Experimental study on forced convective flow and heat transfer in a concentric annular tube

Using the high-temperature and high-pressure boiling two-phase flow test loop, the water flow resistance and heat transfer characteristics were experimentally investigated under the different heat conditions in a concentric annular tube with 2.5 mm gap size. The two heating types were individual inside-tube wall heating or individual outer-tube wall heating separately. The heat transfer coefficients were calculated with the measured tube wall temperature. The results show that the critical Reynolds number is 2300 at the transition from laminar to turbulence flow. The flow friction coefficient is less than that in circular tube, and it becomes smaller under the condition of the outer-tube wall heating than that under the condition of non-tube wall heating. The heat transfer is enhanced in the test tube and becomes greater than that in the circular tube under the same condition. The heat transfer at the outer-tube wall is suppressed under the dual-tube walls heating comparing to that under the outer-tube wall heating. The correlations of calculating the flow friction coefficient and heat transfer coefficient under the different heating conditions were proposed based on the experimental data.