FLUID MECHANICS

What is it?

Fluid Mechanics

The study of fluids and the forces on them.

What are fluids?

Fluid Mechanics

Liquids and gases are fluids.

Fluids take the shape of the container which they occupy.

Pipes Tanks Vessels

Fluid Mechanics

Consists of Fluid Statics The study of fluids at rest Fluid Kinematics The study of fluids in motion and Fluid Dynamics The study of the effect of forces on fluid motion.

Fluid Mechanics

Common Terms:Viscosity- defined as a fluid’s resistance to flow.

Density- a way to express a fluid’s “heaviness”. The density of a fluid is defined as the mass of a substance per unit volume. Expressed in terms of lbs. per gallon or lbs. per cubic foot.The density of water is 8.33 lbs. per gal.

Specific Gravity- is the ratio of a fluid’s density to the density of water or air. This ratio determines the heaviness of a fluid by comparing to a standard, water.The specific gravity of water is one, which implies a ratio less than one means the material is lighter than water.

What do we know about this?

Most hydrocarbons have a specific gravity below 1.0. What does this mean to you?

Problem:What is the specific gravity of gasoline?

The density of gasoline is 6.15 lbs./ gal

The specific gravity of gasoline is the ratio of its density to the density of water.

Specific Gravity = 6.15 lbs. per gal/ 8.33 lbs per gal = 0.738Will this sink or float in water?

API Gravity The American Petroleum Industry sets

standards to measure the heaviness of a hydrocarbon.

The formula to calculate the API gravity is:

API= 141.5/s.g. - 131.5 Specific Gravity of gasoline = 0.738 API= 141.5/.738 -131.5 API= 191.7-131.5= 60.2 API of water = 141.5/1 -131.5 = 10 Most hydrocarbons have an API >10.

Flow Rate of a Liquid

Measured as volume per unit of timeGallons per minute, cubic feet per

hour, etc.

Velocity is measured as distance per unit of time.

feet per second, feet per minute, etc.

Bernoulli’s Principle

In a closed process with constant flow rate,

changes in fluid velocity decrease or increase pressure, pipe diameter changes cause velocity changes, and pressure (energy) and pipe diameter changes are related.

How so?

Changes in pipe size, cause velocity changes.

http://mitchellscience.com/bernoulli_principle_animation

http://library.thinkquest.org/27948/bernoulli.html

and changes in pressure

Pressure changes with pipe diameter changes.Venturi meter used to calculate fluid flow rate using pressure difference through obstructions in the flow.

Turbulent and Laminar Flow Laminar flow moves through a

system in thin cylindrical sheets of liquid flowing inside one another.

Has little if any turbulence.

Exists at low flow rates.

Turbulent and Laminar Flow As flow increases, the laminar

pattern breaks into turbulent.

Turbulent flow is the random movement or mixing of fluids.

Laminar Becomes Turbulent