Velocity erosive

High-fluid velocity will tend to erode off the protective corrosion layer inside process piping. This exposes new, clean, and reactive metal to the corrosive oxygen and water. What is meant by erosive velocity For aqueous systems with a few hundred parts per million (ppm) of particulates, an erosive velocity is 

For example, dirty water (which has a density of 62 lb/ft ) would become erosive at about 8 ft/s. We sometimes design water pipes for velocities of 10 to 12 ft/s. That s fine, provided the water is clean and noncorrosive. For dirty water, a design velocity of 5 to 7 ft/s would be better. 

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The tube-side inlet to an exchanger, i.e. the tube ends, is a highly turbulent region and nylon ferrules in the tube ends of the inlet pass have been used in cupro-nickel-tubed condensers to prevent erosion. Where the flow is two phase the same rules will apply except that an erosion velocity limit is more difficult to specify. 

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. 

If the acoustic velocity in the gas adjacent to the burning surface is small compared with the local mean erosion velocity, then it may be expected to produce small-amplitude oscillations of m that locally may be related to the amplitude of the acoustic velocity oscillation through an admittancelike expression similar to equation (52). Of course, a corresponding response... 

The decrease in the mean advection velocity is due, at least in part, to a decrease in the mean water velocity. The change could also be a manifestation of a decrease in the maximum tidal velocity and/or an increase in the critical erosion velocity due to decreasing mean grain size. [The maximum tidal velocity does decrease by about 12% (4 cm/sec) along the section.] Both of these phenomena would help to reduce the time that sand grains actually spend in motion and to lower the mean velocity of transport with a consequent decrease in the width of the transition zone. The width of the zone will also be decreased by an increase in the sedimentation rate or a decrease in the diffusion coefficient. 

New on-off valves closing speeds shall be reviewed and adjusted to prevent hydraulic shock waves or water hammer. Also, piping velocity shall be checked so that it is well within erosion velocity. The possibility of multi-phase mixtures inside pipes shall be evaluated carefully to apply proper hydraulic equations and estimate adequate pipe sizing. 

After leaving the aperture the jet disintegrates due to air resistance and vaporization. Assuming that disintegration is caused by the resistance of air we obtain the erosion velocity Ue... 

The erosion velocity is calculated according to Eq. (10.41), which gives... 

Impingement plate Used to protect tubes from the erosive velocity of the shell-side inlet fluid. 

Miedema and Ramsdell (2011) demonstrated that the typical disk-shape of shells will reduce the settling velocity of the grains, but increase the erosion velocity required to force settled particles into suspension again. This is caused by the relative orientation of the shells to the direction of the flow during transport and after settlement. 

Line erosion velocity is estimated by following equation for either vapor or liquid tine ... 

V erosion is line erosion velocity, in ft/sec p is fluid density, in Ib/fl3. For solid free or non-conosive fluid, this is a conservative estimation of line erosion velocity. Actual erosion velocity may be 150 to 200% hi er. [1 ]... 

For lines having plerrty available pressure, its line size is limited by erosion velocity, which is calculalcd using Eq. (1) using density of the two phase mixture, p nuK, in 1b/R3. p mix is calculated as follow ... 

Once the optimum line size is estimated, make sure the line velocity is not exceeding its erosion velocity. 

Using erosion velocity or known corrosive line velocity as an upper limit to reduce the line size from the calculated optimum size. 

For the stability of the concrete cylinder the radial heat flux from the melt to the concrete wall is important. If the same heat flux is realized, the type of melt, oxidic or metallic, is of no more importance. Calculations with the WECHSL code for the experiment and the accident are given in Table. 1. The comparison shows that the heat flux in the experiment and the freezing temperature of the melt meet reasonably well the conditions of the oxidic melt in the accident under consideration. Similarly, the measured erosion velocity in this test with 0.027 mm/s=9.7 cm/h meets the desired conditions. Therefore, the result of wall failure is transferable to the accident condition, although in the accident under consideration, because of geometrical reasons, only the oxidic melt would penetrate the cylinder. 

In the BETA facility two experiments were conducted on the failure of a cylindrical concrete wall which is eroded on the inner side by a heated melt while being cooled outside by stagnant water. No decrease of the radial erosion velocity is observed when the melt front approaches the outer concrete surface and wall failure occurs after the residual wall thickness is reduced to about one centimeter. The melt relocates into the water annulus. Melt/water contact in the second test led to an energetic steam explosion which destroyed the crucible and caused considerable damage of the facility. Applicability of the experimental results for LWR severe accidents is discussed. 

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