A,B, and D are rectangular ducts as shown. Pipe-C is a round pipe. (a) (5 points) For each surface, state whether 1-D flux assumption is valid or not, and why. (b) (15 points) Calculate the mass flux of fluid through each of the cross-sections shown. The side views show the pipe where fluid is coming from left to right. The edge-wise view shows the area shape. The answer should be in terms of density , pipe geometry (H,W for pipes A,B,D, and R for Pipe-C), and velocity U. For Pipe-A, B, and D, velocity does not vary in the width direction. For Pipe-C, flow velocity varies in the radial direction with a maximum velocity U at the centerline and 0 at the walls (like a cone)