  Predicting nanoscale thermal transport in dielectrics requires models, such
as the Boltzmann transport equation (BTE), that account for phonon boundary
scattering in structures with complex geometries. Although the BTE has been
validated against several key experiments, its computational expense limits its
applicability. Here, we demonstrate the use of an analytic reduced-order model
for predicting the thermal conductivity in dimensionally confined materials,
i.e., monolithic and porous thin films, and rectangular and cylindrical
nanowires. The approach uses the recently developed "Ballistic Correction
Model" (BCM) which accounts for materials' full distribution of phonon
mean-free-paths. The model is validated against BTE simulations for a selection
of base materials, obtaining excellent agreement. By furnishing a precise yet
easy-to-use prediction of thermal transport in nanostructures, our work strives
to accelerate the identification of materials for energy-conversion and
thermal-management applications.
