Pool Film Boiling Heat Transfer Research Articles

CFD study on film boiling features of cryogenic fluid influenced by heat structures and gravity levels

Understanding bubble behaviors and thermal characteristics under various working conditions is of great significance to the efficient utilization of cryogenic propellants. In the present study, simulation models of pool film boiling at horizontal plate and cylinder surface are proposed with Volume of Fluid (VOF) method combined with Lee’s phase change model. Based on the physical and thermal performance, the gravity levels, physical properties, and heater structure dimensions are investigated respectively, which could satisfy the common application conditions of cryogenic propellants. The results show that the movement of bubbles at gas–liquid interface is critical to the pool film boiling heat transfer, and also the heat transfer mechanism affects the bubble motion behaviors. The critical wavelength and the most dangerous wavelength are significant length scales for the bubble behaviors in pool film boiling. When the cylindrical heater size is larger than the most dangerous wavelength, the bubble behaviors as well as the heat flux appear the similar characteristics with that at the plate heater surface. Moreover, the critical wavelength is approximately two times of the bubble departure diameter in the present cryogenic liquid boiling events, and the parameters, including liquid–vapor density difference, surface tension, and gas thermal conductivity, could affect the boiling heat flux significantly. In addition, under 0.03g condition, the bubble departure diameter could reach 27 mm and the boiling heat flux decreases to 800 W/m2, which are significantly different from that in normal gravity. In general, the present CFD model could execute a film boiling study accurately, and a series of detailed results on the bubble behaviors as well as the heat flux could be revealed.

Subcooled pool film boiling heat transfer from sphere: experiment and modelling

Experiments were conducted to study heat and mass transfer at film boiling on a metal sphere immersed into subcooled liquid. A model was elaborated to calculate the thickness of the vapor film and the speed of vapor flow in the film. The model also includes a detachment model for vapor bubbles lifting off the surface of the film. The model shows agreement with the results of the pool film boiling experiments with various liquids as well as for Leidenfrost drops. Quite reasonable agreement is also observed for the frequency of bubble detachment in saturated liquid. While processing the experimental data the calculations showed that the heat transfer into the bulk of liquid from vapor-liquid boundary is much more intense than expected. The effect is not determined solely by natural convection within the liquid as the heat flows determined by natural convection are two orders of magnitude less than those obtained. An attempt was made to determine the consequent heat transfer coefficient based upon experimental data for the frequency of bubble detachment from off the vapor film around the sphere. The abnormally high heat transfer detected could be important in practical applications.

Subcooled Pool Film Boiling Heat Transfer From Spheres With Superhydrophobic Surfaces: An Experimental Study

Pool film boiling was studied by visualized quenching experiments on stainless steel spheres in water at the atmospheric pressure. The surfaces of the spheres were coated to be superhydrophobic (SHB), having a static contact angle greater than 160 deg. Subcooled conditions were concerned parametrically with the subcooling degree being varied from 0 °C (saturated) to 70 °C. It was shown that film boiling is the overwhelming mode of heat transfer during the entire course of quenching as a result of the retention of stable vapor film surrounding the SHB spheres, even at very low wall superheat that normally corresponds to nucleate boiling. Pool boiling heat transfer is enhanced with increasing the subcooling degree, in agreement with the thinning trend of the vapor film thickness. The heat flux enhancement was found to be up to fivefold for the subcooling degree of 70 °C in comparison to the saturated case, at the wall superheat of 200 °C. A modified correlation in the ratio form was proposed to predict pool film boiling heat transfer from spheres as a function of the subcooling degree.

Film Boiling Heat Transfer Properties of Liquid Hydrogen in Natural Convection

Film boiling heat transfer properties of LH2 for various pressures and subcooling conditions were measured by applying electric current to give an exponential heat input to a PtCo wire with a diameter of 1.2mm submerged in LH2. The heated wire was set to be horizontal to the ground. The heat transfer coefficient in the film boiling region was higher for higher pressure and higher subcooling. The experimental results are compared with the equation of pool film boiling heat transfer. It is confirmed that the pool film boiling heat transfer coefficients in LH2 can be expressed by this equation.

