The main outcomes of a 10-year research activity on pool boiling in microgravity, carried out at Low Gravity and Thermal Advanced Research Laboratory of Pisa University, are summarized. A large part of the article also deals with the effect of electrostatic fields on microgravity boiling. The reported results were obtained in several microgravity experimental campaigns and mainly during one sounding rocket (MASER-8) and one orbital flight on the Russian satellite FotonM2. They refer to wire and plate heaters in FC-72, subjected to the action of strongly nonuniform and nearly uniform electrostatic fields, respectively. Long-term steady state nucleate boiling seems to be possible in microgravity, especially in subcooled conditions, though impaired bubble removal and coalescence lead to an increase of void fraction and could degrade nucleate boiling heat transfer and anticipate CHF. It has been shown that the addition of an appropriate electric field widens the nucleate boiling region (increase of CHF), and the heat transfer coefficient becomes almost insensitive to gravity. These effects are more marked on wires than on plates, where, due to the different field geometry, a higher voltage is needed to attain the same effect and demonstrate the progressive dominance of electric forces over buoyancy.
Pool boiling in microgravity: old and recent results
DI MARCO, PAOLO;GRASSI, WALTER
2007-01-01
Abstract
The main outcomes of a 10-year research activity on pool boiling in microgravity, carried out at Low Gravity and Thermal Advanced Research Laboratory of Pisa University, are summarized. A large part of the article also deals with the effect of electrostatic fields on microgravity boiling. The reported results were obtained in several microgravity experimental campaigns and mainly during one sounding rocket (MASER-8) and one orbital flight on the Russian satellite FotonM2. They refer to wire and plate heaters in FC-72, subjected to the action of strongly nonuniform and nearly uniform electrostatic fields, respectively. Long-term steady state nucleate boiling seems to be possible in microgravity, especially in subcooled conditions, though impaired bubble removal and coalescence lead to an increase of void fraction and could degrade nucleate boiling heat transfer and anticipate CHF. It has been shown that the addition of an appropriate electric field widens the nucleate boiling region (increase of CHF), and the heat transfer coefficient becomes almost insensitive to gravity. These effects are more marked on wires than on plates, where, due to the different field geometry, a higher voltage is needed to attain the same effect and demonstrate the progressive dominance of electric forces over buoyancy.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
