We present planforms of line plumes formed on horizontal surfaces in turbulent convection, along with the length of line plumes measured from these planforms, in a six decade range of Rayleigh numbers (10 5 < Ra < 10 11 ) and at three Prandtl numbers (Pr = 0.7, 5.2, 602). Using geometric constraints on the relations for the mean plume spacings, we obtain expressions for the total length of near-wall plumes on horizontal surfaces in turbulent convection. The plume length per unit area (L p /A), made dimensionless by the near-wall length scale in turbulent convection (Z w ), remains constant for a given fluid. The Nusselt number is shown to be directly proportional to L p H/A for a given fluid layer of height H. The increase in Pr has a weak influence in decreasing L p /A. These expressions match the measurements, thereby showing that the assumption of laminar natural convection boundary layers in turbulent convection is consistent with the observed total length of line plumes. We then show that similar relationships are obtained based on the assumption that the line plumes are the outcome of the instability of laminar natural convection boundary layers on the horizontal surfaces.

High-temperature electrochemical cells based on stabilized zirconia

Refractive index matching (RIM) methods are widely used in combination with optical flow measurement techniques such as particle image velocimetry and laser Doppler velocimetry to investigate fluid flows. In applying RIM, matching the refractive indices of the fluid and solid eliminates the problem of refraction/reflection at the solid–liquid interface. An experimental analysis of the effects of salt mass fraction and temperature on the refractive index of potassium thiocyanate (KSCN) solutions is conducted to quantify its performance as a RIM solution that is used in flow experiments. This enables the researchers to control the refractive index of the test medium under different test conditions by manipulating the KSCN mass fraction in the solution. Empirical correlations are developed by fitting the refractive index results, which highlight a nonlinear dependency on mass fraction and a linear dependency on temperature. The refractive index of the KSCN solution is found to be much less sensitive to changes in salt mass fraction and temperature compared to sodium iodide (NaI) solutions, a salt solution more commonly used for RIM studies. For a demonstration case, the refractive index of a KSCN solution was adjusted to align with borosilicate glass, a common transparent material used in two-phase experiments. The refractive index of the solid is a function of the quality and mass fraction of the ingredients used in the batch manufacturing operation and the process itself. For the batch of borosilicate beads used, a 0.624 (kg/kg) KSCN solution provided a perfect index matching rendering the glass beads transparent. Using this approach, the refractive index of a solid with a small and complex shape could be measured. In flow experiments, in addition to the refractive index, other fluid properties are influential and might need to be matched with the application. A discussion is also provided on the density, viscosity, surface tension, and pH of KSCN solutions to enable fluid dynamic scaling of experimental flow conditions through a set of correlations, developed to predict the properties of different KSCN solutions.

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Eine elektrochemische Hochtemperaturzelle mit festem CaO‐stabilisiertem ZrO2‐Elektrolyten und porösen Pt‐Elektroden wird zur Kontrolle und Messung des Sauerstoffpartialdrucks in einem strömenden inerten Trägergas (Ar) benutzt.