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

•An analytical thermal conductivity model of bi-porous structures was developed and experimentally validated.•The interstitial-pore model was formulated based on the neck formation theory considering the effect of sintering parameters.•The validation shows that the BCC configuration of formation pores concurs well with measured data, while the models of different formation pore sizes can be characterized by pore shapes.•The presented model shows high accuracy and applicability when compared to previous classic ETC models. 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 μm, 88–125 μm) 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.