Estimation of radiation coupling factors in film boiling around spheres by mean of Computational Fluid Dynamics (CFD) tools

In this paper, the CFD (Computational Fluid Dynamics) analysis of the pool film boiling heat transfer on a sphere at saturated conditions is presented. The simulation was performed, in first place, in absence of radiation, and subsequently incorporating it, to determine how the radiation affects to convection and the value of the coupling factor between both mechanisms. The VOF (Volume-of-fluid) method was used to model the multiphase flow and the P-1 method for the treatment of the radiation. A User Defined Function (UDF) was added to the CFD code for the treatment of the mass and energy transfer between the liquid and vapor phases. The results for the convective heat transfer were consistent with the experimental data reported in the literature and with two of the most widely used correlations. The coupling factor between radiation and convection obtained from the simulation analysis was similar to that proposed by known models.

Subcooled pool film boiling heat transfer from small horizontal cylinders at near-critical pressures

Experimental results for subcooled pool film boiling on small horizontal cylinders at near-critical pressures are presented. Experiments were performed with CO2 was the test liquid and platinum wires (25.4, 76.2 and 100μm diameter, D) as the test heaters. The pressure (P), liquid subcooling (ΔTsub) and bulk liquid temperature (Tb) were varied parametrically. For the range of parameters investigated, the heat transfer coefficient (h) was found to be proportional to D−0.5. Because the dependence of h on D varies, a criterion has been developed to predict a priori what this dependence would be any given situation. Subcooled pool film boiling heat transfer coefficient data have been correlated. The correlation developed predicts almost all the experimental data from the current study to within ±10%. The strength of the new correlation is that it is applicable to a much wider range of experimental conditions (including level of gravity) and fluids as demonstrated by the fact that it predicts all of the data reported in the literature to within ±20%. Visual observations during experiments showed that the transitions in film boiling patterns are a function of the dimensionless cylinder diameter.

Pool boiling heat transfer characteristics of vertical cylinder quenched by SiO 2–water nanofluids

This study includes an experimental investigation of the pool boiling heat transfer characteristics of a vertical cylinder quenched by SiO 2–water nanofluids. The experiments are performed through a cylindrical rod, at saturated temperature and atmospheric pressure. As the coolant, pure water and SiO 2–water nanofluid suspensions at four different concentrations (0.001, 0.01, 0.05 and 0.1 vol.%) are selected. The test specimen heated at high temperatures is plunged into cooling fluids at saturated conditions in a pool. The cooling curves are obtained via taking the temperature–time data of the specimen into account. The experimental results indicate that the pool film boiling heat transfer in nanofluids is identical to that in pure water. However, during the repetition tests in nanofluids with high concentrations, the film boiling region disappears, and the critical heat flux increases. In addition, the nucleate pool boiling heat transfer coefficient decreases compared with that of pure water, but a considerable decrease in nucleate pool boiling heat transfer is not observed with the repetition tests. A change in surface characteristics due to the deposition of nanoparticles on the surface has a major effect on the quenching process.

Experimental Investigation of the Effect of Surface Inclination Angle on Saturated Pool Film Boiling Heat Transfer in Transient Regime

In order to examine the effect of surface inclination angle on saturated pool film boiling heat transfer in transient regime, an experimental study was carried out. The experiments were performed through a cylindrical rod, made up of brass 20 mm in diameter and 75 mm in length, placed at six inclination angles about the vertical (from 0 to 50°) under atmospheric pressure. The test specimen heated at high temperatures was immersed in a distilled water pool at saturated condition. Temperature of the specimen during the cooling process was recorded using a K-type thermocouple embedded at the center of the specimen. In the experiments, the pool film boiling was observed for each inclination angle. In the film boiling region, the heat transfer coefficients were calculated by means of a lumped parameter method. The experimental results showed that the heat transfer coefficient increased as the inclination angle increased. In addition, to predict the Nusselt number, an empirical formula including the inclination angle as well as the Grashof, Prandtl, and Jakob numbers was developed, and good agreement between the predicted and experimental data for the vapor Nusselt numbers was observed.

