Effect of channel length on critical heat flux under conditions of high subcooling and high velocity in short heated channels

The characteristics of critical heat flux (CHF) in existing experiments under high subcooling and high velocity in short heated channels were, for the first time, systematically and quantitatively investigated to provide a CHF correlation which could properly predict the effect of channel length, especially when the channel length-to-channel diameter ratio L/D is less than about 20. Major test conditions of existing CHF experiments investigated in this study were 1 to 4 mm of channel diameter, 1 to 25 of L/D, 0.1 to 1.2 MPa of pressure, 34 to 117degC of inlet water subcooling and 500 to 40700 kg/(m2·s) of mass flux in circular channels, and 3 to 20 mm of gap size, 6 to 40 of L/De, 0.1 to 3.1 MPa of pressure, 4 to 166degC of inlet water subcooling and 940 to 27000 kg/(m2·s) of mass flux in rectangular channels. The effect of L/D on CHF was evaluated referring to the analytical solution of CHF, which was previously derived by the author for the channel flow at high subcooling and high velocity. As a result, the effect of L/D was quantitatively clarified as an effect of magnitude in heat transfer of the single-phase forced-convection flow, giving a larger CHF with a smaller L/D in the case of L/D less than about 20. The proposed correlation could predict CHF within a ±35 percent error margin. (author)