The　latent　heat　of　phase　change　material　(PCM)　can　be　used　to　enhance　the　heat　storage　capacity　of　latent　heat　thermal　energy　storage　(LHTES)　system.　However,　the　low　thermal　conductivity　of　PCM　limits　the　application　of　LHTES　systems.　In　this　paper,　the　thermal　conductivity　of　PCM　was　enhanced　by　adding　expanded　graphite　into　PCM,　and　the　thermal　storage　characteristics　of　the　shell-in-tube　LHTES　system　were　experimentally　studied　under　different　water　flow　rates.　The　pure　pentadecane　and　composite　pentadecane　with　a　mass　fraction　of　30%　expanded　graphite　were　adopted.　The　experimental　results　show　that,　for　the　pentadecane　with　a　mass　fraction　of　30%　expanded　graphite　as　thermal　storage　medium,　there　exists　a　significant　peak　for　the　effective　thermal　storage　coefficient　and　relative　thermal　storage　ratio　at　Re　=　4298　during　cooling　discharging,　and　the　heat　exchange　efficiency　and　heat　storage　capacity　achieve　relative　balance.　Moreover,　at　Re　=　4298,　the　effective　energy　storage　coefficient　increases　up　to　336.84%　by　using　pentadecane　with　a　mass　fraction　of　30%　expanded　graphite　compared　with　the　pure　pentadecane.　©　2021,　Science　Press.　All　right　reserved.