The fiber model accounts for all mass, momentum, and heat gained or lost by the fibers and can be incorporated into the subsequent calculations of the surrounding fluid performed by Ansys Fluent. This means that you can incorporate the effects of the fibers on the surrounding fluid, while the surrounding fluid always impacts the fiber flow. This two-way coupling is achieved by alternatively solving the fiber and the surrounding fluid flow equations until both phases have converged. The interphase exchange of heat, mass, and momentum from the fibers to the surrounding fluid is depicted qualitatively in Figure 22.1: Fiber Grid Penetrating Grid of the Gas Flow.