George M. Hauser

Subcooled forced-convection film boiling in the forward stagnation region of a sphere or cylinder

Abstract An analysis is made of forced-convection film boiling in stagnation flow of subcooled liquids. The role of liquid viscosity in film boiling is determined by postulating the existence of a hydrodynamic boundary layer superposed on potential flow and using a perturbation technique. The viscous boundary layer due to shear stress at the vapor-liquid interface is shown to perturb the velocity field only slightly at large liquid subcooling. While the inviscid solution cannot be used to describe liquid motion when the liquid temperature is near its saturation temperature, the vapor is found to move only under the influence of the potential flow pressure distribution, thereby eliminating the coupling between the liquid boundary layer and vapor film without any significant errors in the heat-transfer problem. A rational interpolation formula between these two limiting cases leads to a simple expression for the film boiling heat transfer incorporating the major effects of wall superheat and liquid subcooling. The applicability of this formula to subcooled film boiling from a sphere or a cylinder is demonstrated.

Film boiling on a reactive surface

Abstract To help understand the rapid oxidation of high-temperature materials immersed in water, we treat here the flow of a liquid over a reactive body; the temperature of the body is such that the liquid undergoes film boiling at its surface. Contained within the film that envelopes the surface is the evaporated liquid which diffuses to the surface and reacts there to form product gas which diffuses away from the surface. The two-phase flow and heat and mass transfer problem which arises is formulated within the framework of steady-state stagnation flow theory. The theory is applied to the quasi-steady oxidation of molten zirconium spheres falling through water and predicts results which are consistent with available zirconium sphere oxidation data.

A model of the dilution of a forced two-phase chemical plume in a horizontal wind

Abstract Accidendtal releases of volatile liquid chemicals from pressurized storage vessels result in the formation of high-momentum flashed jets with liquid phases comprised of extremely fine droplets (aerosol). These jets are typically heavier than air. The subject of this paper is the description of a turbulent entrainment model that predicts the trajectory and dilution of such releases when the release point is elevated above ground-level in a horizontal wind. The model is compared with available field test data for pressurized liquid releases and is found to describe the observations to a degree of accuracy adequate for most hazard assessment purposes. The comparisons include the field measurements made during the liquid ammonia (NH 3 ) and liquid hydrofluoric acid (HF) release test series, namely Desert Tortoise and Goldfish respectively, at the US Department of Energy Fuels Test Facility. The model indicates that over the 3000 m distance in which measurements were made, there is no need to invoke atmospheric turbulence to explain the dilution of the ammonia jet. However, atmospheric turbulence is predicted to dominate the mixing in the far field of the weaker HF jet.

Freezing-melting heat transfer in a tube flow

Abstract Consideration is given to the heat-transfer problem involving solidification of a flowing liquid onto a melting wall. In particular, an experimental study of hot Freon 112A (m.p. 40.5°C) in turbulent flow through a thick ice pipe has been carried out. The major emphasis was on the melting attack of the ice pipe wall by the flowing Freon. The effects of both Freon injection pressure and temperature on the amount of melted ice collected at the pipe exit for a fixed injection period were investigated. The shape of the melted ice channel as a function of time, injection pressure and Freon temperature was determined from the frozen Freon “casting” that remained in the ice pipe. Numerical results based on a simple quasi-steady melting model were compared with the experimentally determined ice melting results. The model was found to represent the data reasonably well for Freon temperatures above 70°C, indicating that the ice wall melting process is controlled by the growth and decay of frozen Freon layers on the ice pipe wall.

The onset of two-phase venting via entrainment in liquid-filled storage vessels exposed to fire

Abstract A simple criterion is developed for predicting the onset of liquid entrainment due to venting-induced vapour flow in the free-board volume of a storage vessel exposed to fire. Through the use of potential flow theory, a solution for the two-dimensional axisymmetric velocity distribution in the free-board volume of an upright cylindrical vessel is obtained. The illustrative example considered verifies the hydrodynamic aspects of the entrainment criterion.

The melting of finite steel slabs in flowing nuclear reactor fuel

Abstract The problem of predicting the melting attack of steel structure by flowing reactor fuel arises in the analysis of the potential for subassembly-to-subassembly failure propagation in fast reactors. Frequently the molten fuel-solid-steel interface temperature falls between the fusion temperatures for these substances upon contact, resulting in solidification in the initially molten fuel and melting in the initially solid steel. If, in addition, the steel structure is sufficiently thick, remelting of the fuel crust may take place before melting of the solid steel is complete. A formulation is presented herein to describe the rate of melting of a finite steel slab by solidifying fuel that flows over one side of the slab. A set of charts is provided for making rapid predictions of the rate of erosion of the surface of a steel slab immersed in a flow of molten UO 2 , ThO 2 or ThC. Quantitative criteria are derived defining the validity of the model.

Solidification of a liquid penetrating into a convectively cooled tube

Solidification of a liquid at its fusion temperature as it penetrates into an initially empty tube maintained at constant temperature was treated theoretically and experimentally. An approximate method was introduced which involves postulating a reasonable functional form for the instantaneous shape of the frozen layer along the tube wall. This approximate crust profile method was verified theoretically using a numerical approach in which the governing integro-differential equation of liquid motion was rigorously solved on a digital computer. The good agreement obtained between the numerically exact solution and the crust profile assumption in the special case of constant wall temperature encourages exploitation of the crust profile method to predict the effects of a finite heat transfer coefficient when the flow tube is immersed in a liquid coolant bath. This system has been used in previous experimental studies of freezing of an advancing flow.

A computer model for the estimation of peak pressure for sonic-vented tetrafluoroethylene decompositions

A computer model, «DEFLAG», has been developed to describe quantitatively the buildup of pressure during an accidental tetrafluoroethylene (TFE) vapour phase decomposition within a vented cylindrical or spherical vessel. The model takes full account of non-ideal gas effects and contains a single, constant, empirical parameter, Φ, to describe the enhancement in decomposition rate due to venting. The empirical parameter Φ is determined from small-scale test results on TFE decomposition venting in cylindrical and spherical vessels