Gravity independent subcooled flow boiling heat transfer regime

Using an existing model for vapor bubble detachment, a subcooled flow boiling regime was identified where vapor bubble dynamics are independent of the gravitational field. The Jakob number and a dimensionless flow parameter were used to identify the boundaries of this regime. This work describes an experimental investigation of subcooled flow boiling heat transfer using FC-87 that was conducted with Jakob number ranging from 16-40, bulk flow velocity ranging from 0.39 to 1.17 m/s, and test section orientations of 0 degrees horizontal flow, 45 degrees upflow, 90 degrees upflow, 315 degrees downflow, and 270 degrees downflow. The differences in the Nusselt number with different flow orientations are elucidated over the parameter space considered. Flow conditions where the heat transfer is independent of gravity have been identified and compared with the gravity dependent/independent regime map. It has been observed that at a particular Jakob number, the heat transfer is gravity independent at a lower bulk flow velocity than what is predicted by the theoretically based gravity dependent/ independent regime map. Thus for design purposes, the regime map gives a conservative estimate for when the flow transitions into the gravity independent parameter space. (C) 2006 Elsevier Inc. All rights reserved.