Adjacent Nozzles Research Articles

EXPERIMENTAL STUDY OF ELEMENTARY ACTS OF HYDRODYNAMICS AND HEAT TRANSFER DURING THE INTERACTION BETWEEN WATER DROPS AND FILM AND CASTING ROLLER SURFACE

Experimental studies of the boundary conditions of heat transfer for the thermally stressed state of casting rollers while are spraying with flat-jet nozzles in a thermal preconditioning unit have been carried out.
 It is shown that the hydrodynamic conditions on the sprinkling surface are formed as a result of both the influx of "primary" dispersed water from the flat jet nozzle, and the "secondary" liquid coming from neighboring areas in the form of reflected drops and films.
 The heat transfer effecting individual factors that form the hydrodynamic conditions on the sprinkling surface was studied separately.
 The heat transfer intensity was studied depending on the spraying density, the injection-pressure drop and the temperature of the cooled surface when the "primary" drop flow runs in the heat exchange surface. The local sprinkling density of droplets on the surface under the flat-jet nozzle spray were measured using a sampling tube moved by a coordinator. At the same time, the ingress of “secondary” liquid into it was excluded.
 The specific heat flux and heat transfer coefficient were determined using a heat meter made of a nichrome tape heated by direct current. In this case, the isothermality of the surface of the measuring section was ensured. Thermocouples measured the temperature of the lower surface of the tape, and then the stationary temperature of the upper surface of the heat meter sprinkled with drops is calculated.
 As a result of the multivariate analysis of the experimental data, the correlation dependence of the heat transfer coefficient in dependance on the local spraying conditions of the heat meter surface was obtained.
 Also, studies of the heat transfer during water film flow over the heat meter surface were carried out. A similar situation takes place when water spreads between the adjacent nozzles sprinkling zones of the roller surface.
 The correlation dependence between the heat transfer coefficient, the water film speed and the cooled surface temperature was obtained.
 Studies of heat transfer during combined influence of moving water film and a flat-jet nozzle drop flow on the heat exchange surface showed that the heat transfer rate is approximately 80–90 % of the arithmetic sum of the coefficients obtained by separate cooling the heat meter with drops and a water film.

Design and evaluation of a linear nozzle array with double auxiliary electrodes for restraining cross-talk effect in parallel electrohydrodynamic jet printing

It is attractive and challenging to fabricate micro-nano scale patterns in large area by parallel electrohydrodynamic jet printing (E-jet printing) with nozzle array. However, cross-talk effect (i.e. interference phenomenon) between nozzles may probably lead to poor positioning accuracy and cause jet instability. In this paper, design and evaluation of a special linear nozzle array with double auxiliary electrodes at both ends were proposed to restrain the cross-talk effect. Firstly, the numerical simulation model of multi-nozzle E-jet printing was established considering with electro-hydraulic coupling effect. The corresponding multi-nozzle E-jet printing processes in several geometry configurations were successfully simulated based on a commercial multi-physical software ‘COMSOL’. Secondly, the unique design of new type linear nozzle array with double auxiliary electrodes was proposed after accomplishing theoretical analysis and comparison study of simulation results. Thirdly, several experiments were carried out on a constructed multi-nozzle E-jet printing system to verify feasibility and effectiveness of the provided design. The experiments show that the proposed manner has obvious advantages in restraining cross-talk compared with traditional suppressing method ‘with single flat-head auxiliary electrode at both ends’. When nozzle space is 0.5 mm, the jet deflection angle 2.8° and Taylor cone angle 3.3° could be reduced to 0° and 0.05° with two methods respectively. Finally, the printability of fabricated new multi-nozzle was also characterized. Microscale droplets array (mean diameter about 200–240 μm) could be achieved with no deflection and the gap between them is equal with the distance between adjacent nozzles. This study can provide a reference for the design of high integrated printhead and E-jet printing system.

