先进材料疑固实验室 Momentum tansfer Laboratory of Advanced Materials Solidification Continuity equation in one dimension Pu dA=PudA P,P2---the average density at cross p2,u,,dA section A and cross section A2 pu,dA u,42---the average density at cross section A and cross section A2 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITYMomentum tansfer Continuity equation in one dimension ρ1, ρ2 --- the average density at cross section A1 and cross section A2 u1, u2 --- the average density at cross section A1 and cross section A2