Visualization of the flow adjacent to a vertical ice surface melting in cold pure water

Abstract

Time-exposure photographs of the buoyancy-driven flow adjacent to a vertical ice surface melting in pure water are presented for ambient water temperatures between 3·9 and 8·4 °C. These conditions are of special interest since between about 4 and 8 °C the buoyancy force distribution is locally bi-directional across the thermal transport region, owing to the density extremum at about 4 °C. Although knowledge of the transport for such circumstances is important in both environmental and technological applications, previous experimental studies have provided only limited information, concerning only the gross aspects of the resulting fluid motions. It is now possible, from the extensive experimental results presented here, to understand some of the more subtle mechanisms which arise in such flows. Photographs of the entire flow field document the many complicated flow configurations which occur for these circumstances. As the ambient water temperature is increased from 3·9 to 8·4 °C, regimes of upward, locally bi-directional, and downward flow are observed. Bi-directional flow is seen to result from the reversal of part or all of the upward wake above the top of the ice surface. Local velocities and surface heat-transfer rates, measured from the photographs, are compared, where possible, with the analytical results of Carey, Gebhart & Mollendorf (1980). It was found that the flow velocities for ambient temperatures from 4·05 to 4·70 °C, depart only slightly from the analytical predictions, in spite of an interaction of the outer portion of the upward flow with downward-moving remnants of the upward wake. However, near the surface, the velocity profiles, and consequently the heat transfer and melting rates, agree well with the analytical results. Comparisons at ambient temperatures below 4·05 °C and above 5·9 °C show that the velocity profile and surface heat transfer are in excellent agreement with the results of Carey et al. (1980). At ambient water temperatures between 4·7 and 5·0 °C the flow was found to be bi-directional and weakly time dependent. This weak time dependence is attributed to the instability of the upward wake, which in turn is the source of the outside downward flow in such circumstances.