The two一Phase flow and boiling heat tra一lsfer eharaeteristics in the bends ofU一shaPedtubes are eomPlieated beeause of the combined effeets of gravitational and eentrifugal Ibrees之连5 well as other factorsl sueh as seeondary flow ete.However,little researeh work in this re-sPeet has been eonducted uP to now. Lis et al.t’1 studied the flow and heat transfer behavior