Effects of the inclination angle on pool boiling in an annulus

To identify effects of the inclination angle on pool boiling heat transfer an experimental study has been executed. For the test a single tube of 30 mm diameter and an annulus of 12.7 mm gap size submerged in the saturated water at atmospheric pressure have been considered. The inclination angle changes heat transfer much. The change of the inclination angle from 0° to 45° results in 29.8% and 11.2% decrease in the heat transfer coefficient at 40 kW/m2 for the single tube and the annulus, respectively. For the single tube, no specific changes in heat transfer are observed as the inclination angle increases up to 15° whereas the angle for the annulus is 30°. The major heat transfer mechanisms are considered as the intensity of liquid agitation and bubble coalescence due to the enclosure by the outer tube.