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Fluids > Chapter 1; Basics > Flashcards

Chapter 1; Basics Flashcards

1
Q

Fluids

Equation for Mass Density?
SI Unit for Mass Density?
English Unit for Mass Density?
For Liquids, mass density is not a strong function of _____, and _____. On the other hand, for ______, density varies with both temperature & pressure. -

A

p= m/v ; Density = mass divided by volume

SI Units= kg / m3

English Units= slugs / ft3

temperature & pressure

gasses

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2
Q

Fluids

Specific Weight is also known as _____ _____.

Provide Definition-

Provide Equation-

Provided units-

A

Weight Density

Specific weight is the weight per unit volume.

γ = pg

SI = N / m3

USCS= lb / ft3

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3
Q

Define Specific Gravity

Provide Equation

A

Specific Gravity is the Ratio of the Specific Weight of a given fluis to the Specific Weight of water at 4¤ C (γwater = 9.81 kN/m3 or 62.4 lb/ft3 ).

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4
Q

Fluids

Ideal gas law is also called -

Provide definition-

Provide standard equation and explain

A

perfect gas law

Ideal Gas Law is the relationship between temperature and pressure for most gases.

pV=mRT;

p= absolute pressure

V= Volume

m= mass

R is the gas constant

T is the absolute Temperature (units in Kelvin or Rankine)

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5
Q

Fluids

Derive Ideal gas Law Equation in per mole basis and explain

A

pV=mRT ► pV=nRbarT

R= Rbar / M

n = m / M

p= absolute pressure

V is the volume

m is the mass

M= molecular weight also called atomic weight

n is the number of moles

Rbar is the universal gas constant = 8.314 kj/kmol-K

T is the absolute Temerature (Kelvin or Rankine)

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6
Q

Fluids

What is equation for gas constant used in ideal gas law

A

R= Rbar / M

R = Gas Constant

Rbar = Universal Gas Constant = 8.314 kJ/kmol-K

M = Molecular Weight of the Gas

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7
Q

Fluids

What is the Symbol for the Universal Gas constant, and what is the value and units

A
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8
Q

Fluids

What Temperature should be used for the ideal gas law

A

Kelvin or Rankine

TK= TC + 273

TR = TF + 460

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9
Q

Fluids

How do you convert Temperature to degrees Kelvin

A
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10
Q

Fluids

How do youi convert temperature to degrees Rankine

A
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11
Q

Fluids

How do you determine the number of moles

A

n = m / M

n= number of moles

m = mass

M= Molecular Weight

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12
Q

Fluids

γwater used for Specific Gravity = ?

Provide SI & USCS

A
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13
Q

Fluids

Equation for Compressibility Factor-

A

Z = pV / mRT

Z= Compressibility Factor

p= pressure

V= Volume

m= mass

R= Gas Constant

T= Temperature

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14
Q

Fluids

Explain how the compressibilty factor for various gasses is plotted-

A

The compressibility factor for various gasses is plotted as a function of the reduced pressure( pR), and the reduced temperature (TR) in the compressibility chart.

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15
Q

Fluids

Provide Equation for the Reduced Pressure

& the Reduced Temperature

A

pc = critical pressure; The crtical pressure is the max temperature that liquid and vapor phases can coexist.

Tc = critical temperature

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16
Q

Fluids

What are the conditions when the behavior of real gasses can be approximated using the ideal gas law?

A

This is when Z (the compressibility Factor approaches unit.

pR< 0.1 or TR > 0.2

pR = reduced pressure

TR = reduced Temperature

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17
Q

Fluids

Define Viscosity-

A

Viscosity is a fluid property that measures the resistance of the fluid due to an applied force.

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18
Q

Fluids

What is a Newtonian Fluid?

A

A Newtonian Fluid is a fluid that the shear stress is related to the rate of shear strain in a linear fashion (Like Hooks Law).

19
Q

Fluids

Provide the Equation for the Newtons las of viscosity-

A

For a newtonian fluid the Shear Stress is equal to change in velocity with respect to the heoght (y).

The proportionality constant (μ) is called the absolute viscosity, dynamic viscosity or simply the viscosity.

It has units of N-s/m2 in SI units (lb-s/ft2 in US units)

τ (Tau) is the Shear Stress

u = fluid velocity

20
Q

Fluids

Explain the concept of viscosity

A

To illustrate the concept of viscosity, consider a fluid between two parallel plates, as shown in the figure. If the top plate is moved at a velocity U while the bottom plate is fixed, the fluid is subjected to deformation. The fluid in contact with the top plate moves with the plate velocity U and no-slip condition is applied at the bottom plate (i.e., the fluid is stuck to the bottom plate, u = 0). The velocity profile of the fluid motion between the plates is assumed to be linear and is given by

u = U y/h

21
Q

Fluids

Name 3 common types of fluids that are considered to be Newtonian Fluids.

A

Water, air, and oil

22
Q

Define Kinematic Viscosity

Provide Equation

Provide units

A

Kinematic Viscosity is the ratio of absolute viscosity and density.

