Investigation of Micro CT based method for porosity estimation of sintered-wick heat pipes.

The use of sintered-wick heat pipes in heat exchanger performance-related studies gained popularity owing to the simplicity and affordability of heat pipes. Evaluation of the system performance may be based on various arrangements and numbers of heat pipes applicable to the literature. Wick porosity and permeability are critical parameters for the investigation of wick capillary pumping, which will ultimately determine heat pipe performance. Despite the significance of these parameters to thermal performance, they are difficult to obtain, as the methods for obtaining these parameters before installing the heat pipes are time-consuming and destructive. This study aims to investigate the feasibility of Micro Tomography (Micro CT) to observe the porosity of copper sintered-wick heat pipes. Visual data from three heat pipe samples, namely HP1, HP2, and HP3 are quantified and analyzed. Analysis of the average porosity of HP1 and HP2 samples showed a similar value of 47.6 and 48.1%, respectively; however, the value of porosity along the length of the scanned area shows a bigger range of 42-54%. The accuracy of Micro CT was tested by testing three porosity samples with designed porosity of 26%, 22.3%, and 16.6% which were 3D printed using atomic diffusion additive manufacturing technology. Each sample was designed with pore shapes hexagonal, circular, and elliptical, respectively. Micro CT visualization and analysis showed the porosity reduction of the 3D printed porosity samples compared to the CAD design. Due to the smallest reduction of porosity after the sintered process, the 3D printed sample with a hexagonal pore shape, and the designed porosity of 26%, this sample was recommended for sintered wick fabrication using this technology and to test the accuracy of Micro CT.