Fluid-Thermal Transport Properties of Sintered Wicks

Overview

Porous sintered microstructures are critical to the functioning of passive heat transport devices such as heat pipes. Commercial wick samples of varying particle size were CT scanned at 5.5 µm resolution and solid and pore spaces were segmented based on the scan data. Subsequently, the segmented regions were meshed for pore scale CFD analysis in FLUENT. Multiple realizations were employed to determine the statistical average of the considered samples.

Characteristics:

  • Metal Artefact Reduction
  • Threshold and flood fill segmentation
  • Multipart meshing
  • Multiphysics simulation
  • Computational Fluid Dynamics in ANSYS Fluent

Thanks to

School of Mechanical Engineering, Purdue University & Department of Mechanical Engineering, University of Texas at Austin: 
K.K. Bodla • J.Y. Murthy • S.V. Garimella

The authors acknowledge support for this work from industry members of the Cooling Technologies Research Center, an NSF Industry/University Cooperative Research Center at Purdue University.

Image Processing

The serial 2-dimensional image slices of the sintered wicks were imported into Simpleware ScanIP where the segmentation was performed based on a simple thresholding operation, with the threshold value selected to match the manufacturer quoted porosity (open volume fraction). Prior to segmentation, the scan data was also suitably filtered employing the metal artefact reduction filter in ScanIP. Following this, a flood fill operation was also performed, to retain only the connected solid phase.

Mesh Generation

The segmented data was meshed using the +FE Grid meshing algorithm to produce mixed hexahedral/tetrahedral cells. The generated meshes contained mesh densities of approximately 20 million elements, for both solid and pore domains collectively. The smoothed conformal meshes generated were of very high quality and consisted of approximately 20 x 106 cells for each subvolume (both metal and pore). The mesh was then exported to ANSYS Fluent for flow and heat transfer analysis.

Simulation

Simulations of static effective thermal conductivity, friction factor, permeability and interfacial heat transfer were performed for flow velocities in the Darcy regime, as encountered in a typical heat pipe. The results were compared against empirical and analytical correlations available in literature. Furthermore, new correlations were proposed to better predict the Nusselt number for sintered wicks. From the scan data a critical parameter, the necking ratio, was also estimated; and for the samples of interest, effective thermal conductivity was observed to be a linear function of this parameter.