Numerical Simulation of Multi-Nozzle Droplet Evaporation Characteristics for Desulfurization Wastewater

Spraying flue gas desulfurization wastewater into flue ducts is an emerging technology that is receiving extensive attention in thermal power plants. In order to study the evaporative performance of wastewater-atomizing droplets under variable working conditions, a combined Euler–Lagrange model was developed to demonstrate the thermal behavior of FGD wastewater spray evaporation in flue gas. The effects of several control factors under various operating conditions were numerically determined and validated against experimental data. Due to the complicated parameters and various other conditions, a least-square support vector machine (LSSVM) model relying on numerical results was used to anticipate the evaporation rate of the droplets. We prove that the LSSVM model has high prediction accuracy for the evaporation rate at different cross-sections of flue under a different operating situation. The conclusion is that for the sake of improving the quality of evaporation, the spacing between two adjacent nozzles should be increased while increasing the flow rate. However, using a higher flue gas temperature, higher initial temperature and smaller diameter of droplets can shorten the time and distance of complete evaporation. In summary, this research analysis can be used effectively to determine the design of the FGD wastewater flue gas evaporative process in thermal power plants.

Assessment of nozzle control strategies in weed spot spraying to reduce herbicide use and avoid under- or over-application

Spot spraying is a method that can meet the objectives of reduced herbicide by maintaining a high level of weed control efficiency without lowering crop yield and harvest quality. Individual nozzle control systems show great potential for herbicide reduction. Nevertheless, this method of application also entails the risk of under-application on weed surfaces because of the lack of spray overlap and irregular dosing. Thus, nozzle control strategies need to be refined and assessed, regarding herbicide reduction and the ability to apply the prescribed dose on the target surfaces. Six control strategies were considered by activating complementary adjacent nozzles or increasing the flowrate of specific nozzles. Theoretical analyses and simulations were carried out to compare these strategies using three indicators. Considering a simplified description of the weed spatial distribution, a herbicide reduction indicator was expressed analytically for each strategy as a function of the weed coverage rate and patch width. For each strategy, numerical simulations were also carried out to compute under- and over-application indicators considering six weed coverage rates, eight patch widths and six different spray patterns. Graphs and charts were developed to provide convenient tools to help select the best technical approach for reducing chemical applied whilst keeping the prescribed dose on targets. In particular, a good compromise could consist of setting the weed detection width (associated with each nozzle) at twice the nozzle spacing and using triangular spray patterns combined with double spray overlaps. • Six nozzle control strategies are compared for herbicide spot spraying. • Herbicide reduction is modelled analytically by weed patch and spraying features. • Herbicide misapplications are assessed using numerical simulations. • Setting the detection width at twice the nozzle spacing is a good compromise. • Triangular spray patterns combined with double overlaps are preferred.

Field assessment of a pulse width modulation\xa0(PWM) spray system applying different spray volumes: duty cycle and forward speed effects on vines spray coverage

The pulse width modulation (PWM) spray system is the most advanced technology to obtain variable rate spray application without varying the operative sprayer parameters (e.g. spray pressure, nozzle size). According to the precision agriculture principles, PWM is the prime technology that allows to spray the required amount where needed without varying the droplet size spectra which benefits both the uniformity of spray quality and the spray drift reduction. However, some concerns related to the effect of on–off solenoid valves and the alternating on/off action of adjacent nozzles on final uneven spray coverage (SC) have arisen. Further evaluations of PWM systems used for spraying 3D crops under field conditions are welcomed. A tower-shaped airblast sprayer equipped with a PWM was tested in a vineyard. Twelve configurations, combining duty cycles (DC: 30, 50, 70, 100%) and forward speeds (FS: 4, 6, 8 km h−1), were tested. Two methodologies, namely field-standardized and real field conditions, were adopted to evaluate the effect of DC and FS on (1) SC variability (CV%) along both the sprayer travel direction and the vertical spray profile using long water sensitive papers (WSP), and (2) SC uniformity (IU, index value) within the canopy at different depths and heights, respectively. Furthermore, the SC (%) and deposit density (Nst, no stains cm−2), determined using short WSP, were used to evaluate the spray application performances taking into account the spray volumes applied. Under field-controlled conditions, the pulsing of the PWM system affects both the SC variability measured along the sprayer travel direction and along the vertical spray profile. In contrast, under real field conditions, the PWM system does not affect the uniformity of SC measured within the canopy. The relationship between SC and Nst allowed identification of the ranges of 200–250 and 300–370 l ha−1 as the most suitable spray volumes to be applied for insecticide and fungicide plant protection products, respectively.

