Development of capillary-assisted low pressure evaporator for adsorption chillers
Notice bibliographique
Résumé
The sales of air conditioners are poised to intensely increase over the next several years as incomes and global temperatures rise around the world. Conventional air conditioning systems use vapor-compression refrigeration (VCR) technology that has been the dominant technology for close to a century. However, the environmental impact of VCR systems, particularly their high energy consumption, around 36% of energy consumed in the US building sector, is contrary to sustainable development. In addition to the residential sector, VCR systems for vehicle air conditioning (A/C) applications can cause a 20% increase in fuel consumption. Moreover, while the commonly used refrigerants in VCR systems, hydrofluorocarbons (HFCs), are ozone-friendly, they still contribute to global warming. Alternative, natural refrigerants, such as water, have no toxicity and significantly lower global warming potential compared to HFCs. Furthermore, water is an ideal refrigerant for systems driven by low-grade thermal energy. Solar-thermal and waste-heat from industrial facilities and data centers are all abundant sources of low-grade thermal energy, with a temperature less than 100°C. Low-grade thermal energy can be used to run adsorption chillers for air conditioning of vehicle cabins and residential units. When using water as an air conditioning refrigerant, evaporation occurs at pressures below an atmosphere. In such a low pressure (LP) environment, the performance of a flooded evaporator is negatively affected by the hydrostatic pressure. This problem can be resolved by using a capillary-assisted low-pressure evaporator (CALPE) that exploits thin film evaporation. The focus of this doctoral research is to develop an effective CALPE for proof-of-concept demonstration of an adsorption chiller for vehicle A/C applications. In this research, a low pressure evaporator testbed is designed and built for the first time at Laboratory for Alternative Energy Conversion (LAEC) to test CALPE. In addition, a mathematical model is developed to understand detailed phenomena in capillary-assisted evaporation and to provide insight to design an effective and compact CALPE. Several commercial tubes with different fin geometries are tested. The results show that the capillary-assisted tubes provide two times greater heat transfer rate compared to a plain tube. To further enhance the performance, the outside surfaces of CALPE are coated with a thin film of porous copper to increase the capillary action and the surface area available for thin film evaporation. The coating increased the overall heat transfer coefficient by 30%. However, a significant amount of the thermal resistance is from the inside of the evaporator tubes. Therefore, a new µCALPE is designed with microchannels on the inside and rough capillary channels on the outside is 3D printed by using direct metal laser sintering process. The internal microchannels and external capillary channels led to enhanced heat transfer both internally and externally. The µCALPE increased the overall heat transfer coefficient by a factor of 2.5 when compared to the CALPE built with commercial Turbo Chil-40 FPI tubes, which had footprint of four times larger than that of µCALPE. The developed µCALPE is expandable to the entire low-grade thermal energy driven A/C systems in vehicles as well as residential units.
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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) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,001 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,003 | 0,002 |
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 ».