Experimental Research on Flow Instability in Vertical Narrow Annuli

A narrow annular test section of 1.5mm gap size and 1800mm heat length is successfully designed. The experiment has been conducted to investigate the characteristics of flow instability of forced convection in vertical narrow annuli. Distilled water is used as work fluid. The range of pressure is 1.0～3.0MPa and the mass flow rate is 3.0～25kg/h. Heat power is from 3.0 to 6.5kW and inlet fluid temperature is equal to 20, 40, and 60℃. It is found that the flow instability occurs in fixed inlet condition and heat power, when mass flow rate is below a certain value. The effects of inlet subcooling, system pressure and mass flow rate on the system behavior have been studied and the instability region is given.