VISUALIZATION OF CONVECTION IN A SIMULATED GRADIENT FREEZE CELL DURING CENTRIFUGATION

Experiments were performed in a simulated gradient freeze cell in orde r to reveal the effect of centrifugation on the convection in the cell . A laser light-cut technique was used for flow visualization Flow pat terns were observed in one vertical and two horizontal cross sections of the cell. Flow velocities were measured via particle displacement t racking velocimetry. Five centrifuge rotation rates omega were studied : 10, 15, 20, 30, and 40 rpm. A flow mode transition was found at a om ega of about 30 rpm, which is in agreement with the theoretical predic tion of Arnold [9]. A flow pattern observed in the vertical plane agre es qualitatively with the one calculated by Friedrich et al. [6,11]. T he mean flow velocity in the bottom part of the test cell decreased be yond a rotation rate of 20 rpm, suggesting that a minimum might occur at a rotation rate higher than 40 rpm. (C) 1998 Elsevier Science B.V. All rights reserved.