Critical heat flux subcooled boiling

Figure 5.34 Critical heat flux of boiling sodium under subcooled forced convection versus nonboiling convection heat flux. (From Lurie, 1966. Copyright 1966 by Rockwell International, Canoga Park, CA. Reprinted with permission.)...

C. L. Vandervort, A. E. Bergles, M. K. Jensen, An experimental study of critical heat flux in very high heat flux subcooled boiling, Int.J. Heat Mass Transfer, 1994, 3 3, 161-173. 

All modules use the 2-fluid model to describe steam-water flows and four non-condensable gases may be transported. The thermal and mechanical non-equilibrium are described. All kinds of two-phase flow patterns are modelled co-current and counter-current flows are modelled with prediction of the counter-current flow limitation. Heat transfer with wall structures and with fuel rods are calculated taking into account all heat transfer processes ( natural and forced convection with liquid, with gas, sub-cooled and saturated nucleate boiling, critical heat flux, film boiling, film condensation). The interfacial heat and mass transfers describe not only the vaporization due to superheated steam and the direct condensation due to sub-cooled liquid, but also the steam condensation or liquid flashing due to meta-stable subcooled steam or superheated liquid. 

Available data sets for flow boiling critical heat flux (CHF) of water in small-diameter tubes are shown in Table 6.9. There are 13 collected data sets in all. Only taking data for tube diameters less than 6.22 mm, and then eliminating duplicate data and those not meeting the heat balance calculation, the collected database included a total of 3,837 data points (2,539 points for saturated CHF, and 1,298 points for subcooled CHF), covering a wide range of parameters, such as outlet pressures from 0.101 to 19.0 MPa, mass fluxes from 5.33 to 1.34 x lO kg/m s, critical heat fluxes from 0.094 to 276 MW/m, hydraulic diameters of channels from 0.330 to 6.22 mm, length-to-diameter ratios from 1.00 to 975, inlet qualities from —2.35 to 0, and outlet thermal equilibrium qualities from -1.75 to 1.00. 

Inasaka F (1993) Critical heat flux of subcooled flow boiling in water under uniform heating conditions. Papers Ship Res Inst 30(4) 1-69... 

Mudawar I, Bowers MB (1999) Ultra-high critical heat flux (CHF) for subcooled water flow boiling. I CHF data and parametric effects for small diameter tubes. Int J Heat Mass Transfer 42 1405-1428... 

Cumo, M., and A. Palmieri, 1967, The Influence of Geometry on Critical Heat Flux in Subcooled Boiling, AIChE Preprint 18, 9th Natl. Heat Transfer Conf., Seattle, WA. (5)... 

Dean, R A., R. S. Dougall, and L. S. Tong, 1971, Effect of Vapor Injection on Critical Heat Flux in a Subcooled R-l 13 (Freon) Flow, Proc. Int. Symp. on Two-Phase Flow Systems, Haifa, Israel. (6) Deane, C. W., and W. M. Rohsenow, 1969, Mechanism and Behavior of Nucleate Boiling Heat Transfer to the Alkali Liquid Metals, USAEC Rep. DSR 76303-65, Massachusetts Institute of Technology, Cambridge, MA Also in 1970, Liquid Metal Heat Transfer and Fluid Dynamics J. C. Chen and A. A. Bishop, Eds., ASME Winter Annual Meeting, New York. (4)... 

Staub, F. W., 1967, The Void Fraction in Subcooled Boiling—Prediction of the Initial Point of Net Vapor Generation, ASME Paper 67-HT-36, National Heat Transfer Conf., ASME, New York. (3) Staub, F. W., 1969, Two Phase Fluid Modeling, The Critical Heat Flux, Nuclear Sci. Eng. 3J.T 90-199. (5)... 

Thorgerson, E. J., 1969, Hydrodynamic Aspects of the Critical Heat Flux in Subcooled Convection Boiling, Ph.D. thesis, University of South Carolina, Columbia, SC. (5)... 

Using this in the example of water with an initial subcooling of ArJu = 50 K, mass flux m = 1000kg/m2s and specific heat capacity cpl = 4.186 kJ/kgK, which boils in a 1 m long tube of d = 25 mm inner diameter, assuming the heat transfer coefficient is a. 10000 W/m2K, the critical heat flux has to be... 

The extension of these PECs to two-phase heat transfer is complicated by the dependence of the local heat transfer coefficient on the local temperature difference and/or quality. Heat transfer and pressure drop have been considered in the evaluation of internally finned tubes for refrigerant evaporators [14] and for internally finned tubes, helically ribbed tubes, and spirally fluted tubes for refrigerant condensers [15]. Pumping power has been incorporated into the evaluation of inserts used to elevate subcooled boiling critical heat flux (CHF) [16, 17]. A discussion of the application of enhancement to two-phase systems is given by Webb [373],... 

Megerlin et al. [182] reported subcooled boiling data for tubes with mesh and brush inserts. Critical heat fluxes were increased by about 100 percent however, wall temperatures were very high on account of the onset of partial film boiling. 

In channel flow it is usually necessary to locate the transducer upstream or downstream of the test channel, with the result that the sound field is greatly attenuated. Tests with 80-Hz vibrations [319] indicate no improvement of subcooled boiling heat transfer or critical heat flux. Romie and Aronson [324], using ultrasonic vibrations, found that subcooled critical heat flux was unaffected. Even where intense ultrasonic vibrations were applied to the fluid in the immediate vicinity of the heated surface, boiling heat transfer was unaffected [325]. The severe attenuation of the acoustic energy by the two-phase coolant appears to render this technique ineffective for flow boiling systems. 

R. A. Pabisz Jr. and A. E. Bergles, Using Pressure Drop to Predict the Critical Heat Flux in Multiple Tube, Subcooled Boiling Systems, Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, vol. 2, pp. 851-858, Edizioni ETS, Pisa, Italy, 1997. 

Effect of Dissolved Gas. The presence of dissolved gas can lead to a considerable reduction in critical heat flux in pool boiling, as illustrated by the results of Jakob and Fritz [151] shown in Fig. 15.62. The effect of dissolved gases diminishes with decreasing subcooling (increasing fluid temperature), the effect being minimal near saturation conditions. 

It is for saturated pool boiling only if the liquid in the pool is subcooled, the critical heat flux is higher. 

Effect of Channel Orientation. For the subcooled boiling region, a study of the effect of channel inclination on critical heat flux is reported by Brusstar and Merte [294]. The channel used by these authors was rectangular in cross section with one side heated. The orientation of this heated surface with respect to the horizontal could be varied between 0 and 360°. At low velocities, a sharp decrease in critical heat flux was observed when the heater surface was downward-facing, as exemplified by the results shown in Fig. 15.119. 

CHF in Forced Convective Boiling of Multicomponent Mixtures in Channels. Reviews of critical heat flux data for the forced convective boiling of mixtures are presented by Collier and Thome [3] and by Celata [321], In subcooled boiling and low quality, nucleate boiling predominates and similar effects are observed to those seen with pool boiling. This is exemplified... 

FIGURE 15.132 Critical heat flux in the forced convective subcooled boiling of benzene-ethanol mixtures (from Tolenbinsky and Maturin [322], Reprinted by permission of John Wiley Sons, Inc.). 

Y. Miyasaka, S. Inada, and Y. Owase, Critical Heat Flux and Subcooled Nucleate Boiling in the Transition Region Between a Two-Dimensional Water Jet and a Heated Surface, J. Chem. Eng. Japan, 13, pp. 29-35,1980. 

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