We developed a reference model based on single particles to investigate the diffusional growth. In this model we solve the non-linear time-dependent diffusion equations for vapor and energy transport by a finite element approach. The shape of the ice particles is approximated by ellipsoids, including a space dependent saturation pressure at the surface of the particles. The background water vapor field is time-dependent in order to mimic the impact of turbulence. Different geometrical distributions of droplets and ice particles are prescribed in order to investigate effects of inhomogeneous droplet and crystal distributions.
Additionally we used a bulk-model approach with potential functions to represent the WBF process and solved the evolution equation for the time-dependent mass distribution function with a Galerkin method.