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3
2009
INTRODUCTION TO THE SPECIAL ISSUE ON BOILING
185-186
10.1615/MultScienTechn.v21.i3.10
Olivier
Minster
Anne
Pacros
FLOW BOILING HEAT TRANSFER IN MICROGRAVITY: RECENT PROGRESS
187-212
10.1615/MultScienTechn.v21.i3.20
Gian Piero
Celata
ENEA, Institute of Thermal Fluid Dynamics, ENEA TERM/ISP Heat Transfer Laboratory C.R.E.
Giuseppe
Zummo
ENEA, Institute for Thermal Fluid Dynamics, via Anguillarese, 301, Rome, Italy
Flow boiling heat transfer (FBHT) can accommodate high heat transfer rates due to latent heat transportation. Its possible use is therefore potentially important to reduce the size and weight of space platforms and satellites. A comprehensive knowledge is also important for the safe operation of existing single-phase systems in case of accidental increase of the heat generation rate. For space applications, it is first necessary to identify the possible influence of microgravity conditions and, in the case of g influence, to evaluate the quantitative effect of reduced gravity on forced convective boiling heat transfer. The amount of existing research on flow boiling in reduced gravity is very small due to large heat loads required and reduced available room in a 0-g apparatus for experiments, as well as complexity of the experimental facility for microgravity environment. As can be expected, because of the reduced available data, coherence in existing data is missing. This paper will summarize the results of the research carried out on FBHT in microgravity, with special emphasis to the recent research carried out at ENEA, in the frame of an European Space Agency project.
STEADY MICROSTRUCTURE OF A CONTACT LINE FOR A LIQUID ON A HEATED SURFACE OVERLAID WITH ITS PURE VAPOR: PARAMETRIC STUDY FOR A CLASSICAL MODEL
213-248
10.1615/MultScienTechn.v21.i3.30
Alexey Ye.
Rednikov
Universite libre de Bruxelles, TIPs, CP 165/67, Av. F.D. Roosevelt 50, 1050 Brussels, Belgium
S.
Rossomme
Université Libre de Bruxelles, TIPs-Fluid Physics, CP 165/67, 50 Avenue F. D. Roosevelt, 1050 Brussels, Belgium
P.
Colinet
Université Libre de Bruxelles, TIPs-Fluid Physics, CP 165/67, 50 Avenue F. D. Roosevelt, 1050 Brussels, Belgium
On the basis of a standard one-sided lubrication-type model, an analysis is carried out pertaining to a small vicinity of a contact line of a volatile nonpolar perfectly wetting macroscopic liquid sample surrounded with its pure vapor and attached to a smooth uniformly superheated solid surface. The behavior of the liquid film is governed by the effects of evaporation, capillarity, and the disjoining pressure. The kinetic resistance to evaporation, as well as the dependence of the local saturation temperature on the local liquid pressure are accounted for. Within the localized approach pursued, a steady configuration of the film on a flat substrate is studied such that at one end (say, to the left) it asymptotically attains an adsorbed microfilm in equilibrium with the vapor, while to the right it gets on to a constant slope (contact angle of the "microstructure"). For moving contact lines in the situations like drop spreading or bubble growth in the boiling process, this microstructure is relevant in the quasi-steady sense, provided that the displacement velocity is not too large. The paper focuses on a numerically based parametric study expressing the contact angle and evaporation flux characteristics as functions of the system parameters. Asymptotic expansions at both ends of the film are elaborated in some detail and relied on in the numerics. Asymptotic results from the literature involving certain limiting cases of the system parameters are critically examined. At last, the Marangoni and the vapor-recoil effects are additionally incorporated and their possible importance is assessed.
EFFECT OF SHEAR STRESS AND GRAVITY ON RUPTURE OF A LOCALLY HEATED LIQUID FILM
249-266
10.1615/MultScienTechn.v21.i3.40
Oleg A.
Kabov
Kutateladze Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences, 1, Acad. Lavrentyev Ave., Novosibirsk, 630090, Russia; Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia; Novosibirsk State Technical University, 20 Prospect K. Marksa, Novosibirsk, 630073, Russia
Dmitry V.
Zaitsev
Kutateladze Institute of Thermophysics SB RAS, 1, Lavrentiev Ave, Novosibirsk, 630090, Russia; Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia
Thin liquid films driven by a forced gas/vapor flow (stratified or annular flows) (i.e., shear-driven liquid films in a narrow channel) are promising candidates for an innovative cooling technique optimizing the trade-offs between performance and cost. The present work is a part of the MAP BOILING program of the European Space Agency and a part of the preparation of the SAFIR experiment onboard the International Space Station. The paper focuses on the recent progress that has been achieved by the authors through conducting experiments with locally heated shear-driven and falling liquid films. Rupture of the liquid film was investigated, and it was found that scenario of film rupture differs widely for different flow regimes. The critical heat flux is ~ 10 times higher for a shear driven film than that for a falling liquid film and reaches 250 W/cm2 in experiments with water at atmospheric pressure. Rupture of a subcooled falling liquid film heated from the substrate is preceded by the formation of steady-state film surface deformations. The film spontaneously ruptures at the moment when the film thickness in the thinned region reaches a certain critical minimum independent of both the Reynolds number and the plate inclination angle (gravity force). By means of high-speed imaging, it is found that the process of rupture involves two stages: (i) abrupt film thinning down to a thin residual film and (ii) rupture and dryout of the residual film. As the plate inclination angle is reduced, the threshold heat flux required for film rupture weakly decreases; however, when the angle becomes negative, the threshold heat flux begins to rise dramatically, which is associated with an increase of the stabilizing hydrostatic effect due to the growth of the film thickness. Procedures to organize a gas shear-driven liquid film flow under variable gravity conditions (parabolic flights) have been verified. It was found that the flow dynamics in normal gravity differs significantly from that in microgravity; in particular, the film is wavier under low-gravity conditions.