Using Small Scale Physical Experiments to Improve Enthalpy Based Models of Ice Sheets

Nossokoff, Austin

Graduate Thesis Or Dissertation

Using Small Scale Physical Experiments to Improve Enthalpy Based Models of Ice Sheets Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/qr46r105v

Abstract

Recent work has demonstrated the potential warming influence of meltwater and englacial water bodies on the Greenland Ice Sheet. The equilibrium line has been ascending in altitude, resulting in inland propagation of areas receiving melt. The physical processes involved in the interaction between the liquid and solid phases of water within cold ice bodies is not completely understood. This work is meant to improve the understanding of the thermodynamic interactions between englacial water bodies and surrounding ice in polythermal glaciers and ice sheets. The growth of conduits that carry water through the englacial system due to frictional heating along the conduit walls and refreezing when frictional heating is insufficient is studied based on experimental measurements of heat transfer from water filled conduits in cold ice. The important heat exchange processes involved are conductive loss of energy from the conduit and supply of energy by viscous/turbulent dissipation in water flowing through the conduit.[object Object]Three sets of experiments were designed based on a theoretical analysis which established the threshold water discharge rate in a conduit above which conduit growth can occur. One set focused on a conduit filled with stagnant water, another with a low water flow rate, and a third with a high water flow rate. Refreezing occurred in the first two sets, while conduit growth occurred beyond a critical discharge value. Scalloping of conduit walls occurred in the conduit growth regime, leading to a large roughness of conduit walls. Even in the case where refreezing occurs, the ice temperature surrounding the conduit will increase due to the release of latent heat by refreezing water. Using the assumption of radial symmetry, a numerical model was developed to quantify the temperature distribution in the ice. This model represents the conduction and energy supply at the conduit walls by turbulent dissipation and includes movement of the ice-water interface by either refreezing or conduit growth. The scalloping effects under high flow rates produced relatively high friction factors. The model and experiments agree well in all three experimental cases.

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