1.2 Thermodynamic systems and surroundings

Thermodynamic systems are the building blocks of energy analysis. They come in three flavors: open, closed, and isolated, each with unique ways of interacting with their surroundings. Understanding these systems is key to grasping how energy and matter move in the world around us.

The boundaries between systems and surroundings are where the action happens. It's here that energy transfers through heat and work, and sometimes mass moves too. Knowing how to define and analyze these boundaries is crucial for solving real-world thermodynamic problems.

Thermodynamic Systems and Surroundings

Types of thermodynamic systems

Top images from around the web for Types of thermodynamic systems

• 

  Thermodynamics | Systems and Surroundings | Simulation View original

  Is this image relevant?

• 

  Thermodynamic system - Wikipedia View original

  Is this image relevant?

• 

  ESS Topic 1.2: Systems and Models - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  Thermodynamics | Systems and Surroundings | Simulation View original

  Is this image relevant?

• 

  Thermodynamic system - Wikipedia View original

  Is this image relevant?

1 of 3

Top images from around the web for Types of thermodynamic systems

• 

  Thermodynamics | Systems and Surroundings | Simulation View original

  Is this image relevant?

• 

  Thermodynamic system - Wikipedia View original

  Is this image relevant?

• 

  ESS Topic 1.2: Systems and Models - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  Thermodynamics | Systems and Surroundings | Simulation View original

  Is this image relevant?

• 

  Thermodynamic system - Wikipedia View original

  Is this image relevant?

1 of 3

• Thermodynamic systems represent a region in space or a quantity of matter bounded by a closed surface
  • Three main types of thermodynamic systems: open, closed, and isolated
• Open systems allow the transfer of both energy and mass across the system boundary
  • Examples include a pot of boiling water, a turbine, and a compressor
• Closed systems allow the transfer of energy but not mass across the system boundary
  • Examples include a sealed piston-cylinder device, a closed tank, and a pressure cooker
• Isolated systems do not allow the transfer of either energy or mass across the system boundary
  • Examples include a perfectly insulated container, a thermos flask, and an adiabatic process

Boundaries in thermodynamic systems

• System boundary is the real or imaginary surface that separates the system from its surroundings
  • Defined based on the problem under consideration
• Surroundings encompass everything outside the system boundary
  • Can interact with the system through energy and mass transfer
• Identifying the system and surroundings involves:
  • Clearly defining the system of interest
  • Determining the appropriate system boundary based on the problem statement
  • Considering the interactions between the system and its surroundings (heat transfer, work)

System-surroundings interactions

• Energy transfer occurs through heat ($Q$), the transfer of energy due to a temperature difference, and work ($W$), the transfer of energy due to a force acting through a distance
• Mass transfer occurs in open systems and involves the exchange of matter between the system and its surroundings
• Interactions between the system and surroundings require:
  1. Determining the direction of energy and mass transfer (into or out of the system)
  2. Analyzing the impact of these interactions on the system's properties (temperature, pressure, volume)
  3. Applying the conservation of energy and mass principles

Control volume in thermodynamics

• Control volume is a fixed region in space through which matter may flow
  • Used to analyze open systems
• Conservation equations for a control volume include:
  • Conservation of mass: $\frac{dm_{cv}}{dt} = \sum \dot{m}_{in} - \sum \dot{m}_{out}$
  • Conservation of energy: $\frac{dE_{cv}}{dt} = \dot{Q}_{cv} - \dot{W}_{cv} + \sum \dot{m}_{in}(h + \frac{V^2}{2} + gz)_{in} - \sum \dot{m}_{out}(h + \frac{V^2}{2} + gz)_{out}$
• Steady-state processes involve no change in the properties of the control volume with respect to time
  • Simplifies the conservation equations by setting time derivatives to zero
• Analyzing thermodynamic systems using control volumes requires:
  1. Defining the control volume and its boundaries
  2. Identifying the energy and mass interactions between the control volume and its surroundings
  3. Applying the appropriate conservation equations based on the problem statement (steady-state or transient)