Glenn Harvel

Cross-sectional void fraction distribution measurements in a vertical annulus two-phase flow by high speed X-ray computed tomography and real-time neutron radiography techniques

Abstract A real-time neutron radiography (RTNR) system and a high speed X-ray computed tomography (X-CT) system are compared for measurement of two-phase flow. Each system is used to determine the flow regime, and the void fraction distribution in a vertical annulus flow channel with particular attention on the temporal resolution of the systems and the time behaviour of the two-phase flow. The annulus flow channel is operated as a bubble column and measurements obtained for gas flow rates from 0.0 to 30.0 l/min. Both the RTNR and the X-CT systems show that the two-dimensional void fraction distribution can be obtained. The X-CT system is shown to have a superior temporal resolution capable of resolving the void fraction distribution in an ( r , θ ) plane in 4.0 ms. The RTNR system is shown to obtain void fraction distribution in a ( r , z ) plane in 33.0 ms. Void fraction distribution for bubbly flow and slug flow is determined.

Electrohydrodynamically induced flow direction in a wire-non-parallel plate electrode corona discharge

An experimental investigation has been conducted to study the net flow direction induced by electrohydrodynamic forces in a wire-non-parallel plate electrode corona discharge. The experiments were conducted at two different locations of corona wire electrode for negative and positive applied voltage from 0 to 14 kV at atmospheric pressure and room temperature, where air was used as the working fluid. It was experimentally revealed that the net flow direction of electrohydrodynamically induced gas flow in a wire-non-parallel plate electrode system was changed depending on the location of the corona wire electrode relative to the grounded electrode position.

Narrow-Flow-Channel-Driven EHD Gas Pump for an Advanced Thermal Management of Microelectronics

In order to study the feasibility of applying electrohydrodynamic (EHD) gas pumps for advanced thermal management of microelectronics, an experimental investigation was conducted to drive gas flow through a narrow flow channel by an EHD gas pump. The net gas flow induced by corona discharge was generated by a push-fan (PF)-type EHD gas pump with and without a partially covered corona wire and nonparallel ground plate electrodes to transfer gas through millimeter-order circular channels. Therefore, it is important to know the effect of a narrow channel on the characteristics of the EHD gas pump with the corona wire electrode covered. The results show that the effects of narrow circular flow channels significantly influence the flow characteristics of the PF-type EHD gas pump and that the use of an insulator on the corona wire electrode can significantly enhance the current flux density and the pump performance under dc positive applied voltage.

An image processing approach for two-phase interfaces visualized by a real time neutron radiography technique

Abstract An image enhancement technique for a visualization of gas–liquid metal two-phase interfaces is developed for a real time neutron radiography (RTNR) technique, where the dynamic motion of bubbles inside liquid metal cannot be observed optically. The proposed image enhancement technique consisted of noise reduction, pipe–fluid interface determination, and image smoothing procedures. The results show that the RTNR technique is able to visualize the dynamics of gas–liquid metal interfaces, and also is able to determine more accurate two-phase flow parameters such as void fraction.

Separated two-phase flow regime parameter measurement by a high speed ultrasonic pulse-echo system

In this work, a high speed ultrasonic multitransducer pulse-echo system using a four transducer method was used for the dynamic characterization of gas-liquid two-phase separated flow regimes. The ultrasonic system consists of an ultrasonic pulse signal generator, multiplexer, 10 MHz (0.64 cm) ultrasonic transducers, and a data acquisition system. Four transducers are mounted on a horizontal 2.1 cm inner diameter circular pipe. The system uses a pulse-echo method sampled every 0.5 ms for a 1 s duration. A peak detection algorithm (the C-scan mode) is developed to extract the location of the gas-liquid interface after signal processing. Using the measured instantaneous location of the gas/liquid interface, two-phase flow interfacial parameters in separated flow regimes are determined such as liquid level and void fraction for stratified wavy and annular flow. The shape of the gas-liquid interface and, hence, the instantaneous and cross-sectional averaged void fraction is also determined. The results show that the high speed ultrasonic pulse-echo system provides accurate results for the determination of the liquid level within +/-1.5%, and the time averaged liquid level measurements performed in the present work agree within +/-10% with the theoretical models. The results also show that the time averaged void fraction measurements for a stratified smooth flow, stratified wavy flow, and annular flow qualitatively agree with the theoretical predictions.

