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Impingement of an unsteady two-phase jet on unheated and heated flat plates

Published online by Cambridge University Press:  26 April 2006

İ. Bedii Özdemir  and
J. H. Whitelaw
İ. Bedii Özdemir
Affiliation:
Imperial College of Science, Technology and Medicine, Mechanical Engineering Department, Thermofluids Section, Exhibition Road, London SW7 2BX, UK
J. H. Whitelaw
Affiliation:
Imperial College of Science, Technology and Medicine, Mechanical Engineering Department, Thermofluids Section, Exhibition Road, London SW7 2BX, UK
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Abstract

This paper is concerned with an experimental investigation of the oblique impingement of an unsteady, axisymmetric two-phase jet on heated surfaces. Size and velocity were measured simultaneously with a phase-Doppler velocimeter, and the spatial distributions over the wall jet were found to be correlated with the interfacial activities as inferred from vertical velocity measurements in the vicinity of the wall. These results are discussed together with size measurements by a laser-diffraction technique to quantify the effect of the approach conditions of the inflowing jet droplet field and wall temperature in relation to mechanisms of secondary atomization.

Two mechanisms of secondary atomization were identified; the first did not involve direct wall contact and was due to the strain acting on the droplets by the continuous phase within the impingement region and was enhanced by thermal effects from the wall to cause breakup. The approaching velocity of the inflowing droplets to the plate was important to this process so that higher velocities increased the rate of strain within the impingement region and, consequently, the wall temperature promoting the secondary atomization shifted towards lower values. The second mechanism required direct wall contact and involved atomization of the film deposited on the wall by the impingement of the inflowing two-phase jet. With the penetration of high-speed inflowing droplets into the film, liquid mass was raised into the two-phase medium due to splashes from the film so that a new size class with larger droplets was generated. The resulting large droplets tended to stay close to the wall within the impingement region with small vertical velocities

In between the injections, the suspended droplet field above the film oscillated normal to the plate as a cloud so that the impact of large droplets on the film resulted in coalescence with the film and the ejection of smaller numbers of small droplets. The unsteady wall jet flow, caused by the arrival of the spray at the plate, swept the vertically oscillating droplet cloud radially outwards so that the resulting radial transport caused the dynamics of the unsteady film to be correlated with the size characteristics of the unsteady wall jet. Based on this phenomenological description, a radial droplet transport equation is derived.

The correlation suggests that the secondary atomization with direct wall contact is the dominant process for the generation of a new size class within the wall flow and initiates the mutual interaction between the unsteady film and wall jet droplet field.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 252 , July 1993 , pp. 499 - 523
Copyright
© 1993 Cambridge University Press

