NOZZLE EXPANSION

Expanding jet theory of Jones see Detonation and expansion nozzle theory of Jones4D460—D461... 

By dissolving the compressible media in a liquid, a so-called gas-saturated solution may be formed. By expansion of such a solution in an expansion unit (e.g., a nozzle) the compressed medium is evaporated and the solution is cooled. Owing to the cooling caused by evaporation and/or the Joule-Thompson effect the temperature of the two-phase flow after the expansion nozzle is lowered. At a certain point, the crystallization temperature of the substance to be solidified is reached, and solid particles are formed and cooled further. 

Fig. 4.3 Schematic representation of a rocket combustion chamber with expansion nozzle. For the thrust we can finally write ...

The specific impulse 7sp is the change of the impulse (impulse = mass x velocity, or force x time) per propellant mass unit. The specific impulse is an important parameter for the characterization of rocket propellants and can be interpreted as the effective exhaust velocity of the combustion gases when exiting the expansion nozzle ... 

Means for preventing, or tending to prevent, the formation of a partial vacuum at the muzzle of the barrel is provided within the exi)ansipn chamber 16 in the casing HO 14. This vacuum-prevention means is constituted by an expansion nozzle 62 formed or provided on the muzzle 20, for which purpo.se the latter is serew-threaded externally, and the. stem of the 116 nozzle is screw-threaded internally. Preferably the internal face 64 of the nozzle has the sha]>e shown in Figure 6, which shows a maximum diameter B, a minimum diameter [Pg.89]

In operation the column of air in the barrel and the gas leakage past the bullet 20 first apx>ears at the muzzle of the barrel. This is unavoidable and assists in building up in front of the muzzle of the barrel back pressure which assists the correct functioning of the expansion nozzle fitted 25 td the end of the barrel. 

Figure 13-6 Apparatus for RESS A = SCF reservoir PV = high pressure volumetric pump HI, H2 = heat exchangers V, VI, V2, V3 = on-off valves S = saturation vessel EN = expansion nozzle E = expansion vessel F = flow meter G = rotameter PI = pressure indicator TI = thermometer.

The pure carbon dioxide is pumped to the desired pressure and preheated to extraction temperature using a heat exchanger. The supercritical fluid is then percolated through the extraction unit packed with one or more substrates. In the precipitation unit, the supercritical solution is expanded through a nozzle that needs to be heated in order to avoid plugging by substrates precipitation. Typically used expansion nozzles are capillaries of diameter < 100 p,m or laser drilled nozzles of 20-60 p,m in diameter. The process allows control over several parameters affecting... 

Fig.4 shows a comparison of two series of expansions obtained with the nozzles B1 and B2 at equal stagnation pressure and varied stagnation temperature. The expansions with 1 325 K show no condensation effect within the nozzle they were used for calibration of the effective nozzle profile. With decreasing stagnation temperature the Wilson-point moves upstream. Downstream of the Wilson-point the supersaturation is quickly reduced and the expansion obviously tends to a two-phase flow in which equilibrium between vapour and droplets is nearly attained. For equal values of the stagnation temperature, the Wilson points obtained in the faster expansion (nozzle B2) are found at a somewhat lower pressure ratio p/p j i.e. at a higher supersaturation than with nozzle B1. 

However, if the molecules are cooled, the population of thermally excited vib-rot states falls drastically and the spectrum simplifies. Thus, at 77 K, 69% of UFs is in its lowest vibrational state, and this increases to 85% at 55 K. However, the vapor pressure is untenably low at such temperatures (7 x 10 Pa at 77 K), and equilibrium cooling is out of the question. Still by cooling in a nonequilibrium expansion nozzle, uranium vapor concentration can be kept at a useful level and LIS is possible. None of this changes the fact that molecular LIS was abandoned in favor of AVLIS. 

Matson et al. have used the RESS process to produce silica powders from supercritical water. The solubility of silica in water at 500 °C and 1000 atm is 2600 ppm. It was found that the size of the product depended strongly on the silica concentration in the supercritical fluid prior to expansion. Particle sizes ranged from 0.1 to 0.5 p.m in diameter. The morphology of the particles was found to depend on the nature of the expansion nozzle—an orifice nozzle produced elongated particles, while a capillary nozzle produced spheres. 

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