Experiments on dominant force regimes in flow boiling using mini-tubes

Effects of tube orientation on flow boiling heat transfer coefficients were investigated for FC72 flowing in single mini-tubes with tube diameters of 0.13 and 0.51 mm to define boundaries on a dominant force regime map. For the tube diameter of 0.51 mm, when mass velocity and vapor quality was varied, heat transfer coefficients were influenced by tube orientation at Froude number Fr < 4, while the effect of tube orientation on heat transfer coefficients disappears at Fr > 4. The results indicated that the boundary between the body force dominated and the inertia dominated regimes was given by Fr ≈ 4. On the other hand, for tube diameter of 0.13 mm, almost no effect of tube orientation on heat transfer coefficients was observed for all combinations of mass velocity and vapor quality tested, where heat transfer coefficients were independent of mass velocity and vapor quality at Weber number We < 5, and vice versa. The results indicated that the boundary between the surface tension dominated and the inertia dominated regimes was represented by We ≈ 5. From the above results, the boundary between the surface tension dominated and the body force dominated regimes was existed between Bo = 0.51 and 0.033.