An experimental study of R134a flow boiling heat transfer in a 4.07 mm tube under Earth's gravity and hypergravity

摘要

Two-phase flow boiling systems on some flight vehicles may often encounter hypergravity operations. The experimental investigation of R134a flow boiling heat transfer in a horizontal copper tube with 4.07 mm inner diameter was conducted to observe the effect of gravity on flow boiling heat transfer and to accumulate experimental data for the further studies of hypergravity flow boiling heat transfer. The gravity levels range from 1 to 3.16 g. The hypergravity was generated using a centrifugal acceleration machine. It is found that generally the flow boiling heat transfer under hypergravity is greater than that under Earth's gravity and shows a trend of increase with increasing gravity, which may be in part because the excess temperature for bubble nucleation drops with gravity increasing from Earth's gravity to hypergravity. Gravity has obvious effects on flow patterns and thus on heat transfer coefficients. Increasing gravity makes the flow pattern transition from plug/slug flow to intermittent flow appear earlier. Twenty-seven available correlations proposed for the flow boiling heat transfer under Earth's gravity are compared with the experimental data to evaluate their applicability to hypergravity.