Pool Film Research Articles

Correlations for subcooled pool film boiling heat transfer from large surfaces with different configurations

Experimental saturated and subcooled-pool film-boiling heat-transfer data from horizontal cylinders in liquid nitrogen for wide ranges of surface superheat, liquid subcooling and system pressure showed little dependence on the diameter for relatively large diameters. A correlation for subcooled pool film boiling heat transfer from horizontal cylinders with relatively large diameters was derived by slightly modifying a theoretical solution based on laminar boundary layer theory to accord better with experimental data. A similar correlation applicable to saturated and subcooled local film-boiling heat-transfer on vertical plates and vertical cylinders was similarly derived using existing data. Local pool film-boiling heat-transfer coefficients at the midpoint of a light water PWR-type active fuel rod of a pulsed reactor agreed within experimental error with the values calculated from the correlation for the subcooling ranging from 10 to 80 K.

A General Correlation for Pool Film Boiling Heat Transfer From a Horizontal Cylinder to Subcooled Liquid: Part 1—A Theoretical Pool Film Boiling Heat Transfer Model Including Radiation Contributions and Its Analytical Solution

A rigorous numerical solution of a theoretical model based on laminar boundary layer theory for pool film boiling heat transfer from a horizontal cylinder including the contributions of liquid subcooling and radiation from the cylinder was obtained. The numerical solution predicted accurately the experimental results of pool film boiling heat transfer from a horizontal cylinder in water with high radiation emissivity for a wide range of liquid subcooling in the range of nondimensional cylinder diameters around 1.3, where the numerical solution was applicable to the pool film boiling heat transfer from a cylinder with negligible radiation emissivity. An approximate analytical solution for the theoretical model was also derived. It was given by the sum of the pool film boiling heat transfer coefficient if there were no radiation and the radiation heat transfer coefficient for parallel plates multiplied by a nondimensional radiation parameter similar to the expression for saturated pool film boiling given by Bromley. The approximate analytical solution agreed well with the rigorous numerical solution for various liquids of widely different physical properties under wide ranges of conditions.

A General Correlation for Pool Film Boiling Heat Transfer From a Horizontal Cylinder to Subcooled Liquid: Part 2—Experimental Data for Various Liquids and Its Correlation

Experimental data of pool film boiling heat transfer from horizontal cylinders in various liquids such as water, ethanol, isopropanol, Freon-113, Freon-11, liquid nitrogen, and liquid argon for wide ranges of system pressure, liquid subcooling, surface superheat and cylinder diameter are reported. These experimental data are compared with a rigorous numerical solution and an approximate analytical solution derived from a theoretical model based on laminar boundary layer theory for pool film boiling heat transfer from horizontal cylinders including the effects of liquid subcooling and radiation from the cylinder. A new correlation was developed by slightly modifying the approximate analytical solution to agree better with the experimental data. The values calculated from the correlation agree with the authors’ data within ± 10 percent, and also with other researchers’ data for various liquids including those with large radiation effects, though these other data were obtained mainly under saturated conditions at atmospheric pressure.

Subcooled pool film boiling from a cylinder and from a sphere placedin a liquid saturated bed of beads

In film-boiling heat transfer, the most important modeling assumption may be that the liquid and vapor phases are separated by a sharp boundary without intervening two-phase region. An effort is presently made to extend the results of Cheng et al. (1982) by using a model for a porous medium's effective conductivity which can account for the structure of the porous matrix used, which in this case is a bed of spherical glass beads. Theory and experiment are found to be in good agreement. 8 refs.

Liquid-Solid Contact in Pool Film Boiling From a Cylinder

In film boiling, liquid is separated from the heating surface by the formation of a continuous vapor film. But some experiments have shown evidence of intermittent liquid-solid contact as shown by photographs and signal traces when boiling conditions are near the minimum film boiling point. The present study investigated the possibility of such contact in pool film boiling. The measurement of contact was carried out by using a microthermocouple probe with its thermo-junction flush with heater surface. Surface temperature depressions caused by liquid-solid contacts were obtained through the rapid response of the probe coupled to a data acquisition system. The contact parameters at varying boiling conditions were found from the history of the temperature depressions.

On the stability of vapor film in pool film boiling

The stability of vapor film in pool film boiling on a horizontal surface is considered by taking account of the effect of change in local heat transfer rate due to the perturbation of vapor film thickness. It is shown that a vapor film below a certain critical thickness becomes stable over all disturbances with any wavelength. Assuming that the average film thickness during the actual film boiling is proportional to the foregoing critical film thickness, the heat transfer coefficient can be derived. The predicted heat transfer coefficient agrees well with the recent film boiling data obtained by Shoji in a range of unprecedentedly low surface superheats using a very large surface.

On the stability of vapor film in pool film boiling.

The stability of vapor film in pool film boiling on a horizontal surface is considered by taking account of the effect of change in the local heat transfer rate due to the perturbation of vapor film thickness. It is shown that a vapor film below a certain critical thickness becomes stable over all disturbances with any wavelength. Assuming that the average film thickness during the actual film boiling is proportional to the foregoing critical film thickness, the heat transfer coefficient can be derived. The predicted heat transfer coefficient agrees well with the recent film boiling data obtained in a range of unprecedentedly low surface superheat by Shoji using a very large surface.

