  Effective thermal conductivity of LaNi$_5$ powder packed bed was analyzed
with customized guarded hot-plate (GHP) apparatus. Here, GHP was designed for
precise measurement of effective thermal conductivity of metal-hydride powders
even with small sample amounts (2.12$\times$10$^4$ mm$^3$). Dimensions of
sample container and apparatus were determined through two-dimensional (2-D)
steady-state heat conduction analysis. Calibration experiment and uncertainty
analysis were conducted to validate the accuracy of the GHP. Based on the
measurements of the residual thermal conductivity of the LaNi$_5$ packed bed,
effect of particle size on contact factor of LaNi$_5$ packed bed was estimated.
By applying the Yagi and Kunii (YK) model to the effective thermal conductivity
of LaNi$_5$ packed bed, effect of contact factor and gas thermal conductivity
on characteristic length of gas film were newly analyzed. Factors of YK model
were modified in present work and validated through comparison with
experimental data from previous literature.

Applied Physics