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Flashcards in Definitions Deck (76):
1

Fluid

Deform continuously under applied shear stress

2

Solid

Resist an applied shear stress by deforming

3

Stress

Force/area

4

Normal stress

Normal component of force on a surface per unit area

5

Shear stress

Tangential component of force on surface per unit area

6

Pressure

Normal stress in fluid at rest

7

Steady flow

No change of conditions at a point in time

8

Unsteady flow

Flow conditions at a point change with time

9

Periodic flow

Unsteady flow with oscillations about a steady mean

10

Uniform flow

No change with location over a specified region

11

External flow

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

12

Internal flow

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

13

Open Channel flow

Liquid flow in partially filled ducts with free surface

14

Boundary layer

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

15

Viscous flows

Frictional effects are significant

16

Inviscid flows

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

17

Laminar flow

Highly order to fluid motion characterised by smooth layers of fluid

18

Turbulent flow

Random, chaotic fluid motion characterised by velocity fluctuations

19

Transitional flow

Alternates between being laminar and turbulent

20

Incompressible flow

Density of flowing fluid remains nearly constant

21

Compressible flow

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

22

What is a Mach number?

Velocity of high speed fluid

23

System

A quantity of matter or region in space chosen for study

24

Surroundings

Mass or region outside the system

25

Boundary

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

26

Closed system

Fixed mass, no mass an cross boundary

27

Open system

Mass and energy can cross boundary - control volume not mass

28

Control surface

Boundaries of control volume - can be real or imaginary

29

Accuracy error

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

Associated with repeatable fixed errors

30

Precision error

Value of reading- average of readings

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

Associated with unrepeatable, random errors

31

Intensive fluid properties

Independent of the mass of a fluid in a system
Eg pressure, temp, density

32

Extensive fluid properties

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

33

Specific fluid properties

Extensive fluid properties per unit mass
Eg specific energy, specific volume

34

Continuum approximation

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

35

Coefficient of compressibility

Aka bulk modulus (k)

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

36

Isothermal compressibility
(Alpha)

1/ bulk modulus

Change in density or volume over pressure

37

Isothermal process

Constant temperature

RT = constant

38

Isothermal bulk modulus

K=P

39

Coefficient of volume expansion

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

(Beta)

40

Dynamic viscosity

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

41

Strain rate

Rate of deformation

42

Kinematic viscosity

Ratio of dynamic viscosity and density

43

Shear thinning examples

Colloidal suspensions
Polymer solutions (paint)

44

Shear thickening examples

Water-cornstarch (custard)
Water-sand mixtures

45

Bingham plastic examples

Toothpaste
Mayo

46

Surface tension

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

47

Saturation temp

Temp at which a substance changes phase at a given pressure

48

Saturation pressure

Pressure at which a substance changes phase at a given temp

49

Vapour pressure

Pressure of vapour molecules above liquid in equilibrium

(Strongly dependent on liquid temp)

50

When does boiling occur and what are cavitation bubbles?

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

What is viscosity caused by?

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

52

Equations for gauge pressure

Pabs- Patm

Pabs > Patm

Row g h

53

Specific weight

Weight/volume

54

Vacuum pressure

Pvac= Patm - Pabs

Pabs< Patm

55

Pascals law

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

56

Atmospheric air is ideal gas equation

P= row RT

57

Does mercury barometer give gauge or atm pressure?

Atm
Gauge P is open system

58

Buoyant force

Upward force exerted by fluid on a submerged body

59

Magnitude of buoyant force

Weight of fluid displaced by the body

60

Stable

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

Neutrally stable

CoG and CoB in same place and on same vertical axis

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Unstable

CoG above CoB

63

Condition for floatation

Buoyant force = weight force

64

1st law of thermodynamics

Delta Esys = Wnet in + Qnet,in

65

What are the forms of mechanical energy?

Flow energy p/row

Kinetic energy V^2/2

Potential energy gz

66

Mechanical energy

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

67

What are the forms of energy in a fluid stream

Etotal = kinetic + potential+ internal + flow

68

What is mech energy and what is thermal energy?

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

69

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

Kinetic, potential, flow are mech


Internal is thermal

70

What are the causes of acceleration?

Variation of velocity- dV/dt

Streamwise variation of velocity
a=V x sV/Ss

Normal acceleration due to curvature
V^2 / R

71

Can fluid particles accelerate in a steady flow?

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

72

Static pressure

The actual normal force per unit area of the fluid

73

Dynamic pressure

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

74

Hydrostatic pressure

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

75

Static P+ dynamic P + hydrostatic P = ?

Constant in a steady flow of an incompressible fluid without friction

76

Stagnation pressure

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