Free jet

Jet, free A jet which, on leaving an orifice, is allowed to expand freely without coming into contact with any surfaces. 

Solvent shifts in van der Waals complexes of perylene have been studied in supersonic jet free expansion with rare gas and organic solvent molecules 9. -i complexes give results... 

The backwash system used by Zum, for instance, employs two header pipes one operates continuously at 20 psi, while the other operates at 40-55 psi. Under normal operating conditions, these jets operate at 35 psi. Once a day they are operated at 50 psi for 30 min to keep the jets free of slime buildup. Should this procedure fail to keep the jets clean, the pressure is raised to 55 psi. At this pressure the spring-loaded jet mouth widens to allow for more effective cleaning. 

Concerning the vertical bubbling jets free from the side wall, the half-value radius, bu, of the radial distribution of the axial mean velocity u is approximated by [21] ... 

The characteristic lengths, / rms,max/2 and /v rms,max/2. shown in Fig. 3.29 are larger than ,max/2 just like the vertical bubbling jets free from the Coanda effect. 

Leaving the refinery, jet fuel has generally no free water and contains only a small quantity of dissolved water. But humidity from the air and tank breathing result in continuous intrusion of water that must be then removed by decanting and filtration. This is why jet fuel needs to be tested for its ability to separate the contained water. 

For jet fuels, the elimination of free water using filters and coalescers by purging during storage, and the limit of 5 ppm dissolved water are sufficient to avoid incidents potentially attributable to water contamination formation of micro-crystals of ice at low temperature, increased risk of corrosion, growth of micro-organisms. 

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

Some other extremely iisellil spectroscopic teclmiques will only be mentioned here. Probably the most important one is spectroscopy in free jet expansions. Small molecules have often been studied by gas-phase spectroscopy where sharp rotational and vibrational structure gives detailed iufonnation about molecular... 

Plenary 9. J W Nibler et al, e-mail address niblerj chem.orst.edu (CARS and SRS). High resolution studies of high lymg vibration-rotational transitions in molecules excited in electrical discharges and low density monomers and clusters in free jet expansions. Ionization detected (REMPI) SRS or IDSRS. Detect Raman... 

Miller D R 1988 Free jet sources Atomic and Molecular Beam Methods ed G Sooles (New York Oxford University Press)... 

Yamashita M and Fenn J B 1984 Electrospray ion source. Another variation on the free-jet theme J. Phys. C Solid State Phys. 88 4451... 

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. 

Most of the remarks above refer to unconfined or free flows. Many industrial appHcations involve the use of confined jets. It is customary to consider a jet confined when the ratio of the confinement radius to the source radius Hes in the range 4—100. Below a ratio of 2, the jet does not develop its similarity profile before striking the wall, whereas above a ratio of 100 the jet itself may usually be considered free. Under certain conditions, flow in confined jets is accompanied by the existence of a recirculation 2one which significantly affects the jet behavior by returning material upstream (9). This recirculation can be particularly important in combustion processes. 

The inks formulated for jet printing must be very fluid, stable, and free of any particles that could cause clogging of the jet nozzles, and be capable of depositing and adhering to a substrate with a minimum of character fogging. They are generally formulated with soluble dye colorants in a suitable aqueous or solvent-based vehicle (9). 

Heat is often removed by simply allowing it to escape by convection, radiation, and conduction. However, such uncontrolled escape can lead to very large temperature fluctuations. It is better to surround the entire container, heaters and all, with a controUed-temperature cooled chamber. Even then, buoyancy-driven free convection from the ampul can lead to small temperature fluctuations. Jets of air or cooling water appHed directly onto the ampul adjacent to the heater have been employed. Both temperature and flow rate of the coolant should be controlled. 

A turbulent free jet is normally considered to consist of four flow regions (Tuve, Heat. Piping Air Cond., 25(1), 181-191 [1953] Davies, Turbulence Phenomena, Academic, New York, 1972) as shown in Fig. 6-17 ... 

Witze Am. In.st. Aeronaut. Astronaut. J., 12, 417-418 [1974]) gives equations for the centerline velocity decay of different types of subsonic and supersonic circular free jets. Entrainment of surrounding fluid in the region of flow establishment is lower than in the region of estabhshed flow (see Hill, J. Fluid Mech., 51, 773-779 [1972]). Data of Donald and Singer (T/V7/1.S. In.st. Chem. Eng. [London], 37, 255-267... 

Despite being simple, rugged, reliable, requiring low maintenance, low cost, and vibration free, steam-jet systems are not widely accepted in water chilling for air-conditioning due to characteristics of the cycle,... 

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