Pressure prediction

An afternate method with approximately the same accuracy as the Rackett method is the COSTALD metnod of Hanldnson and Thomson.The critical temperature, a characteristic volume near the critical volume, and an acentric factor optimized for vapor pressure prediction by the Soave equation of state are required input parameters. The method is detailed in the Technical Data Book ... 

If a tube breaks, pressure on the exehanger low-pressure side can spike to a level that exceeds the pressure predicted by a steady-state analysis. This spike is due to pressure buildup before the fluid accelerates out of the shell and/or before the relief device fully opens. 

API RP-521 reeommends transient analysis for exchangers with wide difference in design pressure (such as cases where the two-thirds rule was not applied) because the pressure in the low pressure side of the exehanger ean spike to a level that exceeds the pressure predicted by a steady state analysis when it is liquid-filled. This pressure spike is due to pressure buildup before the liquid is accelerated out of the low pressure side and/or before the relief device opens fully. API RP-521 recommends that the basis for the tube rupture be a sharp... 

Answer Use the plant s PSA to determine the risk of accidents that include containment failure from overpressurization. Then make a preliminary design of a vented containment that has sufficiently low impedance to the gas at the pressure predicted for the most severe accident sequences such that the containment is not damaged. This containment bypass will include iodine and HEPA filters as well as scrubbers and a discharge through a stack. Estimate the dose that the population would get using this bypass for comparison with the PSA result for ruptured containment sequences. 

A large difference in pressure prediction will occur if the formation is not well known. Several exponents might have to be used in Eaton s equation. Exponent 1.2 seems to match the Vicksburg formation as was seen in the preceding example. 

Eaton, B. A., The equation for pressure prediction from well logs, SPE 5544, SPE 50th Ann. Tech. Conf. Exhibit, Dallas, Tx, September 28-October 1, 1975. 

It Is now well established experimentally that the solvation force, fg, of confined fiuld Is an oscillating function of pore wall separation. In Figure 4 we compare the theoretical and MD results for fg as a function of h. Given that pressure predictions are very demanding of a molecular theory, the observed agreement between our simple theory and the MD simulations must be viewed as quite good. The local maxima and minima In fg coincide with those In n y and therefore also refiect porewldths favorable and unfavorable to an Integral number of fiuld layers. 

The net effect of introducing the inertia multiplier is to increase the time step by a factor equal to a. The crucial question is how large a value can a be without substantially distorting the true physical behavior of the system. Yow (Y3) and Wylie et al. (W13) developed correlations for this purpose, but the procedures are apparently somewhat ambiguous and unreliable for pipeline networks. Rachford and Dupont (Rl) gave a counter example for which an apparently reasonable choice of a( = 5) miss the pressure prediction by as much as 100 psi. 

The vapour pressure of BHET is approximately three orders of magnitude lower than that of EG. Nevertheless, evaporation of BHET still occurs in significant amounts under vacuum. In Figure 2.26, the experimentally determined vapour pressure of BHET is compared to the vapour pressure predicted by the Unifac group contribution method [95], The agreement between the measured and calculated values is quite good. In the open literature, no data are available for the vapour pressure of dimer or trimer and so a prediction by the Unifac method is shown in Figure 2.26. The correspondence between measured and predicted data for BHET indicates that the calculated data for dimer and trimer... 

MPa, that is, an error less than 8%. This corrected method provides a pressure prediction that is acceptable for process troubleshooting and design. 

The resin pressure is almost never equal to the autoclave pressure. If the resin pressure drops due to resin flow, then it may become less than the minimum pressure necessary to prevent void stability and growth. In order to produce quality void-free laminates consistently, accurate resin pressure predictive software is a necessity. 

Exact suitability at all values of Garb would require either an infinite number of K-W parameter sets, or equations which adequately expressed the parameters as continuous functions of G or some other appropriate property of the explosive. Although we are not now in a position to offer such equations, it is nevertheless profitable to consider a quantity Pruby which would represent the pressure predicted by the computer if given as input information exactly suitable values of o, j8, k, and 6. 

A first trial by the method of least squares involved fitting detonation pressures predicted by the ruby computer code8 to an expression of the form... 

The variation of m with pressure predicted by this model can now be found. Again noting that Ti = T , Equations 3a and 14 lead to ... 

Before beginning the series of runs to determine the relief size, the physical property and kinetic data need to be correlated in the form required, by the code. In some cases, the code may already have the components required on a database. In all other cases, physical property data must be found, estimated or measured and correlated in the appropriate form. Some codes have a front-end program for curve fitting of data. For tempered systems, the vapour/ liquid equilibrium models are of critical importance since errors will cause the code to open the relief system at the wrong temperature and reaction rate. It is therefore worthwhile to spend time to ensure reasonable behaviour of the vapour pressure predictions. Check that all correlations behave sensibly over the entire temperature range of relevance for relief sizing. A good test for the physical property and kinetic data supplied to the code is to first model the (unrelieved) adiabatic calorimetric test which was used to obtain the kinetic data.. . ... 

Figure 2. Capillary hysteresis of nitrogen in cylindrical pores at 77 K. Equilibrium desorption (black squares) and spinodal condensation (open squares) pressures predicted by the NLDFT in comparison with the results of Cohan s equation (the BJH method) for spherical (crosses and line) and cylindrical (line) meniscus.

However, it was Soave s modification [30] of the temperature dependence of the a parameter, which resulted in accurate vapour pressure predictions (especially above 1 bar) for light hydrocarbons, which led to cubic equations of state becoming important tools for the prediction of vapour-liquid equilibria at moderate and high pressures for non-polar fluids. 

Peng and Robinson [31] used a different volume dependency of the attractive term, which results in slightly improved liquid volumes (because for this E.O.S Zc = 0.307, which is closer to the experimental values) and changed slightly the temperature dependence of a to give accurate vapour pressure predictions for hydrocarbons in the 6- to 10-carbon-number range. 

Figure 5.16 clearly shows the pressure and composition dependence of hydrate structure at a constant temperature. It can be seen that the hydrate can be si, sll, or both depending on the composition and pressure. Predictions also show that there is temperature dependence as well. 

Prediction of the hydrate phase on a laboratory scale is analogous (in vapor-liquid equilibrium) to the prediction of the liquid phase concentration given only the vapor phase concentration, temperature, and pressure. Predictions of either the liquid phase or the hydrate phase are unacceptable because all experimental errors are transferred to prediction of the unmeasured phase. 

It is very satisfying and useful that the COSMO-RS model—in contrast to empirical group contribution models—is able to access the gas phase in addition to the liquid state. This allows for the prediction of vapor pressures and solvation free energies. Also, the large amount of accurate, temperature-dependent vapor pressure data can be used for the parameterization of COSMO-RS. On the other hand, the fundamental difference between the liquid state and gas phase limits the accuracy of vapor pressure prediction, while accurate, pure compound vapor pressure data are available for most chemical compounds. Therefore, it is preferable to use experimental vapor pressures in combination with calculated activity coefficients for vapor-liquid equilibria predictions in most practical applications. 

Group contribution methods can be applied for property prediction of fatty-acid systems. For vapor-pressure prediction the following equation has been recently proposed and tested successfully against experimental data [6, 40] ... 

---