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International Heat Transfer Conference 13

ISBN Imprimir: 1-56700-226-9 (CD)
ISBN En Línea: 1-56700-225-0


DOI: 10.1615/IHTC13.p28.330
page 12

Paolo Di Marco
Department of Energy, Systems, Constructions and Territory Engineering, University of Pisa, largo Lucio Lazzarino 1, 56122 PISA Italy

Walter Grassi
Lo.Th.A.R. (Low gravity and Thermal Advanced Research Laboratory), DESTEC (Department of Energy, Systems, Territory and Constructions Engineering), University of Pisa−Largo Lucio Lazzarino, 56122 Pisa, Italy


The ARIEL experiment was flown on June 2005 aboard of Foton-M2 satellite, and hosted in FLUIDPAC facility, taking advantage of its optical diagnostics and power systems. Its aim was to investigate boiling heat transfer in microgravity on a surface of industrial relevance, at high heat rates. Besides, the effect of an externally applied electrostatic field on boiling performance was tested. The heater consisted of a flat, semi-transparent, 20×20 mm, gold layer (40 nm thickness) sputtered on a ZnS substrate and directly heated by direct current. The working fluid was FC-72 filling a one-liter volume cell, with a bellows operated by nitrogen to control pressure and allow for fluid dilatation. The electrostatic field was imposed by applying up to 10 kV dc to an array of 5 rods laid parallel to the surface, 5 mm apart of it. Optical visualization of the boiling flow patterns from one side and through the heated surface was possible, as well as qualitative infrared mapping of the wall temperature. The boiling curve was derived from voltage and current measurements across the heated surface, after an appropriate data reduction.
The experiment was run for four days in an excellent microgravity environment: several levels of liquid subcooling (from 20 to 6 K) and heat fluxes up to 200 kW/m2 were tested. The experiment revealed interesting and somewhat unexpected features of boiling process in microgravity; as far as known no tests over a large surface at so high heat flux levels were ever run before. A complete counterpart test, carried out on ground before the mission, allowed direct comparison with terrestrial data. The void fraction in microgravity revealed much larger than in normal gravity condition: according to the images transmitted, this may be attributed to increased bubble coalescence that hinders vapor condensation in the bulk of the subcooled fluid. The electric field confirmed to be very effective, even at low values of applied voltage, in reducing bubble size, thus improving their condensation rate in the bulk fluid, and in enhancing heat transfer performance, by increasing the heat transfer coefficient and delaying the onset of surface dryout.

IHTC-13 Digital Library

Measurement of fluid temperature with an arrangement of three thermocouples FLOW BOILING OF A HIGHLY VISCOUS POLYMER SOLUTION