were analyzed with respects to the supercooled solidification process, nucleation behavior of a crystalline phase, and the possibility of the formation of bulk amorphous alloys. In addition, the similar studies were carried out for the specimens containing SiC, which is reported to be effective to enlarge undercooling when used in the containerless process. The results show that the addition of SiC suppresses the nucleation of a crystalline phase, and thus, the undercooling (ΔT) increases in the range of ΔT=0.22 to 0.28 Tm, where Tm is the melting point. In addition, partially crystallized bulk amorphous alloys with a diameter of 6 mm are obtainable for the alloys with 0.2 mass% SiC addition when they are solidified at approximate cooling rate of 100 K/s. Furthermore, the SiC free alloys of La65Cu10Ni5Co5Al15 and Nd60Fe20Co10Al10 are also obtainable as partially crystallized bulk amorphous alloys.

A206 ダイナミックPIVの展開

Particle image velocimetry (PIV) can capture velocity vector fields with high spatial resolution. A dynamic PIV system with 2 kHz at mega-pixel frame up to 10 kHz at 512x256 pixels was developed by combining a high-speed camera, a high-speed pulse laser with double pulse option, and a pulse controller. The system has been successfully applied to various types of jet flow, a channel flow, and so on.

A new approach to estimating the volatilization rates of shower water-contained volatile organic compounds during showering

A mathematical hybrid-showering model was developed in order to describe the dynamic behaviour of volatile organic compounds (VOCs) contained in shower water during personal showering. The approach involves assuming a two-film theory and taking into account the dual flow patterns of “jet” and “spray” from a showerhead in order to estimate the emission of VOCs from tap water to air. The liquid-phase mass-transfer coefficients corresponding to both flow patterns and the gas-phase mass-transfer coefficient for spray droplets are estimated using the penetration theory, while the gas-phase mass-transfer coefficient for a jet-flow stream is calculated using an analogous empirical correlation. Literature-derived data were used to test the validity of the hybrid-showering model and a good correlation between literature-derived and calculated data was obtained. This study confirms the usefulness of the hybrid-showering modelling approach as regards the risk assessment of personal showering. Moreover, our simulated findings indicated that the jet-flow type showerhead should be more beneficial than the spray type showerhead as regards being associated with a lower VOC exposure risk.

A Turbulent Cylindrical Wall Jet Equipped with a Front-Facing Step Impinging Normally on a Flat Plate.

This is an experimental study of a turbulent cylindrical wall jet that issues from an annular nozzle, flows along a cylindrical wall and finally impinges normally on a flat plate. In order to disturb the flow near the wall and to control the thickness of the wall shear layer, a front-facing step is equipped at an arbitrary location on the cylindrical wall. This type of jet flow has properties characterized by a pressure increase and boundary layer growth in the downstream direction, so that the flow separates from the cylindrical wall and reattaches to the impingement plate. This report mainly concerns the effects on the separation and reattachment properties of the flow with various nozzle-step distances and step-impingement distances. Mean velocity and static pressure on the cylindrical wall were measured. The flow patterns in the x-y plane normal to the cylindrical wall in the region near the step and before the impingement plate were obtained by the mean flow vectors and the flow visualization by an oil film method. The results show that the flow patterns can be classified into three main types.

Investigation of a Turbulent Cylindrical Wall Jet Impinging Normally on a Flat Plate. (2nd Report. Impinging Jet Properties by Mean Flow).

This paper presents an experimental study of a turbulent cylindrical wall jet impinging normally on a flat plate. This type of jet flow may have properties including boundary layer separation on the cylindrical wall and reattachment on the impingement plate. The effect of the nozzle impingement distance on the mean flow properties of the jet before and after the impingement was investigated. The changes in the static pressure on the cylindrical wall surface, the maximum jet velocity and the boundary layer thickness were examined. Both the separation point from the cylindrical wall and the reattachment point on the impingement plate were divided into three trends depending on the nozzle impingement distance.

Investigations of ducted jets

Axisymmetric, incompressible ducted jet flows are investigated experimentally. Measurements by hot-wire probes are made of the mean velocity and turbulence fields for three jet flows with different Craya-Curtet members Ct issuing into a constant-area duct. The jets issue as turbulent pipe flows from the nozzle, and the duct/nozzle diameter ratio is 22.3, which is larger than for most previous studies, which have also tended to use idealized potential flow nozzles. It is found that the jets dominate the flows in the first six duct diameters. The unattached jet regions are essentially jets in constant-velocity secondary streams. Particular effort is made to determine the initial conditions for the various flows in the forms required for the application of computational fluid dynamics (CFD) models. The application of various models to the flows will be described separately. Comparisons are made with previous measurements both of ducted jets and of jets issuing into constant-velocity secondary streams. General agreement with trends is found but with differences in detail. For example, the shear covariance uv/u′v′ is found to be at the higher end of the spectrum of values found in other studies while turbulence quantities, normalized by the local excess jet velocity, such as u′/(U 1−U 2) , are at the lower end of the spectrum of values. A tendency for the latter normalized quantities to reduce with reduction of the local velocity ratio U 1/U 2 is found, while the opposite effect has been found in at least one previous study. Turbulent energy balances for the ducted jets are quite similar to the free-jet case. The observations indicate that history effects are important in this type of jet flow, that is, the jet is unlikely to have “forgotten” its initial conditions before wall impaction. These effects can also explain the differences found between the details of the turbulence patterns found in the various previous investigations of both confined and unconfined jet flows. The data provide further evidence of the controlling roles of large eddies, and bulk-convective transport of turbulent energy is also supported by the measurements.

Investigation of a turbulent cylindrical wall jet impinging normally on a flat plate. 1st Report. Fundamental properties of each jet flow.

This paper presents the results of an experimental investigation of a turbulent cylindrical wall jet impinging normally on a flat plate. This type of jet flow may have properties including boundary layer separation and reattachment on the wall. Before dealing with this jet flow, this report describes the fundamental properties of three types of jet flow : a circular free jet from a circular nozzle, a cylindrical wall jet from an annular nozzle, and the impinging jet of a circular free jet with the flat plate normally. The changes of the maximum jet velocity, the jet half-width, the turbulence at the velocity maxima, and the static pressure for each jet flow are examined, and the results are compared with those obtained for the jet flow by the other investigators.

Steady relativistic fluid jets

A numerical simulation is presented of a relativistic jet. Owing to the similar mathematical form of the equations of steady relativistic gas dynamics and steady non-relativistic gas dynamics, the numerical method used to make this calculation can be used to model either type of jet flow. On the basis of simplifying assumptions, the synchrotron emission from the jet is estimated for different viewing angles between it and an observer’s line-of-sight.

The near field behavior of turbulent gas jets in a long confinement

The present investigation reports on the near field behavior of gas jets in a long confinement and points out the differences between this type of jet flow and those of free jets and jets in a short confinement.