1. Gas

1.1 Main heat transfer gases. Physico-chemical properties

Nitrogen, air, helium, carbon dioxide and superheated steam are the main heat transfer gases. With the exception of air, these are simple compounds. In addition, flue gases, when transported out of the boiler to transfer their sensible or latent heat, act as a heat transfer fluid containing a high proportion of nitrogen.

The main heat transfer gases are non-flammable, non-hazardous to health in moderate concentrations, have a low environmental impact and are stable over a wide temperature and pressure range.

Due to its very low molar mass, helium has a very different density from other heat transfer gases, particularly low under normal conditions (0.18 kg/m ^...