Systems and Control Volumes
Systems and control volumes
If we wanted to create a mathematical model of blood flow in an artery, we would first need to define our system. A system is the matter or region in space that we wish to study. A system is separated from its surroundings by a boundary. The surroundings are the regions outside the system. The boundary is an imaginary line (or surface) that separates the system from its surroundings.
Mass can cross the boundary of an open system. No mass can cross the boundary of a closed system. A normal, healthy artery is an example of an open system because blood enters at one end and exits at the other. An artery occluded at both ends is an example of a closed system.
An open system is also called a control volume (CV). A CV can move over time and change its shape. We might use a moving CV if we wanted to follow a particular region of blood as it flows through a vessel. Likewise, if we wanted to analyze the blood flow through an aneurysm, a CV that changes size over time would be appropriate.