Organic　Rankine　cycle　is　a　promising　technology　to　recover　the　waste　heat　of　an　internal　combustion　engine.　Improving　evaporator　performance　plays　a　vital　role　in　achieving　high　heat　to　power　conversion　efficiency　of　this　system.　The　circulating　flow　of　working　fluid　in　the　system　is　realized　by　a　pump,　which　is　beneficial　to　heat　transfer　enhancement　of　the　evaporator　with　pulsating　flow.　In　this　study,　a　twodimensional　axisymmetric　model　of　evaporator　tube　is　built.　Two-phase　flow　characteristics　of　R245fa　under　continuous　and　pulsating　flows　are　analyzed.　Furthermore,　particle　swarm　optimization　(PSO)　is　employed　to　optimize　the　parameters　of　pulsating　flow　when　diesel　engine　(DE)　is　operating　under　the　motorway　road　condition.　Results　show　that　the　heat　transfer　performance　of　R245fa　can　be　improved　effectively　by　the　pulsating　flow　with　a　high　angular　frequency.　Critical　angular　frequency,　which　enhances　the　heat　transfer,　exists.　It　also　has　a　weak　influence　to　flow　performance.　Compared　with　those　in　continuous　flow　under　the　motorway　road　condition　of　DE,　the　average　convective　heat　flux　and　the　volume　fraction　of　R245fa　vapor　at　the　outlet　optimized　by　PSO　can　be　increased　by　158.11%　and　87.24%,　respectively,　whereas　the　pressure　drop　can　be　decreased　by　1.47%.　(c)　2021　Elsevier　Ltd.　All　rights　reserved.