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Abstract
Pulsating Heat Pipes are two phase passive heat transfer devices characterized by a thermally induced two phase oscillating flow. The correct detection of the dominant frequencies of such oscillations is fundamental to fully characterize the device thermofluidic operation but the studies available in the literature are very heterogenous and results are often discordant. In this work, the concept of dominant frequency in Pulsating Heat Pipes is thoroughly discussed and defined analytically. The wavelet transform is used to characterize the fluid pressure signal in the frequency domain varying the heat power input at the evaporator and in the condenser zone of a fullscale Pulsating Heat Pipe tested in microgravity conditions. During the slugplug flow regime, the dominant frequencies falls in the range 0.6–0.9 Hz, showing an increasing trend with the heat load input. The CrossCorrelation reveals that the two signals at the evaporator and at the condenser are very similar. Finally, the instantaneous angle of phase is calculated and lies between 310 and 360 deg. This value can be physically interpreted as a repeatable time shift between the two signals that can be used to evaluate the flow local mean velocity (0.09–0.13 m/s) constituting a valuable alternative to the visualization techniques.
Original language  English 

Article number  115128 
Journal  Applied Thermal Engineering 
Volume  171 
DOIs  
Publication status  Published  27 Feb 2020 
Keywords
 Pulsating Heat Pipe
 Frequency
 Wavelet Cross Correlation
 Flow velocity
 Wavelet cross correlation
 Pulsating heat pipe
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67th European Space Agency Parabolic Flight Campaign
Luca Pietrasanta (Participant)
16 Nov 2017Activity: Events › Event