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Definitions Flashcards

(76 cards)

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

Fluids (3 decks)

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