The unification that bond graph methods bring to the representation of mechanical, electrical, magnetic, and chemical kinetic systems is not completely achieved for fluid flow systems except in the special case of high pressure hydraulic systems. This is because power in fluid systems is not merely the product of two variables such as pressure and volume flow rate, but rather contains components due to the convection of internal and kinetic energy. Using a Lagrangian description rather than the more usual Eulerian description, however, normal bond graph elements succeed in representing fluid and thermal interactions. The approach leads to novel ways of simulating systems in which convection is important. Variable transport delay and dispersion are handled in a way preserving physical intuition since fixed quantities of matter are followed through the system.