This　study　aims　to　conduct　an　experiment　to　understand　the　influence　of　inclination　angle　on　coupled　heat　transfer　process　of　heat　pipe　and　the　phase　change　material　(PCM)　under　constant　heat　flux　conditions.　An　experimental　platform　for　an　angle-adjustable　latent　heat　storage　unit　using　flat　heat　pipe　and　lauric　acid　was　designed　and　fabricated.　Melting　time　of　PCM　and　time-varying　temperature　pattern　of　flat　heat　pipe　and　PCM　under　different　inclination　angles　were　recorded.　Effective　thermal　resistance　and　conductivity　of　flat　heat　pipe,　thermal　resistance,　and　heat　transfer　coefficient　between　flat　heat　pipe　and　PCM　were　also　calculated　and　analyzed.　Results　showed　that　(1)　the　overall　melting　time　of　the　PCM　is　extended　although　heat　transfer　on　the　PCM　side　enhances　with　the　decrease　of　inclination　angle　and　the　average　thermal　resistance　between　PCM　and　flat　heat　pipe　reduces　from　0.084　K·W−1　to　0.071　K·W−1　(heat　transfer　enhancement　of　15.5%)　while　the　melting　time　prolongs　from　78.6　min　to　80.1　min　(1.9%　increment)　when　the　input　heat　is　20　W　and　the　inclination　angle　decreases　from　90°　to　15°　(83.3%　reduction)　and　(2)　the　effective　thermal　conductivity　of　the　flat　heat　pipe　first　decreases　and　then　increases　with　the　increment　of　the　inclination　angle　under　an　inclination　angle　of　30°–90°.　Maximum　and　minimum　thermal　resistance　values　are　0.058　(3.7%　increase　compared　with　those　at　90°)　and　0.053　(6.1%　reduction　compared　with　those　at　90°)　K·W−1　at　30°　when　the　heating　power　is　20　W　and　the　inclination　angle　is　75°.　However,　the　heat　transfer　performance　of　the　flat　heat　pipe　deteriorates　when　the　input　heat　is　high　(>30　W)　under　the　condition　of　small　inclination　angles　(<30°).　For　example,　the　heat　transfer　resistance　of　the　flat　heat　pipe　is　with　the　range　of　0.056–0.058　K·W−1　at　an　inclination　angle　of　30°–90°　when　the　heating　power　is　50　W　and　the　thermal　resistance　suddenly　increases　from　0.056　K·W−1　to　0.074　K·W−1　(an　increase　of　31.5%)　when　the　inclination　angle　decreases　from　30°　to　15°.　©　2022　Elsevier　Ltd