Critical heat flux of subcooled flow boiling in tubes with internal twisted tape

Experiments on critical heat flux (CHF) of subcooled flow boiling in tubes with internal twisted tapes at atmospheric pressure are reported in this paper. The test tube is made of the stainless steel (6 mm in the inside diameter, 0.25 mm in thickness, and 100 mm in heated length). The inserted tapes are made of Zirconia (about 1.2 mm in thickness and 5.4 mm in width and the twisted tape ratios y (number of tube diameters to complete 180 degrees twist of tape insert) are 2.7, 4.3, 8.7, and ∞. Swirl-flow CHF increased in proportional to the one third power of (y-1) at small y. An empirical CHF correlation, which gives the ratio of CHF value to the swirl-flow to that of the straight-flow, is proposed. It was verified that this correlation gave the accurate predictions at nearly atmospheric pressure