Vapor quality

Vapor quality, a. for inlet quality, for outlet quality kg/s IVh... 

X = vapor quality of fluid = 0 for pool boiling and is a low fraction, about 0.1 to 0.3, for most nucleate boiling... 

X = vapor quality in fluid, weight fraction, nucle- ... 

Two-phase flow pattern maps, observed by Revellin et al. (2006), are presented in Fig. 2.31 in mass flux versus vapor quality, and superficial liquid velocity versus superficial vapor velocity formats calculated from the test results as follows ... 

Before describing the transition prediction methods, it is instructive to describe how a diabatic map is used. One chooses a desired mass flux and sets the heat flux to be dissipated (assumed uniform along and around the circular channel) up to the desired local length from the inlet to find the corresponding local vapor quality (from an energy balance) and thus the location of this process condition on the map. The... 

It is important to note here that the CHF depends on the flow conditions, including the mass flux and the vapor quality. Using Eq. (2.25) to eliminate q, we find... 

Dynamic viscosity Kinematic viscosity Density Surface tension Shear stress Vapor quality Contact angle Shear viscosity Shear rate... 

A physical model of ONB for the explosive boiling and dryout, was suggested. In order to understand why dryout occurred even at a low value of vapor quality x, it is important to keep in mind that the liquid film does not cover the entire heated surface of the micro-channel, and two-phase flow is characterized by an unsteady cyclic behavior. The following assumptions are made in the development of the model ... 

Quiben and Thome (2007a,b) presented an experimental and analytical investigation of two-phase pressure drops during evaporation in horizontal tubes. Experiments were performed under diabatic conditions in tubes of d = S and 13 mm in the range of vapor quality x = 0—1, mass velocity G = 70—700kg/m s, heat flux q = 6.0—57.5 kW/m. The test fluids were R-134a, R-22 and R-410A. The results... 

Heat transfer characteristics for saturated boiling were considered by Yen et al. (2003). From this study of convective boiling of HCFC123 andFC72 in micro-tubes with inner diameter 190, 300 and 510 pm one can see that in the saturated boiling regime, the heat transfer coefficient monotonically decreased with increasing vapor quality, but independent of mass flux. 

In the study by Hetsroni et al. (2006b) the test module was made from a squareshaped silicon substrate 15 x 15 mm, 530 pm thick, and utilized a Pyrex cover, 500 pm thick, which served as both an insulator and a transparent cover through which flow in the micro-channels could be observed. The Pyrex cover was anod-ically bonded to the silicon chip, in order to seal the channels. In the silicon substrate parallel micro-channels were etched, the cross-section of each channel was an isosceles triangle. The main parameters that affect the explosive boiling oscillations (EBO) in an individual channel of the heat sink such as hydraulic diameter, mass flux, and heat flux were studied. During EBO the pressure drop oscillations were always accompanied by wall temperature oscillations. The period of these oscillations was very short and the oscillation amplitude increased with an increase in heat input. This type of oscillation was found to occur at low vapor quality. 

The vapor volumetric flow ratio, (3, or volumetric vapor quality, is defined as the ratio of vapor volumetric flow rate to the total volumetric flow rate that is,... 

Laverty, W. F., and W. M. Rohsenow, 1964, Film Boiling of Saturated Liquid Flowing Upward through a Heated Tube High Vapor Quality Range, MIT Heat Transfer Lab. Rep. 9857-32, Massachusetts Institute of Technology, Cambridge, MA. (4)... 

Winkelmann et al. (54) have studied air-water flows in a corrugated heat exchanger. Flow visualization and two-phase pressure drop measurements have been performed. The flow visualizations have shown that the flow pattern is complex and that a wavy or a film flow occurs in most cases (Figure 29). The two-phase pressure drop depends on the total flow rate and vapor quality, and Chisholm-type correlation is proposed. More work is required to characterize the flow structure in compact heat exchangers and to develop predictive methods for the frictional pressure drop and the mean void fraction. 

Let x = fraction of mass that is vapor (quality) x = 0.5 (Guess)... 

Observations of the flow patterns inside of fin passage making the set of rectangular channels were done at apparatuses shown at Fig. 9. Subcooled liquid was pumped through electro-heating coil to provide a certain vapor quality of the flow. Then the flow was passed through adiabatic test section and later through the evaporator, for exception pulsation of flow, into the condenser. The test section can operate both in up... 

To determine the heat transfer coefficient and mass vapor quality in boiling test the following variables were measured ... 

Figure 18. Heat transfer coefficients vs. mass vapor quality for upward flow R21 in heat exchanger with plain fins (20.3FPI). Wall superheat ranged from 0.9 to 1.4 K. a) evaporation for two mass fluxes, b) Comparison of heat transfer coefficients in condensation/evaporation modes at G=50 kg/m s. Mark shows the transition to the annular modes.

Figure 186 presents the comparison of heat transfer coefficient vs. mass vapor quality for upward flow condensation and upward flow boiling modes at mass flux of 50 kg/m s. At low vapor quality the boiling heat transfer coefScient is considerably higher than that for condensation. The difference in heat transfer behavior can be explained by the absence of film mpture in case of condensation. The contact line does not exist in this case and heat transfer level is much less than in case of boiling. 

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