# Vapour void fraction in subcooled flow boiling

TL;DR: In this article, experimental data on steam void fraction and axial temperature distribution in an annular boiling channel for low mass-flux forced and natural circulation flow of water with inlet subcooling have been obtained.

About: This article is published in Nuclear Engineering and Design.The article was published on 1975-04-01. It has received 5 citations till now. The article focuses on the topics: Subcooling & Nucleate boiling.

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TL;DR: In this paper, a method for the calculation of inception and subsequent development of forced convective subcooled boiling in heated annular channels at steadystate conditions is presented, which is a synthesis of single-phase liquid thermal entrance region temperature field calculations and a four-equation drift-flux model representation of the liquid-vapor mixture region.

13 citations

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TL;DR: A conductivity probe has been designed and used to measure the gas holdup at a point in both two and three phase flows of saline solutions as discussed by the authors, and the probe uses a direct current voltage and acts as a simple on-off switch.

Abstract: A conductivity probe has been designed and used to measure the gas holdup at a point in both two and three phase flows of saline solutions. The probe uses a direct current voltage and acts as a simple on-off switch. The probe is a single unit with one electrode being the probe body and the other electrode simulating a massless point.
It was found that the probe gave similar gas holdup trends to the pressure drop method of measuring overall gas holdup. When used in a bubble column the probe could be used to indicate bubble sizes and corresponding rise velocities. Equations are presented which were used to convert the electric output of the probe to these physical parameters.
On a concu une sonde a conductivite que l'on a employee pour mesurer la retention du gaz en un point, aussi bien dans des ecoulements a deux qu'a trois phases de solutions salines. Cette sonde emploie une tension de courant continu et agit a la maniere d'un interrupteur. La sonde constitue une unite separee dont le corps constitue une electrode, l'autre electrode simulant un point sans masse.
On a trouve que la sonde indique des tendances pour les variations de la retention du gaz, semblables a celles obtenues par la methode de perte de charge pour la mesure de la retention globale du gaz. Lorsqu'on l'emploie dans une colonne a bulles, la sonde peut servir a indiquer les dimensions des bulles et les vitesses d'ascension correspondantes. On presente les equations qu'on a employees pour couvertir le signal electrique de sortie de la sonde en ces parametres physiques.

5 citations

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TL;DR: In this paper, an engineering model was developed to simulate the thermal-hydraulic phenomena in pressurized water reactor cores during bottom reflooding, which couples the fluid thermal hydraulics and radial heat transfer in the fuel rods.

Abstract: An engineering model was developed to simulate the thermal-hydraulic phenomena in pressurized water reactor cores during bottom reflooding. The model couples the fluid thermal hydraulics and radial heat transfer in the fuel rods. The system dynamics were formulated in terms of a set of ordinary differential equations, which were integrated using the Gear integration package. A dynamic nodal scheme, which moves with the quench-front location, was utilized to predict the fuel rod temperatures. Model predictions and comparisons with full-scale experiments are provided, and show good agreement with the FLECHT-SEASET and Slab Core Test Facility data. The proposed methodology was found to be computationally fast when compared with previous approaches, and can be readily integrated with other modules to simulate the complete reactor coolant system.

2 citations

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10 Feb 2012

TL;DR: In this article, the authors consider the problem of two-phase flow instability in materials testing ReF, where a small increase in heat flux in some cases causes a sudden large decrease in flow rate, leading to a burnout.

