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Measurement of locally heated liquid film thickness by a double-fiber optical probe

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Abstract

An experimental investigation of thermocapillary deformations in a film of 10% ethyl alcohol solution in water, flowing down a plate with a heater of length 6.7 mm and width 68 mm, is performed. Heating of the film results in the formation of a horizontal liquid bump at the top edge of the heater. On the heater the flow divides into vertical rivulets with a thin film between them. Film deformations in the bump and the thin film between the rivulets are investigated. Local film thickness is measured by means of a double-fiber optical probe. The method is based on the dependence of the intensity of reflected light on the distance between the probe and the reflecting surface. The measurement results are compared to those previously obtained using the schlieren method. The experiment is controlled by three parameters. They are, with their respective values, the plate inclination angle (4–90°), the Reynolds number (0.15–62) and the heat flux density (0–4.5 W/cm2).

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Abbreviations

h :

liquid film thickness (m)

h 0 :

initial liquid film thickness (m)

I 0 :

intensity of incident light beam (W)

I e :

intensity of light reflected from the end of the probe (W)

I l :

intensity of light reflected from the liquid surface (W)

I s :

intensity of light reflected from the substrate (W)

I t :

intensity of total light accepted by the probe, I t=I l+I e+I s (W)

k e :

coefficient of reflection from the end of the probe in working liquid, dimensionless

k s :

coefficient of reflection from the substrate in working liquid, dimensionless

l σ :

capillary constant of liquid, l σ =(σ/ρg)1/2 (m)

q :

average heat flux on the heater (W/m2)

q rol :

heat flux corresponding to the regular structure formation (W/m2)

r :

distance from the end of the probe to the film surface (m)

r 0 :

distance from the end of the probe to the substrate (m)

r sm :

distance from the end of the probe to the smooth film (m)

r def :

distance from the end of the probe to the deformed film (m)

Re :

Reynolds number, Re=Γ/μ, dimensionless

T 0 :

initial temperature of the film (°C)

V :

signal at the output of the amplifier (V)

V α=0 :

signal at the output of the amplifier at α=0 (V)

V ∞ :

signal at the output of the amplifier at r→∞ (V)

α :

deflection angle of the probe from the normal line to the reflecting surface (deg)

Γ :

specific liquid rate (kg/m s)

δ r :

error in determining zero reading of r during calibration (m)

δ r0 :

error in determining r 0 (m)

δ θ :

error from deviation of the probe with respect to the y-axis (m)

Δ :

total systematic error in determining h (m)

Θ :

inclination angle of the plate to the horizon (deg)

μ :

liquid dynamic viscosity (kg/m s)

ρ :

liquid density (kg/m3)

σ :

liquid surface tension coefficient (N/m)

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Acknowledgements

The authors gratefully acknowledge the support of this work by the Russian Academy of Sciences on RFBR Project No. 02-02-16478 and by the Siberian Branch of the Russian Academy of Sciences on integrated Project No. 5.

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Authors and Affiliations

  1. Institute of Thermophysics, Acad. Kutataladze 2, 630090, Novosibirsk, Russia

    D. V. Zaitsev, O. A. Kabov & A. R. Evseev

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  1. D. V. Zaitsev
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  2. O. A. Kabov
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  3. A. R. Evseev
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Correspondence to D. V. Zaitsev.

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Zaitsev, D.V., Kabov, O.A. & Evseev, A.R. Measurement of locally heated liquid film thickness by a double-fiber optical probe. Exp Fluids 34, 748–754 (2003). https://doi.org/10.1007/s00348-003-0621-1

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