Research on the effective thermal conductivity of nickel-based bi-porous capillary wicks: Modeling and validation

This study proposed an analytical model to predict the effective thermal conductivity (ETC) of bi-sized porous capillary wicks with both interstitial pores (formed inside nickel skeleton) and with large pores created by NaCl as the pore-forming agent. The interstitial-pore model was developed utilizing the sintering neck formation theory and thermal resistance network, which was validated by measured data obtained from samples of multiple particle sizes. It is shown that the model works well for fine nickel powders with the root mean square error (RMSE) of 13.8%, while a large deviation was observed when using the coarse powders. Based on the presented interstitial-pore model, an ETC model for samples containing formation pores was formulated. A total of six types of equations were proposed, considering three packing modes and two shapes of formation pores. Samples with NaCl of various granularities (54-75 mu m, 88-125 mu m) and proportions (2.5, 5.0, 7.5, and 10.0 wt.%) were made for the model validation. The results demonstrated that the bi-porous ETC models, with both interstitial pores and those formed by NaCl, exhibit good performance when applying the BCC configuration, while small and large formation pores can be characterized by spherical and cubic models respectively.