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Mechanical FE Exam > Fluid Mechanics > Flashcards

Fluid Mechanics Flashcards

1
Q

[Formula] Specific Weight (γ)

A

γ = pg –> (density)(gravity)

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2
Q

[Formula] Force needed to move single-plate viscometer (F)

A

F = μvA/δ –> [(viscosity)(velocity)(area)] / thickness

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3
Q

[Formula] Force (F)

A

F = ma –> (mass)(acceleration)

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4
Q

[Formula] Mass (m)

A

m = pV –> (density)(volume)

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5
Q

[Formula] Height change due to capillary action (h)

A

h = (4σcosβ) /γd = (4σcosβ) /pgd

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6
Q

[Formula] Specific volume (υ)

A

υ = V/m –> volume/mass
υ = 1/p –> 1/density

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7
Q

Fluid Statics - Hydrostatic Pressure

[Formula] Pressure (P) for a stationary, incompressible fluid

A

P = pgh –> (density)(gravity)(height)
or
P = γh –> (specific weight)(height)

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8
Q

Archimedes Principle (Part 1)

A
  1. The buoyant force exerted on a submerged or floating body is equal to the weight of the fluid displaced by the body.
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9
Q

Archimedes Principle (Part 2)

A
  1. A floating body displaces a weight of fluid equal to its own weight; i.e., a floating body is in equilibrium.
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10
Q

[Formula] Bernoulli Equation

A

P2/γ + v2^2/2g + z2 = P1/γ + v1^2/2g + z1

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11
Q

Specific Gravtiy

What is specific gravity? (definition AND formula)

A

A dimensionless ratio of a fluid’s density to a standard reference density.
SG = p / p_Water (density/density of water) Also can use specific weight.

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12
Q

Pressure

What are “absolute pressures?”

A

Pressures measured with respect to a ‘true zero pressure.’

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13
Q

Pressure

What are “gage pressures?”

A

Pressure measured with respect to ‘atmospheric pressure.’

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14
Q

Pressure

How are absolute and gage pressures related? (Formula)

A

P_absolute = P_atmospheric + P_gage

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15
Q

Pressure

What is a ‘vacuum’ pressure measurement?

A

A pressure below atmospheric pressure (i.e., a negative gage pressure).

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16
Q

Stress

Stress has a different symbol in “Materials” than in “Fluids.” What are those symbols?

A

τ for fluids

σ for materials

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17
Q

Stress

How many primary types of stress are there?
What are they?

A

2 types:

normal stress – area is normal to the force

tangential (or shear) stress – area is parallel to the force

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18
Q

Stress

Ideal fluids that are inviscid and incompressible respond to what type of stress? What other type of stress can they not support?

A

Respond to normal stresses

Cannot support shear stresses

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19
Q

Viscosity

What is “viscosity?”

A

The measure of a fuild’s resistance to flow when acted upon by an external force, such as a pressure gradient or gravity.

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20
Q

Viscosity

What is the formula for viscosity of a Newtonian fluid?

A

τ = µ(dv/dy)

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21
Q

Viscosity

What is the formula for viscosity of a non-Newtonian fluid?

A

τ = K(dv/dy)^n

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22
Q

Viscosity

What is “kinematic viscosity?” (definition and formula)

A

Ratio of absolute viscosity to mass density.

v = µ/p = µg_c / p

(primary units: L^2 / θ)

23
Q

Surface Tension

What is surface tension? (definition and formula)

A

Intermoluecular cohesive forces causing what seams to be a membrane.

σ = F/L

24
Q

Capillarity

What is capillary action?

A

Behavior of a liquid in a thin-bore tube.
Specifically, it is caused by surgace tension between the liquid and a vertical solid surface.

25
Q

Capillarity

What is the “angle of contact,” β?

A

An indication of whether adhesive or cohesive forces dominate.

β < 90 degrees, adhesive forces are dominant

β > 90 degrees, cohesive forces are dominant

26
Q

Capillarity

What is the formula for capillary rise in a small-bore tube?

A

h = (4σcosβ/pgd_tube)

27
Q

Fluid statics - Hydrostatic Pressure

What is hydrostatic pressure? (definition and formula)

A

The pressure a fluid exerts on an immersed object or on container walls.

p = F/A

28
Q

Fluid statics - Hydrostatic Pressure

What is the Hydrostatic Paradox?

A

The pressure at depth h is independent of volume.

29
Q

Fluid statics - P for a stationary, incompressible fluid

Pressure at a point as the same magnitude in all directions. What is this called?

A

Pascal’s law

30
Q

Fluid statics- P for a stationary, incompressible fluid

Pressure is always what to a surface, regardless of shape or orientation?

A

Normal.

(This is a result of the fluid’s inability to support shear stress.)

