Chapter 2.2 Principles of Technology I Edinburg North High School

 Describe how open and closed systems are different.  Explain the relationship between work and pressure in a fluid system, as given by the equation, W = P   V.  Explain the relationship between work and pressure in a fluid system, as given by the equation, W = -  P  V.  Explain what is meant by positive work and negative work in fluid systems  Solve work problems for fluid systems in English and SI units.

 As with mechanical systems, work is done in when a force moves and object through a distance.  But it is easier to calculate work in a fluid system using pressure (prime mover in fluid systems).  Pressure difference can cause a fluid to move.

 A closed fluid system retains and recirculates a working fluid.  Example: Brake system in a car  Fluid flows through an open fluid system only one time.  Examples: city water systems, and irrigation systems, and a fire truck water system.

 When heated, gas in cylinder expands.  Volume changes:  V = V f - V i  Since cross-sectional area does not change,  V = A  d  In this system, pressure does not change because the weight supported by the piston does not change.

  V can be positive or negative ( P is always positive).  W is positive, work is done on the load.  W is negative, work is done on the fluid.

 Open fluid systems  Steady-flow  If density of fluid is constant, volume moved is V = m /   Equation for steady=flow process when density is constant.  Work is positive, the fluid does work.  Work is negative, work is done on the fluid.