Critical boiling phenomena observed in microgravity

Details Critical boiling phenomena observed in microgravity Critical boiling phenomena observed in microgravity

Jan 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aipc..504..737g&link_type=abstract

SPACE TECHNOLOGY AND APPLICATIONS INTERNATIONAL FORUM - 2000. AIP Conference Proceedings, Volume 504, pp. 737-743 (2000).

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Testing In Microgravity Environments, Liquid-Vapor Transitions

Scientific paper

Singular thermodynamic properties of pure fluids near their critical point (diverging specific heat and isothermal compressibility, vanishing thermal conductivity,...) lead to poor thermal diffusion, a large convective sensitivity, and a special heat transfer process through adiabatic compression, the so-called piston effect. The discovery and extensive study of the piston effect were performed in conditions of weightlessness to avoid convection. Although its mechanism in the supercritical range is now well understood, its coupling with an inhomogeneous density distribution and mass transport in the two-phase regime has been relatively less studied and remains puzzling. Recent experiments performed in the French Alice 2 facility built by CNES onboard the Mir station showed undoubtedly that when a liquid-vapor system of SF6 near its critical temperature is heated in microgravity, the apparent contact angle becomes very large (up to 110°). In this slightly out-of-equilibrium configuration the gas appears to ``wet'' the solid surface. In addition, the temperature of the vapor becomes higher than that of the hot wall, whereas the temperature of the liquid evolves qualitatively as in the one-phase regime. Although the difference between the compressibility of liquid and vapor explains a higher vapor temperature compared to the liquid temperature, this paradoxical observation has not yet been modeled. Moreover, the phase distribution plays an important role in the efficiency of the heat transfer near the critical point. A three domains model valid at short time scale is presented. It is similar to the model of supercritical piston effect from Onuki, Hao and Ferrel (Onuki, 1990a), and takes into account the presence of a liquid wetting layer. Indeed, the thermal boundary layer only develops inside the liquid phase and compresses the vapor phase, in contrast to the situation in the one-phase regime. The leading characteristic time of the piston effect in the two-phase regime depends on the compressibility ratio between the two phases. It is larger than for a single liquid phase. Good agreement is obtained between the experimental and theoretical temperature evolution curves in both phases. .

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