The　two-phase　flow　boiling　characteristics　of　liquid　nitrogen　(LN2)　in　horizontal　circular　mini-tubes　were　experimentally　studied.　Experiments　were　performed　in　a　wide　range　of　flow　conditions,　e.g.　inlet　pressure　from　0.17　to　0.35　MPa,　mass　flux　from　140　to　330　kg/m(2)　s,　heat　flux　from　0.5　to　69.4　kW/m(2)　and　tube　diameters　of　2.92　mm　and　3.96　mm.　The　influences　of　mass　flux,　heat　flux,　and　inlet　pressure　on　the　pressure　drop　were　discussed.　The　results　indicated　that　the　pressure　drop　increases　with　the　increasing　mass　flux　and　heat　flux　but　decreases　with　the　increasing　inlet　pressure.　But　the　influence　of　heat　flux　on　the　frictional　pressure　drop　of　LN2　was　weaker　than　mass　flux　and　inlet　pressure.　The　frictional　pressure　drop　of　two-phase　flow　of　LN2　was　compared　with　homogeneous　model　and　several　semi-empirical　correlations.　An　improved　correlation　based　on　the　Lockhart-Martinelli　model,　which　used　coefficient　C　as　a　function　of　Reynolds　number　and　Weber　number　was　proposed.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.