Experimental study of flow instability and CHF in a natural circulation system with subcooled boiling

Flow instability, critical heat flux (CHF) and the relationship between flow instability and CHF have been investigated experimentally in a natural circulation system with subcooled boiling. Freon 12 was used as the working medium. The experiment showed two kinds of flow instabilities, both high frequency and low frequency flow instabilities. The high frequency flow instability is due to acoustic oscillation and the low frequency flow instability is due to density wave instabilities. The experiments show that the heat input power to the heated section and the working medium properties greatly influence the onset of the two kinds of flow instabilities while the CHF mainly depends on the heat flux to the heated section. The stability boundaries were determined experimentally. The CHF data obtained experimentally was compared with the Bowring correlation to develop a modified Bowring correlation which accurately predict the experimental CHF data.