Metodika vyhodnocování tepelných experimentů s hliníkovým vzorkem

Methodology of Evaluation of Heat Transfer Experiment on Aluminum sample

conference paper

en

Cooling is one of the critical points during aluminum casting. Improper cooling leads to a structure which isn't homogenous, full of internal and surface defects. It is necessary to know the boundary conditions (heat transfer coefficient or heat flux) for cooling optimization. The boundary conditions for different types of cooling are obtained from experiments. This article is focused on the cooling of vertical surfaces of aluminum by flat water jets. The sample initial temperature was close to the liquid state. The sample was cooled while in a vertical position by a flat water jet which hit the upper part of the cooling surface, and then the water flow down along the surface. The temperatures were recorded during the experiment by a set of thermocouples which were installed inside the sample. Thermocouples were placed closed to the cooled surface at different heights. The moving horizontal Leidenfrost front between nucleate and film boiling could be observed during the experiment. This front moved downward along the sample surface. The aim of this work is to evaluate the boundary conditions for described measurements. The evaluation held due to the solution of the 2D inverse task, similar to Beck’s sequential methods. The computation procedure was modified to be able to deal with the moving Leidenfrost front between low and height cooling intensities. Results are presented in a form of heat transfer coefficients as a function of position and temperature.

Tento článek se zaměřuje na chlazení svislého hliníkového povrchu plochým vodním paprskem. Počáteční teplota vzorku byla blízká teplotě kapalného hliníku. Vzorek byl chlazený ve svislé poloze. Vodní paprsek se přicházel do kontaktu ve vrchní části vzorku a dále po něm volně stékal dolů. Teploty v různých výškách byly zaznameny pomocí podpovrchových termočlánků. Během experimentu byl pozorován Leidenfrostova hranice mezi dvěma režimy chlazení. Tato hranice se během experimentu pohybuje směrem dolů. Cílem této práce je vyhodnotit okrajové podmínky pro popsané měření. K vyhodnocení bylo použito řešení 2D inverzní úlohy vycházející ze sekvenční Beckovy metody. Vypočetní metoda však byla modifikována tak, aby bylo možné postihnout pohybující se Leidenfrostovu hranici mezi málo a vysoce intenzivním chlazením. Výsledky jsou prezentovány ve formě koeficientu přestupu tepla ve tvaru funkcí polohy a teploty.

Cooling is one of the critical points during aluminum casting. Improper cooling leads to a structure which isn't homogenous, full of internal and surface defects. It is necessary to know the boundary conditions (heat transfer coefficient or heat flux) for cooling optimization. The boundary conditions for different types of cooling are obtained from experiments. This article is focused on the cooling of vertical surfaces of aluminum by flat water jets. The sample initial temperature was close to the liquid state. The sample was cooled while in a vertical position by a flat water jet which hit the upper part of the cooling surface, and then the water flow down along the surface. The temperatures were recorded during the experiment by a set of thermocouples which were installed inside the sample. Thermocouples were placed closed to the cooled surface at different heights. The moving horizontal Leidenfrost front between nucleate and film boiling could be observed during the experiment. This front moved downward along the sample surface. The aim of this work is to evaluate the boundary conditions for described measurements. The evaluation held due to the solution of the 2D inverse task, similar to Beck’s sequential methods. The computation procedure was modified to be able to deal with the moving Leidenfrost front between low and height cooling intensities. Results are presented in a form of heat transfer coefficients as a function of position and temperature.

Aluminum casting, 2D inverse task, heat transfer coefficients, sequential approach

2015

03.06.2015

TANGER

Ostrava

978-80-87294-58-1

METAL 2015 Full Texts of Papers

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