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The purpose of this study reports the effects of aspect ratio (AR) on mean flow characteristics of the cruciform orifice jet.

The aspect ratio is the height-to-width ratio of the lobe of the cruciform shape. The aspect ratios considered are 0.25, 0.5, 0.75, 1, 2, 3 and 4. The turbulent jet flow is issued through an orifice being fitted to the jet tunnel facility. The velocity measurements are recorded with the help of pitot-static tube connected to a digital manometer setup. The Reynolds number calculated using the equivalent diameter 50.46 × 10^–3 m and exit velocity 51.23 m/s was 1.75 × 10⁵. Based on the experimental data, the streamline velocity decay plots, the potential core length (PCL), mean velocity profiles and velocity half widths were plotted, and discussions were made based on the measured data. A smoke-based flow visualization was carried out at moderate Reynolds number 5396.

The PCL remains almost constant for the aspect ratio 0.25:1 and then starts decreasing for the aspect ratio 1:4. The decrease in PCL indicates improved mixing. The off-center peaks are found along the major axis in mean velocity profiles for almost all cruciform jets. More than one axis switching occurs and can be identified by the crossover points. The location of the first crossover point shifts forward, and the second crossover point shows an oscillating trend. The flow visualization exhibits the jet evolution, and the distance up to which the jet maintains the cruciform shape is increased with the aspect ratio.

The experiments are limited to air in air jet under isothermal conditions.

The cruciform orifices can be used as fuel injectors and in air-conditioning systems, thereby improving efficiency and energy usage.

The aspect ratio effects on PCL and axis switching are used to explain the mixing characteristics. Flow visualization was also used to support the discussion.

This study aims to focus on understanding how different jet angles and Reynolds numbers influence the phase change materials’ (PCMs) melting process and their capacity to store energy. This approach is intended to offer novel insights into enhancing thermal energy storage systems, particularly for applications where heat transfer efficiency and energy storage are critical.

The research involved an experimental and numerical analysis of PCM with a melting temperature range of 22 °C–26°C under various conditions. Three different jet angles (45°, 90° and 135°) and two container angles (45° and 90°) were tested. Additionally, two different Reynolds numbers (2,235 and 4,470) were used to explore the effects of jet outlet velocities on PCM melting behaviour. The study used a circular container and analysed the melting process using the hot air inclined jet impingement (HAIJI) method.

The obtained results showed that the average temperature for the last time step at Ф = 90° and Re = 4,470 is 6.26% higher for Ф = 135° and 14.23% higher for Ф = 90° compared with the 45° jet angle. It is also observed that the jet angle, especially for Ф = 90°, is a much more important factor in energy storage than the Reynolds number. In other words, the jet angle can be used as a passive control parameter for energy storage.

This study offers a novel perspective on the effective storage of waste heat transferred with air, such as exhaust gases. It provides valuable insights into the role of jet inclination angles and Reynolds numbers in optimizing the melting and energy storage performance of PCMs, which can be crucial for enhancing the efficiency of thermal energy storage systems.

A domain‐adaptive technique which maps the unknown, time‐dependent, curvilinear geometry of annular liquid jets into a unit square is used to determine the steady state mass absorption rate and the collapse of annular liquid jets as functions of the Froude, Peclet and Weber numbers, nozzle exit angle, initial pressure and temperature of the gas enclosed by the liquid, gas concentration at the nozzle exit, ratio of solubilities at the inner and outer interfaces of the annular jet, pressure of the gas surrounding the liquid, and annular jet's thickness‐to‐radius ratio at the nozzle exit. The domain‐adaptive technique yields a system of non‐linearly coupled integrodifferential equations for the fluid dynamics of and the gas concentration in the annular jet, and an ordinary differential equation for the time‐dependent convergence length. An iterative, block‐bidiagonal technique is used to solve the fluid dynamics equations, while the gas concentration equation is solved by means of a line Gauss‐Seidel method. It is shown that the jet's collapse rate increases as the Weber number, nozzle exit angle, temperature of the gas enclosed by the annular jet, and pressure of the gas surrounding the jet are increased, but decreases as the Froude and Peclet numbers and annular jet's thickness‐to‐radius ratio at the nozzle exit are increased. It is also shown that, if the product of the inner‐to‐outer surface solubility ratio and the initial pressure ratio is smaller than one, mass is absorbed at the outer surface of the annular jet, and the mass and volume of the gas enclosed by the jet increase with time.

In an arrangement for deflecting a propulsive jet forwardly for braking purposes the jet reversal is effected by moving a series of curved blades at the rear end of the jet pipe to intercept the jet stream. As shown in FIG. 1 the jet pipe 10 terminates in an opening in the upper surface 12 of a delta‐wing, the deflecting blades 17 being mounted to form a grille 14 which is normally housed forwardly of the jet discharge opening, but which is movable rearwardly by an electric motor 33 and rack‐and‐pinion gearing 27, 28 into a position where it extends across the discharge opening to reverse the jet. FIG. 2 shows a modification in which the jet is divided into two streams by a wedge shaped vane 109 to discharge through openings 107, 108 in the upper and lower wing surfaces respectively, deflexion of the streams being effected by upper and lower grilles 102, 103. In addition the vane 109 may be rotated about a pivot 140 to deflect the whole of the jet through the upper or lower wing outlet. A similar effect may be obtained without the use of a bifurcated jet pipe by modifying the arrangement according to FIG. 1 to include a downwardly directed branch of the jet pipe 10 opening in the undersurface of the wing and controlling the flow of the jet through this branch by hinged flaps at the junction of the main and branch pipes, and in the undersurface of the wing, respectively. In the case of a circular jet pipe 40, FIG 3, the rear portion of the pipe is cut off along oblique planes 41, 42, and the cut‐away portions occupied by curved vanes 43, 44 hinged about a rear transverse axis 45. The vanes 43, 44 are surrounded by curved blade grills 46, 47 which in turn are enclosed by external plates 51, 52. To effect reversal of the jet the closure plates 51, 52 are first slid forwardly clear of the grilles 46, 47, and jacks 55, 56 are then operated to move the grilles 46, 47 and the tail portion 53 of the jet pipe forwardly, thus causing the vanes 41, 42 to pivot about the axis 45 to obstruct the jet pipe and cause the jet to escape through the grilles 46, 47.

