4.3 Differential Equation of Mass conservation X inlet(mass flow) → mass flux per unit area 12+0(pu)b X outlet pudydz Ipu+cou dx]dya= z dz ax dx X flow out o(pu dxdydz Infinitesimal fixed cv In the like manner a(p Lxdvdz z Flow out off the Cv V. pl)dxdydz6 X inlet (mass flow) udydz X outlet ( ) [ ] u u dx dydz x    +  dx y z x dz dy Infinitesimal fixed CV udydz ( ) [ ] u u dx dydz x    +  u mass flux per unit area → X flow out ( ) u dxdydz x    4.3 Differential Equation of Mass Conservation In the like manner ( ) v dxdydz y    ( ) w dxdydz z    Flow out off the CV  ( ) V dxdydz