Modern microsystems use integrated sensors, controllers and actuators, and involve multi-physics phenomena. Detailed and accurate multi-physics based simulations are a key to device optimization and successful designs. In recent years, CFD-ACE+, a fluid flow solver has been validated and demonstrated on different MEMS devices involving coupled fluid flow, heat transfer, structural mechanics and electrostatics. Presented here are results of dynamic devices such as micropumps with dynamic valves and membrane micropumps as well as priming of a capillary pump and novel valves that use fluid surface tension for operation. Comparisons with experimental and other data are also presented to demonstrate the accuracy of multi-physics simulations. The capabilities of this state-of-the-art software and its usefulness in MEMS design environment is demonstrated.