Thermocapillary Drift of a Drop

These results show that thermocapillary forces generate a complicated circulation liquid motion in the layer, and, the flow changes its direction at the depth equal to 1/3 of the layer depth. Just as one can expect, the flow is symmetric with respect to the plane X = 0 with temperature To the fluid flows out from the near-bottom layer along this plane. 

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Various thermal hydrodynamic phenomena are analyzed, which are related to the dependence of the surface tension coefficient on temperature. Thermo-gravitational and thermocapillary convection in a fluid layer is studied. The problem of thermocapillary drift of a drop in an external temperature-gradient field is considered, as well as other, more complicated problems. 

Radiation-induced thermocapillary motion of a drop. The temperature gradient is the simplest but not the unique method for bringing about the thermocapillary drift of a drop. If the drop is opaque and the fluid is transparent, one can move the drop by a light beam in a uniformly heated fluid. The radiation absorbed by the drop will heat it nonuniformly, thus producing thermocapillary stresses. For dcr/dT < 0, the drop will drift towards the warmer part, that is, towards the beam. 

The corresponding problem was considered in [322, 389], The radiation in [389] was assumed to have the form of a plane-parallel beam being absorbed on the drop surface as on a black body, but freely passing through the exterior fluid. The temperature remote from the drop is assumed to be constant. For the thermocapillary force and for the velocity of thermocapillary drift of the drop in the absence of gravitation, the following expressions were obtained (J is the radiation flux power) ... 

Antanovskii, L. K. and Kopbosynov, B. K., Nonstationary thermocapillary drift of a viscous fluid drop, J. Appl. Mech. Techn. Phys., No. 2, 1986. 

Some additional effects were considered for the thermocapillary motion of drops and bubbles in an external temperature gradient interaction of a drop with a plane wall [285], and interaction of drops with bubbles or of bubbles with each other [12, 146], In particular, it was shown in [12] that the interaction of drops of radius a decreases with increasing distance l between them as (a/i f for thermocapillary drift, compared with a/l for the motion in the gravitational field. 

Let us estimate the thermocapillary force applied to a drop and the velocity of the drop thermocapillary drift in the absence of gravitation. We assume the ambient fluid to be infinite and the nonuniform temperature field remote from the drop to be linear in X ... 

The results (5.10.8) for the thermocapillary force Ft and (5.10.9) for the thermocapillary drift velocity, which were obtained under the assumption of a constant temperature gradient remote from the drop, prove to hold also for a varying gradient. These expressions can be rewritten in a vector form as follows [468] ... 

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