Combined Effects of Axial- and Radial-Gap Spacing on the Mass Transfer Characteristics of a Shrouded Rotor-Stator System

Abstract

Heat transfer characteristics of a shrouded rotor-stator system are examined using a mass transfer analog technique. Both local and average mass-transfer coefficients for a naphthalene-coated disk rotating in a quiescent environment are obtained for 4.0×104 ≤ Re ≤ 2.4×105. The measured results, which correlate well with theoretical predictions, are used to evaluate the influence of radial-gap clearance and axial-gap spacing on average and local mass-transfer rates in a shrouded rotor-stator with no superposed coolant flow. Similar to a rotor-stator system without a shroud, a reduction in the axial gap tends to decrease the average mass transfer, with the magnitude of the decrease being inversely proportional to the Reynolds number. Such a reduction in mass transfer is also found to be influenced by the radial clearance gap. A reduction of the radial clearance from a/D=0.042 to 0.020 is shown to decrease the average Sherwood number by approximately 20 percent of the corresponding free disk value. Local mass transfer distributions illustrate a more significant axial gap effect. For small axial-gap spacings, local Sherwood number profiles are no longer uniform across the rotor face, but exhibit a significant increase near the rotor edge. The magnitude of this increase near the disk edge is shown to be inversely proportional to the radial clearance gap and the rotational Reynolds number.