This　paper　presents　a　simple　and　rapid　mathematical　model　to　calculate　the　non-steady-state　startup　process　and　study　the　isothermal　characteristics　of　a　particular　heat　pipe.　The　model　takes　into　consideration　the　special　structure　and　usage　conditions,　where　vapor　temperature　in　the　heat　pipe　changes　only　over　time.　This　vapor　temperature　change　correlation　is　calculated　numerically　and　is　set　as　the　temperature　boundary　condition　for　the　working　well.　The　temperature,　velocity　and　pressure　distribution　in　the　working　well　are　then　solved　using　FLUENT.　The　results　manifest　that　the　time　required　for　approaching　steady　condition　are　450　s,　550　s　and　600　s　with　water　bath　temperatures　of　330　K,　340　K　and　350　K,　respectively.　The　comparison　of　the　calculations　and　experimental　data　shows　good　agreement,　and　the　maximum　deviation　is　3.7　K.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.