Numerical Analysis of Isothermal Flow in Interacting Swirl-Stabilized Nozzles

The three-dimensional steady incompressible numerical results of an isothermal flowfield resulting from the interaction of two swirl-stabilized air nozzles in a multiple lean direct injection combustor configuration are analyzed. The spacing between nozzles is varied from 1.1 to 2.72 nozzle diameters to analyze the degree of swirl interaction between them and their impact on the resulting flow structure. The numerical results were verified by performing a grid dependence and turbulence model implementation study and validated by comparing them with time-averaged particle image velocimetry and unsteady Reynolds-averaged Navier–Stokes formulation data. The numerical solution resolves aerodynamic flow features typically associated with swirl-based combustion such as a form of vortex breakdown at the center of both nozzles and highly complex flow structures both upstream and downstream of the dome wall. Nozzle spacing has an important effect on the shape of the recirculation region and the flow velocities. In particular, interaction in the tangential velocity between the two nozzles has large effects on the swirl number and the size of the recirculation zone. Most of the changes in flowfield seem to be affected after the inner shear-layer jets of both nozzles have merged into a single jet flow in the axial direction. Two intermediate spacings (, ) exhibit unusual behavior in that the inner shear layers (towards the adjacent nozzle) are drawn into the center of the combustor, and a wide and low-velocity flow is created between the swirlers. This could be due to the inner shear-layer jets between adjacent nozzles not merging properly and behaving in a classical manner of two turbulent opposed planar jets.

Improved gas-jet based extreme ultraviolet, soft X-ray laser plasma source.

We present a new nozzle design for an improved brilliance of laser-produced gas plasmas emitting in the soft X-ray and extreme ultraviolet spectral regime. A rotationally asymmetric gas jet is formed by employing two closely adjacent nozzles facing each other under the angle of 45°. The generated three-dimensional gas density distribution is tomographically analyzed using a Hartmann-Shack wavefront sensor. A comparison with numerical simulations accomplishes an optimization of the nozzle arrangement. The colliding gas jets create an optimized gas distribution with increased density, leading to a significant brilliance enhancement of the extreme ultraviolet, soft X-ray plasma.

Simulation and experimental study of parameters in multiple-nozzle electrospinning: Effects of nozzle arrangement on jet paths and fiber formation

Abstract The electrospinning process is a simple and versatile method for the fabrication of nanofibers. The low production rate of fibers in a conventional single-nozzle setup inhibits the commercialization of the process for large-scale applications. Multiple-nozzle electrospinning is a straightforward approach in the efforts of increasing fiber yield. The installation of multiple nozzles in a single setup alters the electric field in the working space, affecting the process and fiber quality. In this study, the effects of varying the distance between adjacent nozzles are investigated in terms of the jet behavior and fiber distribution, comparing between equally-spaced and unequally-spaced nozzles. The simulation of the electric field shows a more uniform electric field distribution near the nozzle tips for the unequally-spaced nozzles. The unequally-spaced setup also resulted in a more uniform distribution of fiber diameter and deposited fiber mats. Additionally, electrospinnability was also improved by using unequally-spaced nozzles.

