This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Nanoparticle-based direct absorption system is a recent development, which employs nanoparticles to absorb and convert solar energy directly into thermal energy within the fluid volume. This work reports for the first time the use of plasomic nanoparticles (PNPs) to improve the direct photo-thermal conversion efficiency. Rod-shaped silver nanoparticles are synthesized and used as an example to illustrate the photo-thermal conversion characteristics of PNPs and the effect of particle shape. The result reveals a significant role of particle morphology on the photo-thermal conversion efficiency (PTE). For spherical silver particles, constant specific absorption rate (SAR), ~0.14 kW/g, is observed and the PTE increases nearly linearly with the particle concentration. For rod-shaped silver nanoparticles, much higher SARs (2~5 kW/g) are obtained, and the PTE increases from 43% (pure DI water) to 61% at a low concentration of 0.0028%. It is suggested that the increased specific surface area and the absorption spectrum variation are the two main reasons for the strong heating effect of rod-shaped silver nanoparticles
