Production of pipes with topographical internal structures

The principle of the heat exchanger involves transferring heat from one medium to another. They do not come into direct contact with each other, but are guided past each other. As a rule, both liquid and gaseous fluids are passed through pipes. Heat is transferred via the pipe wall. In addition to heat exchangers, the principle is also used in boilers, heat accumulators or solar receivers, for example.

State of the art

If surface structures are incorporated into the inner wall of heat exchanger tubes, the flow behavior of the fluid can be influenced in such a way that the resulting turbulence increases heat transfer. Common manufacturing techniques structure the tube, for example by forming processes or from the inside by laser beam or with tools for mechanical or electrochemical processing. They reach their limits with decreasing pipe diameter and increasing pipe length for complex geometries of internal structuring.

Technology

Researchers at the Institute for Thermal Energy Technology and Safety (ITES) and the Institute of Neutron Physics and Reactor Technology (INR) at KIT have developed a process combination for the production of tubes made of metallic materials with arbitrarily complex inner structures and seamless pressure-bearing outer walls. First, the desired surface structures are applied to sheet metal using cost-effective techniques such as punching, embossing or laser cutting. These are then formed into rings or shell segments and assembled into a tube inner shell. The material for the actual tube body in metal powder form is additively applied to the inner shell from the outside at very high speed using a cold gas spraying process. In contrast to other coating processes for metals, a dense and firmly adhering layer is formed on impact without prior melting or melting of the material. The result is a distortion-free pipe body.

Advantages

The new manufacturing process enables the economical realization of internal pipe structures of any complexity through the use of mass production techniques with rational use of materials. Due to the higher heat transfer, the surface area required for heat transfer is smaller. Pipe lengths and diameters are reduced. The heating surface temperature is lowered, which extends the service life of the components.

Options for companies

KIT is looking for partners from the energy sector, heating or plant engineering for cooperation on the application-specific implementation and optimization of the process.