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Journal ArticleDOI

Study on instability of circular liquid jets at subcritical to supercritical conditions using dynamic mode decomposition

TL;DR: In this article, the effect of variation in the fluid and flow properties of the injecting jet on the nature of instabilities and mixing behavior is investigated, where high-speed imaging techniques are used to capture the jet behavior.
Abstract: The thermodynamic and fluid-dynamic properties associated with the injectant jet significantly influence its fluid dynamic characteristics. In most of the earlier studies on the behavior of liquid jet at high pressure and supercritical environment, the liquid jet is often injected at subcritical initial temperature. In the present study, the effect of variation in the fluid and flow properties of the injecting jet on the nature of instabilities and mixing behavior is investigated. The fluid properties of the injected jet are varied by preheating. High-speed imaging techniques are used to capture the jet behavior. To gain further insight into the instability nature of the jet, linear instability analysis was performed. Dynamic mode decomposition analysis was applied to the obtained high-speed images to extract and understand the relevant dynamic features.
Citations
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Book
01 Dec 1988
TL;DR: In this paper, the basic processes in Atomization are discussed, and the drop size distributions of sprays are discussed.Preface 1.General Considerations 2.Basic Processes of Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.AtOMizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index
Abstract: Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

1,214 citations

01 Jan 1990
TL;DR: In this paper, a cubic equation of state was used to describe the thermodynamic properties of the liquid and the evaporation was modelled as a sonic deflagration followed by an axisymmetrie supersonic expansion.
Abstract: A nozzle expansion into a vacuum chamber was used to investigate the evaporation of highly superheated liquid jets. The large molar specific heat of fluids with high molucular complexity - in this caseC 6 F 14- is responsible for the new phenomena reported here. A modelwas developed to describe the basic physical effects. A cubic equation of state was used to describe the thermodynamic properties of the fluid. The evaporation was modelled as a sonic deflagration followed by an axisymmetrie supersonic expansion. As in the case of hypersonic gas jets the final state is reached by a normal shock. Forsufficiently high temperatures and expansion ratios a complete adiabatic evaporation of the liquid was found. At even higher temperatures the liquid evaporates completely within a rarefaction discontinuity. The predictions of the model are in good agreement with the experimental results.

49 citations

Journal ArticleDOI
TL;DR: In this article, the performance of spray/jet impingement cooling has attracted great attention from the scientific community, and some new functionalities are established such as high heat flux removal capacity, temperature uniformity, lower flow rate demand, and no thermal resistance to the heated test surface.
Abstract: Nanofluid spray/jet impingement cooling is widespread and finds applications in many scientific and industrial paradigms. Because of these ubiquities of nanofluid spray/jet impingement cooling, this branch of fluid dynamics has attracted great attention from the scientific community. The performance of nanofluid spray/jet impingement cooling very often depends on the nanoparticle concentration, shape, and size of the nanoparticle, as well as the mass flow rate of the nanofluid. These aspects lead to interesting variants of the thermo-hydrodynamic analysis of the nanofluid, which are studied meticulously, and some new functionalities are established such as high heat flux removal capacity, temperature uniformity, lower flow rate demand, and no thermal resistance to the heated test surface. We provide an overview of nanofluid spray/jet impingement cooling with an emphasis on the parametric effects, such as the Reynolds number, jet to test surface distance, the Prandtl number, the confinement of the jets, test plate inclination, and the roughness of the test surface, on the underlying phenomenon. Also, we aptly discuss the essential features of the nanofluid spray/jet impingement cooling, which includes spray properties, cooling fluid properties, substrate properties, and environmental conditions, which affect the heat transfer of spray cooling.

46 citations

01 Nov 2001
TL;DR: In this paper, it was shown that absolute instability occurs at We=1, and convective instability occurs in the region where We>1, where ρ and S are the liquid density and surface tension, and H and U are the local half-sheet thickness and the local average liquid velocity.
Abstract: A radially expanding liquid sheet of a finite radius can be formed by impacting a liquid jet on a circular disk [Savart, Ann. Chim. Phys. 54, 55 (1833); Ann. Chim. 54, 113 (1833)] or by impinging two jet heads on against each other [Savart, Ann. Chim. Phys. 55, 257 (1833)]. The breakup of the liquid sheet first observed by Savart at the outer rim of the sheet is explained from the point of view of absolute and convective instability. Whether the sheet is convectively or absolutely unstable depends on the local Weber number We=ρU2H/S, where ρ and S are, respectively, the liquid density and the surface tension, and H and U are, respectively, the local half-sheet thickness and the local average liquid velocity. It is shown that absolute instability occurs at We=1, and convective instability occurs in the region where We>1. In the radially expanding liquid sheet, H decreases inversely with the radial distance from the center of the sheet, but U remains constant. Thus, the local Weber number that is greater th...

