Uncertainty Analysis of Near-Field Thermal Energy Transfer within Nanoparticle Packing

Laser heating of nanoparticles leads to significant near-field thermal effects between the nanoparticles. Due to the interaction between the laser and nanoparticle packings, some laser energy is scattered or absorbed, resulting in attenuation of the laser energy. The absorbed energy within the nanoparticles affects the near-field thermal energy transport. We have analyzed these effects by combining experimental determination of nanoparticle ink morphology with computational electromagnetic simulations. Scanning electron micrographs (SEM) of a representative copper nanoparticle ink show that the nanoparticles are distributed log-normally in size with 116 nm mean radius and 48 nm standard deviation. Hence, four instances of log-normally distributed copper nanoparticle packings which have 116 nm mean radius with 48 nm standard deviations are created by using a Discrete Element Model (DEM) in which a specified number of particles is generated, specifying a position and radius. Each nanoparticle is randomly generated with an initial velocity and a boundary under gravitational forces, which create the nanoparticle packing. Maxwell's equations in the frequency domain are simulated for these nanoparticle packings to understand the uncertainty analysis of near-field thermal energy within the nanoparticles by calculating the absorption, scattering and extinction coefficients. We show that nanoparticle distribution under gravitational forces doesn't significantly affect the absorption cross-section for both TE and TM polarization. Moreover, numerical and experimental results agree well between 400 nm to 800 nm wavelength of laser irradiation for generated different four particle distributions.