1Fluid Mechanics – Lecture 5

Fluid mechanics(wb1225)

Lecture 5:energy equation

2Fluid Mechanics – Lecture 5

Snapping shrimp

[1]

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The energy equation

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The energy equation (cont’d)

small

5Fluid Mechanics – Lecture 5

One-dimensional stationary energy flux equation

enthalpy:

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Bernoulli’s equation

Daniel Bernoulli(1700-1782)

conservation of energy for stationaryflow in a stream tube:• stationary flow• no mechanical work• no viscous frictionand:• incompressible fluid • motion along streamline• no heat transfer

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Example 3.21

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Validity of Bernoulli equation

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Cavitation

sonoluminescence

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Example 3.23

A constriction in a pipe will cause the velocity to rise and the pressure to fall atsection 2 in the throat. The pressure difference is a measure of the flow rate through the pipe.

The smoothly necked-down system shown is called a venturi tube.

Find an expression for the mass flux in the tube as a function of the pressurechange

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Wind turbine

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Wind turbine

V

V

V

f VCA A

P Q RO

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Wind turbineV

V

V

f VCA A

P Q RO

Power:

See Sect. 11-6 in White

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Summary• Chapter 3: 3.6, 3.7

• Examples: 3.20, 3.21, 3.23, 3.24

• Problems: (see BlackBoard)

• Study guideline:

• practice …

• practice …

• practice …

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Source

1. Snapping shrimp, http://youtu.be/ONQlTMUYCW42. Frank M. White, Fluid Mechanics, McGraw-Hill Series in Mechanical Engineering3. Wind turbines of Horns Rev wind farm, Denmark, photo courtesy of Vattenfall