Alfa Laval Double Wall PHE The AlfaNova is the first plate heat exchanger in the world to be made completely of stainless steel – made possible by the unique active diffusion bonding technology patented by Alfa Laval.     Gemini Sanitary PHE Gemini heat exchanger plates consist of two plates with a small air gap in between. This gap is open to the atmosphere and is not in contact with either of the media, helping guard against any contact between them.