Method of calculation the main constructive parameters of additional pugre unit for the multi-tier tuyere

It has been established that under modern working conditions, because of the instability in the provision of raw materials for oxygen-converter production at national metallurgical enterprises of Ukraine it is important, in terms of efficiency, to introduce multi-tier tuyeres. The analysis of literature sources showed that despite the industrial and experimental experience of using multi-tier tuyere in oxygen-converter production, nowadays there are no calculation methods to achieve their design parameters; it may result in lots of drawbacks. Accordingly, there appeared a need to develop a methodology for calculating the design parameters of additional purge units of multi-tier tuyeres. Due to analytical and calculation-statistical studies using the existing methods for calculating the design parameters of the tuyere with upper lances and further processing of the data, a calculation method including nineteen equations for determining the basic design parameters of additional purge units of the multi-tier tuyere has been created. This methodology makes it possible to determine: the quantity of additional purge units in the multi-tier tuyere ; the minimum and maximum height of their location with respect to the end of the head of the multi-tier tuyere; the free length of the lance barrel from the afterburner to the end of the tip . It is also possible to establish the main parameters of the cylindrical nozzles in the nth additional purge unit of the multi-tier tuyere: the angle of inclination to the vertical axis of the tuyere ; quantities ; length ; the angle between the axes of adjacent nozzles ; as well as a number of other auxiliary characteristics for determining the parameters of sound jets flowing from the cylindrical nozzles of additional purge units: the vertical and horizontal length spread of afterburners; the diameter of the curtain of the afterburner . Equations have been proposed to determine the maximum allowable total blowings per a certain number of additional purge units and the minimum expedient consumption of the blowings per one additional unit for basic auxiliary technological operations with the multi-tier tuyere

Research on the Influence of External Parameters of Fan-Type Nozzle on Water Jet Performance

At present, high-pressure water jet technology occupies a very important position in the automobile washing industry. Some automatic washers cannot meet the washing requirements in the washing process due to unreasonable arrangement of nozzles on their spray rods. Based on the theory of computational fluid dynamics (CFD), the internal and external flow field model of the nozzle are established in this paper. Fluent is used to simulate and analyze the flow field, and the external parameters of the nozzle on the side spray bar of the automatic automobile washer are optimized. The simulation results show that after the nozzle and the normal line of the automobile surface are inclined at a certain angle, the target surface is affected not only by normal striking force but also by tangential pushing force, which makes stains easier to remove. The washing effect is the best when the nozzle is inclined 30° to the normal line of the automobile surface. Increasing the nozzle inlet pressure will increase the dynamic pressure on the automobile surface, but the increase of dynamic pressure will decrease after increasing to a certain pressure. The inlet pressure has little effect on the area covered by water jet. The reasonable matching results of jet angle, nozzle spacing, and nozzle distance from the automobile surface (target distance) obtained by numerical simulation can not only make the automobile surface completely covered and cleaned but also ensure less jet interference and no waste of water from adjacent nozzles. The above research conclusions can provide a basic theoretical basis for the optimal design of automatic automobile washing.

Influence of Excitation Frequency, Phase Shift, and Duty Cycle on Cooling Ratio in a Dynamically Forced Impingement Jet Array

Abstract The cooling ratio on a dynamically forced 7 × 7 impingement jet array is studied experimentally. The current study is focused on determining the influence of a phase shift between every row of nozzles as well as the impact of a duty cycle variation on the cooling ratio. Both parameters are studied in dependency of the impingement distance (H/D = 2, 3, 5), the (nozzle-) Reynolds-number (ReD = 3200, 5200, 7200), and the excitation frequency (f = 0 Hz − 1000 Hz). For every set of parameters, the phase shift between every row of nozzles is varied between Φ=0% and 90%, while the variation of the duty cycle is performed between duty cycle (DC) = 35% and 65%. During all investigations, the dimensionless distance between adjacent nozzles is fixed at Sx/D = Sy/D = 5, and liquid crystal thermography is used to acquire the wall temperatures, which are further processed to calculate the local Nusselt numbers. Generally, the implementation of an excitation frequency allows a case-depending increase in the cooling ratio of up to 52%. Further implementation of a phase shift yields an additional frequency-depending improvement of the cooling ratio. In case of duty cycle variation, the best case revealed an additional 19% improvement in the cooling ratio.

