FLUID MECHANICS

Mechanics

Physical science that deals with both stationary and moving bodies under the influence of forces.

Statics

Deals with bodies at rest

Dynamics

Deals with bodies in motion

Fluid Statics

Deals with the behavior of fluids at rest

Fluid dynamics

Fluid in motion

Fluid

A substance in liquid or glas phase is referred to as -

Resist

Distinction between a solid and a fluid is made on the basis of the substance’s ability to — an applied shear stress that tends to change its shape

Liquids

Fluids which offer great resistance to change in volume and occupies a definite portion in which it is contained

Gases

Fluids which have little resistance to change either form or volume and occupies all the space it is contained

deforming, continuously

A solid can resist an applied shear stress by —, whereas a fluid deforms - under the influence of shear stress, no matter how small

Stress, strain rate

In solids stress is proportional to strain, but in fluids — is proportional to —.

Solid

has densely spaced molecules with large intermolecular cohesive forces that allows it to maintain its shape and not easily deformed.

Liquids

molecules are spaced further apart; intermolecular forces are small compared to solid and molecules have more freedom of movement.

can be easily deformed

Gases

greater molecular spaces and freedom of movement with negligible cohesive forces

can be easily deformed

Dimensions

Any physical quantity can be characterized by dimensions

Units

The magnitudes assigned to the dimensions are caleed -

Mass, Length, Time, Temperature

Primary or Fundamental Dimensions

Density, Energy, Volume

Secondary Dimesions or Derived Dimensions

English System

Also known as United States Customary System

Metric SI

International System, from Le Systeme International d’ Unites

Dimensionally homogenous

All terms having the same unit

Specific Gravity

Also known as Relative Density

-Ratio of the density or specific weight of a substance to the density or specific weight of some other standard substance.

Specific volume

Volume per unit of a substance

Fluid Flow

Often confined by solid surfaces.

No slip condition

That is, a fluid in direct contact with a solid "sticks" to the surface due to viscous effects, and there is no slip.

Viscosity

There is a property that represents the internal resistance of a fluid to motion or the "fluidity" and that property is the

Drag force

The force of a flowing fluid exerting on a body in the flow direction is called -

Liquid Platics

Fluids for which rate of deformation is proportional to shear stress.

Example of non-newtoninan fluid

Newtionian Fluid

The rate of deformation (velocity gradient) of a — is proportional to shear stress, and constant of proportionality is the viscosity.

shear thinning fluids

— the apparent viscosity decreases with increasing shear rate— the harder the fluid is sheared, the less viscous it becomes. Many colloidal suspensions and polymer solutions are shear thinning.

shear thickening fluids

the apparent viscosity increases with increasing shear rate—the harder the fluid is sheared, the more viscous it becomes

Absolute Pressure

is the total pressure measured relative to a perfect vacuum (zero pressure

Atmospheric Pressure

Pressure exerted by the Earth's atmosphere at a given point

Gauge Pressure

pressure measured relative to atmospheric pressure

Hydrostatic Pressure

The pressure P at the base of the column – called the — of the fluid – is, by definition, the force exerted on the base divided by the base area A.

Buoyancy

The tendency of a fluid to exert a supporting force on a body placed in the fluid.

Stability

— refers to the ability of a body to return to its original position after being tilted about a horizontal axis

Archimedes Principoles

A body in a fluid, whether floating or submerged, is buoyed up by a force equal to the weight of the fluid displaced

Reynolds Number

It used to predict the type of flow without actually observing it.

Blaise Pascal Principles

Pressure acts uniformly on a small volume of fluid

In a fluid confined by solid boundaries, pressure acts perpendicular to the boundary

Piezometer Tube

-Simplest type of Manometer

-It consist of a vertical tube, open at the top and attached to the container in which pressure is desired.

U-Tube Manometer

It consists of a tube formed into shape of U.

Fluid in the manometer is called the gage fluid.

Differential Manometer

Widely used to measure the difference in pressure between two points in a system.

Consider a manometer connected between points A and B.

Difference again can be found by starting from one end of the system to the other.

Volume flow rate, weight flow rate, mass flow rate

Q – The —- is the volume of fluid flowing past a section per unit time.

W – The —- is the weight of fluid flowing past a section per unit time.

M – The — is the mass of fluid flowing past a section per unit time.

Continuity Equation

For steady flow, the volume flow rate is the same at any section

Nominal Pipe Size

is a North American set of standards used to designate pipe diameter and thickness.

Birmingham Wire Gauge

is the dimensionless number which specifies the thickness of a tube.

NPS, Schedule

Pipe size is specified with two non-dimensional numbers: a nominal pipe size (acronym) for inside diameter based on inches, and a — (Sched. or Sch.) for wall thickness.

40, 80

The most complete series available is of schedule — and —.

Steel pipe

General purpose pipe lines

Standard steel tubing

is used in hydraulics systems, condensers, heat exchangers, engine fuel systems and industrial fluid processing systems.

Ductile Iron pipe

Water, gas and sewage lines are often made of ductile iron pipe because of its strength, ductility and relative ease of handling.

➢

It has replaced cast iron in many applications.

➢

Standard fittings are supplied with pipe for convenient installation above or below ground.

Pump

A — is a common example of a mechanical device that adds energy to a fluid.

Electric motor

An — or some other prime power device drives a rotating shaft in the pump.

-is a common example of a mechanical device that adds energy to a fluid.

Fluid Motors

—, turbines, rotary actuators, and linear actuators are the examples of devices that take energy from a fluid and deliver it in the form of work, causing the rotation of a shaft or the linear movement of the piston.

fluid motion

A — offers frictional resistance to flow

Mechanical energy

can be defined as the form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device such as an ideal turbine.

Efficiency

is the ratio of the power delivered by pump to the fluid to the power supplied to the pump

Critical

In the range of Reynolds numbers between 2000 and 4000, it is impossible to predict which type of flow exists; therefore, this range is called the —.

Schedule numbers

are related to the permissible operating pressure of the pipe and to the allowable stress in the pipe

Darcy’s Equation

This equation can be used to calculate the energy loss due to friction in long straight sections of round pipe for both laminar and turbulent flow.