Subcooled Film Boiling Research Articles

Enhancement of Forced Convection Subcooled Film Boiling Heat Transfer Using Gas Sheet Collapse by Electric Field Application

Enhancement of forced-convection boiling heat transfer by electric field is investigated experimentally. When a high-temperature horizontal filament is immersed in water, a gas sheet is formed around and the above filament due to liquid boiling, in the early immersion process. This gas-sheet markedly decreases the boiling cooling rate of the filament. Here, forced collapse of the gas sheet is attempted by imposing an electric field to enhance the boiling cooling rate, In the experiments, a horizontal platinum wire of 0.5[Formula: see text]mm in diameter is immersed in pure water under atmospheric pressure, and a DC voltage up to 600[Formula: see text]V is applied between the wire surface and an electrode made of glass placed 10[Formula: see text]mm apart. The whole boiling curve is measured under different applied voltages and wire-falling velocities in 0.5 to 2.0[Formula: see text]m/s range, and at subcooling of 60[Formula: see text]K. The experimental results show that the electric field is effective in promoting the disintegration of the gas sheet. Under the tested conditions, boiling cooling rate increased two-fold for an applied electric field of 600[Formula: see text]V/cm. This result shows that the use of an electric field to break up the gas-sheet has resulted in a remarkable increase in the cooling rate at high superheats during initial cooling period, which is even greater than that used in the existing material manufacturing processes by the rapid cooling method, and therefore, this method may contribute to developing new materials.

Free convection film flows and heat transfer

From the contents Introduction.- Part I: Free Convection.- Basic Conservation Equations for Free Convection.- Brief Review of Previous Analysis Methods for Laminar Free Convection.- Laminar Free Convection of Monatomic and Diatomic Gases, Air and Water Vapor.- Laminar Free Convection of Polyatomic Gas.- Laminar Free Convection of Liquid.- Deviation of Laminar Free Convection Heat Transfer Caused due to Boussinesq Approximation.- Experimental Measurement of Free Convection with Larger Temperature Difference.- Relationship on Free Convection Flow and Heat Transfer between Inclined and Vertical Plates.- Part II: Film Boiling and Condensation.- Saturated Film Boiling.- Subcooled Film Boiling.- Film Condensation Free Convection of Saturated Vapour.- Film Condensation Free Convection of Superheated Vapour.- Laminar Film Condensation of Superheated Steam.- Part III: Falling Film Flow of Non-Newtonian Fluids.- Hydrodynamics of Falling Film Flow of Non-Newtonian Power-law Fluids.- Analyses of pseudo-similarity and boundary layer thickness of the Falling Film Flow.- Heat transfer of the Falling Film Flow.

Stability of Vapor Film in Subcooled Film Boiling on a Sphere

Stability of Vapor Film in Subcooled Film Boiling on a Sphere

4603 有限長の垂直円柱まわりのサブクール膜沸騰熱伝達(G06-1 伝熱(1),G06 熱工学)

4603 有限長の垂直円柱まわりのサブクール膜沸騰熱伝達(G06-1 伝熱(1),G06 熱工学)

Theoretical Analysis of the Stability of Vapor Film in Subcooled Film Boiling on a Horizontal Wire.

Linear stability analysis of a thin vapor film in subcooled film boiling on a horizontal cylinder is reported. The effects of liquid inertia, vapor viscosity and compressibility, and heat transfer were taken into account. Theoretical predictions of the heat transfer coefficient at the neutral stability point were compared with experimental data at the minimum-heat-flux point that was obtained during rapid quenching of thin horizontal wires in water and ethanol. At high liquid subcooling, the experimental value was 60% of the theoretical prediction irrespective of the wire diameter and quenching liquid. This difference was considered to be due to the nonuniformity of the vapor film which was neglected in the theoretical analysis

An Experimental Study of Subcooled Film Boiling on a Vertical Surface—Hydrodynamic Aspects

Interface and liquid velocities near the leading edge of a vertical wall 6.3 cm wide and 10.3 cm high were measured during subcooled film boiling of water at 1 atm pressure. The interface and liquid velocities in the boundary layer adjacent to the interface were measured using the hydrogen bubble flow visualization method. Photographs taken from the front and side showed the existence of a finite vapor layer at the leading edge and the existence of ripples and large-amplitude waves (bulges) on the interface. The bulges and ripples did not slide on the interface but moved in unison with the interface. The wave amplitude and wavelength were also measured. For a given subcooling and wall superheat, the amplitude, the interfacial velocity, and the wavelength were found to attain an equilibrium value several millimeters downstream of the leading edge. The waves were highly nonlinear and the interface velocities, which are found to be governed by the wave amplitude, were much larger than those predicted from the smooth interface, laminar flow theory. Streamlines in the liquid were found to expand into the wave valleys. At the wave peaks the streamlines appeared to be clustered together and the measured interface velocity gradients were high. The overall picture is one of expansion in the wave valleys and contraction (of flow) at the wave peaks. The flow field in turn is found to affect the liquid side heat transfer in subcooled film boiling significantly.

Natural-Convection Film Boiling Heat Transfer. 5th Report. Model Analysis of Subcooled Film Boiling with Wavy Interface.

Heat transfer in natural-convection film boiling with a wavy interface is investigated analytically. The vapor-film-unit model proposed in the first report for saturated film boiling is extended to subcooled film boiling with a wavy interface. In this extended model, based on the mean vapor velocity and the vapor film thickness under a subcooled condition, the vapor-film-unit length along an inclined flat plate is determined for subcooled film boiling as a function of the inclination angle. Using this result and accounting for movement of the vapor-film units, vapor-film units are arranged along the vertical surface and the periphery of the horizontal cylinder. The time-averaged local heat transfer coefficient is determined by integrating the time-dependent local heat transfer coefficient. The heat transfer coefficient averaged over the surface is determined by integrating the distribution of the time-averaged local values. The predictions of the model agree well with experimental data for film boiling along long vertical surfaces and around horizontal cylinders of large diameter. It is concluded, thus, that the extended vapor-film-unit model can correctly describe the effects of fluid properties, liquid subcooling, surface superheating and surface dimensions on film-boiling heat transfer with a wavy interface.

A Study of Subcooled Film-Boiling Heat Transfer under Reactivity-Initiated Accident Conditions in Light Water Reactors

The empirical correlations for subcooled film-boiling heat transfer during a reactivity-initiated accident in light water reactors are derived from inverse heat conduction calculations using the cl...