Abstract: Research reactors with power between 1 MW and 50 MW especially materials testing reactors (MTR), cooled and moderated by water at low pressures, are limited, from the thermal point of view, by the onset of flow instability phenomenon. The flow instability is characterized by a flow excursion, when the flow rate and the heat flux are relatively high; a small increase in heat flux in some cases causes a sudden large decrease in flow rate. The decrease in flow rate occurs in a non-recurrent manner leading to a burnout. The burnout heat flux occurring under unstable flow conditions is well below the burnout heat flux for the same channel under stable flow conditions. Therefore, for plate type fuel design purposes, the critical heat flux leads to the onset of the flow instability (OFI) may be more limiting than that of stable burnout. Besides, the phenomenon of two-phase flow instability is of interest in the design and operation of many industrial systems and equipments, such as steam generators, therefore, heat exchangers, thermo-siphons, boilers, refrigeration plants and some chemical processing systems. In particular, the investigation of flow instability is an important consideration in the design of nuclear reactors due to the possibility of flow excursion during postulated accident. OFI occurs when the slope of the channel demand pressure drop-flow rate curve becomes algebraically smaller than or equal to the slope of the loop supply pressure drop-flow rate curve. The typical demand pressure drop-flow rate curves for subcooled boiling of water are shown in Fig. 1 (IAEA-TECDOC-233, 1980). With channel power input S2, operation at point d is stable, while operation at point b is unstable since a slight decrease in flow rate will cause a spontaneous shift to point a. For a given system, there is a channel power input Sc (Fig. 1) such that the demand curve is tangent to the supply curve. The conditions at the tangent point c correspond to the threshold conditions for the flow excursive instability. At this point any slight increase in power input or decrease in flow rate will cause the operating point to spontaneously shift from point c to point a, and the flow rate drops abruptly from M to Mc. For MTR reactors using plate-type fuel, each channel is surrounded by many channels in parallel. The supply characteristic with respect to flow perturbations in a channel (say, the peak power channel) is essentially horizontal, and independent of the pump characteristics. Thus, the criterion of zero slope of the channel demand pressure drop-flow curve is a good approximation for assessing OFI, i.e.

### Cites methods from "Vapour void fraction in subcooled f..."

...…as: l e g l dG S 205.0 (8) The true vapor quality is calculated in terms of the thermodynamic equilibrium quality using empirical relationship from the earlier work of (Zuber et al., 1966; Kroeger & Zuber,1968) as: , , , , exp 1 1 exp 1 eq eq eq OSV eq OSV eq eq OSV eq OSV x x x x x x x x...

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TL;DR: In this paper , a sub-cooled boiling model to predict void fraction profiles in a vertical channel consists of wall heat flux partitioning, the vapor condensation rate, the bubbly-to-slug flow transition criterion, and drift-flux models, and necessary refinements have been incorporated into the Safety and Performance Analysis Code (SPACE) developed by the Korean nuclear industry for the safety analysis of PWRs.

##### References

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TL;DR: In this article, the complex problem of void calculation in different regions of flow boiling is divided in two parts: the first part includes only the description of the mechanisms and the calculation of the rates of heat transfer for vapour and liquid.

637 citations

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General Electric

^{1}TL;DR: In this article, a model was developed to predict the vapor volumetric fraction during forced convection subcooled boiling, which was applied to a variety of available test data, and the agreement was satisfactory for a multitude of flow, heat flux, and fluid property conditions.

370 citations

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TL;DR: In this paper, a physical model for the bubble-flow regime of liquid-gas flow is proposed, where the mixture flows as a suspension of bubbles in the liquid, where radial gradients exist in the concentration of bubbles, and bubble concentration is assumed maximum at the center of the pipe, decreasing monotonically in a radial direction, and vanishing at the pipe wall.

Abstract: A physical model is proposed for the bubble-flow regime of liquid- gas flow which is in good agreement with the important features of the process. In this model it is conceived that the mixture flows as a suspension of bubbles in the liquid, where radial gradients exist in the concentration of bubbles. The bubble concentration is assumed maximum at the center of the pipe, decreasing monotonically in a radial direction, and vanishing at the pipe wall. An important concept introduced is that the gas and liquid have the same velocity at any radial position. The flow parameter assumes different forms for flow in circular pipes and for flow between two flat plates. (M.C.G.)

331 citations

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General Electric

^{1}TL;DR: In this paper, a method for the prediction of the point where a significant amount of net vapor is first formed is derived and compared with experimental measurements at both low and high fluid velocities.

Abstract: The satisfactory prediction of the vapor volume fraction in subcooled boiling depends in large part on the ability to predict the point where a significant amount of net vapor is first formed. A method for the prediction of this point is derived here and compared with experimental measurements at both low and high fluid velocities. The derived relationships for this point include the effect of fluid properties, geometry, and the liquid velocity. A comparison with the empirical formula of Bowring [2] for water is given.

117 citations