31
Q

Fluid Statics - Manometry

What is a manometer used for?

A

Indicating small pressure differences.

32
Q

Fluid Statics - Manometry

What is a differential manometer?
What is an open manometer?

A

differential manometer - When both ends are connected to pressure sources.
open manometer - When one end is open tot he atmosphere.

33
Q

Fluid Statics - Manometry

What is the formula for pressure difference in an open manometer?

A

P0 = P2 + p2gh2 - p1gh1
or
= P2 + γ2h2 - γ1h1

34
Q

Fluid Statics - Manometry

What is the formula for pressure difference in an open manometer, where fluid 1 is absent or has a low density, or if distance h1 is so small as to be insignificant?

A

P2 - P0 = -p2gh2
or
= -γ2h2

35
Q

Fluid Statics - Barometers

What is a barometer?

A

Device for measuring the absolute pressure of the atmosphere. Tube fluid is mercury.

36
Q

Fluid Statics - Barometers

What is the atmospheric pressure equation when the fluid is mercury? (i.e., when the vapor pressure in the tube is neglected?)

A

Pa = pgh
or
= γh

37
Q

Fluid Statics - Barometers

What is the atmospheric pressure equation when the fluid is NOT mercury? (i.e., when the vapor pressure in the tube is significant, such as with water or alcohol?)

A

Pa = Pv + pgh
or
= Pv + γh

38
Q

Fluid Statics - Forces on Submerged Plane Surfaces

Total vertical force on a horizontal plane of area A (formula)

A

R = PA (resultant = pressure x area)

39
Q

Fluid Statics - Forces on Submerged Plane Surfaces

Vertical rectangular plane surface:
Pressure increases linearly with depth.
* If the plane surface extends to the surface, what shape will the pressure distribution be?
* If it does not, what shape will it be?

A
  • Triangular
  • Trapezoidal
40
Q

Fluid Statics - Forces on Submerged Plane Surfaces: Vertical Rectangular

What is the resultant force calculated from?

A

Average pressure. (located at the centroid)

41
Q

Fluid Statics - Forces on Submerged Plane Surfaces

What is the average pressure formula for:
* vertical plane
* inclined plane

A

P = 1/2 γ(h1 + h2)
P = 1/2 γ(z3 + z4)sinα

(symbol for p should have horizontal line on top.)

42
Q

Fluid Statics - Center of Pressure

Nonrectangular plane surface that* may or may not* extend to the liquid surface and that* may or may not* be inclined:

At P0 = 0, what is the formual for:
* average pressure
* Ycp (center of pressure on y axis)
* Zcp (center of pressure on z axis)

A
  • P = pgZc(sinα) or γZcsinα
  • Ycp - Yc = y* = (Iyz)/(A)(Zc)
  • Zcp - Zc = z* = (Iy)/(A)(Zc)
43
Q

Fluid Statics - Buoyancy

What is buoyancy?

A

An upward force that acts on all objects that are partially or completly submerged in a fluid.
(fluid can be liquid or gas)

44
Q

Fluid Dynamics - Conservation Laws

What is the continuity equation?

A

ṁ = ρAv = ρQ

Equation of conservation of mass when applied to fluid flow

45
Q

Fluid Dynamics - Fluid Energy

What is the pressure energy (Ep) of a fluid?

A

Energy in a fluid determined by pressure.
Higher pressure means higher energy, lower pressure means lower energy.

Ep = P/ρ

46
Q

Fluid Dynamics - Fluid Energy

Pressure head (formula)

A

hp = Ep/g

or

= P/ρg

47
Q

Fluid Dynamics - Fluid Energy

What is specific kinetic energy? (definition and formula)

A

The kinetic energy of a fluid evaluated per unit mass.

Ev = v^2 / 2

48
Q

Fluid Dynamics - Fluid Energy

Velocity head (formula)

A

hv = Ev/g

or

= v^2/2g

49
Q

Fluid Dynamics - Fluid Energy

What is specific potential energy? (definition and formula)

A

The potential energy of a fluid evaluated per unit mass.

Ez = zg

50
Q

Fluid Dynamics - Fluid Energy

Elevation head (formula)

A

hz = Ez / g

or

= z

51
Q

Fluid Dynamics - Hydraulic Grade Line

What is the hydraulic grade line (HGL)?

A

The graph of the pressure head, plotted as a position along the pipeline.

52
Q

Fluid Dynamics - Energy Line

What is the energy grade line (EGL)?

A

The graph of the total energy along a length of pipe.

EGL = GHL + v^2/2g (velocity head)

53
Q

Fluid Dynamics - Flow of a Real Fluid

formula for head loss due to friction (hf)

A

hf = (p1 - p2) / γ

Mechanical FE Exam (5 decks)

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