On the Interaction of Swirling Flames in a Lean Premixed Combustor

Abstract Premixed or partially premixed swirling flames are widely used in gas turbine applications because of their compactness, high ignition efficiency, low NOx emissions and flame stability. A typical annular combustor consists of about twenty swirling flames, which interact (directly or indirectly) with their immediate neighbors even during stable operation. These interactions significantly alter the flow and flame topologies thereby bringing in some discrepancies between the single nozzle (SN) and multinozzle (MN), ignition, emission, pattern factor and flame transfer function (FTF) characteristics. For example, in MN configurations, application of a model based on SN FTF data could lead to erroneous conclusions. Due to the complexities involved in this problem in terms of size, thermal power, cost, optical accessibility etc., a limited amount of experimental studies has been reported, that too on scaled down models with reduced number of nozzles. Here, we present a detailed experimental study on the behavior of three interacting swirl premixed flames, arranged in-line in an optically accessible hollow cuboid test section, which closely resembles a three-cup sector of an annular gas turbine combustor with very large radius. Multiple configurations with various combinations of swirl levels between the adjacent nozzles and the associated flame and flow topologies have been studied. Spatio-temporal information of the heat release rate obtained from OH* chemiluminescence imaging is used along with the acoustic pressure signatures to compute the Rayleigh index (RI) so as to identify the regions within the flame that pumps energy into the self-excited thermoacoustic instability modes. It is found that the structure of the flame–flame interaction regions plays a dominant role in the resulting thermoacoustic instability. To resolve the flow and reactive species distributions in the interacting flames, two-dimensional (2D), three component stereoscopic particle image velocimetry (SPIV) and planar laser-induced fluorescence (PLIF) of hydroxyl radical is applied to all the test conditions. Significant differences in the flow structures among the different configurations were observed. Simultaneous OH-PLIF and SPIV techniques were also utilized to track the flame front, from which the curvature and stretch rates were computed. Flame surface density (FSD) which is defined as the mean surface area of the reaction zone per unit volume, is also computed for all the test cases. These measurements and analyses elucidate the structure of the interaction regions, their unique characteristics, and possible role in thermoacoustic instability.

Coalescence Characteristics of Side‐by‐Side Growing Bubbles in Carboxymethyl Cellulose Solutions

AbstractNew experimental data are presented on the coalescence dynamics of twin bubbles at two adjacent nozzles in carboxymethyl cellulose (CMC) solutions. The coalescence process was recorded by using a fast video technique and the images were then analyzed to evaluate the regime, efficiency, and patterns of bubble coalescence. The results reveal that the coalescence process contains the four periods of spherical expansion, rapid mergence, overall growth, and instant departure. The coalescence efficiency always passes through five stages with the gas flow rate; it grows with the CMC solution concentration, but decreases with the surfactant concentration, except at very low gas flow rates. The bubble coalescence pattern strongly depends on the nozzle spacing, but conditionally on the gas flow rate and the solution properties.

Effect of nozzle spacing in the formation of primary and secondary deposits in multi-nozzle inertial impactors part I: Experimental study

Particle deposits in an inertial impactor stage can be classified as primary or secondary. The primary deposits are directly downstream of each nozzle. Secondary deposits can be in the form of a halo around the primary deposit or of straight-lines between adjacent nozzles. Certainly, these additional secondary deposits lead to a deviation from the theoretical efficiency curve in which only a single primary deposit existed and was considered.The jet-to-jet interaction in multi-nozzle inertial impactors and the formation of secondary deposits has been analyzed and quantified as a function of the distance between nozzles and the Reynolds number. This work has been studied experimentally (Part I) and numerically (Part II), using CFD (Computational Fluid Dynamics) analysis to provide insight into the physical mechanisms for the formation of the secondary deposits and to support the experimental results.This paper provides detailed experimental impactor collection efficiency curves for impactor plates with 3 nozzles spaced in the range of 2.5W to 8W, where W is the nozzle diameter, and Reynolds numbers between 465 and 2210, which quantify the effects of the jet-to-jet interactions and the magnitude of the primary and secondary deposits. From the experimental results it may be concluded that the jet-to-jet interactions can produce four non-ideal effects: premature primary deposits with a half-moon shape, straight-line deposits between nozzles, nozzle plate deposits between nozzle exits (losses), and dispersion of the halo deposits.The secondary deposits and premature primary deposits reduce the slope of the efficiency curve, and/or displace the √Stk50 towards smaller values and/or generate tails at the low end. All of which result in the collection of small particles that otherwise would be collected at another stage with a lower cut point. With respect to the design criteria, to avoid the formation of the additional deposits generated by jet-to-jet interactions (premature primary deposits, straight-line and nozzle plate deposits), the nozzle-to-nozzle spacings have to be larger than 4W and/or the impactor should work at low Re (in this work Re≤465), even at 2.5W spacing.

