The　influences　of　primary　nozzle　on　the　performance　of　steam　ejectors　were　investigated　numerically,　and　the　effects　of　the　primary　nozzle　outlet　diameter　as　well　as　the　divergent　section　length　under　different　entrained　stream　pressures　on　the　steam　ejector　were　analyzed　and　discussed.　The　results　revealed　that　the　entrainment　ratio　of　steam　ejector　initially　increases　sharply　with　the　primary　nozzle　outlet　diameter　and　then　decreases　after　the　outlet　diameter　exceeds　a　certain　value.　Therefore,　there　is　an　optimum　range　for　the　primary　nozzle　outlet　diameter　at　which　the　ejector　obtains　its　best　performance.　It　was　also　disclosed　that　the　divergent　section　length　has　only　a　comparatively　weak　effect　on　the　ejector　performance.　The　entrainment　ratio　increases　slowly　first　with　the　divergent　section　length　to　its　maximum　and　then　decreases　gradually　due　to　the　increase　of　flow　frictional　drag.　Hence　there　also　exists　an　optimum　value　for　the　divergent　section　length　at　which　the　steam　ejector　performs　best.　However,　it　should　be　stressed　that　this　largest　entrainment　ratio　corresponding　this　optimum　divergent　Section　length　differs　little　from　the　non-optimum　value　which　means　we　can　design　the　divergent　section　with　a　wider　range　of　the　length.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.