engleski

Modelling Of Transient Heat Transfer In Zinc Fixed Point Cell

Current practice in fixed-point calibration recommends usage of furnaces that provide best achievable uniform temperature distribution at the outer segment of the immersed portion of the fixed-point cell. The effect of any inhomogeneous temperature distribution is somewhat unrevealed, and its coverage in literature is insufficient. In order to establish some estimation of the influence of the inhomogeneous furnace temperature distribution to the calibrating process, a numerical study was conducted. The study was conducted using FLUENT software package employing finite volume method on non-structured grids. The problem was considered as axially symmetric. The domain of the calculation consisted of the whole cell volume and its geometry was modeled such to distinguish each of the individual elements of the fixed point cell assembly. The material properties of the assembly elements were treated as temperature dependent, while their surface properties were kept constant. The mathematical model employs transient conductive heat transfer along with solidification model for Zinc so as radiation heat transfer between surfaces in all argon - filled cavities. The effect of natural convection was assumed to be of minor importance and was therefore neglected thus saving significant amount of computational effort. The calculations covered the whole duration of Zinc solidification process. Several variants of boundary conditions at the fixed - point cell's outer surface were applied. The variants distinguish: the homogeneous temperature distribution at the outer skin of the immersed part of the fixed point cell, the plus and minus 1 K/m of gradient added to base temperature distribution in axial direction and the presence or absence of cold-roding. The base outer temperature was kept 1 K below the solidus temperature giving approximately 6 hours of calibration process. The study shows that such linear gradient of +/- 1 K/ m influences the process solely in its duration, prolonging it or shortening it for approximately 20minutes.

Modelling; Transient heat transfer; Fixed-point

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