Surface Condensers Automotive radiators seem well designed, high heat density and conductivity make water readily cooled by tubes, having less thermal density and conductivity air benefits from the increased surface area and division into narrower streams provided by fins. A good “surface condenser” would likewise keep the exhaust steam and air qualities in mind and dedicate a more similar amount of surface area to both. Doble honeycomb condensers obey this precept, comprising an array of hexagonal or square cells separated by hollow cavities.  Steam flows between the cells, condensing on contact with the cooler metal while air flowing through the cells carries the heat away, the surface area in contact with air and steam are nearly identical. Doble also employed an air pump to help his cars maintain partial condenser vacuum when cruising. Automotive super and turbocharger intercoolers may be good candidates for an off-the-shelf surface condenser.  The heavy aluminum structure withstands pressure and readily transfers heat, making it ideal for vacuum condensing.  The internal and external passages both contain fins, making their surface areas nearly identical.  A number of models are on the market and there are shops that build them to specification.