Velocity inlet nozzle

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 ... 

CALCULATE THE VAPOR-LIQUID INLET NOZZLE VELOCITIES. 

Sometimes tubes are omitted from the tube bundle in order to provide space for an impingement plate. The impingement plate in this case is generally a circular or rectangular plate located a short distance from the row of tubes and secured by various means. A modification of this type is to form the plate and surround the bundle with it as a partial shroud. Omitting tubes from the tube bundle has many advantages, especially when inlet nozzle velocities are very high or when tubes must be omitted from the baffle windows in order to prevent problems associated with tube vibration. 

What happens if you introduce non-uniform inlet nozzle velocity profile BC ... 

Impingement Baffle The tube bundle is customarily protected against impingement by the incoming fluid at the shell inlet nozzle wmen the shell-side fluid is at a high velocity, is condensing, or is a two-phase fluid. Minimum entrance area about the nozzle is generally equal to the inlet nozzle area. Exit nozzles also require adequate area between the tubes and the nozzles. A full bundle without any provision for shell inlet nozzle area can increase the velocity of the inlet fluid by as much as 300 percent with a consequent loss in pressure. 

Erosion-corrosion problems on the outside of tubes are frequently associated with impingement of wet, high-velocity gases such as steam. This typically involves peripheral tubes at the shell inlet nozzle (Fig. 11.9). Baffle and tube interfaces may also be affected. 

An example will help illustrate one use of velocity head. A compressor is being considered for reuse in another application, and the question was raised as to the size of the inlet nozzle. The original conditions are stated as follows ... 

Nozzles should be sized according to pipe sizing criteria, such as those provided in API RP 14E. The outlet nozzle is generally the same size as the inlet nozzle. To prevent baffle destruction due to impingement, the entering fluid velocity is to be limited as ... 

Another source of pressure drop will be the flow expansion and contraction at the exchanger inlet and outlet nozzles. This can be estimated by adding one velocity head for the inlet and 0.5 for the outlet, based on the nozzle velocities. 

Steam is flowing through a horizontal nozzle. At the inlet the velocity is 1000 ft/s and the enthalpy is 1320 Btu/lbm. At the outlet the enthalpy is 1200 Btu/lbm. If heat is lost through the nozzle at a rate of 5 Btu/lbm of steam, what is the outlet velocity ... 

Simulations are then performed for gas bubbles emerging from a single nozzle with 0.4 cm I.D. at an average nozzle velocity of lOcm/s. The experimental measurements of inlet gas injection velocity in the nozzle using an FMA3306 gas flow meter reveals an inlet velocity fluctuation of 3-15% of the mean inlet velocity. A fluctuation of 10% is imposed on the gas velocity for the nozzle to represent the fluctuating nature of the inlet gas velocities. The initial velocity of the liquid is set as zero. An inflow condition and an outflow condition are assumed for the bottom wall and the top walls, respectively, with the free-slip boundary condition for the side walls. 

The impaction efficiency (17) for particles depends directly on the particle diameter (D), the flow velocity of the air (V), and the particle density (p) it varies inversely with the gas viscosity (p,) and with a parameter (Db) that is representative of the impactor s physical dimensions (e.g., the inlet nozzle diameter) and that is related to the curvature of the airstream. 

The second device shown is a cyclone inlet that uses centrifugal force, rather than mechanical agitation, to disengage oil and gas. This inlet can have a cyclonic chimney, as shown, or may use a tangential fluid race around walls. Designs arc proprietary, but most use an inlet nozzle sized to create a fluid velocity of about 20 fps around a chimney whose diameter is two-thirds the vessel diameter. 

The flow of vapor and entrained droplets in the piping upstream of a drum separator can be treated as homogeneous with no inierfacial slippage. At the inlet nozzle, the droplets have a "momentum of p r with being the velocity of the vapor and entrained droplets. 

To see if this drum size can be significandy reduced using the approach proposed in this article, some additional information is needed and the following is assumed inlet nozzle angle 0,=3O deg. inlet nozzle dia. vapor-droplet velocity ( , 56.6 ft/s hence. t/ = L cos 0,=49 ft/s, and Lp— stn 0,=28.6 ft/s. (The parameters 0( and dn can. of course, be adjusted. The effects of varying these parameters will be discussed.)... 

Shell-side flow. The hot shell-side flow enters the exchanger, as shown in Fig. 19.1, through the top inlet nozzle. Not shown on this sketch is the impingement plate, which is simply a square piece of metal, somewhat larger than the inlet nozzle. Its function is to protect the tubes from the erosive velocity of the shell-side feed. The plate lies across the upper row of tubes. 

Exauple 13 A high-velocity nozzle is designed to operate with steam at 700 kPa and 300°C. At the nozzle inlet the velocity is 30 m s 1. Calculate values of the ratio A/A (where A, is the cross-sectional area of the nozzle inlet) for the sections where the pressure is 600,500,400,300, and 200 kPa. Assume that the nozzle operates isentropi-cally. 

Calculate the pressure drop for the conditions of Example 7.20. Assume that the nozzle velocities are 5 ft/s (1.52 m/s), that the fluid density is 55 lb/ft3 (881 kg/m3), and that there are 24 baffles. Assume that there is also an impingement plate at the inlet nozzle. Calculate the pressure drop for both fouled and clean conditions. 

To completely design the vessel, the minimum and maximum velocity in the inlet nozzle is obtained by using the empirical criteria ... 

Step 5. Estimate the vapor-liquid inlet nozzle based on the following velocity criteria. 

Figure 11.8 Axial velocity profiles near the inlet (nozzle confignration 304545) 1 — LDV, = 0.05/ 2 — LDV, = 0.125/ 3 — LES, and 2 = 0 (inlet boundary conditions).

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