3-D　numerical　simulation　results　are　presented　for　fin-and-tube　heat　transfer　surface　with　vortex　generators.　The　effects　of　Reynolds　number　(from　800　to　2000),　the　attack　angle　(30°　and　45°)　of　delta　winglet　vortex　generator　are　examined.　The　numerical　results　are　analyzed　based　on　the　field　synergy　principle　to　explain　the　inherent　mechanism　of　heat　transfer　enhancement　by　longitudinal　vortex,　namely　second　flow　generated　by　the　vortex　generators　causes　the　reduction　of　the　intersection　angle　between　the　velocity　and　fluid　temperature　gradient.　In　addition,　the　computational　evaluations　indicate　that　the　heat　transfer　enhancement　of　delta　winglet　for　aligned　tube　bank　heat　exchanger　is　more　significant　than　that　for　staggered　tube　bank　heat　exchanger,　the　heat　transfer　enhancement　of　delta　winglet　with　the　attack　angle　of　45°　is　more　obvious　than　that　of　30°;　the　delta　winglet　with　the　attack　angle　of　45°　leads　to　an　increase　in　pressure　drop,　while　the　delta　winglet　with　the　attack　angle　of　30°　results　in　a　slight　decrease.　The　heat　transfer　enhancement　per　unit　pumping　power　for　attack　angle　of　30°　is　larger　than　that　for　attack　angle　of　45°　either　for　staggered　or　for　aligned　tube　bank　arrangement.