Performance Assessment of Ultrasonic Waves for Bubble Control in Cryogenic Fuel Tanks

Abstract

An efficient long-term storage of cryogenic pro-1 pellants is a challenge for future space exploration missions. 2The vapour bubbles formed as a result of boil-off in the tank 3 walls can generate foam structures, which could be hazardous 4 in different operations in orbit. A recently proposed approach 5 to control the dynamics of bubbles is based on the generation 6 of an acoustic field by means of a piezoelectric transducer.7This technology needs to be validated at cryogenic tempera-8 tures in order to be applicable in space. In this perspective, 9 different piezoelectric elements and matching layer materials 10 have been tested at cryogenic temperatures to assess their 11 performance at such environmental conditions. We consider 12 the use of soft PZT piezoceramics coupled with an epoxy 13 resin as the matching layer. Experimental data reveal that 14 epoxy resin-based acoustic matching layers exhibit a linear 15 increase in the transmittance of the acoustic amplitude at 16 cryogenic conditions. The peak-to-peak amplitude increases 17 as temperature decreases up to a factor of 1.6. This result 18 opens the possibility of generating and transmitting acoustic 19 waves at cryogenic temperatures, which could be used in 20 the recently proposed technology to control the dynamics of 21 vapour bubbles in cryogenic fuel tanks.

Trade-off analysis of phase separation techniques for advanced life support systems in space

“…Static-active techniques can be used to achieve phase separation with the aid of external forces different to centrifugal. Artificial accelerations may be created by thruster/rocket firings [22,23], or by by electric [24], magnetic [25], acoustic [26,27,28,29,30,31,32,33,34], or other external forces.…”

“…An acoustic technique for the management of vapor bubbles generated by boil-off in cryogenic fuel tanks in microgravity is currently under development [32,33]. In this approach, bubbles generated at hot spots in the tank are detached by means of controlled acoustic waves and moved to colder regions where they condensate.…”

Magnetic phase separation in microgravity

“…As an alternative, the use of electrohydrodynamic forces has been studied since the early 1960s 20 and successfully tested for boiling [21][22][23] , two-phase flow management 24,25 , and conduction pumping 26 applications. Hydroacoustic forces arising from the application of ultrasonic standing waves 27 have been used to enhance a wide variety of terrestrial processes 28 and are also proposed to control bubbly flows in propellant tanks 29,30 and life support systems 31 . Small amplitude vibrations can also be employed to manage multiphase flows and induce phase separation in microgravity 32 by selecting viscoequilibrium configurations 33 or exploiting frozen wave instabilities 34 .…”