Folder containing letters between UK and North American Research Engineers involved with heat recovery work, as well as reports on the development of equipment for recovery heat energy normally lost as waste from American milk cooling installations. The file includes published papers from the United States, particularly concerning the application of Heat Recovery technology to Bulk Collection installations. The file includes a photographic print showing equipment, one article in French and two in German. Most of the material dates to the 1950s and 1960s.