Polarity Effect and Flow Characteristics of Wire-Rod Type Electrohydrodynamic Gas Pump

The electrohydrodynamic (EHD) flow characteristics for a wire to rod type EHD gas pump have been experimentally investigated. Experiments were conducted for DC negative and positive applied high voltage to a corona wire of diameter 0.24 mm from 0-24 kV, grounding rod electrode diameter from 1.5 mm to 3.1 mm and wire/rod electrode distance to pipe diameter ratio from 0.63 to 1.16. It was observed that the polarity plays an important role, where a negative high voltage generates a higher gas flow than that of a positive polarity. The results show that a maximum of 40 L/min of gas flow rate is generated at 0.37 W energy input when the pipe diameter is 20 mm with the corona wire electrode and grounding rod electrode gap distant set to 12.6 mm under negative applied voltage compared to 25 L/min at 0.23 W energy input for the positive case at the same specific energy density.

Investigation of large amplitude stratified waves in a CANDU-type 37 rod nuclear fuel channel by a real-time neutron radiography technique

A real-time neutron radiography (RTNR) system is used to determine two-phase flow parameters for a horizontal co-current two-phase flow channel with a cylindrical 37 rod bundle. Image processing techniques are applied to visualize the two-phase flow, and to determine flow regime, cross-sectional averaged void fraction, time averaged void fraction, and void distribution. The experimentally determined flow regime map disagrees with existing flow regime models developed for the cylindrical rod bundles. A new flow regime is observed and designated large amplitude stratified wavy (LASW) flow. The results show that the LASW flow regime may be due to a combination of undeveloped flow phenomena, boundary conditions, and circumferential cross flow occuring in the bundle. The rods in the bundle may act as a dampener to the vertical flow component and hinders the development of the wave into plug or slug flow by changing the momentum of the fluid in the circumferential direction. The effect of gas and liquid superficial velocities and axis position on the void fraction is observed. The existence of a cylindrical bundle in a circular flow channel is found to affect the flow regime, void fraction, void migration, and void fraction fluctuation and these effects are discussed in detail.

Electrohydrodynamically enhanced capillary evaporator

A two-phase capillary evaporator has been enhanced using electrohydrodynamic (EHD) forces. The evaporator was experimentally investigated under DC applied electric field operating modes as well as without an applied electric field. The results without the applied EHD forces show that the induced flow increases with increasing applied heat loads until a dry out condition is reached. The applied DC voltage electric field provides flow enhancements as high as 200%. A slight polarity effect was observed.

Capillary/Narrow Flow Channel Driven EHD Gas Pump for an Advanced Thermal Management of Micro-Electronics

In order to study the feasibility of applying electrohydrodynamic (EHD) gas pumps for advanced thermal management of micro-electronics, an experimental investigation was conducted to drive gas flow through capillary or narrow flow channel by EHD gas pumps. The net gas flow induced by corona discharge was generated in PF (push fan) type EHD gas pump with and without partially covered corona wire and non-parallel ground plate electrodes to transfer gas through sub-millimeter order circular channels. Therefore, it is important to know the effect of narrow or capillary channel on the characteristics of EHD gas pump with the corona wire electrode covered. The results show that the effects of narrow and capillary circular flow channels significantly influence flow characteristics of PF type EHD gas pump with the corona wire electrode covered under dc positive applied voltage.

Neutron Transport Characteristics of a Nuclear Reactor Based Dynamic Neutron Imaging System

An advanced dynamic neutron imaging system has been constructed in the McMaster Nuclear Reactor (MNR) for nondestructive testing and multi-phase flow studies in energy and environmental applications. A high quality neutron beam is required with a thermal neutron flux greater than 5.0×106 n/cm2 -s and a collimation ratio of 120 at image plane to promote high-speed neutron imaging up to 2000 frames per second. Neutron source strength and neutron transport have been experimentally and numerically investigated. Neutron source strength at the beam tube entrance was evaluated experimentally by measuring the thermal and fast neutron fluxes, and simple analytical neutron transport calculations were performed based upon these measured neutron fluxes to predict facility components in accordance with high-speed dynamic neutron imaging and operation safety requirements. Monte-Carlo simulations (using MCNP-4B code) with multiple neutron energy groups have also been used to validate neutron beam parameters and to ensure shielding capabilities of facility shutter and cave walls. Neutron flux distributions at the image plane and the neutron beam characteristics were experimentally measured by irradiating a two-dimensional array of Copper foils and using a real-time neutron radiography system. The neutron image characteristics — such as neutron flux, image size, beam quality — measured experimentally and predicted numerically for beam tube, beam shutter and radiography cave are compared and discussed in detail in this paper. The experimental results show that thermal neutron flux at image plane is nearly uniform over an imaging area of 20.0-cm diameter and its magnitude ranges from 8.0×106 – 1.0×107 n/cm2 -sec while the neutron-to-gamma ratio is 6.0×105 n/cm2 -μSv.Copyright