INTRODUCTION

For this example, we will use FluxTracer to investigate the radiant energy distribution within a Compound Parabolic Concentrator (CPC), which is used as a secondary concentrator around the focal region of a parabolic dish geometry. Figure 1 shown the geometry as implemented in Tonatiuh++.

Figure 1: The Tonatiuh++ scene showing the dish and CPC secondary concentrator

The Compound Elliptical Concentrator (CEC) surface was implemented in Tonatiuh++ using an object (.obj) file with a very fine mesh to enhance the accuracy of the simulations (Figure 2). To see a how to guide on how to import CAD models in Tonatiuh++ please refer to the corresponding Tonatiuh++ documentation by pressing here. The dish is normally designed in Tonatiuh++ using a combination of a spherical and a circular parabolic sector. The CPC receiver inlet is located at (X ,Y ,Z)=(0 , 0, 4.384)m.

Figure 2: Details of the dish-CPC geometry

RAY TRACING

For the ray tracing simulations, instead of placing a virtual surface, the CPC receiver surface is now considered as a VirtualRoof surface. The reflectivity of the dish and CPC surfaces is set to 0.85, while for the sun parameters, the Buei sunshape is chosen with a circumsolar ratio of 5%. The reflecting surfaces slope error was set as 2mrads. After setting up the Tonatiuh++ scene, the entire photon map is saved in a corresponding folder. For this case, 300.000.000 rays have been casted from the sun.

FLUXTRACER

In FluxTracer, we will use the voxel traversal functionality in order to investigate the radiant energy distribution within the CPC. For this reason, a bounding box is defined around the entire receiver geometry using 500x500x500 voxels. This voxel density is quite fine but is needed in order to resolve the geometry of the CPC and to filter out the receiver geometry in high resolution during post processing.

Figure 3: Setting-up FluxTracer

This is set in the voxel traversal functionality as follows:
<VoxelTraversal cornerMin="-0.1, -0.1, 4.384" cornerMax="0.1, 0.1, 4.566" dimensions="500, 500, 500" output="VoxelTraversal.vtk"/>

This will create a bounding box of (X, Y)=(0.1x0.1)m with the height of the CPC in the Z direction. After running FluxTracer, the .vtk output can be then post processed using Paraview. In order to optimize the positioning of the CPC along the Z axis, another set-up has been simulated where the CPC inlet is now located at Z=4.5m instead of Z=4.384.

POST-PROCESS

Figure 4 shows a comparison between the radiant energy distribution within the CPC for the two cases, i.e. when the CPC inlet is at Z=4.5m and Z=4.384 respectively

Figure 4: Comparison of the distribution of radiant energy within the CPC