The experimental investigation of thermal parameters of free elementary convective cell
Keywords:
elementary convective cell-free border, convective processes, heat transfer, temperature gradientAbstract
This work substantiates the existence of an elementary convective cell by comparing the theoretical model and experimental data, as well as experimental determinations of characteristic velocities of fluid convection within a cell. It was assumed that suspension near the bottom of the vessel should be regarded as separate environment, with distinct from of a pure oil density and viscosity, which moves along an oil substrate of a pure oil without friction. In these conditions, boundary conditions of layer fluid can be considered as free. This assumption is supported by results of the numerical processing of experimental results on formation of convective rings in a layer of fluid, heated from below, obtained by other authors. Geometric dimensions and the velocity of mass transfer of the elementary convection cell were experimentally investigated in this work. As a result of experiments on formation a cylindrical convective cell by overlay of the copper ring on a surface of oil, qualitative and quantitative correspondence of the theoretical model to the experimental data was shown. Results of experimental studies were adequately described by the theoretical model of elementary convection cell. It is shown, that the adding of aluminum powder in oil, transforms oil to a suspension, such that boundary conditions on the solid wall can be regarded as free, because we have a slip through the tape of pure oil. Change in the character boundary conditions is confirmed by results of numerical processing of experimental results on formation of convective rings by other authors. Two independent methods for determining the velocity of mass ttransfer in cells with various diameters were described in this work. For cells with large diameter (17 mm), the maximum velocity of mass transfer was measured at the upper boundary on a deflection angle of the probe. Measured in this way velocity was equal 0,2 mm/sec. For cells with smaller diameter (2 mm), the velocity of oil on the surface of a cell was measured using an optical method and constituted the value from 3,5 mm/sec to 5,2 mm/sec..
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