Within　the　Reynolds　number　range　from　5000　to　40000,　experiments　were　performed　by　using　cross-ribs　(three　angles:　45,　60,　75　degrees;　two　heights:　4　mm,　5　mm)　roughened　ducts　to　determine　the　effect　of　building　repeated　turbulators　in　the　inner　surface　of　rectangular　duct　on　forced　convection　and　fluid　friction.　The　experimental　results　show　that　for　the　cross　rib　arrangements,　the　rib　height　and　cross　angle　have　positive　effect　on　heat　transfer;　the　larger　the　cross　angles　and　the　rib　height,　the　higher　the　heat　transfer　coefficients.　At　the　meantime,　the　friction　factor　also　increases　significantly.　Compared　with　the　parallel　rib　configuration,　the　cross-rib　arrangement　can　enhance　heat　transfer　with　greater　penalty　in　pressure　drop.