Gas-solid fluidization is a process where a gas flows upward through a bed of solid particles, causing the particles to become suspended and behave like a fluid. This occurs when the upward gas velocity exceeds a certain threshold, known as the minimum fluidization velocity. The solid particles can be various materials, such as powders or granules, and the gas can be air or other gases. In fluidized beds, the solid particles are evenly distributed, allowing for efficient mixing and heat transfer. This technique is widely used in industries such as chemical engineering, pharmaceuticals, and food processing for processes like drying, coating, and reaction.