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Final Exam Flashcards

1
Q

Reynolds number

A

Is a dimensionless parameter used to characterize flow regimes. Re = pVD/u

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2
Q

Entrance length

A

The length from the pipe entrance to where the velocity boundary layer emerges at the centerline

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3
Q

Fully developed laminar

A

The flow beyond the entrance that is laminar the velocity profile is a parabola, and the maximum velocity occurs at the pipe centerline

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4
Q

Fully develop developed turbulent flow

A

The flow beyond the entrance length that is turbulent. The velocity profile is much more uniform due to a rapid exchange of momentum along different fluid layers.

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5
Q
A
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6
Q

What do hydraulic and energy grade lines represent?

A

They are graphical representation of head. They’re used to illustrate the variation of head and friction loss along the pipe.

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7
Q

Hydraulic grade line

A

HGL represents the sum of pressure head and elevation head. P/pg + z

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8
Q

Energy grade line

A

EGL represents the total head or total mechanical energy.
P/pg +v^2/2g + z

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9
Q

What causes EGL to drop across a pipe?

A

The friction losses along the pipe

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10
Q

What causes HDL to rise in the diffuser?

A

The decrease of a flow velocity and the increase of pressure

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11
Q

Why are EGL and HDL parallel in a pipe section?

A

The pipe diameter remains constant

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12
Q

Why do both EGL and HDL rise in the pump and dropping the turbine?

A

Pump adds energy to the fluid passing through it, turbine extracts energy from the fluid

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13
Q

Major head loss

A

Refers to the loss occurred in straight pipe sections of constant cross-sectional area. Major head losses are typically significant in long pipes.

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14
Q

Minor head loss

A

Refers to the loss from pipe fittings and transitions minor head losses could be greater than major head losses for short pipe sections with many fittings and transitions

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15
Q

How to calculate major head loss

A

Use the Darcy Weisbach equation which is valid for laminar or turbulent.
hL= fLV^2/D2g

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16
Q

Hydraulic diameter for non-circular conduits

A

Non-circular conduits are often seen in pipe and deck systems and these applications the hydraulic diameter used in the density wish back equation and in the calculations for our E is dependent on the shape.

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17
Q

Fraction factor for affinity developed laminar flow in a circular pipe

A

F= 64/Re

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18
Q

Friction factor for steady fully developed laminar flow in a non-circular pipe

A

Is dependent on shape, but can be found in equation table

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19
Q

What is three methods? Can you use to find the friction factor of turbulent flows?

A

Colebrook Haaland and graphical interpretation

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20
Q

What are the three common types of fluid flow problems?

A

One determine the pressure drop or head loss or pump head/power
Two determine the flow right
three determine the pipe diameter

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21
Q

Solution strategy for determining the pressure drop head loss pump, head or power problem

A
  1. Determine the flow regime, laminar or turbulent.
  2. Determine the friction factor using Moody, Colebrook or Holland.
  3. determine the head loss using Darcy equation, then pressure drop and pump power
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22
Q

Solution strategy for determining the flow rates or the pipe diameter

A
  1. List all unknown, and possible equations, Darcy, or Holland the number of unknown must be the same as the number of equations.
  2. Iterative processes using guested initial value.
  3. Use spreadsheet or equation solver to solve for all unknowns.
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23
Q

Total head loss

A

A combination of minor and major head loss

24
Q

Fluid kinematics

A

Is a study of the fluid motion without referring to the forces and momentum that caused the motion. There are two ways of describing a fluid motion and fluid kinematics.

