Void fractions in two‐phase steam‐water flow

Abstract

The pressure-drop characteristics associated with one liquid and one gaseous phase flowing concurrently in a pipe or tube have yet to be understood. The operation of evaporators, boilers, and condensers has long stimulated interest in the pressure drop of steamwater mixtures, and more recently this specialized case of one-component, two-phase flow has received even greater attention from the applications in cooling nuclear reactors. The two-phase-flow problems have not been amenable to thorough theoretical analyses, and therefore empirical and semiempirical correlations have attained unusual prominence in practical applications. The present investigation employs a new research tool for the study of two-phase-flow structure.A variety of geometric flow patterns is possible. Bergelin, Alves, and others have classified these patterns according to visual appearance ; whereas the Martinelli classifications were based upon whether the flow in each phase was termed viscous or furbu2ent. The distinction between viscous and turbulent flow in either phase is rather arbitrary, and if the Reynolds number for one phase, calculated on the basis of the total tube diameter, is greater than 2,000, the flow in the phase is called furbu2ent. This investigation is confined to the study of annular flow, in which most of the liquid is found in an annular ring surrounding the central vapor core and the flow in each phase is turbulent.Boiling or flashing occurs when superheated water rises in an insulated vertical tube at atmospheric pressure. For a separated two-phase flow geometry, the mean linear steam velocity may exceed that of the water. The fraction of the tube occupied by the steam (void fraction) at a given cross section cannot be obtained directly from a determination of the thermodynamic quality. Void fractions, however, must be known for the estimation of the pressure drops due to head and momentum changes.Void fractions and pressure drops for steam-water flows were measured in an 0.872-in. I.D. vertical tube at atmospheric pressure over a quality range of 0 to 4%. The test section was the hot leg of a natural-circulation loop, and the inlet liquid flow rate ranged from 1 to 3 ft./sec. A new technique for measuring void fractions was used, and the method utilizes the difference between the gamma-ray absorption coefficients of water and steam.

Holdup and pressure drop with gas‐liquid flow in a vertical pipe

“…Isbin, Sher, and permit reliable prediction of holdup rotameter. After the manometer had Eddy (7) reported holdup data for and pressure drop in vertical upward reached a steady reading, the desired gas the steam-water system at essentially flow was metered with a second rotame- ter. 5.8 and 28.6 centipoises.…”

Choking two-phase flow literature summary and idealized design solutions for hydrogen, nitrogen, oxygen, and refrigerants 12 and 11

“…They also used the figure 8b. In a later [29] study, Isbin, et al , found that slight changes in the void fraction curves from the Martinelli values would improve the predictions of maximum mass flow rates considerably.…”

“…[13,18] [29] correlations and the results of entrainment experiments. The Isbin, et al , modified [42] momentum [29] ri9l c(HO)(TH) [75] by Isbin, et [44] and by pressure drop studies such as that of Mendler, et [41] dieted by the Martinelli-Nelson correlation, reaches the sonic velocity for the vapor phase. (20) is shown in figure 12.…”

“…Although p does not appear in that expression, all of the thermodynamic property terms are a function of p. Substitution of this relationship into (28) \. (29) In (29) (25) may be solved for v and that expression differentiated with respect to p. That expression with (3) and (5) will result in [57] an expression identical with that of Sajben which gives G in terms of the desired Thus, for critical flow the values of p , p and G must be satisfied in (29) and (30 (1) and (4) become (v + xv ) dp f f g a T (31) Then, from (2), (5) and (9) (v f + xv ) dp…”

Heat transfer with phase change in vertical upward, horizontal, and vertical downward tube flow

“…Dukler et al (1964) showed that the Hughmark (1962) correlation for holdup is a good representation of the experimental data for these regimes. Isbin et al (1957) report pressure drop data for steam-water flows at atmospheric pressure in a 2.2-cm i.d. A correlation of the pressure drop from eq 8 with the data of Hughmark (1969) was found to be where N F r = ( g ) & 2 Table I11 shows the average absolute deviations between calculated and experimental total pressure drops for these data.…”