Flow boiling heat transfer in a vertical spirally internally ribbed tube

Experiments of flow boiling heat transfer and two-phase flow frictional pre ssure drop in a spirally internally ribbed tube (phi 22 x 5.5 mm) and a smo oth tube (phi 19 x 2 mm) were conducted, respectively, under the condition of 6 x 10(5) Pa (absolute atmosphere pressure). The available heated length of the test sections was 2500 mm. The mass fluxes were selected, respectiv ely, at 410, 610 and 810 kg/m(2) s. The maximum heat flux was controlled ac cording to exit quality, which was no more than 0.3 in each test run. The e xperimental results in the spirally internally ribbed tube were compared wi th that in the smooth tube. It shows that flow boiling heat transfer coeffi cients in the spirally internally ribbed tube are 1.4-2 times that in the s mooth tube, and the flow boiling heat transfer under the condition of small er temperature differences can be achieved in the spirally internally ribbe d tube. Also, the two-phase flow frictional pressure drop in the spirally i nternally ribbed tube increases a factor of 1.6-2 as compared with that in the smooth tube. The effects of mass flux and pressure on the flow boiling heat transfer were presented. The effect of diameters on flow boiling heat transfer in smooth tubes was analyzed. Based on the fits of the experimenta l data, correlations of flow boiling heat transfer coefficient and two-phas e flow frictional factor were proposed, respectively. The mechanisms of enh anced flow boiling heat transfer ill the spirally internally ribbed tube we re analyzed.