BeginnerTopic 2 of 105Thermodynamics & Fluids
Open, closed and isolated systems
Classified by whether mass and energy can cross the boundary.
In depth
Closed systems exchange energy but not mass; open systems (control volumes) exchange both; isolated systems exchange neither. Pumps, turbines and nozzles are open; a sealed piston-cylinder is closed; a perfectly insulated sealed flask is approximately isolated.
Key points
- Steady-flow analysis for open systems
- Closed system first law ΔU=Q-W
- Isolated: energy constant
ExampleA boiler is an open system because water flows through it.
What is Open, closed and isolated systems?
Classified by whether mass and energy can cross the boundary.
Why is it important to understand open, closed and isolated systems?
Whether mass and energy can cross a boundary decides which balance equations apply, so classifying the system is the first analysis step.
What is the difference between a closed and an open system?
A closed system exchanges energy but not mass with its surroundings. An open system exchanges both, as in pipes and engines.
Is a perfectly isolated system realistic?
No, but it is a useful idealisation for checking whether a process can occur in principle.
How is Open, closed and isolated systems used in practice?
Typical applications include modelling a sealed piston in a test rig as a closed system, treating a turbine as an open system with steady mass flow and describing a vacuum flask as an approximately isolated system.
What should I learn before Open, closed and isolated systems?
Study "System and surroundings" first (topic 1 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Open, closed and isolated systems?
Steady-flow analysis for open systems. Closed system first law ΔU=Q-W. Isolated: energy constant.
Can you give an example of Open, closed and isolated systems?
A boiler is an open system because water flows through it.
What comes after Open, closed and isolated systems?
The next topic is "Properties and state", which builds directly on this one.
How difficult is Open, closed and isolated systems?
It is classed as Beginner in Thermodynamics & Fluids (topic 2 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.