Three different diameter ice spheres were formed and allowed to melt in air. Each sphere was suspended by a string from a cantilevered beam, which had strain gages attached. A four active element Wheatstone Bridge was used to measure the output of the strain gages. The output signal was calibrated to measure weight of the sphere at any time during the phase change process. Data on weight versus time were thus obtained using a recorder, and used to calculate values of Nusselt and Rayleigh numbers at various instants in time. The geometry of each sphere changed during the melting process as did surface area and volume. A satisfactory determination of characteristic length was proposed which yielded excellent results. An equation relating Nusselt number to Rayleigh number was derived with a correlation coefficient of 0.975. Rayleigh numbers ranged 1.0 × 104 to 1.2 × 107, while Nusselt number ranged from 4 to 10.2. It was found that the Nusselt number could be predicted with
Nu = 1.45 Ra0.126
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