Experimental　investigations　of　two　different　flat　plate　heat　pipes　(FPHPs)　are　presented.　The　capillary　structure　is　made　of　intersected　narrow　grooves　for　the　first　FPHP　and　interlaced　channels　for　the　second　FPHP.　The　copper　heat　pipes,　filled　with　deionized　water,　were　tested　in　different　heat　fluxes　and　working　fluid　filling　ratios.　The　temperature　fields　and　overall　thermal　resistances　of　the　heat　pipes　under　different　experimental　conditions　are　studied.　The　experiments　were　performed　with　copper　radiator　and　electronic　fan　which　have　been　commercially　applied　for　CPU　cooling　to　simulate　a　practical　application.　The　results　indicate　that　the　optimal　filling　ratios　of　the　FPHPs　are　65%　for　FPHP　1　and　70%　for　FPHP　2.　The　smallest　thermal　resistances　of　FPHPs　at　their　optimal　filling　ratios　are　0.183　K/W　and　0.071　K/W　for　FPHP　1　and　FPHP　2　respectively.　The　thermal　performances　of　the　FPHPs　in　both　axial　and　radial　directions　at　various　heat　fluxes　are　also　investigated.　The　results　disclose　that　the　special　design　of　FPHP　2　can　improve　the　heat　conduction　in　axial　direction　and　enhance　the　capillary　effect.　Otherwise,　the　temperature　leveling　ability　of　both　FPHPs　on　cooling　surface　is　similar　in　radial　direction.　(C)　2013　Elsevier　Inc.　All　rights　reserved.