Benjamin Gal-Or

Convective mass or heat transfer from size-distributed drops, bubbles or solid particles

Abstract Available analyses of convective mass or heat transfer in particulate systems treat only a single drop or bubble in the ideal case of a completely pure system. There is, therefore, a definite need to establish correlations for assemblages of many drops or bubbles in practical two-phase systems where surfactant impurities are ever present. Such correlations are developed in the present work by employing the von Karman-Pohlhausen integral method to the boundary layer formed in moving clouds of spherical drops, bubbles, or solid particles. The results obtained generalize previous analyses for single particles and for assemblages of solid particles. In particular this method allows the evaluation of the yet untreated practical cases of convective transfer in intermediately circulating ensembles of drops or bubbles. Employing these new results the applicability of the method is extended to the analysis of total average convective transfer in size-distributed populations. For the establishment of an appropriate particle size distribution function a large number of experimental data are correlated by a single parameter function which is readily integrated to give total average interfacial transfer rates. A comparison with other correlations demonstrates the generality and applicability of the present results which include to a first approximation most available correlations for drops or bubbles at rapid, intermediate, and zero internal circulation.

GENERAL VARIATIONAL ANALYSIS OF HYDRODYNAMIC, THERMAL AND DIFFUSIONAL BOUNDARY LAYERS?

Abstract A general variational formulation of fluid flow in the boundary layer, including viscous effects. coupled heat and multicomponent mass transfer and chemical reactions, is presented. The resulting functional. which is based on the “local potential” concept recently put forward by Glansdorff and Prigogine, is separated. by use of the so-called Curie principle, into two parts representing the transfer of momentum, and the combined heat and mass transfer (including chemical reactions). Approximate analytical solutions for the velocity, enthalpy (or temperature) and species concentrations fields for steady-state boundary conditions can thus be derived from the two resulting functionals. Some examples, including isothermal incompressible flow on a flat plate, and a new general solution for multicomponent flow with diffusion for arbitrary Schmidt numbers are presented, and the results are shown to be in excellent agreement with known or numerical solutions, for simple approximating functions..

Gas-Liquid Dispersions

Publisher Summary Dispersion of gases in a liquid can be achieved by bubbling the gas through the liquid by using sparge pipes at the bottom of the contactor. Mixing impellers of the turbine type are frequently used to increase the rate of mass or heat-transfer over that obtained without the use of the mixer. Consequently, the contacting of gas and liquid in a mixing vessel equipped with a rotating impeller is generally used for the absorption of sparingly soluble gases. Some of the more common applications are in biochemical fermentation, hydrogenation, hydrocarbon oxidation and various other oxidation processes. Efficient contact is produced between the phases in agitated gas–liquid contactors and, therefore, this type of equipment can also be useful for those absorption and stripping operations for which conventional plate or packed towers may not be suited. This chapter refers to mechanically agitated gas–liquid dispersions. However, most of the theoretical and experimental conclusions also apply to any type of gas–liquid dispersion. The total surface area for diffusion is increased because the bubble diameter is smaller than for the free-bubbling case at the same gas flow rate; hence there is a resultant increase in the overall absorption rate. One approach to the analysis of gas–liquid dispersion has been to develop simplified theoretical models that provide an approximation to the real processes and mechanisms operating in the system. Typically, their application to the design problem requires knowledge of factors, such as bubble velocity relative to the agitated liquid and rate of surface renewal or film thickness as functions of mixing conditions.

Maximizing thrust-vectoring control power and agility metrics

A new set of standard agility comparison maneuvers (SACOM) is proposed for testing the maximization of thrust-vectoring control power during post stall, manned, and unmanned flight tests. An innovative approach is presented to help define and simulate agility in a low cost manner by means of unmanned scaled models. Debated agility metrics are reassessed in light of new developments in multiaxis thrust vectoring. A methodology for measuring and maximizing TV-agility under PST conditions has been identified. Excellent controllability and very rapid nose pointing are easily obtainable during PST-TV maneuvers. TV-agility is an interdisciplinary subject involving a revolution in engineering and pilot education.

Mathematical phenomenology for thrust-vectoring-induced agility comparisons

The recent introduction of thrust-vectoring (TV) maneuverability/controllability into fighter aircraft design methodologies requires reassessment of aircraft equations of motion, especially in the deep poststall (PST) domain. Therefore, a mathematical phenomenology has been developed in this article to assess the main components which affect TV-induced agility and PST-maneuverability. This article identifies the TV-induced forces and moments required to maximize TV control power. It then presents a number of simplified approximate equations for assessing maximized standard agility comparison maneuvers (SACOM) of separate pitch, yaw, and roll TV-induced reversal maneuvers. Such SACOMs are required to compare the performance of future different designs of tailless vectored fighters.

