Donald E. Beasley

Development of Swirling Flow in a Rod Bundle Subchannel

Experimental measurements of the axial development of swirling flow in a rod bundle subchannel are presented. Swirling flow was introduced in the subchannel from a split vane pair located on the downstream edge of the support grid. Particle image velocimetry using an optical borescope yielded full-field lateral velocity data. Lateral flow fields and axial vorticity fields at axial locations ranging from 4.2 to 25.5 hydraulic diameters downstream of the support grid were examined for a Reynolds number of 2.8×10 4

Evaporation from a packed bed of porous particles into superheated vapor

Abstract An experimental and computational study of evaporation into superheated steam from porous particles, which form a packed bed, is performed. The goal of the study is to develop a predictive model of the drying process in packed beds with steam as the drying medium. The direct experimental measurement using load cells of the weight of alumina particles of various diameters in a packed bed during the drying process produced a complete continuous drying curve. A range of experimental conditions are examined, and a correlating equation for the overall heat transfer coefficient developed. Evaporation from a single spherical porous particle is modeled as occurring at a receding liquid/vapor interface within the particle. The drying process in a single particle is assumed to be thermally controlled. The single particle model is incorporated into an overall model for drying in a packed bed. The model predicted overall and local drying rates, as well as transient temperature distributions in the packing. The results of this study indicate that drying in a packed bed of significant depth occurs in three phases. The three phases of drying correspond to periods where the entire bed is in the constant drying rate regime, portions of the bed have entered the falling rate regime, and the entire bed is in the falling rate regime, respectively. The existence of these phases of drying are confirmed by both measured temperature distributions and measured drying rates. Predictions of the overall drying rate from the model show favorable agreement with measured drying curves.

Mapping of the Lateral Flow Field in Typical Subchannels of a Support Grid With Vanes

Lateral flow fields in four subchannels of a model rod bundle fuel assembly are experimentally measured using particle image velocimetry. Vanes (split-vane pairs) are located on the downstream edge of the support grids in the rod bundle fuel assembly and generate swirling flow. Measurements are acquired at a nominal Reynolds number of 28,000 and for seven streamwise locations ranging from 1.4 to 17.0 hydraulic diameters downstream of the grid. The streamwise development of the lateral flow field is divided into two regions based on the lateral flow structure. In Region I, multiple vortices are present in the flow field and vortex interactions occur. Either a single circular vortex or a hairpin shaped flow structure is formed in Region II. Lateral kinetic energy, maximum lateral velocity, centroid of vorticity, radial profiles of azimuthal velocity, and angular momentum are employed as measures of the streamwise development of the lateral flow field. The particle image velocimetry measurements of the present study are compared with laser Doppler velocimetry measurements taken for the identical support grids and flow condition.

The Effect of Support Grid Design on Azimuthal Variation in Heat Transfer Coefficient for Rod Bundles

Support grids are an integral part of nuclear reactor fuel bundle design. Features, such as split-vane pairs. are located on the downstream edge of support grids to enhance head transfer and delay departure from nucleate boiling in the fuel bundle. The complex flow fields created by these features cause spatially varying hert transfer conditions on the surfaces of the rods. Azimuthal variations in heat transfer for three specific support grid designs, a standard gird, split-vane pair grid, and disc grid, are measured in the present study using a heated, thin film sensor. Normalized values of the azimuthal variations in Nusselt number are presented for the support grid designs at axial locations ranging from 2.2 to 36.7 D h . Two Reynolds numbers, Re = 28,000 and Re = 42,000 are tested

Heat Transfer and Surface Renewal Dynamics in Gas-Fluidized Beds

Local instantaneous heat transfer between a submerged horizontal cylinder and a gas-fluidized bed operating in the bubble-flow regime was measured and the resulting signals analyzed. Unique to this investigation is the division of particle convective heat transfer into transient and steady-state contact dynamics through analysis of instantaneous heat transfer signals. Transient particle convection results from stationary particles in contact with the heat transfer surface and yields a heat transfer rate that decays exponentially in time. Steady-state particle convection results from active particle mixing at the heat transfer surface and results in a relatively constant heat transfer rate during emulsion phase contact. The average time of contact for each phase is assessed in this study. Signals were acquired using a constant-temperature platinum film heat flux sensor. Instantaneous heat transfer signals were obtained for various particle sizes by varying the angular position of the heat transfer probe and the fluidization velocity. Individual occurrences of emulsion phase heat transfer that are steady-state in nature are characterized by contact times significantly higher than both the mean transient and mean emulsion phase contact times under the same operating conditions. Transient and steady-state contact times are found to vary with angular position, particle size, and fluidizing velocity. Due to the extremely short transient contact times observed under these fluidization conditions, mean transient heat transfer coefficients are approximately equal to the mean steady-state heat transfer coefficients.