Film boiling on a horizontal plate — new correlation

An approach to pool film boiling on a horizontal surface on the basis of the Reynolds analogy is suggested. Within the framework of the model considered, the influence of vapour film thickness and vapour velocity on Taylor instability of the interface has been investigated. Four limiting solutions have been obtained for laminar and turbulent vapour flow in the film with and without allowance for friction at the liquid-vapour interface. The relations suggested practically correlate all of the available experimental data with an accuracy of ± 25 %. The boundary of the region where heat-transfer rate depends on the size of the heating surface has been established and an empirical formula allowing for this effect has been obtained.

Investigation of variable thermophysical property problem concerning pool film boiling from vertical plate with prescribed uniform temperature

By the development of laminar two-phase boundary-layer analysis on pool film boiling heat transfer, system parameters and their fundamental effect on heat transfer have been disclosed. However theoretically obtained characteristics of heat transfer do not fairly compare with the experimental data, because the relevant thermophysical properties vary significantly across the vapor film, and the nature of flow process is often turbulent and of non-boundary layer. In this investigation an analysis was made on pool film boiling heat transfer from vertical plate of uniform temperature to saturated or subcooled liquid, taking into account temperature variation of all properties, and the significance of variable properties in pool film boiling was examined. By getting solutions for water at the pressure of 1,50,100 and 200 {bar}, effect of variable properties on heat transfer and distribution of velocity and temperature were clarified. The heat-transfer results were compared with the available data of pool film boiling from horizontal cylinder.

Investigation of Variable Property Problem Concerning Pool Film Boiling from Vertical Plate with Prescribed Uniform Temperature

Investigation of Variable Property Problem Concerning Pool Film Boiling from Vertical Plate with Prescribed Uniform Temperature

An Investigation of the Collapse and Surface Rewet in Film Boiling in Forced Vertical Flow

A transient boiling experiment has been run in such a way that one can acquire data in forced convection film, transition, and nucleate boiling regions for a specified pressure, quality, and mass flux. Transient boiling experiments were conducted at the Nuclear Energy Division of the General Electric Company for water in a 0.492 in. ID inconel X-750 tube at mass fluxes of 50,000, 100,000, and 250,000 lbm/hr-ft2, quality range of 30–100 percent and a pressure of 1000 psia. The reduced boiling curves for these data indicated temperature differences at burnout on the order of 100–200° F and temperature differences at the minimum ranging from 700 to 1100° F. These results (higher than in other experiments) are felt to be caused by scale deposit, axial conduction, and roughnesses on the test surface. Physical evidence indicates that the test surface became coated with an appreciable scale deposit when subjected to the initial temperatures in excess of 1500 °F in a steam atmosphere. It has been found (reference [1]) that BWR fuel will normally have scale deposit on the heat transfer surface and thus the qualitative effects of scale deposits in this report are expected to apply in BWR Loss-of-Coolant accident evaluation. An empirical correlation was developed for the data for minimum film boiling temperature differences. The correlation was based on Berenson’s minimum pool film boiling temperature difference correlation in order to provide a technique for extrapolating to different pressures.

Pool film boiling heat transfer from a horizontal cylinder to saturated liquids

Referring to free convective film boiling heat transfer from a horizontal cylinder, many kinds of correlations of heat transfer have been proposed. However, none of them correlates the available data for a wide range of kind of the boiling liquid, the diameter of the cylinder, the degree of superheat and the system pressure. The integral method of boundary layer was applied to solve the equation of momentum and that of energy for this problem, taking into account of the inertia force in the former and the convective term in the latter and two nondimensional parameters were derived from this analysis. By employing these parameters, a semi-theoretical correlating equation accurate enough for practice over a wide range of parameters was proposed.

Pool Film Boiling Heat Transfer from a Horizontal Cylinder to Saturated Liquid

Pool Film Boiling Heat Transfer from a Horizontal Cylinder to Saturated Liquid

Some Effects of Geometry, Orientation, and Acceleration on Pool Film Boiling of Organic Fluids

Ethanol, pentane, and Freon-113 were tested for atmospheric pressure, saturated film-boiling characteristics. Turbulent waves arise close to the bottom of vertical platinum plates and the data become identical to those obtained with horizontal plates, verifying an earlier contention by Y. P. Chang. The equation of Berenson fits the data for both horizontal and vertical heaters fairly well if modified for geometry, and the equation also correctly predicts the effect of acceleration on film-boiling heat-transfer coefficients. At high temperature differences, Berenson’s equation for the heat-transfer coefficient is slightly conservative, which is qualitatively predictable by analyzing the departures of the actual system from the idealized model of Berenson.

Film Boiling on a Horizontal Tube in Increased Gravity Fields

The influence of acceleration on saturated pool film boiling from the outside of a horizontal 0.188 in. OD, stainless-steel tube is reported. Freon-113 at approximately atmospheric pressure was used as the test liquid. Heat-transfer coefficients were determined for the experimental ranges: (a) temperature differences of 200 to 500 deg F; (b) heat fluxes of 5000 to 25000 Btu/hr-ft2; and (c) accelerations of 1 to 10 times normal acceleration. Data were correlated by adding a dimensionless parameter to the theoretical equation derived by Bromley for film boiling. High-speed motion pictures were taken from which interbubble distances, bubble periods, and bubble breakoff diameters were measured.