Roberta Perna

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University of Brighton

University of Brighton

C. de Falco

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Time-Frequency Analysis of a Thermally Induced Pulsating Slug Flow

The thermofluidic operation of two-phase heat transfer devices is affected by thermally induced f... more The thermofluidic operation of two-phase heat transfer devices is affected by thermally induced fluid oscillations of unknown frequency and amplitude. In line with previous studies, the time-frequency analysis of experimental signals is performed to investigate the existence of local characteristic frequencies. This work applies the wavelet transform to the evaporator fluid pressure signal of a passive two-phase heat transfer which can work as a Thermosyphon or as a Pulsating Heat Pipe, depending on the gravity acceleration. The results, obtained by means of a parabolic flight campaign, shows that the local characteristic frequencies are present only during the microgravity phase and in a frequency range from 0.8 to 2 Hz. Understanding the complex phenomena related to thermally induced oscillation is essential for the development of reliable heat transfer models and robust design tools for Pulsating Heat Pipes.

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Time-Frequency Analysis of a Pulsating Heat Pipe in Microgravity Environment

A pulsating heat pipe embedded radiator: Thermal-vacuum characterisation in the pre-cryogenic temperature range for space applications

Thermal Science and Engineering Progress, 2020

The use of Pulsating Heat Pipes (PHPs) in the space field is still an open issue because of the l... more The use of Pulsating Heat Pipes (PHPs) in the space field is still an open issue because of the lack of data obtained during actual operation in relevant environment. A considerable amount of data is available in the literature on the thermal response of PHPs to a variable gravity condition and on the operation in the cryogenic field but in both cases the heat load at the condenser is rejected by convection to a constant temperature sink. On the other hand, barely any work in the PHP's literature deals with thermal radiation to a low temperature sink as only heat transfer mode. The present work attempts to fill the gap by testing a PHP radiator (16 turns, 1.1 mm inner diameter, 50% filled with FC-72 at 293K) in thermo-vacuum conditions in horizontal orientation at different heat loads and different environment (chamber) temperature. Fluid pressure measurements coupled with the frequency analysis characterised the effect of the cold source temperature on the device operational limits and efficiency. Results show that the device thermal performance in the radiative configuration is mostly affected by the lower operating temperatures needed to obtain a sensible heat rejection, rather than the heat transfer mode itself. The decrease of the environment temperature shortens the operational heat load range: the start-up occurs at higher heat input levels while the thermal crisis occurs at lower heat loads. The frequency analysis reveals that the equivalent thermal resistance is positively affected by higher values of the dominant frequency for all the cases.

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Flow characterization of a pulsating heat pipe through the wavelet analysis of pressure signals

Applied Thermal Engineering, 2020

Pulsating Heat Pipes are two phase passive heat transfer devices characterized by a thermally ind... more 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 full-scale Pulsating Heat Pipe tested in microgravity conditions. During the slug-plug flow regime, the dominant frequencies falls in the range 0.6 − 0.9 , showing an increasing trend with the heat load input. The Cross-Correlation 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.

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Wavelet Analysis of the Pressure Signal in a Pulsating Heat Pipe

On the use of shape memory alloys for deployable passive heat radiators in space satellites

IOP Conference Series: Materials Science and Engineering, 2021

The present work presents a multifunctional structure for space engineering application part of t... more The present work presents a multifunctional structure for space engineering application part of the TOPDESS project, funded by ESA. The main aim of the project is the design of a thermal control device able to deploy through passive actuation. A combined device has been designed, made up of a Pulsating Heat Pipe (PHP) foldable heat exchanger and Shape Memory Alloy (SMA) wire. The deployment of the SMA wire is conceived to be controlled by thermal contact with the heat source and by conduction along the wire. Since the heat sources are lumped and the wire is subject to convection, a temperature gradient develops along the wire. A monodimensional mode able to predict the behavior of an SMA wire subjected to a spatial temperature gradient, is presented in this paper. The results show that the system can carry out folding and unfolding cycles with rotation angles greater than 80° only if the wire is subjected to uniform temperature distribution; in the case of temperature gradient, the ...

Time-Frequency Analysis of a Thermally Induced Pulsating Slug Flow

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Time-Frequency Analysis of a Pulsating Heat Pipe in Microgravity Environment

A pulsating heat pipe embedded radiator: Thermal-vacuum characterisation in the pre-cryogenic temperature range for space applications

Thermal Science and Engineering Progress, 2020

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Flow characterization of a pulsating heat pipe through the wavelet analysis of pressure signals

Applied Thermal Engineering, 2020

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Wavelet Analysis of the Pressure Signal in a Pulsating Heat Pipe

On the use of shape memory alloys for deployable passive heat radiators in space satellites

IOP Conference Series: Materials Science and Engineering, 2021

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