Fundamentals and similarity transformations of vectored aircraft

Fundamental concepts and new similarity transformations for emulating rapidly rotating-translating, poststall (PST), thrust vectoring flight controlled (TVFC) aircraft are defined and employed to design scaled-model flight tests aimed at proof of concept, maximization of agility during PST supermaneuvers, and the estimation of g loads on the pilot during such maneuvers. Deficiencies vs compromises regarding drop and powered model methodologies are defined, and a basic rule regarding maximization of jet-deflection rates is formulated. The new similarity laws are combined with standard agility comparison maneuvers (SACOM) conducted with powered, PST, TVFC F-15, F-16, and F-22 models. The new SACOM methodology helps define safe vs forbidden pilot-airframe, space-time domains that infer far-reaching safety vs combat-agility consequences for future fighters, including tailless vectored designs.

Thrust Vectoring: Theory, Laboratory, and Flight Tests

Fundamental concepts of vectored propulsion are defined and represented by novel designs of thrust-vectoring (TV) nozzles for maximized post-stall (PST)-agility. The concepts are employed to formulate a unified mathematical phenomenology for PST vectored fighter aircraft. The phenomenology is combined with an unorthodox methodology to test alternative prototypes of agile tailless vectored fighters and the efficiency of upgraded (conventional) fighters. Two PST-TV control rules have also been formulated.

Variational analysis of high mass transfer rates from spherical particles boundary-layer injection suction considerations at low particle reynolds numbers and high peclet numbers

Abstract A general variational analysis for hydrodynamic, thermal, and diffusional boundary-layer flows previously developed by the authors is adapted here to characterise relatively high mass transfer rates from moving spherical drops, bubbles, or solid particles. This work takes into account the effect of radial velocity at the particle surface (due to the very process of interfacial mass transfer) on the analysis of convective mass transfer rates-an important effect which has been neglected so far in studies of droplet dynamics. The error introduced by neglecting this effect is shown to amount to tens of per cents even when the interfacial radial velocity due to mass transfer is relatively small. In general it is found that the errors introduced in predicting convective transfer rates or boundary-layer thickness with neglected radial velocity at the interface are much more pronounced when circulation inside fluid particles is small. Comparison of our method with existing “exact” or integral methods (for calculating the mass transfer coefficients with a neglected radial velocity) clearly demonstrates its general property to extract the “best” trial solution from any assumed family of possible approximate solutions.

High Reynolds number fluid dynamics and heat and mass transfer in real concentrated particulate two-phase systems

Abstract Correlations for high Reynolds number interfacial convective heat and mass transfer and fluid behaviour of real (i.e. not extraordinarily purified) concentrated two-phase systems of drops or bubbles are derived. The theoretical results obtained compare favourably with various reported experimental data on separation angles, drag coefficients and Nusselt numbers.

The New Era of Stealth, Tailless, Vectored Aircraft. A 2010 Review on Current & Future Designs and Applications of Manned and Unmanned, Super-Agile and Safest Military v. Civil Jets

A new era in aviation has evolved since the introduction of integrated Stealth, Tailless, Vectored Systems [STVS] in 1986 to various U.S. Government agencies and non-government entities 121. The so disclosed STVS technologies include partial and complete roll-yaw-pitch Thrust Vectoring Flight Control [TVFC], which is free from the dangerous stall and spin phenomena that characterize current uses of the obsolete, 110-years-old, Conventional Flight Control [CFC] in current civil and military jets. Military TVFC-based designs are aimed at providing super-agility, enhanced safety and new flight control options. In turn, the slowly emerging civil TVFC technologies convert military TVFC to civil ones that include various land and sea safety means /30/. By 2010 the new STVS and TVFC technologies have well been tested and proven via different subscalc and full-scale prototypes [Appendix]. Currently, the new technologies appear to potentially apply to an almost endless set of civil and military safety needs. Much of the current effort remains in the military domain, where STVS and TVFC provide clear-cut advantages over CFC by providing super-agility in flight domains in which CFC fails. Indeed, by now, TVFC has been well-proven to enhance survivability, efficiency and stealth, and in preventing air catastrophes in take-off, landing, mid-air collision and when all airframe hydraulics fail. Such STVS-TVFC applications are reviewed here beyond the authors 1990/1991 book/4/, U.S. patent /30/, publications /4-32/ and seminars-disclosures. /33/, which contain much more details than in this general review. Introduction · improved efficiency/cruise performance, • enhanced capability for ground attack, The following quotations were taken from Reference · enhanced high altitude operations, l.p. 132: · capability for extremely short take-off and