Co-Flow Laminar Diffusion Flames of Monodisperse Sprays: Structure, Evaporation and Microgravity Effects

Chen, G.; Gomez, Alessandro

doi:10.1080/00102209608935528

Cited by 22 publications

(6 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This configuration, often called "extractor electrode", is typically used in electron beam applications. It was also used in early electrospray applications to electric propulsion (e.g., Hendricks, 1962) and combustion (e.g., Chen & Gomez, 1996). The generated droplets would eventually reverse their paths and be attracted back to the lower potential electrode, causing flooding and eventual interruption of the flow.…”

Section: Design Criterionmentioning

confidence: 98%

Increase of electrospray throughput using multiplexed microfabricated sources for the scalable generation of monodisperse droplets

Deng

Klemic

et al. 2006

Journal of Aerosol Science

174

138

View full text Add to dashboard Cite

The development, fabrication, and testing of a compact multiplexed system of electrosprays are presented with the dual goal of increasing by orders of magnitude the liquid flow rate to be dispersed and of retaining the quasimonodispersity of the generated droplets. The system was microfabricated as an array of nozzles etched in silicon, with a density of 250 sources/cm 2 . Although the operation of a single electrospray is rather forgiving with respect to the electrode geometry, successful performance of the multiplexed system is critically dependent on a careful selection of the electrode configuration, which in the present work entails an extractor electrode mounted at a distance from the spray sources that is comparable to the distance between sources (on the order of 0.5 mm). The electrode has the dual function of limiting electric field cross-talk between neighboring sources and minimizing space charge feedback from the spray cloud. Measurements of current and droplet size as a function of flow rate and of droplet size distribution using ethanol demonstrated that the system may be optimized to produce uniform droplets simultaneously from all parallelized electrosprays, each one operating as an isolated spray in the quasimonodisperse cone-jet mode. Ease of operation and uniformity in size from spray to spray require strategies to increase the pressure drop in the liquid flow path and/or to uniformize the electric field at the spray sources.

show abstract

Section: Design Criterionmentioning

confidence: 98%

Increase of electrospray throughput using multiplexed microfabricated sources for the scalable generation of monodisperse droplets

Deng

Klemic

et al. 2006

Journal of Aerosol Science

174

138

View full text Add to dashboard Cite

show abstract

“…We have been pursuing the objective of bridging the gap between classical singledroplet burning studies and practical spray flames by using some well-defined configurations, encompassing at first laminar spray diffusion flames. The laminar configurations include counterflow (Chen & Gomez 1992) and co-flow (Chen & Gomez 1996. The experimental systems are simple and amenable to detailed numerical modelling (Gao et al 1996).…”

Section: Introductionmentioning

confidence: 99%

Self-similarity, momentum scaling and Reynolds stress in non-premixed turbulent spray flames

Karpetis

Gomez

1999

J. Fluid Mech.

Self Cite

View full text Add to dashboard Cite

An experimental study was conducted in a turbulent spray flame in which droplets were produced ultrasonically at low velocity relative to the host gas. In this fashion, injector-specific effects on the two-phase flow were minimized and a scenario generally characteristic of the far field of practical spray systems could be simulated. Close to the burner exit, the spray flame appeared as a dense column of drops burning with an envelope flame. Further downstream, it opened up slowly in the radial direction and developed a turbulent ‘brush’ appearance. Measurements of the size, velocity and concentration of the droplets, and of gas-phase velocity and temperature were made by combining a Phase-Doppler interferometric technique with Stokes/anti-Stokes Raman thermometry. The experimental data were used to derive scaling and self-similarity for the Reynolds-averaged continuity and momentum equations using suitable transformations.Results showed three distinct regions, on the basis of the behaviour of the gas axial velocity in the spray flame. In the lower part of the flame, the gas momentum increased because of vaporization. In the intermediate region of the spray flame, the axial velocity decayed along the centreline as an inverse power of the distance from the virtual origin, with exponents smaller than unity. In the upper part of the spray flame, the flow field recovered the axial velocity decay that is typical of incompressible jets, namely as an inverse of the axial distance. Self-similar behaviour held for the axial velocity throughout the intermediate region. The vapour source term in the gas continuity equation scaled approximately as an inverse power of axial distance, and exhibited self-similarity throughout the spray flame. As a result, a simple model of the Reynolds stress term could be formulated, in which two competing contributions appear: one, that is due to turbulent transport, tends to increase the value of the velocity correlation; another, that is due to the vaporization term, tends to reduce the value of the velocity correlation and can be construed as a vaporization-induced tendency towards relaminarization. The first term is modelled by a classic gradient-transport approach yielding an empirical mixing length relating the velocity correlation to the average velocity gradient. Model and experiments are found to be in good agreement, especially sufficiently far from the injector, where one-way coupling between the two phases holds.

show abstract

“…Electrospraying has applications in a wide variety of research areas such as: colloidal propulsion [28][29][30][31], mass spectrometry [32], material production and coating [33][34][35][36][37][38], bio-sciences [33,[39][40][41][42], and microcombustion [43][44][45][46]. Electrospraying is an attractive proposition for cooling applications given its generation of monodisperse micron sized charged droplets [23,[47][48][49], avoidance of droplet coalescence and self spray dispersion due to Coulomb repulsions [23], negation of droplet impact rebound and increased droplet spreading upon impact due to Coulomb attraction [24], and minimal energy and space requirements [6,17].…”

Section: Introductionmentioning

confidence: 99%

Electrospray array heat transfer

Gibbons

Robinson

2018

International Journal of Thermal Sciences

View full text Add to dashboard Cite

Multiple source electrospraying enables higher droplet mass flux and greater cooling coverage area in comparison with its single source counterpart. The local convective heat flux to a multiple source electrospray array operating in the evaporative cooling regime has been investigated using thin foil thermography. The designed array had a packing density of 115 N n cm −2 and was operated in the cone-jet regime of spraying with ethanol as the working fluid. The electrospray array heat transfer performance is explored for varied flow rate (Q = 2-4 µL min −1 N −1 n) and electric field (E d = 4-8 kV cm −1). Cooling performance was shown to be dependent on both parameters. An 89% and 64% increase in the peak and average heat flux respectively was noted for the increasing driving electric fields case. This was due to increasing droplet mass flux, resulting in increasing contact line length density on the heated substrate, from narrowing of the spray plume, reduced residence time and droplet evaporation en-route to the target surface. This narrowing spray plume, at higher driving electric fields, also resulted in a more defined radial convective heat flux profile. The performance of the array was compared with that of a single source under similar experimental conditions. The array achieved more uniform cooling over a larger area than its single source counterpart. Comparing both devices for similar total working fluid flow rate highlight that the array delays the onset of pool cooling. This enables higher total working fluid flow rates in the evaporative cooling regime and subsequently higher convected thermal energy.

show abstract

Co-Flow Laminar Diffusion Flames of Monodisperse Sprays: Structure, Evaporation and Microgravity Effects

Cited by 22 publications

References 15 publications

Increase of electrospray throughput using multiplexed microfabricated sources for the scalable generation of monodisperse droplets

Increase of electrospray throughput using multiplexed microfabricated sources for the scalable generation of monodisperse droplets

Self-similarity, momentum scaling and Reynolds stress in non-premixed turbulent spray flames

Electrospray array heat transfer

Contact Info

Product

Resources

About