As for the type of tube, we use a pipe of elliptical cross sectional shape with semi-major axis a and semi-minor axis b where a uniform pressure drop is imposed along the tube length dimension which defines the flow direction. The pressure is supposed to be constant temporally and spatially at each cross section perpendicular to the flow direction where the pressure is assumed to be a sole function of the axial dimension in the flow direction (i.e. the pressure linearly varies along the axial dimension and hence the pressure gradient as a function of the axial dimension is constant). [3] The pipe is assumed to be straight with a cross sectional area that is constant in shape and size along the flow axial direction. We also assume rigid mechanical properties of the tube wall and hence the tube wall is not deformable under the considered range of pressure (as well as any other physical conditions such as temperature as hinted earlier). In fact, we should assume that the tube wall and shape are inert in their physical and geometrical properties to all the involved physical conditions and variations of the flow system and its ambient conditions.