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Heat transfer and convection in liquid metal

University of British Columbia

This investigation was undertaken to examine the heat flow characteristics of a liquid metal system in which fluid flow is present due to buoyancy forces. Previous investigations of heat flow in liquids has been confined to transparent materials, which have very different flow characteristics compared to liquid metals. Measurements were made on liquid tin contained in a thin square cavity which had a temperature difference imposed across the cell to produce natural convection. The heat flow across the cell was calculated from the measured temperature difference across the cold end plate and the thermal conductivity of the plate. Using the calculated heat flow and the measured temperature difference across the melt the effective thermal conductivity of the melt was calculated. Two cell sizes were studied. The thermal conductivity of the cold end plate was found to have a significant effect on the heat transfer through the cell. Radioactive tracers were used to observe the flow pattern in the melt and to measure the flow velocity as a function of the temperature difference across the cell. The technique involved insertion of radioactive Sn¹¹³ into the melt, then quenching the sample after a given length of time. The sample was then autoradiographed to determine the path of the tracer after insertion into the melt. The flow was found to be very fast for the smaller of the two cell sizes which exhibited three-dimensional flow characteristics. The larger cell produced laminar, two-dimensional flow. A correlation was observed between the time per cycle and the temperature difference across the large cell. The study also includes a finite-difference model which was developed to provide further insight into the thermal and fluid flow behaviour of the melt. The model examines the effect of nonuniform temperatures along the ends and bottom of the cell on the temperature and velocity fields and is used to compare the response of liquid tin and liquid steel to identical temperature differences. Results from the model indicate that either a temperature drop along the hot and cold ends of the cell or the presence of a linear gradient along the bottom of the cell would decrease the maximum fluid velocity in the cell. The present investigation shows that the enhancement of the thermal conductivity due to the presence of natural convection in the liquid metal can be as high as ten times the stagnant thermal conductivity. However the degree of enhancement is influenced by the thermal resistance at the boundaries.

Text

2010-05-22

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http://hdl.handle.net/2429/24927

Materials Engineering

University of British Columbia

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