The　effect　of　the　tube　wall　on　the　fluid　flow　and　heat　transfer　would　be　important　in　the　packed　bed　with　low　tube　to　particle　diameter　ratio,　which　may　lead　to　flow　and　temperature　maldistributions　inside,　and　the　heat　transfer　performance　may　be　lowered.　In　the　present　paper,　the　flow　and　heat　transfer　performances　in　both　the　composite　and　uniform　packed　beds　of　spheres　with　low　tube　to　particle　diameter　were　numerically　investigated,　where　the　composite　packing　means　randomly　packing　with　non-uniform　spheres　and　the　uniform　packing　means　randomly　packing　with　uniform　spheres,　including　radially　layered　composite　packing　(RLM),　axially　layered　composite　packing　(ALM),　randomly　composite　packing　(RCM)　and　randomly　uniform　packing　(RPM).　Both　the　composite　and　uniform　packings　were　generated　with　discrete　element　method　(DEM),　and　the　influence　of　the　wall　effect　on　the　flow　and　heat　transfer　in　the　packed　beds　were　carefully　studied　and　compared　with　each　other.　Firstly,　it　is　found　that,　the　wall　effect　on　the　velocity　and　temperature　distributions　in　the　randomly　packed　bed　of　uniform　spheres　(RPM)　with　low　tube　to　particle　diameter　ratio　were　obvious.　The　average　velocity　of　the　near-tube-wall　region　is　higher　than　that　of　the　inner　-tube　region　in　the　bed.　When　the　tube　wall　is　adiabatic,　the　average　temperature　of　the　near　-tube　-wall　region　is　lower.　With　radially　layered　composite　packing　method　(RLM),　smaller　pores　would　be　formed　close　to　the　tube　wall　and　big　flow　channels　would　be　formed　in　the　inner　-tube　region　of　the　bed,　which　would　be　benefit　to　restrain　the　wall　effect　and　improve　heat　transfer　in　the　bed　with　low　tube　to　particle　diameter　ratio.　Furthermore,　it　is　also　found　that,　with　composite　packing　method　(RLM,　ALM　and　RCM),　both　the　pressure　drop　and　heat　flux　are　higher　than　those　in　the　uniform　packing　(RPM).　And　with　radially　layered　packing　method　(RLM),　the　flow　resistance　would　be　reduced,　and　both　the　heat　flux　and　overall　heat　transfer　efficiency　would　be　further　improved　for　the　composite　packing　with　low　tube　to　particle　diameter　ratio.　(C)　2016　Elsevier　B.V.　All　rights　reserved.