  The effect of orientation on near-field radiative heat transfer between two
complex-shaped superellipsoid particles of SiO2 is presented. The particles
under study are 50 nm in radius and of variable concavity. Orientation is
characterized by the degree of rotational symmetry in the two-particle systems,
and the radiative conductance is calculated using the discrete system Green's
function approach to account for all electromagnetic interactions. Results
reveal that the total conductance in some orientations can be up to twice that
of other orientations when particles are at center-of-mass separation distances
of 110 nm. Orientation effects are not significantly correlated with system
rotational symmetries but are strongly correlated with the minimum vacuum gap
distance between particles. As such, orientation effects on near-field
radiative heat transfer are a consequence of particle topology, with more
extreme topologies leading to a continuation of orientation effects at larger
particle center-of-mass separation distances. The concave superellipsoid
particles display significant orientation effects up to a center-of-mass
separation distance approximately equal to 3.9 times the particle radius, while
the convex superellipsoid particles display significant orientation effects up
to a center-of-mass separation distance approximately equal to 3.2 times the
particle radius. In contrast to previous anisotropic, spheroidal dipole
studies, these results of complex-shaped superellipsoid particles suggest that
orientation effects become negligible when heat transfer is a volumetric
process for all orientations. This work is essential for understanding
radiative transport between particles that have non-regular geometries or that
may have geometrical defects or abnormalities.