31 citations

Journal ArticleDOI
TL;DR: In this article, the influence of unsteadiness in the liquid jet disintegration process on downstream fluctuations of spray characteristics in a coaxial twin-fluid injector was investigated for different axial locations downstream of the injector exit at z = 0, 8Dl, and 30Dl.
Abstract: This paper intends to investigate the influence of unsteadiness in the liquid jet disintegration process on downstream fluctuations of spray characteristics in a coaxial twin-fluid injector. Time-resolved high-speed shadowgraphic imaging of the spray was obtained for different axial locations downstream of the injector exit at z = 0, 8Dl, and 30Dl, where Dl is the central liquid tube diameter. The primary jet breakup unsteadiness close to the injector exit was characterized by measuring both shear-driven Kelvin–Helmholtz (KH) instability and flapping instability in addition to jet breakup length fluctuations. Downstream of the liquid jet core region, the liquid shedding rate (fshed) was measured at z = 8Dl. The power spectrum of time series data of instantaneous volume mean diameter (VMD) measured at z = 30Dl indicated periodic variation of the droplet size. The corresponding frequency (fVMD) was obtained. It was found that for lower range of gas-to-liquid momentum flux ratio (M < 4), both fshed and fVMD are larger than the frequency of KH instability. Also, for such conditions, larger temporal variation of the droplet size is realized, and this leads to higher fluctuations of the local liquid mass flux. Proper orthogonal decomposition analysis of the shadowgraph images for different axial locations identified similar topology of the dominant mode that corresponds to flapping instability. The results suggest that even far downstream of the injector exit, some memory of the upstream unsteady jet breakup process is retained, which strongly influences spatio-temporal evolution of droplet characteristics, thereby contributing to local spray fluctuations.

21 citations

References
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Journal ArticleDOI
TL;DR: In this article, a method is introduced that is able to extract dynamic information from flow fields that are either generated by a (direct) numerical simulation or visualized/measured in a physical experiment.
Abstract: The description of coherent features of fluid flow is essential to our understanding of fluid-dynamical and transport processes. A method is introduced that is able to extract dynamic information from flow fields that are either generated by a (direct) numerical simulation or visualized/measured in a physical experiment. The extracted dynamic modes, which can be interpreted as a generalization of global stability modes, can be used to describe the underlying physical mechanisms captured in the data sequence or to project large-scale problems onto a dynamical system of significantly fewer degrees of freedom. The concentration on subdomains of the flow field where relevant dynamics is expected allows the dissection of a complex flow into regions of localized instability phenomena and further illustrates the flexibility of the method, as does the description of the dynamics within a spatial framework. Demonstrations of the method are presented consisting of a plane channel flow, flow over a two-dimensional cavity, wake flow behind a flexible membrane and a jet passing between two cylinders.

4,150 citations

Journal ArticleDOI
TL;DR: A review of the fundamental and technological aspects of these subjects can be found in this article, where the focus is mainly on surface tension effects, which result from the cohesive properties of liquids Paradoxically, cohesive forces promote the breakup of jets, widely encountered in nature, technology and basic science.
Abstract: Jets, ie collimated streams of matter, occur from the microscale up to the large-scale structure of the universe Our focus will be mostly on surface tension effects, which result from the cohesive properties of liquids Paradoxically, cohesive forces promote the breakup of jets, widely encountered in nature, technology and basic science, for example in nuclear fission, DNA sampling, medical diagnostics, sprays, agricultural irrigation and jet engine technology Liquid jets thus serve as a paradigm for free-surface motion, hydrodynamic instability and singularity formation leading to drop breakup In addition to their practical usefulness, jets are an ideal probe for liquid properties, such as surface tension, viscosity or non-Newtonian rheology They also arise from the last but one topology change of liquid masses bursting into sprays Jet dynamics are sensitive to the turbulent or thermal excitation of the fluid, as well as to the surrounding gas or fluid medium The aim of this review is to provide a unified description of the fundamental and the technological aspects of these subjects

1,583 citations

Book
01 Dec 1988
TL;DR: In this paper, the basic processes in Atomization are discussed, and the drop size distributions of sprays are discussed.Preface 1.General Considerations 2.Basic Processes of Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.AtOMizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index
Abstract: Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

1,214 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present current scientific knowledge on the subject of liquid jet deblurring and discuss the unresolved scientific issues, including the physical mechanisms involved in the deblating process.
Abstract: A liquid jet emanating from a nozzle into an ambient gas is inherently unstable. It may break up into drops of diameters comparable to the jet diameter or into droplets of diameters several orders of magnitude smaller. The sizes of the drops formed from a liquid jet without external control are in general not uniform. The sizes as well as the size distribution depend on the range of flow parameters in which the jet is produced. The jet breakup exhibits different characteristics in different regimes of the relevant flow parameters because of the different physical mechanisms involved. Some recent works based on linear stability theories aimed at the delineation of the different regimes and elucidation of the associated physical mechanisms are reviewed, with the intention of presenting current scientific knowledge on the subject. The unresolved scientific issues are pointed out.

752 citations