INFLUENCE OF SURFACE HEATING CONDITION ON LOCAL HEAT-TRANSFER IN A ROTATING SQUARE CHANNEL WITH SMOOTH WALLS AND RADIAL OUTWARD FLOW

The effect of a surface heating condition on the local heat transfer c oefficient in a rotating square channel with smooth walls and radial o utward flow was investigated for Reynolds numbers from 2500 to 25,000 and rotation numbers from 0 to 0.352. The square channel, composed of six isolated copper sections, has a length-to-hydraulic diameter ratio of it. The mean rotating radius to the channel hydraulic diameter rat io is kept at a constant value of 30. Four surface heating conditions were tested: (1) four walls at uniform temperature, (2) temperature ra tio of leading surface to side wall and trailing surface to side wall is 1.05 and 1.10, respectively, (3) trailing surface hot and remaining three walls cold, and (4) leading surface hat and remaining three wal ls cold. The results show that the heat transfer coefficients on the l eading surface are much lower than that of the trailing surface due to rotation. For case (1) of four walls at uniform temperature, the lead ing surface heat transfer coefficient decreases and then increases wit h increasing rotation numbers, and the trailing surface heat transfer coefficient increases monotonically with rotation numbers. However, th e trailing surface heat transfer coefficients for cases (2) and (3) ar e slightly lower than case (1), and the leading surface heat transfer coefficients for cases (2) and (4) are significantly higher than for c ase (1). The results suggest that the local wall heating condition cre ates the local buoyancy forces, which reduce the effects of the bulk b uoyancy and Coriolis forces. Therefore, the local heat transfer coeffi cients on the leading and trailing surfaces are altered by the surface local heating condition.