Microscales of saturated pool film boiling

Two thermal Kolmogorov scales for pool film boiling η θ B ∼ να 2 2 B 1/4, η θ C ∼ α 2 3 B 1/4, are introduced. Here ν, k and ρ respectively denote the vapor kinematic viscosity, thermal conductivity and density, α 2= k/ ρc p2 and c p2 = h fg /Δ T (a two-phase thermal diffusivity and specific heat) suggested for notational convenience, and B the rate of buoyant production of turbulent vapor energy. In terms of these scales, the pool film boiling heat transfer is shown to be ℓ η θ B ∼Nu∼Ra 2 1/3, ℓ η θ C ∼Nu∼ Ra 2Pr 2 1/3, where ℓ is an integral scale, Ra 2 and Pr 2 are the Rayleigh and Prandtl numbers based on α 2. The microscale foundation of the earlier correlations of the turbulent pool film boiling data of all fluids except for liquid metals is demonstrated in terms of η θ B. An original correlation in terms of η θ C Nu=0.17(Ra 2Pr 2) 1/3, is proposed for turbulent pool film boiling data of liquid metals.

Film boiling heat transfer from a horizontal circular plate facing downward

AbstractThe two‐dimensional, steady, pool film boiling heat transfer from a horizontal circular plate facing downward to a stagnant saturated liquid is studied theoretically. It is assumed that the vapor‐liquid interface is smooth and that radiation can be disregarded. The relevant governing equations for the vapor film are solved for saturated water at atmospheric pressure using an improved two‐equation boundary‐layer integral method. It is shown that the dimensionless temperature profile is affected by the wall superheat ΔTsat and that the ratio of Nu to X0.2 is an increasing function of ΔTsat. Here, Nu represents the mean Nusselt number and X the film‐boiling Rayleigh number. In addition, it is revealed that the one‐equation boundary‐layer integral method developed by Nishio and colleagues is fairly accurate in predicting the film thickness, the representative radial velocity, and the mean Nusselt number. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(1): 72–84, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10071

Pool Film-Boiling Heat Transfer from a Horizontal Downward-Facing Surface

Pool Film-Boiling Heat Transfer from a Horizontal Downward-Facing Surface

Improvement of one-equation boundary-layer integral method for pool film-boiling heat transfer from a downward-facing surface

Improvement of one-equation boundary-layer integral method for pool film-boiling heat transfer from a downward-facing surface

415 下向き水平伝熱面のプール膜沸騰熱伝達(G.S.4-4 熱工学)

415 下向き水平伝熱面のプール膜沸騰熱伝達(G.S.4-4 熱工学)

Pool Film Boiling Heat Transfer from a Horizontal Circular Plate Facing Downward.

The two-dimensional, steady, pool film boiling heat transfer from a horizontal circular plate facing downward to a stagnant saturated liquid is studied theoretically on the basis of the assumption that the liquid-vapor interface is smooth and radiation can be disregarded. The relevant governing equations for the vapor film are solved for water at atmospheric pressure using two-equation boundary-layer integral method. It is shown that the dimensionless temperature profile is affected by the wall superheat ΔTsat and that a ratio of Nu to X0.2 an increasing function of ΔTsat. Here, Nu represents the mean Nusselt number and X the film-boiling Rayleigh number. In addition, it is revealed that one-equation boundary-layer integral method developed by Nishio et al. is fairly accurate in predicting the film thickness, the representative radial velocity and the mean Nusselt number.

A general correlation for pool film boiling heat transfer from a horizontal cylinder to saturated binary liquid mixtures

An approximate analytical solution of theoretical pool film boiling model of binary mixtures without radiation effect is derived by using an integral method. By including radiative contribution through a radiation parameter, a general correlation for predicting pool film boiling heat transfer coefficient of binary mixtures over horizontal cylinder is then proposed. As examined by five nonazeotropic and azeotropic binary systems, the predictions by this general correlation are shown to agree well with the rigorous numerical results. Furthermore, the proposed correlation is given an advantage over previous correlations in that it predicts also the extent of the mass diffusion effect on pool film boiling heat transfer of binary mixtures.

Erratum: “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” (Journal of Heat Transfer, 1990, 112, pp. 430–440)

Erratum: “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” (Journal of Heat Transfer, 1990, 112, pp. 430–440)

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.

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.