Leungs method

Once it has been checked that the method is applicable (see above), it can be used for relief system sizing. Leung s method is[2,3,6]  

The average value of q can be calculated using equations (6.2) or (6.3) above and adiabatic experimental data which should be corrected to a thermal inertia of 1 (see Annex 2). The temperatures corresponding to the relief pressure and maximum accumulated pressure are obtained from vapour pressure data. The temperature difference between the relief pressure and the maximum pressure, , can also be obtained from experimental data, as described in A2.4. 

The physical properties, latent heat (hfg), specific volume change (vfg), and liquid specific heat capacity (Cf),-are, all required to evaluate the method. Liquid specific heat capacity can usually be measured quite easily. Data are required from the 

The required relief flow area can be evaluated using equation (5.1) knowing the two-phase mass flow rate per unit cross-sectional area of the relief system, G  

Alternatively, the mean of G (calculated at the relief pressure) and G (calculated at the maximum accumulated pressure) can be used. Since Leung s method assumes that the reactor contents are homogeneous during relief, the consistent assumption for the vapour fraction at inlet to the relief system (needed to calculate G) is that it is the same as the average for the reactor, i.e. at the inlet to the relief system the void fraction is given by  

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Where the Leung methods are inapplicable, a detailed computer simulation can be used to sizing the relief system (see Annex 4). In such cases, care should be taken that the computer code models all necessary features of the relieving runaway reaction. Therefore computer simulations are best carried out by competent specialists. 

A5.7 MODIFIED LEUNG METHOD FOR EXTERNAL HEATING FOR VAPOUR PRESSURE SYSTEMS... 

In a series of papers by Leung and coworkers (AlChE J., 32, 1743-1746 [1986] 33, 524-527 [1987] 34, 688-691 [1988] J. Loss Prevention Proc. Ind., 2[2], 78-86 [April 1989] 3(1), 27-32 [Januaiy 1990] Trans. ASME J. Heat Transfer, 112, 524-528, 528-530 [1990] 113, 269-272 [1991]) approximate techni ques have been developed for homogeneous equilibrium calculations based on pseudo-equation of state methods for flashing mixtures. 

These systems are ealled tempering (i.e., to prevent temperature rise after venting) systems beeause there is suffieient latent heat available to remove the heat of reaetion and to temper the reaetion at the set pressure. The vent requirements for sueh systems are estimated from the Leung s Method [31,32] ... 

It is reeommended that a safety faetor of at least 2.0 be used [34]. In eertain eases, lower safety faetors may be employed. The designer should eonsult the appropriate proeess safety seetion in the engineering department for adviee. Table 12-4 lists the applieability of both Leung and Fauske s methods. 

The answer obtained from the Leung s method should not be signifieantly smaller than that of Fauske s method. 

Using the Leung s method and assuming L/D = 0 and F = 1.0, two-phase mass flux from Equation 12-14 gives... 

Besides the conventional classification of flow shown in Fig. 14.3, there arc also other possibilities, sec, e.g., Leung, Independent of the method of classification, the essential point is that there is no general method and there are no general simple parameters that reliably predict the behavior of the flow in a new application. For each case the type ot flow has to be examined experimentally. 

Grolmes, M. A., Leung, J. C. and Fauske, H. K, A Review of Simplified Multiphase Flow Methods for Emergency Relief Calculations, Paper Presented at the AIChE 1990 Spring National Meeting, Orlando, FL, March 18-22, 1990. 

Leung, J. C. and Nazario, F. N., Two-Phase Flashing Flow Methods and Comparisons, Journal Loss Prevention Process Industries, (3), 253-260, April 1990. 

The SOM is mainly used as a qualitative tool, to identify groups rather than to provide some numerical estimate of similarity. Nevertheless, these methods also show promise as quantitative tools. Recent unpublished work by Leung and Cartwright4 on the fluorescence of dyes has shown that the SOM can be used as a sensitive way to determine quantitatively the composition of mixtures containing several fluorescent species. When a sample of unknown composition is fed into the trained map, the node to which the sample points indicates the concentration of each species by the value of each of the different weights (Figure 3.31). 

Leung, D.W., Chen, E. and Goeddel, D.V. (1989) A method for random mutagenesis of a defined DNA segment using a modified polymerase chain reaction. Technique, 1, 11-15. 

Leung IYF. 2008. Macular pigment new clinical methods of detection and the role of carotenoids in age-related macular degeneration. Optometry 79 266—272. 

Leung et al. [ 104] and Kim and Zeitlin [105] described a method for the separation and determination of uranium in seawater. Thoric hydroxide (Th(OH)4) was used as a collector. The final uranium concentration was measured via the fluorescence (at 575 nm) of its Rhodamine B complex. The detection limit was about 200 jLg/l. 

Grolmes, M. A. and J. C. Leung, "Code Method for Evaluating Integrated relief Phenomena," Chem. Eng. Prog., 81,47 (1985). 

Omega Method Model for Compressible Flows The factored momentum balance, Eq. (23-42), can be analytically integrated after first relating the dimensionless specific volume 8 to the dimensionless pressure ratio r. A method to do this, designated the omega method, was suggested by Leung (1986) ... 

This method has been extended to inclined pipe discharge [Leung and Epstein, The Discharge of Two-Phase Flashing Flow from an Inclined Duct, Trans. ASME J. Heat Transfer 112 (May), pp. 524-528, 1990], which together with some useful design charts is presented in the earlier subsection "Discharge Rates from Punctured Lines and Vessels. ... 

Cacciola, A. and P. S. Leung. 1981. Process for the production of a dry inorganic ultrafiltration membrane and membrane produced by such a method. European Patent Appl. 040,282. 

S.-A. Leung, R.F. Winkle, R.C.R. Wootton and A.J. deMello, A method for rapid reaction optimisation in continuous-flow microfluidic reactors using online Raman spectroscopic detection, Analyst, 130, 46-51... 

In 1989, a very practical mutagenesis method was described by Leung et al. 39), which was later improved by Cadwell and Joyce 40). Error-prone polymerase chain reaction (epPCR), as it is called, is based on the classical DNA amplification... 

Calculate required relief rate, W, using, t Leung s method (see 6.3)... 

LEUNG S METHOD FOR RELIEF SYSTEM SIZING FOR VAPOUR PRESSURE SYSTEMS "... 

Leung s method is given in 6.3.2 below. The method.is an approximate solution to the differential mass and energy balances for the reactor during relief and takes account of both emptying via the relief system and the tempering effect of vapour production due to relief. The method makes use of adiabatic experimental data for the rate of heat release from the runaway reaction (see Annex 2). Nomenclature is given in Annex 10. 

Leung s method (as given in equation (6.5) below) is applicable if all the above assumptions are true. Assumption (d) above, regarding the use of an average rate of heat release, tends to be the most limiting in terms of the maximum difference that can be allowed between the relief pressure and the maximum pressure. The absolute overpressure (often referred to simply as the "overpressure") has been sometimes used to characterise this. This is given by ... 

If.equation (6.2) is used, then comparison with dynamic simulation131 suggested that Leung s method would increasingly oversize at absolute overpressures above 50%. Provided the rate of temperature rise due to the runaway continues to increase at high overpressures, the arithmetic mean (equation 6.2) overestimates the true average q. 

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