Experimental Research on Onset of Flow Instability in Narrow Rectangular Channel

The onset of flow instability（OFI） was investigated under the condition of: P=1~15MPa,G=500~2000kg/（m².s）,ΔT_sat=20~100℃,q=40~1000kW/m² in a narrow rectangular channel（1000×25× 2mm） with upflow deionized water.The experimental results showed the effects of the system pressure,heat flux,inlet subcooling,and the exit equilibrium void fraction on OFI.A relationship between the Stanton number and Peclet number at OFI was proposed:St=0.542Pe^-0.438（Pe＜70000）,St=0.0042（Pe＞70000）.The deviation is within ±30% when heat flux is below 400kW/m² and within ±10% when heat flux is above 400kW/m².A new purely empirical correlation was developed by comparing the heat flux leading to OFI with that leading to saturation: q_OFI=1.95 q_ast^0.87.The deviation is within ±15% when heat flux is below 400kW/m² and within ±5% when heat flux is above 400kW/m².