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References

Ashgriz, N. & Poo, J. Y. 1990 Coalescence and separation in binary collisions of liquid drops. J. Fluid Mech. 221, 183–204.Google Scholar
Austin, L. J., Ying, W. E. & Sawistowski, H. 1966 Interfacial phenomena in binary liquid-liquid systems. Chem. Engng Sci. 21, 1109–1110.Google Scholar
Bracco, F. V. 1985 Modelling of engine sprays. SAE Paper 850394.
Clift, R., Grace, J. R. & Weber, M. E. 1978 Bubbles, Drops and Particles, pp. 339–347.
Cossali, E. & Hardalupas, Y. 1992 Comparison between laser diffraction and phase-Doppler velocimeter techniques in high turbidity, small width sprays. Exps Fluids 13, 414–422.Google Scholar
Cumo, M. & Farello, G. E. 1967 Heated wall-droplet interaction for two-phase flow heat transfer in liquid deficient region. Proc. Symp. on Two Phase Flow Dynamics, Eindhoven, vol. 2, 1325–1357.
Dimitrov, D. S. & Ivanov, I. B. 1978 Hydrodynamics of thin liquid films. On the rate of thinning of microscopic films with deformable interfaces. J. Colloid Interface Sci. 64, 97–106.Google Scholar
Dodge, L. G. 1984 Change of calibration of diffraction-based particle sizers in dense sprays. Opt. Engng 23, 626–630.Google Scholar
Ellis, S. R. M. & Biddulph, M. 1966 Interfacial turbulence measurements. Chem. Engng Sci. 21, 1107–1109.Google Scholar
Felton, P. G., Hamidi, A. A. & Aigal, A. K. 1985 Measurement of drop size distributions in dense sprays by laser diffraction. Proc. 3rd Intl Conf. on Liquid Atomisation and Spray Systems, Imperial College, London, ICLASS-85, IVA/4/1.
Fujimoto, H., Sugihara, H., Tanabe, H. & Sato, G. T. 1983 Investigation on combustion in medium-speed marine diesel engines using model chambers. Proc. of 15th Intl Congress on Combustion Engines, Paris, CIMAC, DI3.3.
Gallily, I. & La Mer, V. K. 1958 On the behavior of liquid droplets after impinging on solid surfaces. J. Phys. Chem. 62, 1295–1299.Google Scholar
Hammond, D. C. 1981 Deconvolution technique for line-of-sight optical scattering measurements in axisymmetric sprays. Appl. Optics 20, 493–499.Google Scholar
Hanratty, T. J. 1983 Interfacial instabilities caused by air flow over a thin liquid layer. In Waves on Fluid Interfaces (ed. R. E. Meyer), pp. 221–259. Academic.
Hirleman, E. D., Oechsle, V. & Chigier, N. A. 1984 Response characteristics of laser diffraction particle analyzer: optical sample volume extent and lens effects. Opt. Engng 23, 610–619.Google Scholar
Hoogendoorn, C. J. & Hond, R. Den 1974 Leidenfrost temperature and heat-transfer coefficients for water sprays impinging on a hot surface. Proc. Fifth Intl Heat Transfer Conference, vol. 4, pp. 135–138.
Hori, M. & Sugiyama, H. 1980 Combined measurement by photography and gas sampling for combustion analysis in a diesel engine cylinder. SAE Paper 800986.
Jayaratne, O. W. & Mason, B. J. 1964 The coalescence and bouncing of water drops at an air/water interface. Proc. R. Soc. Lond. A280, 545–565.Google Scholar
Katsura, N., Saito, M., Senda, J. & Fujimoto, H. 1989 Characteristics of a diesel spray impinging on a flat wall. SAE Paper 890264.
Lefebvre, A. H. 1989 Atomisation and Sprays. Hemisphere.
Meyer, P. & Chigier, N. 1986 Dropsize measurements using a Malvern 2200 particle sizer. Atomis. Spray Technol. 2, 261–298.Google Scholar
Middleman, S. 1974 Drop size distributions produced by turbulent pipe flow of immiscible fluids through a static mixer. Ind. Engng Chem., Process Des. Dev. 13, 78–83.Google Scholar
Naber, J. D. & Reitz, R. D. 1988 Modelling engine spray/wall interaction. SAE Paper 880107.
Özdemir, İ. B. 1991 Impingement of single and two-phase jets on unheated and heated flat plates. PhD thesis, Imperial College, University of London.
Özdemir, İ, B. & Whitelaw, J. H. 1992a An optical method for the measurement of unsteady film thickness. Exps Fluids 13, 321–331.Google Scholar
Özdemir, İ. B. & Whitelaw, J. H. 1992b Impingement of an axisymmetric jet on unheated and heated flat plates. J. Fluid Mech. 240, 503–532.Google Scholar
Pandit, A. B. & Davidson, J. F. 1990 Hydrodynamics of the rapture of thin liquid films. J. Fluid Mech. 212, 11–24.Google Scholar
Pedersen, C. O. 1970 An experimental study of the dynamic behavior and heat transfer characteristics of water droplets impinging upon a heated surface. Intl J. Heat Mass Transfer 13, 369–381.Google Scholar
Ranz, W. E. & Hofelt, C. 1957 Determining drop size distribution of a nozzle spray. Ind. Engng Chem. 49, 288–293.Google Scholar
Reitz, R. D. & Bracco, F. V. 1979 Ultra-high-speed filming of atomizing jets. Phys. Fluids 22, 1054–1064.Google Scholar
Reitz, R. D. & Bracco, F. V. 1982 Mechanism of atomization of a liquid jet. Phys. Fluids 25, 1730–1742.Google Scholar
Rumscheidt, F. D. & Mason, S. G. 1961 Particle motions in sheared suspensions; deformation and burst of fluid drops in shear and hyperbolic flow. J. Colloid Interface Sci. 16, 238–261.Google Scholar
Skiepko, J. & Panas, J. 1989 Instability of the motion of a spherical drop in a vertical temperature gradient. Arch. Mech. 41, 811–820.Google Scholar
Torza, S., Cox, R. G. & Mason, S. G. 1972 Particle motions in sheared suspensions; transient and steady deformation and burst of liquid drops. J. Colloid Interface Sci. 38, 395–411Google Scholar
Türkdogan, E. T. 1966 Fluid dynamics of gas jets impinging on surface of liquids. Chem. Engng Sci. 21, 1133–1144.Google Scholar
Wachters, L. H. J., Bonne, H. & Van Nouhuis, H. J. 1966a The heat transfer from a hot horizontal plate to sessile water drops in the spheroidal state. Chem. Engng Sci. 21, 923–936.Google Scholar
Wachters, L. H. J., Smulders, L., Vermeulen, J. R. & Kleiweg, H. C. 1966b The heat transfer from a hot wall to impinging mist droplets in the spheroidal state. Chem. Engng Sci. 21, 1231–1238.Google Scholar
Wachters, L. H. J. & Westerling, N. A. J. 1966 The heat transfer from a hot wall to impinging water drops in the spheroidal state. Chem. Engng Sci. 21, 1047–1056.Google Scholar
Woodmansee, D. E. & Hanratty, T. J. 1969 Mechanism for the removal of droplets from a liquid surface by a parallel air flow. Chem. Engng Sci. 24, 299–307.Google Scholar
Yao, S. C. & Cai, K. Y. 1985 Dynamics and heat transfer of drops impacting on a hot surface at small angles. Proc. 3rd Intl Conf. on Liquid Atomisation and Spray Systems, Imperial College, London, ICLASS-85. VII/B/1–11.
Zhang, S. & Gogos, G. 1991 Film evaporation of a spherical droplet over a hot surface: fluid mechanics and heat/mass transfer analysis. J. Fluid Mech. 222, 543–563.Google Scholar