Effect of gas impurities in coolants of supercritical pressure on the heat transfer laws

Heat transfer in vertical heated tube to the carbon dioxide turbulent flow of supercritical pressure with different nitrogen impurity concentrations was investigated experimentally. Measurements were conducted for the tube with diameter d=22,67 mm and heat length of 130 d in 100-2400 kg/m2s range of flowrate; 7,65 and 9,0 MPq; 10-39 deg C inlet temperature and N≤4% nitrogen concentration. Experiment results showed, that in the nitrigen concentration investigated range the nitrogen impurity effect was inessential in case where heat exchange conditions were satisfied in supercritical or one-phase subcritical ranges. With nitrogen impurity increase higher than the limit value and heat exchange conditions realization during mixture boiling the presence of gas impurity results in heat transfer improvement with subcritical heat fluxes, and with supercritical heat fluxes, in heat transfer abrupt deterioration. Critical heat flux values are essentially lower than thermal loads under which analogous temperature peaks occur in supercritical range