This　study　presents　numerical　computation　results　on　laminar　convection　heat　transfer　in　a　rectangular　channel　with　a　pair　of　rectangular　winglets　longitudinal　vortex　generator　punched　out　from　the　lower　wall　of　the　channel.　The　effect　of　the　punched　holes　and　the　thickness　of　the　rectangular　winglet　pair　to　the　fluid　flow　and　heat　transfer　are　numerically　studied.　It　is　found　that　the　case　with　punched　holes　has　more　heat　transfer　enhancement　in　the　region　near　to　the　vortex　generator　and　lower　average　flow　frictional　coefficient　compared　with　the　case　without　punched　holes.　The　thickness　of　rectangular　winglet　can　cause　less　heat　transfer　enhancement　in　the　region　near　to　the　vortex　generator　and　almost　has　no　significant　effect　on　the　total　pressure　drop　of　the　channel.　The　effects　of　Reynolds　number　(from　800　to　3000),　the　attack　angle　of　vortex　generator　(15　degrees,　30　degrees,　45　degrees,　60　degrees　and　90　degrees)　were　examined.　The　numerical　results　were　analyzed　from　the　viewpoint　of　field　synergy　principle.　It　was　found　that　the　essence　of　heat　transfer　enhancement　by　longitudinal　vortex　can　be　explained　very　well　by　the　field　synergy　principle,　i.e.,　when　the　second　flow　generated　by　vortex　generators　results　in　the　reduction　of　the　intersection　angle　between　the　velocity　and　fluid　temperature　gradient,　the　heat　transfer　in　the　present　channels　will　be　enhanced.　Longitudinal　vortices　(LVs)　improve　the　synergy　between　velocity　and　temperature　field　not　only　in　the　region　near　LVG　but　also　in　the　large　downstream　region　of　longitudinal　vortex　generator.　So　LVs　enable　to　enhance　the　global　heat　transfer　of　channel.　Transverse　vortices　(TVs)　only　improve　the　synergy　in　the　region　near　VG.　So　TVs　can　only　enhance　the　local　heat　transfer　of　channel.　(C)　2007　Published　by　Elsevier　Ltd.