The　thermal　and　heat　transfer　characteristics　of　stearic　acid　during　the　solidification　processes　were　investigated　experimentally　in　a　vertical　annulus　energy　storage　system.　The　temperature　distribution　and　temperature　variations　with　time　at　different　radial　positions　during　the　freezing　processes　were　obtained.　The　thermal　characteristics　of　the　stearic　acid,　including　movement　of　the　solid-liquid　interface　in　the　radial　direction,　and　the　effects　of　Reynolds　number　on　the　heat　transfer　parameters　were　studied.　The　heat　flux　was　estimated　by　using　a　simple　approximate　model.　A　new　copper　fin　was　designed　and　fixed　to　the　electrical　heating　rod　to　enhance　the　thermal　conductivity　of　the　stearic　acid.　The　results　show　that　the　new　fin　can　enhance　both　the　conduction　and　the　natural　convection　heat　transfer　of　the　PCM,　and　the　enhancement　factor　during　solidification　is　estimated　to　be　as　high　as　250%.　The　effect　of　the　fin　width　on　the　enhancement　was　also　examined　experimentally,　and　it　is　found　that　the　fine　fin　usually　produce　more　effective　enhancement.　(C)　2004　Elsevier　Ltd.　All　rights　reserved.