Molten　salt　is　popularly　applied　in　solar　thermal　power　generation　as　high-temperature　heat　transfer　medium.　The　thermophysical　properties　of　nitrate　molten　salt　nanofluids　can　be　improved　compared　with　that　of　pure　molten　salt.　In　order　to　improve　the　heat　transfer　performance　of　molten　salt　nanofluids,　a　new　heat　transfer　enhanced　tube　with　converging–diverging　bulge　is　proposed.　In　this　study,　the　convective　heat　transfer　characteristics　of　molten　salt　nanofluids　in　the　enhanced　tube　with　converging–diverging　bulge　are　studied　numerically.　The　effects　of　the　height-width　ratio　(J)　and　length–width　ratio　(K)　on　heat　transfer　and　flow　resistance　are　investigated.　The　results　show　that　Nussel　number　(Nu)　increases　with　the　increase　of　J　value,　and　Nu　decreases　with　the　increase　of　K　value.　The　range　of　Reynolds　number　(Re)　is　8000–24,000,　the　range　of　PEC　in　enhanced　tube　is　1.15–1.48.　When　J　=　0.27,　K　=　2.08,　and　Re　=　8000,　the　PEC　of　the　enhanced　tube　is　the　largest　1.48.　The　mechanism　of　heat　transfer　enhancement　is　analyzed　based　on　the　field　synergy　principle,　and　the　simulation　results　are　analyzed　based　on　the　improved　entropy　theory.　The　change　trend　of　heat　transfer　efficiency　and　heat　transfer　entropy　production　is　opposite.　With　the　increase　of　J,　the　heat　transfer　exergy　loss　number　(NHT)　decrease,　the　heat　transfer　effectiveness　(ε),　flow　resistance　entropy　number　(Np)　and　pressure　drop　(Δp)　increase.　With　the　increase　of　K,　the　heat　transfer　exergy　loss　number　(NHT)　increase,　the　heat　transfer　effectiveness　(ε),　flow　resistance　entropy　number　(Np)　and　pressure　drop　(Δp)　decrease.　The　new　enhanced　tube　could　be　used　to　promote　the　further　development　of　molten　salt　heat　exchanger.　©　Akadémiai　Kiadó,　Budapest,　Hungary　2024.