Optimization on segmentation spraying for cooling a moving source at high temperature in a confined space

Heavy trucks, train carriages, and other moving vehicles with heating sources, are often loaded into a confined space for parking and maintenance. When the heating source from the vehicle is at high temperature, spray cooling using nozzles can be applied for at least two purposes. First, to further decrease the temperature of the surrounding areas. Second, to flush the surfaces of the vehicle as a primary cleansing method. To reduce water consumption, the number and positions of the running nozzles along the way need to be adjusted and optimized according to the position of the moving vehicle. To achieve that, the optimization of a segmented control method for the nozzles is discussed using both theoretical and computational fluid dynamics (CFD) methods in this paper. 120 ~ 240 nozzles in total were uniformly and linearly distributed on the ceiling of a 120m-long narrow space. The space between two adjacent nozzles are set at 0.5m, 0.7m and 1.0m, respectively. All the nozzles are divided into one to ten groups for segmentation control. One 35m-long vehicle with a heating source at over 800 K was moving at 0.05 m/s to 0.20 m/s. The results showed that, first, for one spraying group, at least 39 running nozzles were needed to minimize the areas of interior structure at temperature > 350K. Second, the water consumption can be reduced dramatically by increasing the number of groups. However, when dividing into more than six groups, the capacity of water saving is no longer significant. Third, when the vehicle is entering, multiple- group of running nozzles are needed to overcome the sudden heating source at high temperature.

Effects of multiple-nozzle distribution on large-scale spray cooling via numerical investigation

Spray cooling has been widely employed in many applications due to its high flux removal ability. A previous study has been conducted to reveal the large-scale spray cooling performance of an industrial used single nozzle. Continuously, influence of multiple-nozzle distribution has also been numerically investigated in present work. The mean heat flux and its standard deviation and uniformity are used to qualify the cooling performance. A flat wall with 1.6 m in length and 1.0 m in width has been taken as the research object. Effects of nozzle number, distance and offset have been parametrically compared. It is found that increasing nozzle number could promote mean heat flux, improve the uniformity of cooling patterns and enhance heat transfer performance. A best nozzle number of 10 could be obtained by an equation fitting. Decreasing nozzle distance turns out to be detrimental to heat transfer. The reason comes from the collisions and interactions of two too adjacent nozzles. Based on choices in real practice, two types of arrays i. e. perpendicular and skew array have been discussed and compared. It is concluded that the skew array could obtain higher heat flux with more uniform distribution.

Fabrication and evaluation of controllable deposition distance for aligned pattern by multi-nozzle near-field electrospinning

To mass-volume fabricate micro- and nano-scales aligned pattern, multi-nozzle near-field electrospinning (NFES) direct-writing technology is well proposed as a high-efficiency method in electrohydrodynamic (EHD) printing process. However, the interference effect among adjacent nozzles and coupling effect of various parameters have restricted to investigate deposition characteristic of multi-nozzle NFES and control EHD multi-jet deposition accuracy. In order to improve the accuracy of EHD multi-jet deposition with high-efficiency printing process, the experimental result compared with theoretical method were discussed. In this work, the influence of multi-nozzle geometry distribution and electrospinning parameters on deposition characteristic was studied with multi-nozzle NFES setup, and nozzles were in linear array. The deposition distance and homogeneity of aligned nanofibers were measured and explained with coefficient of dispersion on electric field among nozzles by simulation. Moreover, deposition distance of multi-nozzle NFES process was evaluated by modified theoretical derivation based on our previous studies. The modified theoretical derivation showed a good agreement with experiment results, and indicated that multi-nozzle NFES could accurately and efficiently direct-write aligned array pattern in future.

