This　study　conducts　experimental　visualization　and　numerical　study　on　the　melting　of　phase　change　material　(PCM)　in　a　rectangular　enclosure　of　a　latent　heat　storage　unit　based　on　micro-heat　pipe　arrays.　The　solid-liquid　interface　and　temperature　distribution　in　the　melting　of　PCM　are　recorded　by　photographic　observation　and　data　measurement.　Numerical　results　based　on　the　enthalpy-porosity　model　are　validated　by　using　experimental　results.　The　effects　of　enclosure　geometry　on　the　melting　process　of　PCM　are　numerically　explored.　The　transition　point　of　a　pure　conduction　mode　into　the　natural　convection　mode　is　analyzed　by　comparing　the　results　obtained　in　the　numerical　simulation　with　and　without　considering　thermal　convection.　The　correlations　of　the　transient　heat　transfer　and　the　melting　rate　in　the　pure　conduction　and　natural　convection　modes　are　determined　through　the　analysis　of　the　different　heat　transfer　characteristics　in　both　stages.　The　results　are　expected　to　provide　guidance　for　the　design　of　latent　heat　storage　units　using　micro-heat　pipe　arrays　in　engineering　applications.　(c)　2022　Elsevier　Ltd.　All　rights　reserved.