Enhancement of Thermocapillary Effect in Heated Liquid Films for Large Waves at High Reynolds Numbers

[+] Author and Article Information
E. A. Chinnov

S.S. Kutateladze Institute of Thermophysics,
Novosibirsk State University,
Novosibirsk 630090, Russia
e-mail: chinnov@itp.nsc.ru

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received August 21, 2014; final manuscript received September 30, 2015; published online June 1, 2016. Assoc. Editor: Dennis A. Siginer.

J. Heat Transfer 138(9), 091005 (Jun 01, 2016) (8 pages) Paper No: HT-14-1553; doi: 10.1115/1.4032945 History: Received August 21, 2014; Revised September 30, 2015

The characteristics of the heated water film flowing down a vertical plate at Re = 150, 300, and 500 were studied. The fluorescence method was used for measuring the film thickness. The temperature field on the film surface was measured by an infrared scanner. The analysis of the temperature pulsations on the heated film surface was made. The high-frequency component of temperature pulsations faded at the bottom area of the heater. Part of the temperature perturbations (small waves) was removed from interrivulets regions (valleys) to the rivulets by transverse thermocapillary forces. At high heat flux, only largest waves with maximum ripple of temperature reached the lower edge of the heater. There is a decrease in the mean integral energy fluctuations of temperature in the interrivulets regions near the heater lower edge. In the heated regions between rivulets, the relative amplitude of large waves increases with decreasing average thickness (or local Reynolds number). The analysis of results obtained for large Reynolds numbers showed that the relative amplitudes of large waves in the regions between rivulets at high heat fluxes are much greater than those for small Reynolds numbers and in isothermal falling films. In the interrivulet zone, Marangoni number increases with a rise of the heat flux. The growth of relative amplitude of low-frequency waves in interrivulets regions helps prevent film rupture and crisis of heat transfer.

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Fig. 1

Temperature distributions on the surface of the heated falling film: (a) the 3D instantaneous at q = 0.1 W/cm2 and Re = 0.1 (the arrow indicates the flow direction) and (b) temperature and temperature gradient distributions along line 1

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Fig. 2

The averaged thickness distribution at Re = 300 and q = 2.2 W/cm2: (1) rivulets and (2) interrivulets area (valley) between the rivulets

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Fig. 3

The scheme of the experimental setup: (1) film-former, (2) plate, (3) temperature stabilizer, (4) liquid film, (5) heater, (6) liquid collector, (7) laser, (8) camera, (9) filter, and (10) IR scanner

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Fig. 4

Temperature of the heater surface: (1) q = 0.57 W/cm2, (2) q = 1.34 W/cm2, (3) q = 2.2 W/cm2, (4) q = 3.5 W/cm2, (5) q = 4.9 W/cm2, and (6) q = 6.0 W/cm2

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Fig. 5

Distributions of thickness in a heated flowing film at Re = 300: (a) instantaneous 3D, q = 3.7 W/cm2, (b) along the heater, q = 1.8 W/cm2, and (c) along the heater, q = 5.5 W/cm2. (1) Thickness distribution in a rivulet, (2) thickness distribution in a valley, (3) averaged thickness in a rivulet, and (4) averaged thickness in a valley.

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Fig. 6

Temperature distributions on the surface of the heated falling film: (a) the 3D instantaneous at Re = 500 and q = 2.05 W/cm2 (the arrow indicates the flow direction) and (b) time dependence in the point of valley X = 75 mm between rivulets at Re = 300 and q = 1.5 W/cm2

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Fig. 7

Evolution of temperature pulsations and shear stresses in the interrivulets area near the lower edge of the heater, X = 100 mm, Re = 500, and q = 1.3 W/cm2. The arrows indicate the flow direction. The solid lines show the temperature isolines, indicating the approximate border of the area between the rivulets.

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Fig. 8

The density of spectral energy of temperature pulsations depending on frequency in the center of the interrivulet area at different distances from the upper edge of the heater: (1) X = 50 mm, (2) X = 75 mm, and (3) X = 100 mm

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Fig. 9

Integral energy of temperature pulsations per unit of time, averaged by all rivulets and interrivulet areas, depending on X: (a) Re = 150 and q = 2.5 W/cm2, (b) Re = 500 and q = 1.3 W/cm2, (c) Re = 500 and q = 2.9 W/cm2, and (d) Re = 500 and q = 8.6 W/cm2. Triangles (1) indicate data for the interrivulet areas and circles (2) for rivulets.

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Fig. 10

Plot of the maximum relative amplitude Amax versus Reloc/Kaloc1/11: (1) valleys (Re = 38 and Xp = 344 mm) [7], (2) data from Refs. [1] and [19] at the adiabatic conditions, (3) isothermal film (Xp = 360 mm) [17], (4) rivulets (Re = 38 and Xp = 344 mm) [7], (5) valleys (Re = 33 and Xp = 264 mm) [7], (6) rivulets (Re = 33 and Xp = 264 mm) [7], (7) valleys (Re = 300 and Xp = 360 mm), and (8) rivulets (Re = 300 and Xp = 360 mm)

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Fig. 11

The dependence of the modified Marangoni number on the dimensionless heat flux for the valley between rivulets: (1) Re = 300 valley between rivulets, (2) Re = 300 rivulet, (3) Re = 22 valley between rivulets [9], and (4) Re = 22 rivulet [9]. The solid line marked the averaged data for the valley between rivulets at Re = 300.




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