In plain tubes (no inserts), fluid flow is essentially laminar, and skin friction retards the flow of fluid in contact with the tube wall. At the same time this outer fluid cools faster and becomes more viscous, further retarding the flow.
The result is a build up of concentric fluid layers, with the hot fast-flowing inner fluid surrounded by cooler, slower flowing outer fluid. These outer layers-boundary layers-insulate the hotter fluid from the cool tube wall resulting in a very low heat transfer rate.
Wire loop inserts eliminate boundary layers by completely disrupting laminar flow.
The insert is made from a continuous wire which is formed into loops. The loops are spirally wound around a small diameter rod and solder bonded in place.
When installed in a tube the wire loops keep the fluid in a constant state of turbulence, preventing the formation of thick boundary layers and continually presenting hot fluids to the cool tube wall.
Even with the viscous fluids at low velocities the wire loop insert provides extremely efficient mixing giving vastly improved heat transfer. Any pressure loss experienced is more than compensated for by the increased heat transfer rate.
These wire loop inserts can be solder bonded into any externally finned tube with a variety of geometries and densities to suit particular heat transfer and pressure loss requirements.