Analysis of flow boiling heat transfer in narrow annular gaps applying the design of experiments method:

摘要

The axial heat transfer coefficient during flow boiling of n-hexane was measured using infrared thermography to determine the axial wall temperature in three geometrically similar annular gaps with different widths (s?=?1.5?mm, s?=?1?mm, s?=?0.5?mm). During the design and evaluation process, the methods of statistical experimental design were applied. The following factors/parameters were varied: the heat flux q·=30?190kW/m2, the mass flux m·=30?700kg/m2s, the vapor quality x·=0.2?0.7, and the subcooled inlet temperature TU=20?60K. The test sections with gap widths of s?=?1.5?mm and s?=?1?mm had very similar heat transfer characteristics. The heat transfer coefficient increases significantly in the range of subcooled boiling, and after reaching a maximum at the transition to the saturated flow boiling, it drops almost monotonically with increasing vapor quality. With a gap width of 0.5?mm, however, the heat transfer coefficient in the range of saturated flow boiling first has a downward trend and then inc...