A novel non-destructive methodology for the analysis of deformed heat pipes

This paper presents a non-destructive methodology to analyze the influence of bend angle on the thermal performance of a sintered copper wick heat pipe. A calorimeter-based technique is used to characterize the thermal performance of a concentric tube sintered wick heat pipe under bending deformation, for a range of bend angles. It is seen that the thermal resistance of this heat pipe increases by up to 31% as the pipe was bent by 90° while its maximum heat input reduces by 29%. X-ray tomography (µ-CT) is used to obtain geometric (pipe diameter, vapor channel, etc.) and morphological (porosity, pore size distribution) data for the pipe and wick at the bend site, and this data is utilized in a thermo-fluidic model of the pipe. The methodology quantifies the local vapor and liquid pressure drops caused by deformations to the wick and vapor channel of the pipe, and their influence on the capillary pressure limit. The X-ray method revealed that, when the heat pipe was bent to 90°, there was a 23% reduction in the vapor core area, a 7% increase in the wick area, and a 48% reduction in permeability at the bend site. These geometric changes accounted for a 12% increase in the vapor phase pressure drop and a 70% increase in the liquid phase pressure drop at the bend site. When compared to the overall capillary limit the increase in liquid pressure drop demonstrated a greater contribution (12 %) in comparison to the vapor pressure drop (0.5%). In spite of the fact that the methodology presents results for a heat pipe under a specific bending case, µ-CT inspection represents a novel diagnostic tool that can underpin the optimization of heat pipe manufacture, in order to mitigate the influence of bending deformations.