The system that exchange both the mass and energy (or Heat and work) with the surrounding of it. The mass within the system is necessarily constant. The nature of the processes happening in such system is flow type. For instance
1. Water Pump: Water enters at low level and pumped to higher level, pump is driven by an electric motor. The mass (that is water) and energy (that is electricity) cross the boundary of system (which is pump and motor). 2. Scooter engine: Air arid petrol enters and burnt gases leave the engine. The engine provides mechanical energy to wheels.
3. Boilers, turbines, heat exchangers. Fluid flow through them and heat /work is taken out or supplied.
Mostly all the engineering machines and equipment are open systems.