N. Zuber

Bio: N. Zuber is an academic researcher from Nuclear Regulatory Commission. The author has contributed to research in topics: Boundary layer & Subcooling. The author has an hindex of 2, co-authored 2 publications receiving 196 citations.

An Experimental Investigation of the Thermally Induced Flow Oscillations in Two-Phase Systems

Abstract: An experimental study on the onset of thermally induced two-phase flow oscillations has been carried out in a uniformly heated boiling channel using Freon-113 as the operating fluid. The effects of inlet subcooling, system pressure, inlet and exit restrictions, and inlet velocity have been studied. The experimental data have been compared with the equilibrium as well as the nonequilibrium theory including the effect of subcooled boiling. It has been found that the effect of thermal nonequilibrium should be included in a theoretical model for accurate prediction of the onset and the frequency of thermally induced flow oscillations. A simplified stability criterion has also been presented and compared with the experimental data.

Bubble Growth in Variable Pressure Fields

Abstract: The case of a spherical vapor bubble growing in an infinite, uniformly heated liquid, has been analyzed under the thin boundary layer approximation for the effects of a variable pressure effects can be quite important and dominate the rate of growth. For the case where pressure changes cause the vapor temperature to behave as t/sup n/, (t being time), the bubble radius will grow as t/sup n+1/2/, significantly faster than the ..sqrt..t behavior usually expected. The analysis has been shown to compare favourably with existing data.

Cavitation and Bubble Dynamics

Abstract: This book describes and explains the fundamental physical processes involved in bubble dynamics and the phenomenon of cavitation. It is intended as a combination of a reference book for those scientists and engineers who work with cavitation or bubble dynamics and as a monograph for advanced students interested in some of the basic problems associated with this category of multiphase flows. A basic knowledge of fluid flow and heat transfer is assumed but otherwise the analytical methods presented are developed from basic principles. The book begins with a chapter on nucleation and describes both the theory and observations of nucleation in flowing and non-flowing systems. The following three chapters provide a systematic treatment of the dynamics of the growth, collapse or oscillation of individual bubbles in otherwise quiescent liquids. Chapter 4 summarizes the state of knowledge of the motion of bubbles in liquids. Chapter 5 describes some of the phenomena which occur in homogeneous bubbly flows with particular emphasis on cloud cavitation and this is followed by a chapter summarizing some of the experiemntal observations of cavitating flows. The last chapter provides a review of the free streamline methods used to treat separated cavity flows with large attached cavities.

A Review of two-phase flow dynamic instabilities in tube boiling systems

Abstract: The earliest research in the field of two-phase flow was conducted by Lorentz (1909) The studies on the analysis of two-phase flow instabilities by Ledinegg (1938) created considerable interest concerning the phenomenon of thermally induced flow instability in two-phase flow systems The objective of this review is to sum up the experimental and theoretical work carried out by various investigators over a period of several years, demonstrating and explaining three main instability modes of two-phase flow dynamic instabilities, namely, density-wave type, pressure-drop type and thermal oscillations, encountered in various boiling flow channel systems The typical experimental investigations of these instabilities in tube boiling systems are indicated and the most popular models to predict the two-phase flow dynamic instabilities, namely the homogenous flow model and the drift-flux models are clarified with the solution examples and the validation of the model results with experimental findings are also provided

Closed loop pulsating heat pipes: Part A: parametric experimental investigations

Abstract: Closed loop pulsating heat pipes (CLPHPs) are complex heat transfer devices having a strong thermo-hydrodynamic coupling governing the thermal performance. In this paper, a wide range of pulsating heat pipes is experimentally studied thereby providing vital information on the parameter dependency of their thermal performance. The influence characterization has been done for the variation of internal diameter, number of turns, working fluid and inclination angle (from vertical bottom heat mode to horizontal orientation mode) of the device. CLPHPs are made of copper tubes of internal diameters 2.0 and 1.0 mm, heated by constant temperature water bath and cooled by constant temperature water–ethylene glycol mixture (50% each by volume). The number of turns in the evaporator is varied from 5 to 23. The working fluids employed are water, ethanol and R-123. The results indicate a strong influence of gravity and number of turns on the performance. The thermophysical properties of working fluids affect the performance which also strongly depends on the boundary conditions of PHP operation. Part B of this paper, which deals with development of semi-empirical correlations to fit the data reported here coupled with some critical visualization results, will appear separately.

Two-phase flow instabilities: A review

Abstract: An updated review of two-phase flow instabilities including experimental and analytical results regarding density-wave and pressure-drop oscillations, as well as Ledinegg excursions, is presented. The latest findings about the main mechanisms involved in the occurrence of these phenomena are introduced. This work complements previous reviews, putting all two-phase flow instabilities in the same context and updating the information including coherently the data accumulated in recent years. The review is concluded with a discussion of the current research state and recommendations for future works.

Flash-boiling atomization

Abstract: Flash-boiling atomization is one of the most effective means of generating a fine and narrow-dispersed spray. Owing to its complexity its potential has not been fully realized to date. The paper reviews the present knowledge of the different mechanisms involved in the flash-boiling atomization process. These include intense nucleation, fast bubbles’ growth and liquid atomization. The inter-relationships between the distinctive processes determine the spray quality. Recent experimental observations and physical interpretations have improved our insight and led to better understanding of the whole process. One practical result is the establishment of design criteria for an optimal flash-boiling atomizing system.