Non-equilibrium condensation of supercritical carbon dioxide in a converging-diverging nozzle

[摘要] Carbon dioxide (CO2) is a promising alternative as a working fluid for future energy conversion and refrigeration cycles. CO2has low global warming potential compared to refrigerants and supercritical CO2Brayton cycle ought to have better efficiency than today's counter parts. However, there are several issues concerning behaviour of supercritical CO2in aforementioned applications. One of these issues arises due to non-equilibrium condensation of CO2for some operating conditions in supercritical compressors. This paper investigates the non-equilibrium condensation of carbon dioxide in the course of an expansion from supercritical stagnation conditions in a converging-diverging nozzle. An external look-up table was implemented, using an in-house FORTRAN code, to calculate the fluid properties in supercritical, metastable and saturated regions. This look-up table is coupled with the flow solver and the non-equilibrium condensation model is introduced to the solver using user defined expressions. Numerical results are compared with the experimental measurements. In agreement with the experiment, the distribution of Mach number in the nozzle shows that the flow becomes supersonic in upstream region near the throat where speed of sound is minimum also the equilibrium reestablishment occurs at the outlet boundary condition.

[发布机构] Laboratory of Fluid Dynamic, Lappeenranta University of Technology, Finland^1

[效力级别] 力学 [学科分类] 力学，机械学

[关键词] Converging-diverging nozzles;Global warming potential;Non-equilibrium condensation;Numerical results;Operating condition;Outlet boundary condition;Refrigeration cycles;Supercritical carbon dioxides