Critical heat flux during natural convective boiling in inclined annular tubes submerged in saturated liquids

An experimental study was carried out to investigate the critical heat flux (CHF) during natural convective boiling in an inclined annular tube with a heated inner tube submerged in a pool of saturated liquids under atmospheric pressure. The test conditions are as follows: the outer diameter of the inner tube was fixed at 16 mm; the tube gap ranged from 1.0 min to 4.0 mm; the effectively heated lengths ranged from 100 mm to 400 mm; and inclination angles varied from 30degrees to vertical position. The test fluids were Water and R-11. The experimental results show that the CHF decreases with increasing the ratio of the heated length to the tube gap, and CHF decreases slightly with reducing the inclination angle. A semi-theoretical correlation originally used for the CHF during natural convective boiling in vertical annular tubes was modified to predict the CHF occurs in the inclined annular tubes. The modified correlation agreed reasonably well with the present experimental data and other CHF data for the narrow inclined annular tubes. (C) 2004 Elsevier Science Ltd.