What are the methods to enhance heat transfer on the process side?

Passive methods: extended surfaces (fins for gases), tube inserts (twisted tape, wire coils increase turbulence), internally finned tubes, corrugated tubes, and roughened surfaces. Active methods: mechanical vibration, surface rotation, and fluid pulsation (rarely used in industry). Considerations: enhanced surfaces may increase fouling, pressure drop increases, manufacturing cost increases, and cleaning may be more difficult. Most effective when one side has low heat transfer coefficient (gas side, viscous liquids) that limits overall U.