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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - NPMSSES (Nanoparticle Enhanced Molten Salts for Solar Energy Storage)

Teaser

Summary

Thermal energy storage is a useful method to adjust temporal mismatch between the demand and supply of solar energy systems, and latent heat thermal energy storage (LHTES) using phase change material (PCM) has drawn increasing attentions for its high energy storage density and small temperature variation. Molten salt is a promising candidate for solar energy storage media at middle temperature range (140~300 oC). However, the low thermal conductivity of pure salt hampers the development of this technology. This proposal aims to introduce high conductive nanoparticles (NP) and metal foam to improve the stability and thermo-physical properties of conventional PCMs for solar energy storage, termed as NPMSSES. Solar salt and HITEC salt were used as the matrix, and aluminum oxide (Al2O3) nanopowder and graphene were applied to enhance pure salt. This work have successfully addressed four main tasks: i) synthesis and characterization of composite PCMs with good stability ii) identification thermo-physical properties of salt/metal foam composites seeded with nanoparticles under high temperature, e.g. measuring the dynamic viscosity of nanocomposite; iii) experimental investigation a solar energy storage unit infiltrated with composite PCMs, and iv) cascaded latent heat thermal energy storage with composite PCMs and optimize the performance of the system. The fellowship has highly beneficial to establish myself as an independent researcher, and new career perspectives are achieved for a faculty position. Various outreach activities have been are designed and done, which strengthen the impact on nanotechnology and energy issues.

Work performed

WP1:
Solar salt and HITEC salt as typical molten salts were used as the base PCMs. Aluminium oxide (Al2O3) nanopowder and graphene with different mass fractions, and metal foam with the porosity of 95.0% were added into salt, respectively. The salt/metal foam composites seeded with nanoparticles were prepared and characterized subsequently. The morphologies of the composites were extensively characterized with SEM, XRD and FT-IS.
WP2:
The effective thermal conductivities of the salt/metal foam composites seeded with Al2O3 nanopowder or graphene were theoretically predicted with the models, while differential scanning calorimeter (DSC) and Thermo-gravimetric Analyser (TGA) were used to characterize the thermal behaviour of the composites. It is also indispensable to understand and characterize the viscosities of nanocomposites, which would provide basic information for the experimental and numerical researches on how nanoparticles affect the flow of liquid salt fluid. Thus the dynamic viscosity of pure salt and salt/nanoparticles composite were tested under high temperature.
WP3:
None of the previous studies reported heat transfer study of nanocomposite with and without porous medium in a large scale rig setup. A pilot experimental rig was built to investigate the performance of salt, nano-salt (salt with 2 wt.% Al2O3) and nano-salt/copper foam composite as storage media. Heat storage and retrieval tests in the storage system were conducted at various heating temperatures, and the temperature distributions of the PCMs at different locations were measured, including radial, theta, and axial locations. The results show that both Al2O3 nanopowder and copper foam can significantly improve the heat transfer of pure salt, e.g., the time-duration of heat storage can be reduced by 46.6% and 70.7% for nano-salt and nano-salt/copper foam composite, respectively.
WP4:
HITEC salt, solar salt and pure sodium nitrate with the volume ratios of 1:1:1 were used as the PCMs, and the oil was adopted as the HTF. An enthalpy-porosity model was developed to numerically investigate the heat transfer characteristics of the shell-tube LHTES unit. Various structures infiltrated with the PCMs were studied to optimize the performance of the LHTES unit, while different mass flow rates and inlet temperatures of oil were carried out simultaneously. Temperature evolutions showed that the charging process were enhanced by the nanoparticles with high thermal conductivity.

Final results

The impact of the research can be divided into two parts:
i) New career perspectives
Energy and environmental concerns have promoted rapid development of renewable energy technologies especially solar energy, latent thermal energy storage (LTES) using phase change material (PCM) is an effective method to adjust temporal mismatch between the demand and supply of solar energy systems. This NPMSSES research project has contributed towards high efficiency of solar energy storage.
High motivation and initiative in leading the project has helped the fellow formulate independent and critical thinking capability, and possessed all needed project management and leadership skills needed for a faculty position. Nanotechnology and energy solution in China is regarded as a means of national development. The theoretical and experimental expertise in the field of nanotechnology will complement the line of research on solar energy application. I have successfully obtained the offer of associate professor from DHU (Donghua University).
In addition, Dr Weiping Wu, who is a lecturer from City University of London and Group Chair of Society of Chemical Industry, recommended a collaboration work of high efficiency solar absorption and water steam generation. Dr Wenjing Ding, who is the sub-team leader of thermal process technology of German Aerospace Center, suggested the measurement of effective thermal conductivity of salt at high temperature. Those collaboration will lead to a new international partnership between EU and China.
ii) Communication and results dissemination
In this fellowship, various outreach activities have been are designed and done, which will aid me to understand better public interests. Those activities strengthen the impact on nanotechnology and energy issues, as outlined below.
i) At the beginning, I gave a presentation of the previous research and work plan in the group meeting. I had a good discussion with PhD candidate Afrah about the solar energy storage research at host organization.
ii) I attended the UK Particle Technology Forum 2017 at University of Birmingham, had in-depth discussion with the participants, and built the collaboration with Birmingham Centre for Energy Storage.
iii) In order to broaden the impact of the research on nanotechnology and energy storage, I attended the School Internal Research Exchange Event on Jan 18th, 2019. I presented my report in the panel of sustainable systems processes, and had rich discussion with the researchers at School of Chemical and Process Engineering.
iv) I presented the report â€œSynthesis and characterization of salt/metal foam composite seeded with nanoparticles and application to performance enhancementâ€ in our group meeting on July 31th, 2018, which is related to the whole progress of my Marie Curie Fellowship. I had a good discussion with group members, including line manager, research fellow and PhD candidate, several good suggestions were recommended by the team.
v) I attended 25th Annual Conference of CSCST-SCI, and won a third prize of excellence in Chemical Research for oral presentation. This annual conference helped me discuss with the researcher of Chemical Science and Technology in the UK, and I became a member of Society of Chemical Industry.