Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Effervescent atomization spray: Understanding the modeling process

03.01.2012
Understanding the atomization spray process is not only of academic interest but is also important to various industry applications such as combustion, coating, and chemical synthesis. Significant experimental investigations concerning spray behavior have been conducted in the past.

Fundamental understanding of the spray process is, however, still lacking and lags behind applications due to the high complexity of its stochastic behavior. Prof. LIN Jianzhong and his group proposed a comprehensive three-dimensional model to predict the droplet mean size and other spray characteristics by describing both primary and secondary atomization. Recently, they reviewed the theories, practical modeling treatments and the main achievements of modeling on effervescent atomization. Their work, entitled "Modeling on effervescent atomization: A review", was published in SCIENCE CHINA, 2011, DOI: 10.1007/s11433-011-4536-1.

Effervescent atomization is a method involving a twin-fluid process that involves bubbling gas within a liquid. Compared to conventional pressure, rotary and twin-fluid atomizers, the effervescent atomizer offers advantages of smaller drop sizes, reduced injection pressure, lower gas flow, a larger exit orifice, and tolerance for high viscosities. Effervescent atomization has been widely used in gas turbine combustors, IC engines furnaces and boilers, incineration, spray deposition, powder formation and other applications. Recently, the effervescent atomization method has been successfully applied in pharmaceutical coating and suspension plasma spray. Because effervescent atomization can handle a variety of liquids, it can play a pivotal role in reducing energy consumption during combustion and has potential for broad applications in the manufacture of high quality materials.

Effervescent atomizer performance has been the object of extensive research since the late 1980s. Studies on the atomization spray can be grouped into two broad categories: diagnostic measurements and numerical modeling. Diagnostic measurements have made a significant contribution to the development of effervescent atomization technology over the past two decades. Fundamental understanding of the spray process is challenging due to the high complexity of two-phase phenomena statistic behavior. Lin and his co-workers from Jiliang University and Zhejiang Universities, China, have devoted their efforts to establish a comprehensive numerical model to explain the phenomena involved in effervescent atomization spray. Their studies cover modeling of liquid fragmentation, the parametric study of various operating conditions, and the development of a fitting formula for droplet mean size and impinging factors.

The effervescent atomization process involves complex fluid-dynamic and transport phenomena. A typical effervescent atomization spray can be divided into four sub-domains, according to the different mechanisms involved. As shown in Fig.1, in the schematic for effervescent atomization spray generation, the first sub-domain is internal-mixing atomization, in which atomizing gas is bubbled into the liquid. The second step is a resulting two-phase mixture that is discharged from the atomizer orifice. Leaving the nozzle exit, the rapidly expanding gas phase will shatter the liquid into fine droplets, which can be referred to as primary atomization. The third domain lies downstream of the spray. The droplets produced by primary atomization are unstable in the turbulent spray and undergo a series of events such as collision, breakup and coalescence, and finally the droplets entrained in the gas jet will impinge on the plate or undergo further mass and heat transfer. Most modeling work has focused on the external two-phase flow out of the effervescent atomizer exit. The review paper focused on the Lagrangian treatment and introduced a comprehensive model capable of describing both primary and secondary breakup processes and correlating the droplet mean diameter and other spray characteristics with first principle operating conditions. The model comprises two sub-models. The first sub-model is used for simulating the primary breakup of the annular liquid sheath near the orifice and calculating the atomized droplet size. The second sub-model is based on a hybrid Eulerian/Lagrangian coordinate system to simulate the turbulent gas jet and injected droplets. This latter sub-model describes the gas jet and the droplet trajectory in three-dimensional geometry and also considers droplet breakup and collision.

The paper reviews the mechanism of droplet events and the numerical treatments of effervescent atomization, which involved the primary atomization of a Newtonian and a non-Newtonian fluid, particle tracking, secondary atomization and droplets collision. A comprehensive three-dimensional model of droplet-gas flow is introduced to describe the evolution of spray in the effervescent atomization spray. The evolution of droplet mean diameter along the axial distance, the mean size and statistical distribution of atomized droplets at cross sections, as well as the change in droplet velocity are calculated and analyzed to reveal their inner driving forces. The influence of operating conditions and liquid physical properties on atomization performance are discussed. The factors that promote the achievement of good atomization effects are identified. Based on the extensive computation, the influences of various operating conditions and liquid physical properties on atomization effects are quantified. The expressions for the Weber number and the K number, which is related to the operating parameters and liquid properties, are deduced. The formula can be used conveniently and effectively to judge the deposition behaviors of droplets onto surfaces for various Newton liquids. In addition to these achievements, the challenges for future numerical research and the scope for further applications are outlined.

Through academic study and modeling, the critical mechanisms and important parameters involved in effervescent atomization have been deeply understood and the applications of effervescent atomization technology have been successfully extended. This research project was mainly supported by the National Natural Science Foundation of China with Grant Nos. 11132008 and 11002136. The development of modeling approaches to atomization spray is based on previous studies involving many researchers from various institutions and universities.

Modeling of the external flow of effervescent atomization can be divided into two sub-models. The first sub-model is used to simulate the primary breakup of the annular liquid sheath near the orifice and calculating the atomized droplet size. The second sub-model is based on a hybrid Eulerian/Lagrangian coordinate system to simulate the turbulent gas jet and injected droplets.

See the article: Qian Lijuan, Lin Jianzhong. Modeling on effervescent atomization: A review. Science China Physics, Mechanics & Astronomy, 2011, DOI: 10.1007/s11433-011-4536-1

Lin Jianzhong | EurekAlert!
Further information:
http://www.zju.edu.cn

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>