Jet turbulence

Texturing. The final step in olefin fiber production is texturing the method depends primarily on the appHcation. For carpet and upholstery, the fiber is usually bulked, a procedure in which fiber is deformed by hot air or steam jet turbulence in a no22le and deposited on a moving screen to cool. The fiber takes on a three-dimensional crimp that aids in developing bulk and coverage in the final fabric. Stuffer box crimping, a process in which heated tow is overfed into a restricted oudet box, imparts a two-dimensional sawtooth crimp commonly found in olefin staple used in carded nonwovens and upholstery yams. 

Morinda citrifolia submerged jet turbulent membrane integrity morphology non-growth [59, 129,130]... 

Because of such factors as wave formation, jet turbulence, and secondary breakup, the drops formed are not of uniform size. Various ways of describing the distribution, including the methods of Rosin and Rammler (R9) and of Nukiyama and Tanasawa (N3), are discussed by Mugele and Evans (M7). A completely theoretical prediction of the drop-size distribution resulting from the complex phenomena discussed has not yet been obtained. However, for simple jets issuing in still air, the following approximate relation has been suggested (P3) ... 

A further example of the dramatic effects of stress is given by a VC-10 aircraft of the same company. While flying over Mount Fuji, Japan, the tail assembly of one such plane became detached from the rest of the jet. Turbulence was the stated cause. However, H related fatigue was probably a forerunner of the disaster. 

Dash, S. M., D.C. Kenzakowski, and J.L. Papp. 2002. Progress in jet turbulence modehng for aero-acoustic applications. AIAA Paper No. 2002-2525. 

The use of turbulence generation placed in the nozzle or upstream is wasteful as the jet turbulence decays rapidly as it approaches the impingement surface. Thus the added pumping power leads to little or no increase in the impingement transfer rate. 

A commonly used primary atomization model for liquid jets has been developed by Huh et al. [1], The model considers the effects of both infinitesimal wave growth on the jet surface and jet turbulence including cavitation dynamics. Initial perturbations on the jet surface are induced by the turbulent fluctuations in the jet, originating from the shear stress along the nozzle wall and possible cavitation effects. This approach overcomes the inherent difficulty of wave growth models, where the exponential wave growth rate becomes zero at zero perturbation amplitude. 

Many experimental studies have been carried out to investigate the turbulence characteristics in gas-liquid and gas-solid two-phase jets under various flow conditions [31-35]. In single-phase jets, turbulence is produced mainly by entrainment of surrounding fluid into the jets, [29,30] while in two-phase jets, turbulence production takes place also in the wake of bubbles or solid particles in addition to turbulence production due to the entrainment typical of single-phase jets. The size and shape of bubbles or soUd particles are considered to affect the structure of turbulence [36,37]. The effects of the size of bubbles or solid particles on the modulation of turbulence characteristics have been reported by many researchers [35-38]. However, the information on the effect of bubble shape is quite limited. 

There exists only one coherent structure of turbulence in an air-water bubbling jet. Turbulence is produced mainly by ejection everywhere in the bubbling jet. The difference in the turbulence structures in the two types of bubbling jets is attributable to the shape and size of bubbles. Bubbles in the He-Wood s metal bubbling jet are of the skirted type, while those in an air-water bubbling jet adopted for comparison can be classified into the wobbling type. 

Tang, Q., Xu, J., Pope, S.B. Probability density function calculations of local extinction and no production in piloted-jet turbulent methane/air flames. Proc. Combust. Inst. 28, 133-139 (2000)... 

Values of interfacial tension of nucleus from turbulent jet measurements, by various equations [44]. 

The air jet textured yam process is based on overfeeding a yam into a turbulent air jet so that the excess length forms into loops that are trapped in the yam stmcture. The air flow is unheated, turbulent, and asymmetrically impinges the yam. The process includes a heat stabilization zone. Key process variables include texturing speed, air pressure, percentage overfeed, filament linear density, air flow, spin finish, and fiber modulus (100). The loops create visual and tactile aesthetics similar to false twist textured and staple spun yams. 

In a free jet the absence of a pressure gradient makes the momentum flux at any cross section equal to the momentum flux at the inlet, ie, equations 16 and 17 define jet velocity at all points. For a cylindrical jet this leads to a center-line velocity that varies inversely with (x — aig), whereas for slot jets it varies inversely with the square root of (x — Xq As the jet proceeds still further downstream the turbulent entrainment initiated by the jet is gradually subordinated to the turbulence level in the surrounding stream and the jet, as such, disappears. 

Fig. 17. Comparison of the predictions of k-Q model with experimental data for a turbulent jet inside a 5° conical duct, (a) Flow geometry and inlet conditions, where geometry =1.6 cm, = 16 cm, L = 64 cm, 0 = 5°-, flow conditions, p = 0.998 g/mc, p = 0.01 g/cm-s, Uj = 40 cm/s,...

For a known flow rate the no22le diameter is set by the largest si2e that satisfies the turbulent jet requirement for both heavy and light jets, ie,... 

J ct Spra.y, The mechanism that controls the breakup of a Hquid jet has been analy2ed by many researchers (22,23). These studies indicate that Hquid jet atomisation can be attributed to various effects such as Hquid—gas aerodynamic interaction, gas- and Hquid-phase turbulence, capillary pinching, gas pressure fluctuation, and disturbances initiated inside the atomiser. In spite of different theories and experimental observations, there is agreement that capillary pinching is the dominant mechanism for low velocity jets. As jet velocity increases, there is some uncertainty as to which effect is most important in causing breakup. 

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