Published Online: 30 December 2008
Page Count: 18
Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA
Faxénlaboratoriet, KTH, Stockholm,
(Received 30 April 2008; accepted 25 November 2008)
To learn about cooling of gas quenched batches, this paper reports on numerical predictions of local and average convective heat transfer coefficients, and overall pressure drops, on batches of five axially aligned, constant temperature, short cylindrical disks (25 cm diameter, 5 cm thickness) with and without a concentric hole, with interdisk spacings of 5–20 cm, in axial turbulent flows of 20 bar nitrogen gas at inlet speeds from 10 m/s to 100 m/s, corresponding to Reynolds numbers (Re) between 3.27×106 and 32.7×106. The heat transfer coefficients along the disk surfaces vary strongly up to a worse case of two orders of magnitude for the upstream disk. This nonuniformity is much lower for the disks downstream, especially after spacing is increased beyond 0.1 m. As expected, the upstream disk exhibited rather different heat transfer coefficients than the ones downstream, the magnitude of the heat transfer coefficient and its uniformity increased with the interdisk spacing, and varied by a factor of about 4–5 along the surfaces. The average heat transfer coefficient (Nusselt number, Nu) on the disks increased approximately with Reynolds number as Re0.85. Re did not have much influence on the nonuniformity of Nu on the disk surfaces. The overall pressure drop along the flow increases with the interdisk spacing, rising by about 60 % as the spacing is increased from 0.05 m to 0.20 m. The presence of a hole increases the heat transfer coefficient in all cases. Some suggestions for reducing the heat transfer coefficient nonuniformity are made.
Paper ID: JAI101849