Dropwise condensation of steam on ion implanted condenser surfaces

Modern developments in surface treatment which reduce the energy of condensing surfaces and hence allow permanent, reliable dropwise condensation are described. The work has been carried out in China since 1984 by various methods, concluding with the patented Activated Reactive-Magnetron Sputtering Ion Plating (ARE-MSIP) technique. Successful application of this technique to coating brass and 70Cu: 30Ni white copper condenser tubes is described and the performance of a vertical 800 tube bundle in an industrial condenser is recounted. The overall U-value of this condenser at 2–3 m/s⁻¹ cooling water velocities has remained at 6–8 kW m⁻² K⁻¹ from its installation, in October 1989, to the present day. The paper concludes with an account of recent work aimed at improving the thermal conductivity and adherence of “dropwise” polymer films by ion implantation and methods of reducing the cost of the ARE-MSIP surface coating technique. Dropwise condensation seems unlikely to find a place in compact heat exchanger designs, but the development of surface treatment methods offers great possibilities in reducing corrosion and erosion and in inhibiting fouling.