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Nanoparticle based direct absorption oscillating heat pipes for solar thermal systems

Final Report Summary - NANODAOHP (Nanoparticle based direct absorption oscillating heat pipes for solar thermal systems)

With diminishing availability of fossil fuels and increasing concerns on global warming, to develop sustainable and renewable energy technologies, especially solar energy related, becomes extremely important to secure our energy future. In the current project, a highly novel solar thermal technology, from both nanotechnology and phase change approaches, is proposed to address the limitations associated with conventional solar thermal collectors. In this project, direct absorption nanoparticles including Au, Ag and Cu are selected to overcome the surfaced-controlled heat transfer limitation by absorbing solar energy directly in the carrying fluid due to their strong local surface plasmonic resonance effect, and oscillating vapor bubbles are used to drive the fluid circulation instead of pumps. Experimental studies have validated the feasibility of this new concept, which has both scientific and application prospects. Scientifically, it extends the direct absorption nanoparticles into a phase change domain, and practically, it could promote the emergence of a new generation of solar collector.
A systematic study has been carried out in this project, to address the challenges associated with this novel concept, which extends from suitable direct nanofluids formulation, understanding the role of nanoparticles in the evaporation and condensation processes, to its performance in the oscillating heat pipe. The experimental results validated this innovative idea of a pump-free solar collector concept by using direct absorption nanoparticles for efficient solar energy harvesting. The results show that by using direct absorption gold nanoparticles, much higher amount of solar energy can be captured that allows a vigorous generation of bubbles, which enables the circulation of fluids between the evaporator and the condenser, and efficient transport of energy without using extra pumping power. The performance is however related to particle concentration and filling ratio. Different flow modes can be formed at different nanoparticle concentrations, and there is an optimum filling ratio to reach the minimum thermal resistance. Further optimization of the system is recommended on proper selection of nanoparticle type and nanoparticle concentration. Through the implementation of this project, potential long term collaborations and mutually beneficial co-operation between Europe and China has been created.