25
What are the two ways of describing fluid motion and fluid kinematics?
Lagrangian description or Eulerian description
26
Lagrangian Description
In this description, the motion of individual fluid particles are tracked, similar to the approach used for solids and classical mechanics. Therefore, the principles of classical mechanics can be applied the problem in this description relies on the difficulty of tracking large number of the particles.
27
Eularian description
In this description, the motion of a moving fluid is defined by using field variables within a control volume. A field variable at a particular location and a control volume at a particular time takes the value of the fluid particles which happened to occupy that location at that time.
28
Extensive properties
Depend on the mass. Their volume change accordingly as the mass of the fluid system changes.
29
Intensive properties
Are independent of mass for example, pressure temperature specific volume and density are all intensive properties. All specific properties are intensive properties. They referred to the corresponding extensive property per unit mass.
30
Surface flux (B)
Surface flux refers to the amount of an extensive property passing through a surface per unit time some examples of surface flux fluid mechanics include mass flux, or mass flow rate and momentum flux
31
System
System refers to a collection of same fluid particles at all times therefore the mass of the system is always constant
32
Control volume
Refers to fixed finite volume which may contain different fluid particles at different times. The boundary between a control volume and its surroundings is called the control surface. The control volume allows fluid particles pass through the control surface. Therefore, the mass of control volume may not remain constant at all times in the control volume approach we study the time rate of change of extensive properties in the control.
33
Reynolds transport theorem for a fixed control volume
The time rate of change of an extensive property be in a system equals the time rate of change of the extensive property in a control volume plus the flex of the extensive property be out of the control surface
34
Momentum flux correction factor
Used to correct the effect of the non-uniform velocity profile for turbulent flows and pipes. It is between 1.01 1.04 and for laminator flows. It is significantly greater than one.
35
General solution strategy for momentum, conservation equations
1. Set up a proper control volume making the control surface normal to the flow direction so that the flexes are easy to calculate 2. Apply mass conservation equation for the control. 3. Apply the momentum conservation equation for the control volume use algebra form if uniform or correction factor is known integral form if the flow profile is highly non-uniform or the flex correction factor is unknown. 4. The number unknown, and the number of equations apply energy conservation equation for the control volume if more equations are needed to solve for the unknown. 5. Solve all unknown conservation equations check the physics of the solved variables.
36
Setting up a control volume
Different control volumes may be set for the same problem as a rule of them always look for a good control volume with which makes the fluxes and forces easy to calculate. For example, the control surface normal to the velocities if possible, make the pressures on all most parts of the control surface known or obtainable
37
I’m
38
A momentum flux correction factor
is introduced to correct the effect of the uniform velocity profile. For turbulent flows in pipes B~1.01-1.04 for laminar flow B>>1.
39
General strategy for mass conservation
1. Set up a proper control volume for example making the control surfaces normal to the flow direction so fluxes are easy to calculate. 2. Apply mass conservation equation for the control. 3. Apply the momentum conservation equation use the algebraic form if the flow velocity profile is uniform or the momentum. Correction factor is known. Use the integral form if the flow velocity profile is highly nonuniform momentum flux correction factor is unknown. 4. Count the number of unknowns the number of equations apply the conservation equation for the control if more equations are needed to solve for the unknown. 5. Solve all the unknowns with the mass momentum and energy conservation equations. Check the physics of the solved variables.
40
Good practices for setting up a control volume
Set up the control surface, normal to the velocities and make the pressures on all or most of the control surfaces known if attainable
41
Body force
The magnitude of a body force is proportional to the volume of the body
42
Surface force
The magnitude of a surface force is proportional to the surface area of the body pressure force is an example of surface force as the net pressure force depends on the pressure difference that creates the force. It is usually more convenient to use use gauge pressure for the calculations of net pressure force.
43
Reaction force
A control value may be supported by various structures. The forces that control volume receives from its supporting objects in contact are called reaction forces.
44
Dimension
Is a measure of physical quantity example wait time acceleration without referencing the numerical values of the quantity
45
For primary dimensions and fluid mechanics
Mass, M length L, time t, temperature T
46
Dependent or secondary dimensions
Can be expressed in terms of the primary dimensions both primary and secondary dimensions can be written in different units systems such as the SI or imperial unit unit system
47
Dimensional homogeneity
Each of its additive terms must have the same dimension. All laws of physics follow this rule
48
Buckingham PI theory
For physical phenomenon that is dimensionally homogeneous, the number of independent dimensionless parameters covering the physical phenomenon can be found as k=n-j Where Anna is the number of independent parameters and J is the number of primary dimensions for a mechanical system 3, or 4 depending on heat transfer
49
Method of repeating variables for finding dimensionless parameters
1. List the number of dimensional quantities and their dimensions. 2. Determine the number of primary dimensions. 3. Calculate the number of dimensionless parameters. 4. Express the dimensional equation. 5. Find the exponents associated with each dimensional variable. 6. Express the physical phenomenon in terms of the dimensionless parameters.
50
Common dimensionless parameters and fluid mechanics
Reynold’s number, mock number, Freud number, Nault number, specific heat ratio
51
Complete similarity
Requires the model and the prototype to achieve geometric, cinematic, and dynamic similarities.
52
Geometric similarity
The model must have the same shape as the prototype and be scaled by a constant scale factor
53
Kinematic similarity
The velocity at any point in the model flow must be proportional by constant scale factor to the velocity at the corresponding point in the prototype flow
54
Dynamic similarity
All forces in the model flow must be proportional to the corresponding forces in the prototype flow by a constant scale factor
55
KeyPoint on model flow similarities
If a model and a prototype are in complete similarity, all independent dimensionless parameters in a model must match those in the prototype, for example Reynolds number
56

APSC 253 (7 decks)

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