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Title: Fabrication, characterization and thermo-physical properties of micro- and nano- scaled phase change materials for thermal energy storage
Author: Zhang, Guanhua
ISNI:       0000 0004 2749 1081
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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Latent heat storage is one of the most efficient ways of storing thermal energy. Organic phase change materials are latent heat storage materials and they have been widely used as suitable materials for thermal energy storage applications due to their high latent heat and small temperature difference between storing and releasing heat. In this thesis, micro- and nano- scaled phase change materials were fabricated for thermal energy storage. A novel microencapsulated phase change material slurry (MPCS) was introduced by dispersing microencapsulated phase change materials (MEPCMs) into water with an amount of surfactants and its thermal and rheological properties were also investigated. The results showed that MPCS fabricated in the current research are suitable for potential application as heat transfer media in the thermal energy storage. A new methodology was proposed to investigate the heat transfer characteristics of MPCSs. Experiments were carried out in laminar, transition and turbulent flow for MPCSs in a circular tube under constant heat flux, respectively. The experimental results demonstrated that in comparison to water as a heat transfer fluid at the same flow rate, the heat transfer of 10 wt. % MPCS could be enhanced by 10 % in transition flow condition while the PCM particles were in solid/liquid state, and the heat transfer of 5 wt. % MPCS could be enhanced by 21.9 % and 19.2 % in turbulent flow condition while the PCMs are in solid and solid/liquid states, respectively. Nevertheless, the heat transfer enhancement depends on the combination factors, including concentration of the slurry and flow rate of the slurry. A novel heat transfer fluid containing microencapsulated phase change material and multi-walled carbon nanotubes was prepared. The results showed that addition of MWCNTs to microencapsulated phase change material slurry can effectively improve the thermal conductivity of suspensions and it is also found that a blend of 10 wt. % MEPCM and 1 wt. % MWCNTs suspension can achieve the best thermal performance and stability among other blends in the experiment. A novel nanocapsule containing n-octadecane with an average 50 nm thick shell of poly (ethyl methacrylate) (PEMA), and with a core/shell weight ratio of 80/20 was synthesized by direct miniemulsion method. The results showed that PEMA/octadecane nanocapsule had good thermo-physical properties and had much higher encapsulation ratio (89.5%) and encapsulation efficiency (88.9%). For the first time, a novel PCM nanoparticle suspension (nano-PCS) was synthesized by direct miniemulsion method for thermal energy system application. It was found that the nano-PCSs had good thermo-physical properties and durability. All nano-PCSs presented narrow size distribution and stable particles. In comparison to the convectional PCM emulsion and MPCS, the nano-PCS tends to be more stable and is much easier and cheaper to fabricate in terms of the method and materials used, however, the heat transfer characteristics of the nano-PCS require further experimental investigation
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC) (EP/F061439/1) ; Guo jia zi ran ke xue ji jin wei yuan hui (China) (National Natural Science Foundation of China) (NSFC) (51071184) ; Birmingham Science City (SY/SP8008) ; School of Engineering ; University of Warwick
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TA Engineering (General). Civil engineering (General) ; TJ Mechanical engineering and machinery