Thermal analysis with OpenFOAM® of a neutron flux furnace in order to study the thermal gradients in the sample
In the Laue-Langevin Institute (ILL, Grenoble), research center for science and technology in which experiments with neutrons are developed, neutron diffraction experiments, among others, are carried out to study the structure of materials. So that the results obtained in the experiments, carried out in the instrument D4, are valid it is necessary that the sample does not have regions with different structure. For this reason, it is necessary that the sample does not show a noticeable temperature difference.
Materials undergo phase change at certain temperatures, that is to say, its internal structure changes. If an experiment shows coexistence of regions with different structure in the sample, the experiment is not valid.
First of all, the value of the thermal gradient in the sample is determined, by means of a set of thermal simulations made with OpenFOAM®, for certain situations. Next, critical factors that facilitate gradient’s existence in the sample are detected in order to proceed to its minimization. These factors are listed below:
- Geometric asymmetry with respect to the horizontal plane of the instrument D4 which causes horizontal thermal asymmetry in the sample. This phenomenon causes:
- Thermal losses from the sample to its support
- Asymmetric thermal distribution in the heating cylinder
With the aim of minimizing the thermal gradient in the sample, the thickness reduction of the alumina tube that makes up the support has been studied. Thus, a reduction in the effective area of conductive heat transfer is reached. This measure means a great enhancement in the sample’s thermal behaviour, leading to reduce the thermal gradient in the sample up to 80%.