Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.
A nozzle design tool for real gases has been devised for investigating the features of gasdynamic nozzles operating with supercritical or close to critical carbon dioxide. Three exemplary real-gas expansions, originating from a reservoir at a temperature of 400 K and at a pressure of 10, 5 and 1 MPa, respectively, were considered and compared to the corresponding dilute gas case, for which reservoir conditions are 400K and 0.1 MPa. Differently from the well-known ideal-gas results, the nozzle shape depends on the reservoir or total flow conditions and therefore diverse designs are obtained for a given exit Mach number depending on the relative
location of the initial state in the volume-pressure thermodynantic plane with respect to the liquid-vapor saturation curve. For flow states close to the liquid-vapor saturation curve and critical point, the nozzle length and height are larger than the corresponding ideal gas designs. Differences are as large as 17% for the divergent length and 18.4% for the nozzle height. More relevant differences are found for the mass flow, which for high pressure exceeds its ideal gas value by two order of magnitudes. This difference is mainly due to the effect of the density, which is increases with increasing reservoir density.