Lockhart-Martinelli method

Lock-and-key type receptor, 16 770, 771 Lockhart-Martinelli method, 16 716 Locking and tagging practices, 21 853-854 Locust bean (carob) gum, 4 724t, 726-727 12 53 13 67 properties of, 13 74t... 

The definition of friction factor using mean fluid properties has been most widely used because it reduces to the correct single-phase value for both pure liquid and pure gas flow. This technique is very similar to the so-called homogeneous model, because it has a clear physical significance only if the gas and liquid have equal velocities, i.e., without slip. Variations of this approach have also been used, particularly the plotting of a ratio of a two-phase friction factor to a single-phase factor against other variables. This approach is then very similar to the Lockhart-Martinelli method, since it can be seen that (G4)... 

Liquid with the properties of water at 5 atm and 307°F is reboiled at a feed rate of 28001b/(hr)(tube) with 30wt% vaporization. The tubes are 0.1 ft ID and 12 ft long. The pressure drop will be figured at an average vaporization of 15%. The Lockhart-Martinelli, method will be used, following Example 6.14, and the formulas of Tables 6.1 and 6.8 ... 

TEMA classification, 200 tube count table, 203 Turbine pumps, 134, 139, 140, 142, 143 Turner equation, leaching, 466 Turbogrid trays, 426 Two-phase fluid flow. 111, 113-117 correlations, 115 granular beds, 118 homogeneous model, 113 Lockhart-Martinelli method, 115, 116... 

Two-phase, gas/liquid flow occurs in many industrial processes. To determine the pressure drop in such situations, the Lockhart-Martinelli method is recommended as the most reliable and simplest of approaches not specifle to a particular two-phase system.t... 

Some correlations of multipliers are listed in Table 6.7. Lockhart and Martinelli distinguish between the various combinations of turbulent and laminar (viscous) flows of the individual phases in this work the transition Reynolds number is taken as 1000 instead of the usual 2000 or so because the phases are recognized to disturb each other. Item 1 of Table 6.7 is a guide to the applicability of the Lockhart-Martinelli method, which is the oldest, and two more recent methods. An indication of the attention that has been devoted to experimentation with two phase flow is the fact that Friedel (1979) based his correlation on some 25,000 data points. 

A particularly simple and frequently used method comes from Lockhart and Martinelli [4.84], It is based on measurements of air-water and air-oil mixtures in horizontal tubes at low pressure. However the procedure has also proved itself in upward, vertical flow of two-phase single and multicomponent mixtures. The basic idea of the Lockhart-Martinelli method is that the frictional pressure drop in a two-phase flow can be determined, with use of a correction factor, from the frictional pressure drop in the individual phases. This means that the two-phase multipliers and are defined according to (4.127) and (4.128). 

The Lockhart-Martinelli method is especially simple and clear. In certain parameter regions its accuracy is surpassed by other methods, but it delivers satisfactory values for the pressure drop, irrespective of the application, within a range of uncertainty of around 50%. Larger deviations are to be expected for tube diameters d > 0.1 m. Furthermore, it should also be taken into account, that the two-phase multipliers L and G were determined from measurements at low pressures. Other equations have been developed for higher pressure and greater demands on the accuracy of the result. They are normally only valid for certain substances and in a narrow range of parameters. The extensive literature on two-phase flow, in particular the summary in [4.83], is suggested for further information on this subject. 

---