Experimental prediction of multi-nozzle spray characteristics for optimal design in a lead frame etching process

The objective of this paper is to provide quantitative information of uniform impact forces on the sprayed surface in order to optimize the multi-nozzle spray etching system. Spray characteristics obtained from optical non-intrusive measurements using particle image velocimetry (PIV) and particle motion analysis system (PMAS) are measured in single- and twin-nozzle sprays, and then the multi-nozzle spray characteristics is simulated based on those of measurement data. The influences of the multi-nozzle arrangement, nozzle pitch, and pipe pitch on the spray characteristics such as droplets’ velocity, diameter, number density, impact force and their uniformity are properly evaluated. The experimental cases E1 and E2 represent single-spray nozzle A and B, respectively. For twin-spray tests, three nozzle combinations, namely E3 (nozzle A-A), E4 (nozzle A-B) and E5 (nozzle B-B) are considered with different nozzle pitches. The multi-spray simulation cases S1 and S6 represent the multi-spray cases with a homo-nozzle arrays which is consisted in all nozzles of nozzle A or B. For cases from case S2 to S5, the multi-spray cases with a hybrid-nozzle arrays which is consisted in all nozzles of nozzle A and B. The results show that the impact force increases approximately twice as much for changing of experimental test cases from E1 to E5 owing to the differences in nozzle characteristics of single-sprays and the overlap region between two adjacent nozzles. For the multi-nozzle spray simulation, the uniformity of impact force (UI) is increased with increasing the number of nozzle B which has larger orifice diameter and a wider spray angle. The optimum multi-nozzle spray arrangement is case S4 with more than 90 % UI, based on the fact that the UI is quite stable with increasing the nozzle pitch ranging from 90 mm to 145 mm.

Measurements and Analysis of Alternating Flow Patterns in a Multinozzle Combustor

In some cases, a multinozzle combustor may exhibit flowfields in which individual nozzles hold two distinct flow or flame shapes in an alternating pattern. This study presents flowfield measurements for nonreacting and reacting flows in a rectangular combustor with two adjacent swirl-stabilizing nozzles at varying internozzle spacing. During tests of the wider nozzle spacings, with a reacting flow fueled by propane, there are differences between the flows of the two nozzles. Planar laser-induced fluorescence of the OH molecule (OH PLIF) shows that the flame remains anchored in the shear layer. Thus, the flame from one nozzle penetrates into the combustor, whereas the other flame is anchored close to, and almost parallel with, the dome wall. When the fuel is changed to methane, the asymmetry between the two nozzles is removed; therefore, the combustion properties, in addition to nozzle design, have an effect on the presence of this alternating flow pattern. A hypothesis based on turbulent opposed jets is presented to explain this change in the flowfields. When the nozzle design, flow, or combustion characteristics cause the shear layers of the adjacent nozzles to become sufficiently opposite in direction, the two flows can no longer mix. Instead, one shear layer goes underneath the other, which results in the differing flow features of the adjacent nozzles.

Coalescence Deformation of Bubble Pairs Generated from Twin Nozzles in CMC Solutions

AbstractA coupled level‐set/volume‐of‐fluid method, under the consideration of the rheological characteristics of a fluid, is employed to investigate numerical coalescence deformation of bubble pairs generated at two adjacent nozzles in carboxymethyl cellulose aqueous solutions. The satisfactory agreement between numerical results and experimental measurements proves the validity of this approach in predicting the surface evolution of bubbles. Simulated results show that the bubble coalescence process involves four stages of independent growth, rapid mergence, radial expansion, and vertical stretching. The various effects of surfactant concentration, gas flow rate, nozzle spacing, and nozzle diameter on the aspect ratio depend greatly on each coalescence period.