Investigation of Swirling Flow in Rod Bundle Subchannels Using Computational Fluid Dynamics

The fluid dynamics for turbulent flow through rod bundles representative of those used in pressurized water reactors is examined using computational fluid dynamics (CFD). The rod bundles of the pressurized water reactor examined in this study consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids are often used to create swirling flow in the rod bundle in an effort to improve the heat transfer characteristics for the rod bundle during both normal operating conditions and in accident condition scenarios. Computational fluid dynamics simulations for a two subchannel portion of the rod bundle were used to model the flow downstream of a split-vane pair support grid. A high quality computational mesh was used to investigate the choice of turbulence model appropriate for the complex swirling flow in the rod bundle subchannels. Results document a central swirling flow structure in each of the subchannels downstream of the split-vane pairs. Strong lateral flows along the surface of the rods, as well as impingement regions of lateral flow on the rods are documented. In addition, regions of lateral flow separation and low axial velocity are documented next to the rods. Results of the CFD are compared to experimental particle image velocimetry (PIV) measurements documenting the lateral flow structures downstream of the split-vane pairs. Good agreement is found between the computational simulation and experimental measurements for locations close to the support grid.Copyright

A study of the dynamic response of a local heat flux probe

A study of the transient and frequency response of a heat flux probe is reported. The probe consists of a metallic film sensor deposited onto a substrate and covered by a thin protective coating. This study considers the case of constant sensor temperature operation with the probe mounted in an isothermal wall and one probe surface exposed to a convecting environment. A two-dimensional numerical analysis of the probe subjected to both step change and periodic boundary conditions is presented. The effect of probe design on temporal and frequency response and probe sensitivity is demonstrated.

Heat transfer in pulse-stabilized fluidization - Part 1: overall cylinder and average local analyses

Abstract The present study examines the effect of an opposing oscillatory flow on heat transfer from an immersed horizontal cylinder in a bubbling gas-fluidized bed. This opposing oscillatory flow creates a state of fluidization termed pulse-stabilized fluidization. Heat transfer rates were measured for a monodisperse distribution of particles for fluidization ratios ranging from 1.1 to 2.7. Overall heat transfer measurements from a submerged horizontal cylinder show that the heat transfer characteristics are significantly altered by an opposing oscillatory flow. A modified form of the Strouhal number effectively characterizes the particle Nusselt number. Time-averaged local heat flux measurements showed that the local heat transfer distribution was altered by the hydrodynamics induced by the opposing oscillatory flow.

Continuous Wavelet Transforms of Instantaneous Wall Pressure in Slug and Churn Upward Gas-Liquid Flow

Continuous wavelet transforms are employed to determine the time-localized frequency content (scalogram) of instantaneous wall pressure signals in upward gas-liquid flow. The flow conditions correspond to well-defined slug flow, well-defined churn flow, and flows near the transition from slug-to-churn flow. Scalograms demonstrate that the frequency content of the pressure signals is time-dependent, and visual observations of the flow conditions suggest that the time-dependent frequencies are related to identifiable physical behaviors of the flow. In well-defined slug flow, the scalograms are characterized by the presence of a dominant frequency throughout the duration of the signal and by frequency shifting events. Scalograms representing well-defined churn flow contain intermittent frequencies, and the energy density in churn flow is spread over a wider range of frequencies than in slug flow. The present results provide evidence that flows near transition alternately display characteristics of both well-defined slug and well-defined churn flows. @DOI: 10.1115/1.1490376#

Heat transfer in pulse-stabilized fluidization - Part 2: local, instantaneous analysis

Abstract Enhancements in overall heat transfer from a heated, submerged horizontal cylinder in a pulse-stabilized fluidized bed were observed in Part 1 for operating conditions with low primary and secondary flow rates and low pulse frequencies. These increases in overall heat transfer were found to be a consequence of significant localized enhancements. In the present paper, through spectral and contact time analyses of local, instantaneous heat transfer, increases in both bubble phase and emulsion phase heat transfer coefficients were observed. Instantaneous measurements in a monodisperse distribution of 345 μm particles, fluidized to rates from 1.1 to 1.5 times greater than that required for minimum fluidization, are investigated. Waveforms of these time traces are characterized as exhibiting either locally or globally dominated hydrodynamic phenomena. Heat transfer with an opposing oscillatory flow exhibits characteristics of globally dominated hydrodynamics, whereas heat transfer traces acquired near minimum fluidization with no secondary flow are dominated by hydrodynamics localized at the surface of the cylinder.