Nozzle velocity maximum

The following table gives suggested maximum velocities in exchanger nozzles. The pressure drop through nozzles should be checked, especially where pressure losses are a problem such as in low pressure systems. 

Ludwig, E. E., Applied Process Design For Chemical and Petrochemical Plants, 2nd Ed., Gulf Publishing Co., 1983. 

Maximum Recommended Velocities Through Nozzle Connections, Piping, etc. Associated With Sheil and/or Tube Sides of Heat Exchanger 

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This is a low value, therefore, the possibility exists of an up-rate relative to any nozzle flow limits. At this point, a comment or two is in order. There is a rule of thumb that sets inlet nozzle velocity limit at approximately 100 fps. But because the gases used in the examples have relatively high acoustic velocities, they will help illustrate how this limit may be extended. Regardless of the method being used to extend the velocity, a value of 150 fps should be considered maximum. When the sonic velocity of a gas is relatively low, the method used in this example may dictate a velocity for the inlet nozzle of less than 100 fps. The pressure drop due to velocity head loss of the original design is calculated as follows ... 

It is also true that in the converging section of a converging/diverging nozzle the maximum obtainable fluid velocity is the speed of sound, reached at the throat. This is because a further decrease in pressure requires an increase in cross-sectional area, i.e., a diverging section. The explanation for this is as follows. At the relatively high pressures in the converging section, a given pressure drop... 

FORMAT (5X, MINIMUM VAPOR-LIQUID NOZZLE VELOCITY, ft/s. , T60, F8.3,/,5X, MAXIMUM VAPOR-LIQUID NOZZLE VELOCITY, ft/s. , T60,... 

For example, T /T0 = 0.833, p /po = 0.528, and p /po = 0.634 are obtained when y = 1.4. The temperature T0 at the stagnation condition decreases 17 % and the pressure p0 decreases 50% at the nozzle throat. The pressure decrease is more rapid than the temperature decrease when the flow expands through a convergent nozzle. The maximum flow velocity is obtained at the exit of the divergent part of the nozzle. When the pressure at the nozzle exit is vacuum, the maximum velocity is obtained by the use of Eqs. (1.48) and (1.6) as... 

Centrifugal separators cannot be sized with the F factor approach used with other types of separators because the maximum allowable velocity is a weaker function of gas density than the square root dependence in the F factor correlation. Maximum velocities for centrifugal separators depend upon the design and are different for each of the several manufacturer units. Pressure drop varies from 1 to 10 velocity heads depending upon the manufacturer. Velocity head should be based on inlet (outlet) nozzle velocity. 

Vm = maximum vapor velocity, feet per second Vn = nozzle velocity, feet per second... 

In addition, other rhologyical properties are helpful to understand this process. The velocity profile of axis and radius at 278K are shown in Fig 5(a) and Fig 5(b), respectively. From Fig 5(a), we can find the axis velocity increases as the nozzle contracts. In the exit part of nozzle, the maximum velocity is even higher than 500 m/sec. Moreover, the boimdary slip will happen because the nozzle is constructed by perfect FCC lattice with no fnction to hold water molecules near the wall. Fig 5(b) shows the velocity profile of radius. The maximum radius velocity occms at where nozzle starts contracting (X=2.1nm). This is because the water molecules are compressed to the center when the nozzle contracts,. This also leads to radius velocity profiles are symmetrical at the center of nozzle (Y = 5.5nm). 

Droplet size, particularly at high velocities, is controlled primarily by the relative velocity between liquid and air and in part by fuel viscosity and density (7). Surface tension has a minor effect. Minimum droplet size is achieved when the nozzle is designed to provide maximum physical contact between air and fuel. Hence primary air is introduced within the nozzle to provide both swid and shearing forces. Vaporization time is characteristically related to the square of droplet diameter and is inversely proportional to pressure drop across the atomizer (7). 

The shape of the converging section is a smooth trumpet shape similar to the simple converging nozzle. However, special shapes of the diverging section are required to produce the maximum supersonic-exit velocity. Shocks result if the divergence is too rapid and excessive boundary layer friction occurs if the divergence is too shallow. See Liepmann and Roshko (Elements of Gas Dynamic.s, Wiley, New York, 1957, p. 284). If the nozzle is to be used as a thrust device, the diverg-... 

Critical and Subcritical Flow - The maximum vapor flow through a restriction, such as the nozzle or orifice of a pressure relief valve, will occur when conditions are such that the velocity through the smallest cross-sectional flow area equals the speed of sound in that vapor. This condition is referred to as "critical flow" or "choked flow . 

Flare stack sizing and pressure drop is included with considerations of pressure drop through the safety valve headers, blowdown drums, flare headers, seal drum, etc. Elevated flare tips incorporating various steam injection nozzle configurations are normally sized for a velocity of 120 m/s at maximum flow, as limited by excessive noise and the ability of manufacturers to design tips which will insure flame stability. This velocity is based on the inclusion of steam flow if injected internally, but the steam is not included if added through jets external to the main tip. 

Compact air jets are formed by cylindrical tubes, nozzles, and square or rectangular openings with a small aspect ratio that are unshaded or shaded by perforated plates, grills, etc. Compact air jets are three-dimensional and axisymmetric at least at some distance from the diffuser opening. The maximum velocity in the cross-section of the compact jet is on the axis. 

The ratio to z depends only on (gag-, zjx, = 2/3 tga.g, and the ratio of x, /Xq has a constant value equal to 0.578. To clarify the trajectory equation of inclined jets for the cases of air supply through different types of nozzles and grills, a series of experiments were conducted. The trajectory coordinates were defined as the points where the mean values of the temperatures and velocities reached their maximum in the vertical cross-sections of the jet. It is important to mention that, in such experiments, one meets with a number of problems, such as deformation of temperature and velocity profiles and fluctuation of the air jet trajectory, which reduce the accuracy in the results. The mean value of the coefficient E obtained from experimental data (Fig. 7.25) is 0.47 0.06. Thus the trajectory of the nonisothermal jet supplied through different types of outlets can be calculated from... 

The average experimental value of the coefficient 0 is 1.7 with a standard deviation (og) of 0.05. Equation (7.160) allows one to calculate the momentum ratio (/rj2/foi) required to extend the length of zone I to the value equal to Xj, given that the distance between the directing nozzles is equal to The graph presented in Fig. 7.56 is plotted according to Eq. (7.160) for and X,2 equal to 6.2. The maximum value of reverse flow velocity (n,, .) was found to be in the cross-section at X equal to Xy... 

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