Thermal Science and Engineering
Online ISSN : 1882-2592
Print ISSN : 0918-9963
ISSN-L : 0918-9963
Volume 14 , Issue 2
Showing 1-2 articles out of 2 articles from the selected issue
  • Masaki KUDO, Hiroshi KAWAMURA
    2006 Volume 14 Issue 2 Pages 19-25
    Published: 2006
    Released: October 26, 2007
    A new scheme of active control was tested on nonlinear thermocapillary convection in a half-zone liquid bridge of a high Prandtl number fluid. In the half-zone method, two co-axial cylindrical rods hold a liquid bridge by surface tension. By applying a temperature difference between the rods, a thermocapillary flow is induced in the liquid bridge. The convection changes from a two-dimensional steady flow to a three-dimensional oscillatory one at a critical value of temperature difference or of Marangoni number. The control was realized by introducing concentric circular wire heater in order to heat round of the liquid bridge azimuthally. With this control scheme, one can suppress the oscillatory convection without minding the spatio-temporal fluctuation of the temperature over the free surface. The comparison between the present control scheme and the previous local heating by our group was conducted in terms of the time series of the surface temperature variations and the visualized flow field from the top. The experiment was conducted on a unit-aspect-ratio liquid bridge where the most unstable azimuthal mode had wavenumber 2 without control. The control with the present scheme achieved more significant attenuation of the temperature oscillation for a wider range of Marangoni number. The amplitude of the oscillation was able to be suppressed to a few percent of the initial value up to about 200 percent of the critical Marangoni number. The dependence of the control performance upon the position of the heater was investigated and found significant for both the control schemes. A mechanism of the stabilization from the oscillatory to the steady flow was examined. The stabilization is due to the reduction of the thermocapillary flow caused by the variation of the axial surface temperature distribution.
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  • Masakazu OBA, Fumio TAKEMURA, Akira YABE
    2006 Volume 14 Issue 2 Pages 27-33
    Published: 2006
    Released: October 26, 2007
    For realizing high heat flux cooling to control the temperature of high energy consumption devices such as high coherency laser diodes, a new idea utilizing the thermoelectric property difference of dissimilar metals has been experimentally demonstrated. By measuring the thermoelectric potential for the thermoelectric cooling devices composed of several kinds of metal electrode, the combination of metals has been selected to obtain the largest thermoelectric potential. Then, the maximum value of the cooling heat flux has been experimentally obtained for the selected composition of the thermoelectric devices utilizing dissimilar metals. The thermoelectric potentials have been measured for the combination of three kinds of metal electrodes and n-type and p-type thermoelectric materials (TEM) in π-shape structure accompanied with positive electrode of Pt without solder. Temperature distribution was measured by thin film thermocouples and optical thermography. Consequently, by using the two kinds of electrode metal for the combination of Pt (+electrode) - n-type TEM - Pd - p-type TEM—Pt (-electrode), the maximum value of the thermoelectric potential was obtained. Furthermore, by utilizing the three kinds of metal for the combination of Pt (+electrode) - n-type TEM - Pd - p-type TEM—Au (-electrode), a larger value of the thermoelectric potential was obtained. With the utilization of the three kinds of dissimilar metals, maximum heat flux for the thermoelectric cooling device has been enhanced up to 2.3 W/cm2 by a factor of 1.4 compared with the case using one kind of metal.
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