The purpose of this paper is to present the findings on jet array instabilities of molten caprolactam. Initial investigations showed that although a suitable range of parameters was found for stable jetting, there were cases where instabilities occurred due to external sources such as contamination.

The inkjet system consisted of a melt supply unit, filtration unit and printhead with pneumatic and thermal control. A start‐up strategy was developed to initiate the jetting trials. A digital microscope camera monitored the printhead nozzle plate to record the jet array stability within the recommended range of parameters from earlier research. The trials with jet instabilities were studied to analyse the instability behaviour.

It was found that instabilities occurred in three forms which were jet trajectory error, single jet failure and jet array failure. Occasionally, the jet with incorrect trajectory remained stable. When a jet failed, bleeding of melt from the nozzle due to the actuations influenced the adjacent jets initiating an array of jets to fail similar to falling dominos.

The research concept is novel and investigating the jet array instability behaviours could give an understanding on jetting reliability issues.

The literature on jets is extensive but scattered. A concise guide is needed, and this paper attempts (at the risk of over‐simplification) to summarise some of the available information, both theoretical and experimental (some of it obtained in the Department of Mechanical Engineering) on those jet properties which are important in engineering — velocity profile and decay, spread, entrainment and static pressure.

Recent years have seen a rapid development of ink‐jet printing technology. This paper reviews the state‐of‐the‐art in ink‐jet printing technology and gives an overview of ink‐jet printing into the immediate future. The focus is placed on various applications of jet printing technology. The potential of applying jetting technology in the conventionally surface coating dominated applications will also be explored.

This study aims to investigate the effects of nozzle momentum flux distribution on the flow field characteristics.

The nozzle configuration consists of a central nozzle surrounded by four nozzles. All nozzles have the same diameter and constant separation between nozzles. OpenFOAM® is used for simulating the jet flow. Reynolds-averaged Navier-Stokes (RANS) equations are solved iteratively with a first-order closure for turbulence. Pitot-static tube with differential pressure transducer is used for mean velocity measurements. The comparison of computed results with experimental data shows similar trend and acceptable validation.

According to the results, the momentum flux distribution significantly alters the near field of multiple turbulent round jets. Highly non-linear decay region in the near field is found for the cases having higher momentum in the outer jets. As a result of merging, increased positive pressure is found in the mixing region. Higher secondary flows and wider mixing region are reported as a result of momentum transfer from axial to lateral directions by Reynolds stresses.

The present study is limited to isothermal flow of air jet in air medium.

Optimum momentum flux distribution in multijet injector of a combustor can reap better mixing leading to better efficiency and lesser environmental pollution.

As summary, the contributions of this paper in the field of turbulent jets are following: simulations for various momentum distribution cases have been performed. In all the cases, the flow at the nozzle exit is subsonic along with constant velocity profile. To simulate proper flow field, a large cylinder-type domain with structured grid is used with refinements toward the nozzle exit and jet axis. The results show that the non-linearity increases with increase in momentum of outer jets. Longer merging zones are reported for cases with higher momentum in outer nozzles using area-averaged turbulent kinetic energy. Similarly, wider mixing regions are reported using secondary flow parameter and visualizations.

This paper analyses numerically the effects of sinusoidal g—jitter on the fluid dynamics of, and mass transfer in, annular liquid jets. It is shown that the pressure and volume of the gases enclosed by the jet, the gas concentration at the jet’s inner interface, and the mass absorption rates at the jet’s inner and outer interfaces are sinusoidal functions of time which have the same frequency as that of the g—jitter. The amplitude of these oscillations increases and decreases, respectively, as the amplitude and frequency, respectively, of the g—jitter is increased. The pressure coefficient and the gas concentration at the jet’s inner interface are in phase with the applied g—jitter and the amplitude of their oscillations increases almost linearly with the amplitude of the g—jitter. The mass absorption rates at the jet’s inner and outer interfaces exhibit a phase lag with respect to the g—jitter.

A simplified method for estimating the aerodynamic properties of thin flapped aerofoils influenced by high velocity jet sheets is developed. It is assumed that the main flow around the aerofoil does not influence the velocity distribution in the jet. Considering also the effect of the mixing with the surrounding air, a real jet is supposed to be replaced by an appropriate aerodynamic model, having a linear downstream distribution of velocity adopted on the basis of test data. Both thin aerofoil and the jet sheet are adequately replaced by vortex distributions,so that the lift and the pitching moment of the aerofoil influenced by the jet may be evaluated in the usual manner. Comparison with some available experimental results shows that the proposed semi‐empirical method gives good agreement with experiment.