SI units is m2 / s

CGS Units= cm2 / s; Called a Stoke (St.)

23
Q

Fluids

Definition for Cohesion-

A

The force attraction between like molecules (e.g., molecules within a liquid).

24
Q

Fluids

Definition for adhesion-

A

The attraction between unlike molecules (e.g., molecules between liquid and solid).

25
Q

Fluids

Explain how the forces are actiing in the water and at the surface in the attached Image.

A

The net cohesive force exerted on a molecule inside a liquid is zero; whereas there is a net inward cohesive force exerted on a molecule at the surface. As a result, this inward force holds the liquid together and forms a definite volume. In addition, the liquid surface acts like a thin stretched membrane. For example, a rubber band, which is denser than water will float on water. The weight of the rubber band is balanced by the force created by the surface tension of the water and the buoyancy force.

26
Q

Fluids

Define Surface Tension

A

Surface Tension is the force (per unit length) required to change the surface shape of a liquid and is denoted by the Greek symbol σ

σ = F / L

27
Q

Fluids

What is the units for Surface Tension

A

SI = N / m

USCS = lb / ft.

28
Q

Fluids

Surface tension (σ) is a function of ?

A

Temperature

29
Q

Fluids; Surface Tension

A good way to observe Surfacr Tension (σ) ?

A

Looking at the riese and fall in a capilary tube

30
Q

Fluids; Surface Tension

When looking at Surface Tension in a Capillary tube, when will the liquid rise in the tube?

A

If the adhesion between the liquid and glass is greater than the cohesion of the liquid molecules, then the liquid rises up the tube. The liquid is said to wet the glass surface

31
Q

Fluids

When looking at surface tension in a Capillary tube, when will the liquid fall in the tube.

A

if cohesion is greater than adhesion and it does not wet the surface.

32
Q

Fluids

For Surface Tension in a Capillary Tube, explain how to determine the height of the rise or fall.

A

The height of the rise (h) can be obtained by a force balance (i.e., the vertical component of the force created by surface tension must be balanced by the weight of the liquid column),

2πRσ cosθ = ρgπ R2h

which can be simplified to yield

h = 2σ cosθ / (ρgR)

where θ is the contact angle or wetting angle and σ is the surface tension (N/m, lb/ft). For wetting liquids, θ is less than 90o; for non-wetting liquids, θ is greater than 90o.

33
Q

Fluids

Name all 4 dimensionless groups and explain

A

Run Mother Fukcer, Win

34
Q

Fluids

Equation for Reynolds Number

Explain

A

ρ = density

V = velocity

L = characteristic length or Hydraulic Radius

μ =viscosity.

L term is different for each flow type. For example, for a pipe, L is the diameter of the pipe. For open channel flow, the hydraulic radius, Rh (see diagram) is commonly used.

35
Q

Fluids

What is Reynolds number used for?

A

To charachterize if the flow is laminar or turbulant

Used for almost all flow including open channel flow

36
Q

Fluids

When talking about Reynolds number, the flow is generally assumed to be

Laminar when Re ?

Turbulent when Re ? .

The flow is referred to as transitional flow when the Reynolds number is between ?.

A

laminar when Re < 2,100
turbulent when Re > 10,000.
transition flow when between 2,100 and 10,000.

37
Q

Fluids

Froude number is an important dimensionless parameter in the study of ?

A

open-channel flow

38
Q

Fluids

Provide equation for Froude Number-

Explain

A

V = average velocity

L= characteristic length associated with the channel (hydraulic depth for open channel flow)

g= gravitational acceleration.

For rectangular cross sections, the hydraulic depth is the water depth.

39
Q

Fluids

Physically, the Froude number represents the ratio ?

A

ratio of inertial forces to gravitational forces.

40
Q

Fluids

open-channel flow can be classified according to the Froude number in the following manner:

A

(a) Fr < 1: subcritical (tranquil) flow
(b) Fr = 1: critical flow
(c) Fr > 1: supercritical (rapid) flow

41
Q

Fluids

What is Mach Number used for?

Provide Equation

A

Mach number is used to indicate if a flow is incompressible or compressible, and it is given by

a (Usually denoted the letter c) is the speed of sound (343 m/s at 20oC)
V is the fluid velocity.

42
Q

Fluids

Flow can be characterized using the Mach number as folllows:

A

(a) Ma ≤ 0.3: incompressible
(b) 0.3 < Ma < 1.0: compressible subsonic flow
(c) Ma ≥ 1.0: compresible supersonic flow

43
Q

Fluids

The dimensionless parameter associated with surface tension effects is ?

Provide Equation & explain

A

Weber number

σ is the surface tension.

44
Q

Fluids

Open-channel flow can also be classified according to the Froude number in the following manner:

A

(a) Fr < 1: subcritical (tranquil) flow
(b) Fr = 1: critical flow
(c) Fr > 1: supercritical (rapid) flow

Fluids (2 decks)

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