先进材料疑固实验室 Momentum transfer Laboratory of Advanced Materials Solidification When a fluid is flowing in the x direction parallel to a solid surface, the fluid has x-directed momentum,and its concentration is vp.By random diffusion of molecules there is an exchange of molecules in the z direction.Hence the x-directed momentum has been transferred in the =-direction from the faster-to the slower-moving layer. 1 V(y) V(y) 上游文通大学 SHANGHAI JIAO TONG UNIVERSITYMomentum transfer When a fluid is flowing in the x direction parallel to a solid surface, the fluid has x-directed momentum, and its concentration is υxρ. By random diffusion of molecules there is an exchange of molecules in the z direction. Hence the x-directed momentum has been transferred in the z-direction from the faster- to the slower-moving layer. v V(y) v V(y)