WORK IN FLUID SYSTEMS Chapter 2 2 Principles

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WORK IN FLUID SYSTEMS Chapter 2. 2 Principles of Technology I Edinburg North High

WORK IN FLUID SYSTEMS Chapter 2. 2 Principles of Technology I Edinburg North High School

Objectives � � � Describe how open and closed systems are different. Explain the

Objectives � � � 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.

Introduction � As with mechanical systems, work is done in when a force moves

Introduction � 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.

Open and Closed Fluid Systems � A closed fluid system retains and recirculates a

Open and Closed Fluid Systems � 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.

Work Done in Fluid Systems � When heated, gas in cylinder expands. � Volume

Work Done in Fluid Systems � When heated, gas in cylinder expands. � Volume changes: V = Vf - Vi � � 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,

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

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.