HelixChute2 uses spherical particles to model bulk material. Closely-packed spherical particles (cubic close packing) reach a density of about 0.74 of the solid material's own density – see Cubic Close Packing for background.
It's therefore reasonable to estimate a Particle Density no greater than Bulk Density / 0.74 (voids of 26% of the volume, void ratio e = 0.26/0.74 = 0.35). For random close packing, a factor closer to 0.64 is more realistic, so Bulk Density / 0.64 is a reasonable working value.
Where possible, obtain the actual particle density by test methods rather than estimating it.