In-situ acoustic detection of critical heat flux for controlling thermal runaway in boiling systems

Heat transfer deteriorates and thermal runaway is observed due to the formation of a vapor blanket during boiling crisis. Such temperature excursions are undesired in practical applications and may cause device failure. Inherent complexities and the associated uncertainties with boiling systems have not allowed development of robust critical heat flux (CHF) prediction tools. Hence, a high factor of safety is adopted, limiting the practical application of boiling to low heat flux nucleate boiling regime only. Here we identify a unique feature in audible acoustic emissions wherein a sudden shift in peak frequency from approximate to 200 - 250 Hz in the nucleate boiling regime to approximate to 400 - 500 Hz is observed at CHF. We show that a simple threshold-based feedback control strategy with a threshold frequency can be used to accurately detect the CHF and turn off the system to minimize thermal runaway. We show that the control strategy is equally robust on smooth and nanostructured copper surfaces. We believe that the ability to detect CHF and then power down the system within one second avoids transition to the undesired film boiling regime and is critical for safety and reliability of boiling-based systems and devices. (C) 2019 Elsevier Ltd. All rights reserved.