A rotameter, also known as a variable area flow meter, is a device used to measure the flow rate of a fluid in a closed conduit. It operates based on the principle of a variable area, where the area of flow passage changes in response to the flow rate of the fluid passing through it. The typical design of a rotameter includes a tapered tube, often made of glass or plastic, with a smaller diameter at the bottom and a larger diameter at the top. Within this tube is a float—a spherical or cylindrical object—positioned in the path of the flowing fluid. As the fluid flows through the tube, the float rises, indicating the flow rate.

Pall rings are a type of random packing used in chemical processing and various gas and liquid treatment applications. These rings are typically made of materials like metals, plastics, or ceramics and are characterized by their cylindrical shape with several internal and external structural features. The key design elements of pall rings include a series of internal and external structural elements—inner crossbars or struts and outer cylindrical walls—that provide a high surface area within a relatively small volume. This configuration ensures efficient contact between gas or liquid and the packing material, facilitating processes like gas absorption, distillation, and chemical reactions.