Flow boiling heat transfer with HFC mixtures in a smooth horizontal tube. Part I: Experimental investigations

The substitution of working fluids in vapour-compression plants causes major problems, because of a reduced plant performance. Therefore, extremely accurate design procedures are needed, because the relative sizing of each plant-component is essential for the cycle performance. For this reason, the knowledge of the heat-transfer characteristics of new fluids in condensers and evaporators is mandatory. The heat-transfer characteristics of R410A and R404A were experimentally investigated and analyzed as a function of evaporating pressure, heat- and mass flux. The test section was a smooth, horizontal, stainless steel tube (6 mm ID, 6 m length) uniformly heated by the Joule effect. The working parameter was varied within the following ranges: evaporating pressure 3-12 bar, refrigerant mass-flux 290-1100 kg/m2 s, heat flux 11-39 kW/m2, respectively.