Heat transfer and pressure drop during condensation of refrigerant 134a in an axially grooved tube

摘要

R134a condensation experiments have been petfonned over a mass flux range of 75 to 450kg/m2-s (55 to 330 klbm/ft2-hr) in an 8.91 rom (0.351") inside diameter, axially grooved, microfintube. At 75 kg/m2-s (55 klbm/ft2-hr), the axially grooved tube petfonns marginally better thana smooth tube, but worse than a similarly grooved tube with an 18 degree helix angle over a broadrange of refrigerant qualities. Mass fluxes at 150 kg/m2-s (110 klbm/ft2-hr) and greater showbroad quality ranges in which the axially grooved tube petfonns significantly better than bothsmooth and helically grooved tubes. Examination of a Froude rate parameter indicates that theaxially grooved tube is able to maintain an annular film flow characteristic that results in moreefficient heat transfer. Pressure drop characteristics of the axially grooved tube are similar to thosefound in an 18 degree helix angle tube.