This　paper　presents　a　theoretical　investigation　of　the　behavior　of　the　jacket-type　radial　heat　pipe　in　a　transient　regime.　We　used　a　simple,　rapid　mathematical　model　to　calculate　the　unsteady-state　startup　process　of　the　jacket-type　radial　heat　pipe.　We　also　developed　a　computer　simulation　program　based　on　the　method　that　estimates　the　temperature　of　the　heat　pipe　as　well　as　the　time　needed　to　reach　a　steady-state　condition.　This　paper　presents　an　analysis　of　the　startup　performance　of　the　heat　pipe　with　variation　of　the　input　heat　power.　Experiments　were　focused　on　defining　the　influence　of　the　input　heat　power　on　the　steady-state　heat　transfer　characteristics　of　the　jacket-type　radial　heat　pipe.　The　simulation　results　are　in　good　agreement　with　experimental　data.　Other　favorable　outcomes　were:　the　locations　near　the　orifice　have　good　temperature　uniformity　in　the　inner　tube;　an　increasing　Reynolds　number　results　in　a　decreasing　Nusselt　number　on　a　smooth　surface,　and　the　total　thermal　resistance　of　the　heat　pipe　decreases　with　increase　in　the　input　heat　power　and　filling　ratio.