UNIT 1 Lesson 2 CONDUCTANCE

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UNIT1

Syllabus for automobile engineering

UNIT 1

Fluids: Definition, Ideal fluids, real fluids, Newtonian and non-Newtonian fluids.

Properties of Fluids: Unit of measurement, Mass density, Specific weight, Specific volume, Specific Gravity, Viscosity, Surface tension and Capillarity, Compressibility and Elasticity.

1.1 What is fluid? definitionFor a laymanFluid is anything which flows yes water flows, air flows. So liquid and gases are both fluid. There are three states of matter: solids, liquids and gases.

Both liquids and gases are classified as fluids.

Fluids do not resist a change in shape. Therefore fluids assume the shape of the container they occupy.

Liquids may be considered to have a fixed volume and therefore can have a free surface. Liquids are almost incompressible.

Conversely, gases are easily compressed and will expand to fill a container they occupy.

We will usually be interested in liquids, either at rest or in motion.

For Technical person

The technical distinction lies with the reaction of the two to an applied shear or tangential stress.

A solid can resist a shear stress by a static deformation; a fluid cannot. Any shear stress applied to a fluid, no matter how small, will result in motion of that fluid. The fluid moves and deforms continuously as long as the shear stress is applied. As a corollary, we can say that a fluid at rest must be in a state of zero shear stress, a state often called the hydrostatic stress condition in structural analysis. In this condition, Mohrs circle for stress reduces to a point, and there is no shear stress on any plane cut through the element under stress.

The strict definition of a fluid is:

A fluid is a substance which conforms continuously under the action of shearing forces.

Definition Applied to Static Fluids

According to this definition, if we apply a shear force to a fluid it will deform and take up a state in which no shear force exists. Therefore, we can say:

If a fluid is at rest there can be no shearing forces acting and therefore all forces in the fluid must be perpendicular to the planes in which they act.

Note here that we specify that the fluid must be at rest. This is because; it is found experimentally that fluid in motion can have slight resistance to shear force. This is the source of viscosity. Definition Applied to Fluids in Motion

For example, consider the fluid approaching a fixed surface. At the surface there will be little movement of the fluid (it will stick to the surface), whilst further away from the surface the fluid flows faster (has greater velocity):

If one layer of is moving faster than another layer of fluid, there must be shear forces acting between them.

1.2 Ideal fluid and real fluidFor example, if we have fluid in contact with a conveyor belt that is moving we will get the behavior shown:

Therefore, to represent real fluids in motion we must consider the action of shear forces. A fluid which has no viscosity is a ideal fluid. Gases can be considered as ideal fluids.

A fluid which has viscosity is a real fluid. All fluid in practice is real fluids.

Among fluids, two rough broad divisions can be made: ideal and non-ideal fluids. An ideal fluid really does not exist, but in some calculations, the assumption is justifiable. An Ideal fluid is non viscous- offers no resistance whatsoever to a shearing force.

What is fluid mechanics?

Fluid mechanics is a branch of science which deals with property and behavior of fluids at rest and in motion. And effects of the fluid upon the boundaries.Both gases and liquids are classified s fluids, and the number of fluids engineering applications is enormous: breathing, blood flow, swimming, pumps, fans, turbines, airplanes, ships, rivers, windmills, pipes, missiles, icebergs, engines, filters, jets, and sprinklers, to name a few. When you think about it, almost everything on this planet either is a fluid or moves within or near a fluid.

Fluid mechanics is a sub discipline of continuum mechanics, as illustrated in the following table.

Continuum mechanicsThe study of the physics of continuous materialsSolid mechanicsThe study of the physics of continuous materials with a defined rest shape.ElasticityDescribes materials that return to their rest shape after an applied stress.

PlasticityDescribes materials that permanently deform after a sufficient applied stress.RheologyThe study of materials with both solid and fluid characteristics.

Fluid mechanicsThe study of the physics of continuous materials which take the shape of their container.Non-Newtonian fluids

Newtonian fluids

In a mechanical view, a fluid is a substance that does not support shear stress; that is why a fluid at rest has the shape of its containing vessel. A fluid at rest has no shear stress.

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