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Fluids > Definitions > Flashcards

Definitions Flashcards

1
Q

Fluid

A

Deform continuously under applied shear stress

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2
Q

Solid

A

Resist an applied shear stress by deforming

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3
Q

Stress

A

Force/area

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4
Q

Normal stress

A

Normal component of force on a surface per unit area

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5
Q

Shear stress

A

Tangential component of force on surface per unit area

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6
Q

Pressure

A

Normal stress in fluid at rest

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7
Q

Steady flow

A

No change of conditions at a point in time

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8
Q

Unsteady flow

A

Flow conditions at a point change with time

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9
Q

Periodic flow

A

Unsteady flow with oscillations about a steady mean

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10
Q

Uniform flow

A

No change with location over a specified region

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11
Q

External flow

A

Flow of unbounded fluid over surfaces eg flow over a plate or wire

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12
Q

Internal flow

A

Flow in pipes of ducts with a fluid bounded by solid surfaces eg water flow in a pipe

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13
Q

Open Channel flow

A

Liquid flow in partially filled ducts with free surface

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14
Q

Boundary layer

A

The flow region adjacent to the wall in which the viscous effects (and velocity gradient) are significant

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15
Q

Viscous flows

A

Frictional effects are significant

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16
Q

Inviscid flows

A

Regions (typically far from solids) where friction is negligible compared to inertial or pressure forces

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17
Q

Laminar flow

A

Highly order to fluid motion characterised by smooth layers of fluid

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18
Q

Turbulent flow

A

Random, chaotic fluid motion characterised by velocity fluctuations

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19
Q

Transitional flow

A

Alternates between being laminar and turbulent

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20
Q

Incompressible flow

A

Density of flowing fluid remains nearly constant

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21
Q

Compressible flow

A

Density of fluid changes during flow (eg high speed gas flow)

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22
Q

What is a Mach number?

A

Velocity of high speed fluid

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23
Q

System

A

A quantity of matter or region in space chosen for study

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24
Q

Surroundings

A

Mass or region outside the system

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25
Q

Boundary

A

Real/ imaginary surface that separates the system from its surroundings
Can be fixed or moveable

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26
Q

Closed system

A

Fixed mass, no mass an cross boundary

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27
Q

Open system

A

Mass and energy can cross boundary - control volume not mass

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28
Q

Control surface

A

Boundaries of control volume - can be real or imaginary

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29
Q

Accuracy error

A

Value reading -> true value
Accuracy of a set of measurements-> average of readings- true value

Associated with repeatable fixed errors

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30
Q

Precision error

A

Value of reading- average of readings

Of a set-> fineness of resolution and repeatability of the instrument

Associated with unrepeatable, random errors

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31
Q

Intensive fluid properties

A

Independent of the mass of a fluid in a system

Eg pressure, temp, density

32
Q

Extensive fluid properties

A

Depend on the amount of fluid in the system, ie on the size of the system
Eg volume, momentum, energy

33
Q

Specific fluid properties

A

Extensive fluid properties per unit mass

Eg specific energy, specific volume

34
Q

Continuum approximation

A

Atomic/ molecular nature of matter is neglected, properties can be extrapolated to zero- size regions (point)

35
Q

Coefficient of compressibility

A

Aka bulk modulus (k)

Measures relative change of density or volume for a given pressure change at constant Temp

36
Q

Isothermal compressibility

Alpha

A

1/ bulk modulus

Change in density or volume over pressure

37
Q

Isothermal process

A

Constant temperature

RT = constant

38
Q

Isothermal bulk modulus

A

K=P

39
Q

Coefficient of volume expansion

A

Measures relative change of density or volume for a given temp change at constant P

(Beta)

40
Q

Dynamic viscosity

A

(Mue)

Measures resistance to deformation of a fluid as a ratio of shear stress and strain rate

41
Q

Strain rate

A

Rate of deformation

42
Q

Kinematic viscosity

A

Ratio of dynamic viscosity and density

43
Q

Shear thinning examples

A 
Colloidal suspensions
Polymer solutions (paint)
44
Q

Shear thickening examples

A

Water-cornstarch (custard)

Water-sand mixtures

45
Q

Bingham plastic examples

A

Toothpaste

Mayo

46
Q

Surface tension

A

Strength of tension force from intermolecular attraction per unit length along any line in the interface

47
Q

Saturation temp

A

Temp at which a substance changes phase at a given pressure

48
Q

Saturation pressure

A

Pressure at which a substance changes phase at a given temp

49
Q

Vapour pressure

A

Pressure of vapour molecules above liquid in equilibrium

Strongly dependent on liquid temp

50
Q

When does boiling occur and what are cavitation bubbles?

A

When P~Pv
Bubbles form and collapse as they move from low P to high P causing destructive, extremely high P waves

(Causes drop in performance and erosion of impeller blades)

51
Q

What is viscosity caused by?

A

Cohesion between molecules (fluids) and molecular collisions (gases)

52
Q

Equations for gauge pressure

A

Pabs- Patm

Pabs > Patm

Row g h

53
Q

Specific weight

A

Weight/volume

54
Q

Vacuum pressure

A

Pvac= Patm - Pabs

Pabs< Patm

55
Q

Pascals law

A

The pressure applied to a confined fluid increases the pressure throughout by the same amount

56
Q

Atmospheric air is ideal gas equation

A

P= row RT

57
Q

Does mercury barometer give gauge or atm pressure?

A

Atm

Gauge P is open system

58
Q

Buoyant force

A

Upward force exerted by fluid on a submerged body

59
Q

Magnitude of buoyant force

A

Weight of fluid displaced by the body

60
Q

Stable

A

CoG is below CoB and there’s a gap between them and on same vertical axis

Or not in line but metacentre is above CoG

61
Q

Neutrally stable

A

CoG and CoB in same place and on same vertical axis

62
Q

Unstable

A

CoG above CoB

63
Q

Condition for floatation

A

Buoyant force = weight force

64
Q

1st law of thermodynamics

A

Delta Esys = Wnet in + Qnet,in

65
Q

What are the forms of mechanical energy?

A

Flow energy p/row

Kinetic energy V^2/2

Potential energy gz

66
Q

Mechanical energy

A

Fluid energy that can be converted without loss to useful work output in an ideal mechanical device

67
Q

What are the forms of energy in a fluid stream

A

Etotal = kinetic + potential+ internal + flow

68
Q

What is mech energy and what is thermal energy?

A

Mech can be converted to mech work (ideally without energy loss) thermal cannot even in an ideal situation

69
Q

Which forms of fluid energy are mechanical and which are thermal?

A

Kinetic, potential, flow are mech

Internal is thermal

70
Q

What are the causes of acceleration?

A

Variation of velocity- dV/dt

Streamwise variation of velocity
a=V x sV/Ss

Normal acceleration due to curvature
V^2 / R

71
Q

Can fluid particles accelerate in a steady flow?

A

Yes if the area and/or density change. (Ie changes in temp) or if the streamlines are curved

72
Q

Static pressure

A

The actual normal force per unit area of the fluid

73
Q

Dynamic pressure

A

The additional pressure due to the velocity of a flowing fluid that arises if the fluid is brought to a stop isotropically

74
Q

Hydrostatic pressure

A

The pressure relative to a certain elevation due to the weight of the fluid

75
Q

Static P+ dynamic P + hydrostatic P = ?

A

Constant in a steady flow of an incompressible fluid without friction

76
Q

Stagnation pressure

A

The sum of static and dynamic pressure can be measured with a pitot tube

Fluids (3 decks)

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