Erosive velocities calculation

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

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 ... 

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. 

Tube-side water velocities should be kept within reasonable limits, even though calculations would indicate that improved tube-side film coefficients can be obtained if the water velocity is increased. Table 10-24 suggests guidelines that recognize the possible effects of erosion and corrosion on the system. 

The critical velocity, which when exceeded may result in erosion corrosion, can be calculated by the equation presented in API RP 14E, which is [199]... 

Consideration will now be given to the various flow regimes which may exist and how they may be represented on a Flow Pattern Map to the calculation and prediction of hold-up of the two phases during flow and to the calculation of pressure gradients for gas-liquid flow in pipes. In addition, when gas-liquid mixtures flow at high velocities serious erosion problems can arise and it is necessary for the designer to restrict flow velocities to avoid serious damage to equipment. 

Fig.13.8 Erosive burning model calculation and experimental data for erosive ratio as a function of gas flow velocity or mass flow velocity.

Fig. 13.21 shows another example of oscillatory burning of an RDX-AP composite propellant containing 0.40% A1 particles. The combustion pressure chosen for the burning was 4.5 MPa. The DC component trace indicates that the onset of the instability is 0.31 s after ignition, and that the instability lasts for 0.67 s. The pressure instability then suddenly ceases and the pressure returns to the designed pressure of 4.5 MPa. Close examination of the anomalous bandpass-filtered pressure traces reveals that the excited frequencies in the circular port are between 10 kHz and 30 kHz. The AC components below 10 kHz and above 30 kHz are not excited, as shown in Fig. 13.21. The frequency spectrum of the observed combustion instability is shown in Fig. 13.22. Here, the calculated frequency of the standing waves in the rocket motor is shown as a function of the inner diameter of the port and frequency. The sonic speed is assumed to be 1000 m s and I = 0.25 m. The most excited frequency is 25 kHz, followed by 18 kHz and 32 kHz. When the observed frequencies are compared with the calculated acoustic frequencies shown in Fig. 13.23, the dominant frequency is seen to be that of the first radial mode, with possible inclusion of the second and third tangential modes. The increased DC pressure between 0.31 s and 0.67 s is considered to be caused by a velocity-coupled oscillatory combustion. Such a velocity-coupled oscillation tends to induce erosive burning along the port surface. The maximum amplitude of the AC component pressure is 3.67 MPa between 20 kHz and 30 kHz. - ...

Each person should find the remaining parameters and physical property data for this material required to solve the three models [Eqs. (8.14), (8.19), and (8.20)] for the erosive wear of a coal slurry that is, each person will have three calculations to do and three erosion rates as a result. Assume that the test temperamre is 343°C, the slurry velocity is 100 m/s, and the angle of attack is 50°. 

Line sizes based on velocity limitations are calculated only in special cases where corrosion, erosion or deposits on the pipe wall have to be accounted for or where critical flow conditions exist. 

Water containing 0.01 wt% sand is flowing through a pipe at a flow velocity of 60 m/s. Describe how the annual erosion depth increment in the pipe wall can be calculated on the basis of short duration tests in a similar pipe where the sand concentration in the water is varied in the range 0.1-10 wt% and the flow velocity in the range 20—40 m/s. Assume in the first instance that the deterioration process is mainly erosion and only little corrosion. 

Calculated sand erosion mass loss values at 80 m/s for ZnS and Ge (to allow a comparison with CVD diamond) are based upon up-scaling theories (using erosion rate velocity scaling factors) from work undertaken at the Cavendish Laboratory [45]. 

Equation (X.69) is valid for the removal of a layer of sand or coal particles 0.5-1 mm in thickness, with a particle size of 15-90 /xm, in ducts with a diameter of 100-400 mm. This formula can be used to determine the air velocity required to overcome the forces of autohesion in the process of erosion. For complete detachment of the adherent particles, i.e., in order to overcome the forces of dust-layer adhesion to the inside surface of the duct, the air velocity must be substantially greater than the value calculated by the use of Eq. (X.69). As the air-flow velocity is increased, it becomes possible to overcome the adhesive forces of the remaining particles and to clean the surface so that it is free of the adherent dust layer. Hence, for Fad > Faut, we must distinguish two different air-flow velocities, the first of which characterizes the conditions under which the forces of autohesion are overcome and the second the conditions under which the forces of adhesion are overcome. The first velocity is always lower than the second. 

On the basis of Eq. (XII.28) Zvonkov [349] calculated the critical velocities characterizing the main stages of erosion Pc-i > the first critical velocity, at which = F1, when the particles roll or slide but are not removed from the original ground surface Pc-2 > the second critical velocity, at which Fiif =... 

If stream velocities, scour and erosive forces are high, abutments with wingwall construction maybe necessary. Drift will affect the horizontal clearance and the minimum vertical clearance line of the proposed structure. Field surveys should note the size and type of drift found in the canal. Design based on the 50-year flow requires drift clearance. On major streams and rivers, drift clearance of 2 to 5 m above the 50-year discharge is needed. On smaller streams, 0.3 to 1 m maybe adequate. A formula for calculating freeboard is... 

On the basis of formula (XI.7), Zvonkov [501] calculated the critical velocities characterizing the main stages of erosion ... 

It is obvious that surface-eroding polymers allow for the control of drug release via the erosion process, which usually proceeds at constant velocity. A classification of polymers as surface and bulk eroding can be made based mainly on the nature of the bond between the monomers. As a rule of thumb, one can assume that the faster a bond is cleaved (usually by hydrolysis) the more the material is hkely to undergo surface erosion. In recent years, models have been developed that allow for the calculation of a dimensionless erosion number that predicts the erosion mechanism of a polymer device [50]. 

The kinetic constants of the Tedmon law are obtained by adjustment of experimental results. The external magnetite layer is assumed to dissolve in the liquid metal and that its dissolution is mass transfer-controlled. Its rate thus depends on the dissolved oxygen and dissolved iron concentrations, on the diffusion coefficient and the solubility of iron in the liquid metal or alloy. The code calculates the dissolved iron concentration on each point of the circuit and takes into account the influence of the fluid velocity on the dissolution of the magnetite layer. However, the erosion or the spallations of the oxide layer are not taken into account by the MATLIM code. 

The onset of erosion-corrosion in inhibited systems (straight portions) occurs at a velocity of about 1.5 times the calculated API erosional velocity. 

---