In　latent　heat　storage　units,　phase　change　materials　are　often　combined　with　metal　foams　to　enhance　heat　transfer　due　to　their　low　thermal　conductivity.　However,　the　current　metal　foam　structure　cannot　solve　the　problems　of　long　melting　time　and　uneven　melting　caused　by　natural　convection.　To　obtain　superior　heat　storage　structures,　this　paper　uses　a　multichannel　flat　tube　as　the　heat　exchange　element　and　designs　units　with　a　variable　volume　ratio　of　gradient　copper　foam.　This　tube　is　divided　into　parts　A　and　B　and　has　a　decreasing　porosity　along　the　vertical　direction　from　top　to　bottom.　Results　of　orthogonal　tests　show　that　low　porosity,　a　large　volume　ratio　of　part　A,　and　a　large　gradient　can　improve　the　performance.　An　average　porosity　of　0.84,　gradient　of　9%,　and　part　A　volume　ratio　of　80%　are　selected　as　the　optimal　structural　parameters.　Compared　with　a　homogeneous　porosity　structure　having　a　porosity　of　0.96　under　original　working　conditions,　the　optimal　structure　has　48.64%　higher　heat　storage　capacity　and　54.13%　shorter　melting　time.　Meanwhile,　compared　with　a　homogeneous　porosity　structure　having　the　same　porosity　of　0.84,　the　optimal　structure　has　an　11.37%　higher　heat　storage　capacity　and　4.09%　shorter　melting　time.　©　2023　Elsevier　Ltd