Figure 12 compared the results of four different experiments performed with FC-72 sprayed onto the copper-block heater at nearly the same volume fluxes. The parameters of interest here are the gravity level and We. The heat transfer in the film boiling region suffers a substantial deterioration with a reduction in gravity when We is low (less than 80), but does not when We is rather high. These results are consistent with those for water exemplified in Fig. 8 (We = 33) and Fig. 9 (We = 622).

CONCLUDING REMARKS

　　A series of spray cooling experiments were carried out over a wide range of target-surface superheat under reduced and elevated gravity conditions. As far as the gravity effect is concerned, the present experiments have provided the following new findings. 1. The gravity dependency of spray cooling heat transfer characteristics alters with a variation in the spray volume flux over the target surface. The CHF and the heat fluxes at given superheatings in the transition boiling region are increased with a reduction in gravity when the spray volume flux is high enough to cause formation of liquid films on the surface. This gravity effect is not available at lower spray volume fluxes. 2. When We for impinging droplets is low (typically less than 80), the heat transfer in the film boiling region is considerably deteriorated with a reduction in gravity. This fact is ascribed to a reduction in the contribution of rebounding droplets to the heat removal from the surface with a reduction in gravity.

ACKNOWLEDGMENTS

　　The present authors would like to express their sincere gratitude to the staff of the Diamond Air Service and Mr. N. Saito of IHI for their faithful assistance during the parabolic flight campaign. The main part of the present study was financially supported by the Science and Technology Agency, Japan.

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