Fluid enters and flows through a rectangular channel at x = 0 with no drug present in the fluid (i.e. C = 0). The free stream velocity V is uniform at x = 0. The bottom surface of the is coated with a drug between x = 0 and x = L (the shaded region in Figure Q4(c)) and the concentration along the surface is C_surf. Inside the channel, the concentration in the fluid above the surface is described by a cubic relationship as shown in Figure Q4(c,right). The height of the concentration boundary layer δ_c at the end of the channel is small relative to the height of the channel H, i.e. H >> δ_c. After the fluid passes the end of the coated surface at x = L, the fluid becomes well mixed and the concentration has the same value C_∞. Determine an expression for the well mixed concentration C_∞.

  

W y H y Csurf Figure Q4(c)