EFFECT OF SURFACE FINISH ON BOILING UNDER JET IMPINGEMENT Effect of Surface Finish on Boiling Heat Transfer at Stagnation Point under Free Liquid Jet Impingement By

iii Experiments were performed to study the effect of surface finish and jet velocity on the boiling performance at the stagnation point under a free liquid planar jet. A rectangular jet with dimensions 9 mm x 1 mm was used to impinge subcooled water on the center of a copper surface 8 mm width x 20 mm length. Jet velocities ranged from 0.9 to 2.5 m/s while the degree of subcooling was kept constant at 10°C. Three surfaces were prepared using emery paper #1200, #500 and #320 and the arithmetic mean square of the roughness Ra = 18.72, 401.65 and 533.53 nm. Increasing the jet velocity has shown to increase the heat flux slightly in the single phase regime. Also by increasing the jet velocity, boiling was found to start at higher surface superheat achieving higher values of burn out heat flux BOF for jet velocities Vj ≤ 1.5 m/s. This trend agrees with studies reported in literature. Some contradicting results occurred at higher jet velocities which i