Enhancing the performance of a self-oscillating fluidic heat engine (SOFHE) through thermodynamic cycle and phase change characterization
Notice bibliographique
Résumé
The aim of this thesis is to better understand the working principles of a recently discovered self-oscillating fluidic heat engine (SOFHE) by characterizing the thermodynamic cycle (P-V diagram) and phase change (evaporation-condensation). The SOFHE is proposed for thermal energy harvesting, coupled with an electromechanical transducer, for powering wireless sensors used in the Internet of Things (IoT). The SOFHE is a vapor bubble trapped by a liquid plug (acting as a piston) in a small diameter tube. This vapor bubble-liquid plug is set in oscillations by a cyclic evaporation-condensation of a thin liquid film formed by a wicking fiber. The first experimental demonstration of the SOFHE showed a low electrical power of 1 μW. However, it is still unclear how the unknown thermodynamic cycle of the SOFHE behaves under a load and how much mechanical power density the SOFHE can generate. To address this question, the thermodynamic cycle and power density of the SOFHE are experimentally characterized for the first time under a varying mechanical load. The main contribution of this characterization is to provide a baseline for impedance matching that is crucial for designing a compatible load for the SOFHE. It is also shown that the mechanical power density of the SOFHE is in the range of milliwatts/cm3 (maximum 0.5 mW/cm3) which makes it a promising solution to power a range of wireless sensors with a power requirement of tens of microwatt. We also studied the effect of the operating heat source temperature and two design parameters, including the length of the wicking fiber and the length of the liquid plug on the power of SOFHE. The significant increase of the power by increasing the fiber length was the driving force behind the second phase of our study in which we characterized the complex and unknown phase change profile (evaporation-condensation) of the SOFHE. A new setup was designed to visualize the variation of the thin film around the fiber as we played with its length inside the vapor zone. The observations proved our hypothesis of forming capillary corners between the fiber and the inner wall of the tube that pumps liquid from the liquid plug toward the vapor zone. This leads to the formation of a thin film with a very small thermal resistance that feeds evaporation. The rate of change of mass of vapor, the so-called phase change rate, is also measured. It is shown that to maximize the amplitude of the oscillation and consequently the power of the SOFHE, the amplitude of the phase change rate should increase and be completely out of phase with the position. A dimensionless number is also proposed to evaluate the effectiveness of the phase change rate profile. Finally, to better control the phase change, a new design of the SOFHE is proposed in which we can integrate tailored wicking structures to mimic the effect of the inserted fiber. The device is a square cross-section microchannel with sharp corners as well as an etched capillary path on the bottom wall that is fabricated by a standard microfabrication process. It is shown that the amplitude and consequently the power of SOFHE increase (a fivefold increase from 30 to 150 μw/ cm3) as we add a capillary path. This opens a new path towards engineering the phase change of the SOFHE by designing different wicking structures to improve its performance.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».