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Direct contact heat transfer to a drop translating in a transverse electric field

Direktkontakt-Wärmeübergang an einen in einem elektrischen Feld bewegten Tropfen

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Abstract

An experimental study has been performed on heat transfer to a single drop translating in an immiscible liquid on which a steady uniform electric field is imposed perpendicular to the drop path. Particular attention has been paid to the effect of field-induced circulations inside and outside the drop. Three different combinations of liquids were tested: one for which the drop-to-medium permittivity ratio ɛ* multiplied by the drop-tomedium resistivity ratio χ* is large compared to unity and two for which ɛ* χ* ≪ 1. In the former a remarkable enhancement of heat transfer was obtained which could be ascribed to the induced circulations. However, a less remarkable enhancement obtained in the latter two could not be explained by the circulations which are predicted to be vanishingly weak.

Zusammenfassung

Es wurden Experimente über den Wärmeübergang an einem einzelnen Tropfen durchgeführt, der sich in einer mit ihm nicht mischbaren Flüssigkeit senkrecht zu einem elektrischen Feld bewegt. Besondere Aufmerksamkeit wurde der durch das elektrische Feld induzierten Zirkulation im Inneren des Tropfens gewidmet. Es wurden drei verschiedene Kombinationen von Flüssigkeiten getestet, nämlich eine, bei der der Faktor aus der Dielektrizitätskonstanten und dem spezifischen elektrischen Widerstand zwischen Tropfen und Medium groß gegenüber 1 ist, und zwei, für die dieser Faktor klein gegen 1 ist. Im ersten Fall wurde eine merkliche Verbesserung des Wärmeübergangs beobachtet, die man auf die induzierte Zirkulation zurückführen kann. Jedoch kann die Verbesserung, die sich bei den zwei letztgenannten Bedingungen einstellte, nicht durch die dort verschwindend geringen Zirkulationsströmungen erklärt werden, wenn sie auch weniger stark ausgeprägt war.

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Abbreviations

D n :

axis of drop normal to electric field

D p :

axis of drop parallel to electric field

D 0 :

equivalent spherical diameter of drop

E :

strength of electric field

Nu :

Nusselt number,α D 0/λc

p:

normalized strength of electric field, Eq. (2)

Re :

Reynolds numbr, ϱc Ut D0/ηc

Uc :

maximum circulation velocity at the interface

U t :

translational velocity of drop

U + :

circulation-to-translation velocity ratio, Eq. (4)

U +1 :

circulation-to-translation velocity ratio, Eq. (5)

V :

specific circulation velocity to a given system, Eq. (3)

α :

heat transfer coefficient based on surface area of spherical drop

Γ :

dimensionless parameter characterizing circulation velocity, Eq. (1)

δ :

distortion ratio of drop,(D p − Dn)/(Dp+Dn)

ɛ :

permittivity

η :

dynamic viscosity

λ :

thermal conductivity

ϱ :

mass density

σ :

interfacial tension

Φ :

dimensionless parameter characterizing drop deformation, Eq. (2)

χ :

electrical resistivity

c :

continuous phase (medium)

cr:

critical condition for drop burst

d :

dispersed phase (drop)

ex:

experimental

HR:

Hadamard-Rybczynski theory

max:

maximum

th:

theoretical

0:

under no electric field

*:

drop-to-medium ratio

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Authors and Affiliations

  1. Department of Automobiles, The Institute of Vocational Training, 1960 Aihara, 229, Sagamihara, Japan

    N. Kaji (Assistant Professor)

  2. Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, 223, Yokohama, Japan

    Y. H. Mori (Associate Professor)

Authors
  1. N. Kaji
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  2. Y. H. Mori
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Kaji, N., Mori, Y.H. Direct contact heat transfer to a drop translating in a transverse electric field. Wärme- und Stoffübertragung 20, 11–18 (1986). https://doi.org/10.1007/BF00999731

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  • DOI: https://doi.org/10.1007/BF00999731

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