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

62

## 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