An experimental investigation of flow boiling heat transfer and pressure drop of R134a in a horizontal 2.168Â mm tube under hypergravity. Part I: Frictional pressure drop

An experimental investigation on flow boiling of R134a under hypergravity is conducted to observe the effect of gravity on the two-phase frictional pressure drop. A series of experiments were conducted with a horizontal 2.168 mm inner diameter tube under both hypergravity (1.12-3.16 g) and normal gravity (1 g) with mass flux of 725 and 910 kg/m2 s, heat flux of 19.0 and 28.5 kW/m2, saturation pressure of 0.71 and 0.82 MPa (saturation temperature of 27.2 and 32.2 °C), and vapor quality from 0 to 0.65. The hypergravity environment was generated with a centrifugal acceleration machine. A comparison between the experimental frictional pressure drop under hypergravity and normal gravity is made and the results indicate that the frictional pressure drop under hypergravity is greater than that under normal gravity at high vapor quality while less than that at low vapor quality, but the difference is not significant for hypergravity within 3.16 g. The experimental frictional pressure drop under different gravity levels is also compared with three best existing correlations proposed for normal gravity, and the results evince that the best correlation has a mean absolute deviation of 14.5% for normal gravity and 15.4% for hypergravity.