Experimental studies of soot particle thermophoresis in nonisothermal combustion gases using thermocouple response techniques

Eisner, Alfred D.; Rosner, Daniel E.

doi:10.1016/0010-2180(85)90161-0

Cited by 87 publications

(18 citation statements)

References 15 publications

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“…The importance of this deposition mechanism has been exhaustively studied theoretically with models [25], experimentally with latex particles [26], and specifically with soot particles [27]. The authors of these studies have indicated the importance of thermophoresis for small particles.…”

Section: Mean Valuesmentioning

confidence: 99%

Experimental evaluation of the critical local wall shear stress around cylindrical probes fouled by diesel exhaust gases

Paz

Suárez

Eirís

et al. 2012

Experimental Thermal and Fluid Science

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The problem of fouling in the heat exchangers of exhaust systems has yet to be resolved. This results in enormous costs for engine manufacturers due to the required over-sizing during design and due to unscheduled maintenance needs.This article presents an experimental layout developed for measuring fouling in diesel engine exhaust gas systems. This facility was based on a circular cylindrical cross-flow device, with one straight and smooth stainless steel probe positioned transverse to the flow of exhaust gases. The probe can be cooled from the inside with water and fouled on the outside as a result of particle deposition from exhaust gases.The tests were conducted under constant engine operating conditions. Therefore, the asymptotic depth of the fouling layer could be measured at different angular positions at the end of each test.The critical wall shear stress rate is proposed as the controlling mechanism of the local removal process that leads to different fouling depths around each probe. This is in contrast to the critical velocity concept, which cannot be applied at a local scale due to its formulation. The experimental results, although subject to the usual uncertainties of fouling processes, seem to support this idea.

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Section: Mean Valuesmentioning

confidence: 99%

Experimental evaluation of the critical local wall shear stress around cylindrical probes fouled by diesel exhaust gases

Paz

Suárez

Eirís

et al. 2012

Experimental Thermal and Fluid Science

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“…All the measurements were found to be repeatable within the experimental uncertainties that will be addressed together with the results. Main sources of uncertainties were associated with the flame intrusion by the sampling probe, dependence of thermophoretic velocity on particle size/morphology (Eisner and Rosner 1985), analysis of finite number of particles/aggregates, above-mentioned image enhancement procedures, and translucent particles. The propagations of measurement errors to the calculated parameters were evaluated following the standard uncertainty analysis of Moffat (1982); please see Fang et al (1998) and Hu (2002) for detailed considerations.…”

Section: General Observationsmentioning

confidence: 99%

Size and Morphology of Soot Particulates Sampled from a Turbulent Nonpremixed Acetylene Flame

Köylü

2004

Aerosol Science and Technology

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Soot processes within a turbulent nonpremixed flame burning acetylene/air were investigated by conducting thermophoretic sampling experiments at various axial and radial locations. Analyses of transmission electron microscope images yielded the mean soot spherule diameter, number of spherules per aggregate, and fractal morphology within this highly luminous turbulent flame. Specifically, translucent particles were observed at low-to-intermediate heights above the flame with the formation and evolution of young soot precursors. The soot spherule diameter peaked at 34 nm halfway along the centerline, identifying the flame regions of surface growth and oxidation processes. In the meantime, the aggregation was continuous along the flame axis with the mean number of spherules per aggregate reaching 150 at the highest sampling location. Size ranges of spherules and aggregates were narrow and broad, respectively, while the relative widths of both size distributions remained similar throughout the flame. In contrast to the observed axial variations, the radial changes of the mean spherule and aggregate sizes appeared to be small. Aggregate morphologies were universally characterized by a fractal dimension of 1.82 and a fractal prefactor of 1.9 for all the flame positions. In comparison to a lightly sooting ethylene flame, these measurements in the acetylene turbulent flame revealed that the fuel type mainly affected the axial evolution of spherule diameters but not their range, and enhanced the aggregate sizes but not their morphology. The effective decoupling of spherule and aggregate sizes permitted the separation of soot surface growth and oxidation from aggregation. This key aspect provided a stringent test for the existing particulate diagnostics and predictive models in their ability to quantify the actual particle surface area, particularly in optically thick conditions that are encountered in many practical combustion environments.

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“…The importance of thermophoresis has been exhaustively studied, particularly with soot particles [17,38], and this phenomenon has been shown to be most relevant for small particles [39]. The thermophoretic effect was result in a mean mass increase of approximately 50% under the conditions used for our previous experiments [16].…”

Section: Mean Valuesmentioning

confidence: 90%

Experimental study of soot particle fouling on ribbed plates: Applicability of the critical local wall shear stress criterion

Paz

Suárez

Concheiro

et al. 2013

Experimental Thermal and Fluid Science

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This article examines the notion of critical wall shear stress as the key control parameter of the local fouling removal process. In this study, an experimental setup was developed for measuring fouling on enhanced surfaces. Specifically, the experimental configuration consists of a forced convection plate heat exchanger containing a one-pass rectangular channel with two ribbed plates arranged in a symmetrically staggered manner. The exhaust gases flow by the rib-roughened sides of the plates, and the flat sides can be cooled with water from the independent external coolant circuit.As a result of soot particle deposition from exhaust gases, a layer of fouling is deposited over the ribs.After asymptotic conditions were reached during the tests, detailed fouling thickness measurements were conducted. The dimensionless particle relaxation time during these tests was determined to be in the range of 0.3-10. The measurements were then complemented with a numerical analysis. In particular, the local wall shear stress was calculated using a commercial computational fluid dynamics (CFD) software package.The fouling thickness profiles deposited over the ribs and the local critical shear stress values were compared and discussed for two different geometries. The results obtained clearly support the idea that critical wall shear stress is an appropriate criterion for facilitating the understanding of the local behaviour of fouling deposits.

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Experimental studies of soot particle thermophoresis in nonisothermal combustion gases using thermocouple response techniques

Cited by 87 publications

References 15 publications

Experimental evaluation of the critical local wall shear stress around cylindrical probes fouled by diesel exhaust gases

Experimental evaluation of the critical local wall shear stress around cylindrical probes fouled by diesel exhaust gases

Size and Morphology of Soot Particulates Sampled from a Turbulent Nonpremixed Acetylene Flame

Experimental study of soot particle fouling on ribbed plates: Applicability of the critical local wall shear stress criterion

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