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The Fire/Smoke simulator is intended to produce gaseous effects like fire, smoke and explosions, as well as sparks or embers.

You can think of the simulator as a 3D box, inside which simulations of fluids and Rigid Body Dynamics are performed. Fire/Smoke simulations are grid-based, meaning they consist of an array of voxels that contain the fluid's properties at a position and given time, such as the fluid’s temperature, its velocity, its color, and so forth.

These fluid properties are written inside what are called Grid Channels. Each channel stores a type of value, such as Temperature or Velocity, with its own Grid Channel Range, which is the range of possible values that is most efficient for that specific channel type. Phoenix determines the fluid’s behavior at a given time, based on the content of these Grid Channels.

When running a simulation, the Fire/Smoke sim will typically output an entire animation sequence. That sequence is saved as individual files, called caches, which contain raw simulation data for each timeline frame. In essence, the cache data contains grids and particles, which describe the fluid’s behavior.

Fire/Smoke sim cache files can then be previewed in the viewport, as well as rendered, in order to create captivating and realistic images. The simulator offers multiple render modes, where the volumetric render modes are typically used for rendering Fire/Smoke sims, and the mesh render mode is typically used for Liquid sims. Phoenix offers a lot of flexibility though, so there is the option to render Fire/Smoke sims as meshes and Liquids as volumes, in order to achieve even more diverse effects.