| Author: | Lin, Yao |
| Title: | Dynamic heat and mass transfer characterization and performance enhancement of absorption thermal energy storage system |
| Advisors: | Wang, Shengwei (BEEE) Xiao, Fu (BEEE) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Department: | Department of Building Environment and Energy Engineering |
| Pages: | xvi, 139 pages : color illustrations |
| Language: | English |
| Abstract: | The pursuit of sustainable energy solutions has led to the development of advanced thermal energy storage (TES) systems. Among various TES technologies, absorption TES offers several advantages over sensible and latent TES, including high energy storage density (ESD), minor heat loss, high flexibility, and potential for long-term and mobilized storage. The ESD is the main performance criterion of the absorption TES system. Expanding the concentration difference of the working fluids is recognized as the most effective method for enhancing ESD. However, the large concentration difference could also increase the crystallization risks, which poses a challenge to the exploitation of ESD potential in current research. Besides, despite the promising ESD potential indicated by thermodynamic modeling in existing studies, there is a scarcity of experimental studies examining the dynamic characteristics and energy performance of the absorption TES systems. The main reasons lie in insufficient heat and mass transfer performance within the heat exchangers, which are critical components of the absorption TES system. Therefore, this research aims to enhance the ESD of the absorption TES system at material, cycle, component, and system levels. The main works and contributions of this research are detailed as follows. Firstly, a novel modified LiCl solution is developed for three-phase absorption thermal energy storage. Ethylene glycol (EG) and silica nanoparticles (SNPs) are introduced as additives into the LiCl solution. EG enhances the solubility of LiCl, while SNPs facilitate the growth suspension of fine LiCl crystal slurry in the saturated LiCl solution. The effects of EG and SNPs on the thermal and physical properties of LiCl solution are investigated. A three-phase absorption TES cycle using novel working fluids is proposed, and the ESD of the modified solution is assessed. The results show that the modified working fluids have a significant ESD enhancement potential. Secondly, a closed absorption TES test rig with novel designed heat exchangers has been built. The dynamic heat and mass transfer characteristics and the energy performance of the two-phase absorption TES system are studied experimentally. The impact of the mass fraction of EG and working conditions are revealed experimentally. The results show that the ESD ranges from 108-177 kWh/m³ at different working scenarios, with an enhancement of 18-48%. Thirdly, experimental studies of three-phase absorption TES are conducted. The dynamic charging and discharging characteristics and performance evaluation of the three-phase absorption TES system are conducted experimentally. The ESD is further enhanced by 19.3%-80.3% compared with two-phase absorption TES. After that, a closed three-phase absorption TES model is developed and validated using experimental data. The model is then used to simulate the performance under all working conditions, providing a comprehensive understanding of the system's capabilities. Finally, the proposed closed three-phase absorption TES system using novel working fluids is investigated with a distributed energy system. An enhanced load following strategy considering the state of storage system is proposed for system capacity design and operational control. The dynamic response, storage performance, and energy-saving potentials are investigated on the TRNSYS simulation platform, which further extends the application of the absorption TES system. This PhD study can be regarded as a seminal work in the research field, providing substantial and valuable insights and references for absorption thermal energy storage, with focuses on working fluids modification, dynamic heat and mass transfer characterization, experimental investigation on cycle performance, and the integration with distributed energy system. Additionally, it has the potential to catalyze the development of related industries, especially heat exchanger and absorption machine industry. |
| Rights: | All rights reserved |
| Access: | open access |
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