Chapter 1; Basics

Question 1

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. -

Answer 1

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

SI Units= kg / m³

English Units= slugs / ft³

temperature & pressure

gasses

Question 2

Fluids

Specific Weight is also known as _____ _____.

Provide Definition-

Provide Equation-

Provided units-

Answer 2

Weight Density

Specific weight is the weight per unit volume.

γ = pg

SI = N / m³

USCS= lb / ft³

Question 3

Define Specific Gravity

Provide Equation

Answer 3

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

Question 4

Fluids

Ideal gas law is also called -

Provide definition-

Provide standard equation and explain

Answer 4

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)

Question 5

Fluids

Derive Ideal gas Law Equation in per mole basis and explain

Answer 5

pV=mRT ► pV=nR_barT

R= R_bar / 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

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

T is the absolute Temerature (Kelvin or Rankine)

Question 6

Fluids

What is equation for gas constant used in ideal gas law

Answer 6

R= R_bar / M

R = Gas Constant

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

M = Molecular Weight of the Gas

Question 7

Fluids

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

Answer 7

Question 8

Fluids

What Temperature should be used for the ideal gas law

Answer 8

Kelvin or Rankine

T_K= T_C + 273

T_R = T_F + 460

Question 9

Fluids

How do you convert Temperature to degrees Kelvin

Answer 9

Question 10

Fluids

How do youi convert temperature to degrees Rankine

Answer 10

Question 11

Fluids

How do you determine the number of moles

Answer 11

n = m / M

n= number of moles

m = mass

M= Molecular Weight

Question 12

Fluids

γ_water used for Specific Gravity = ?

Provide SI & USCS

Answer 12

Question 13

Fluids

Equation for Compressibility Factor-

Answer 13

Z = pV / mRT

Z= Compressibility Factor

p= pressure

V= Volume

m= mass

R= Gas Constant

T= Temperature

Question 14

Fluids

Explain how the compressibilty factor for various gasses is plotted-

Answer 14

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

Question 15

Fluids

Provide Equation for the Reduced Pressure

& the Reduced Temperature

Answer 15

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

T_c = critical temperature

Question 16

Fluids

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

Answer 16

This is when Z (the compressibility Factor approaches unit.

p_R< 0.1 or T_R > 0.2

p_R = reduced pressure

T_R = reduced Temperature

Question 17

Fluids

Define Viscosity-

Answer 17

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

Question 18

Fluids

What is a Newtonian Fluid?

Answer 18

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).

Question 19

Fluids

Provide the Equation for the Newtons las of viscosity-

Answer 19

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

Question 20

Fluids

Explain the concept of viscosity

Answer 20

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

Question 21

Fluids

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

Answer 21

Water, air, and oil

Question 22

Define Kinematic Viscosity

Provide Equation

Provide units

Answer 22

Kinematic Viscosity is the ratio of absolute viscosity and density.

SI units is m² / s

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

Question 23

Fluids

Definition for Cohesion-

Answer 23

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

Question 24

Fluids

Definition for adhesion-

Answer 24

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

Question 25

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

Answer 25

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.

Question 26

# Fluids Define Surface Tension

Answer 26

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

Question 27

# Fluids What is the units for Surface Tension

Answer 27

SI = N / m USCS = lb / ft.

Question 28

# Fluids Surface tension (σ) is a function of ?

Answer 28

Temperature

Question 29

# Fluids; Surface Tension A good way to observe Surfacr Tension (σ) ?

Answer 29

Looking at the riese and fall in a capilary tube

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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.

Question 33

# Fluids Name all 4 dimensionless groups and explain

Answer 33

Run Mother Fukcer, Win

Question 34

# Fluids Equation for Reynolds Number Explain

Answer 34

![]() ## Footnote 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.

Question 35

# Fluids What is Reynolds number used for?

Answer 35

To charachterize if the flow is laminar or turbulant Used for almost all flow including open channel flow

Question 36

# 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 ?.

Answer 36

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

Question 37

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

Answer 37

open-channel flow

Question 38

# Fluids Provide equation for Froude Number- Explain

Answer 38

![]() ## Footnote 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.

Question 39

# Fluids Physically, the Froude number represents the ratio ?

Answer 39

ratio of inertial forces to gravitational forces.

Question 40

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

Answer 40

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

Question 41

# Fluids What is Mach Number used for? Provide Equation

Answer 41

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.

Question 42

# Fluids Flow can be characterized using the Mach number as folllows:

Answer 42

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

Question 43

# Fluids The dimensionless parameter associated with surface tension effects is ? Provide Equation & explain

Answer 43

Weber number  σ is the surface tension.

Question 44

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

Answer 44

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