Acoustic effects on heat transfer on the ground and in microgravity conditions

A critical issue in future long-term space exploration missions is the storage and management of cryogenic propellants. Storage tanks are exposed to extreme temperatures and radiation, which can generate hot spots on the tank internal walls even with an efficient temperature insulation. Counteract the effects of the sources of heat on the propellant is a necessity as vapor bubbles may be created, which can become dangerous for some engine components apart from decreasing the amount of available propellant. We present an experimental study carried out in terrestrial gravity and in microgravity conditions on the effects of acoustic actuation in the heat transfer between a two-dimensional heating element and a liquid in a nucleate boiling regime. Two configurations of the heater orientation with respect to the direction of propagation of the acoustic wave and several acoustic frequencies were considered. Heater surface temperature and heat flux were measured in all the performed tests. Acoustic actuation in microgravity increased the heat flux from the heater to the liquid an 8.6% in comparison with the gravity scenario without actuation, and an 8.4% in comparison with a microgravity scenario without actuation. The heat transfer enhancement is larger at frequencies providing higher acoustic amplitudes, which are the frequencies close to the nominal frequency of the piezoelectric acoustic actuator. The influence of the material of the heater substrate on the acoustic field plays a role in the behavior of temperature and heat flux. The results of this work show that acoustic actuation is a feasible approach for the thermal management of boil-off in cryogenic propellants. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )