EXAM 2 Flashcards
What does compressible mean?
fluid can change shape/size as we change P/T
Are gases compressible/incompressible?
compressible
Mach number equation
u/c where c is speed of sound in fluid
What mathematically is true for incompressible flow?
(rho1/rho2) < 2 AND (Ma < 0.3)
What energy balance do you follow for incompressible flow? What fluids does this describe?
Chapter 2 … all liquids and slow moving gases
What two things could prove the show is compressible?
pressure ratio large or flow very fast
When compressible flow, what are the dominant terms of mechanical energy balance?
kinetic energy and compressible effects (large change in density)
What kind of flow is air through AC duct?
incompressible
What find of flow is flow from a high pressure tank through a short tube?
compressible
What does Mach number indicate?
importance of compressibility and velocity
What variable represents mass velocity?
G
Eqn of mass velocity?
G = (velocity)*(density)
What are the units of mass velocity?
kg/(m^2*s)
What does k represent?
ratio of heat capacity (Cp/Cv)
What is the k value for monoatomic processes?
1.67
What is the k value of diatomic processes?
1.40
What is the k value of triatomic processes?
1.32
What does it mean when a system is adiabatic?
There is no mass/heat transfer between system and environment
What kind of system is an isolated system?
adiabatic
What happens to velocity as a fluid moves down an adiabatic system?
it increases
What happens to density as a fluid moves down an adiabatic system?
it decreases because pressure decreases
What happens to pressure as a fluid moves down an adiabatic system?
it decreases
What happens to temperature as a fluid moves down an adiabatic system?
unknown without knowing about flow… if the frictional loss is greater than the impact of velocity change, temperature will increase
What happens to Ma as a fluid moves down an adiabatic system?
it increases
What happens to mass velocity as a fluid moves down an adiabatic system?
it stays the same
What is the relationship between the pressure at the outlet of an adiabatic system and the pressure of the surroundings?
they are equivalent
What is choked flow?
Largest possible flow rate in pipe with friction (sonic velocity at outlet)
If the pressure of the surroundings of an adiabatic system at choked flow continues to decrease, what happens to velocity and flow rate?
Velocity remains sonic because gas leaving system cannot go any faster, and flow rate remains unchanged
What are the outlet temperature, pressure, and density dependent on in an adiabatic system with friction?
Mach number only
What is the difference between equations of adiabatic and isothermal systems?
adiabatic system eqns contain Y terms
What does the mechanical energy balance relate for an adiabatic system?
Ma and frictional loss in length of pipe
In an isothermal system, as the pressure of the surroundings decreases, what happens to the flow rate?
it increases until reaching choked flow
What is the limiting exit for isothermal?
Ma = 1/sqrt(k)
What is the limiting exit for adiabatic?
Ma = 1
What happens to the temperature of the system as fluid moves down an isothermal system?
It stays the same
What happens to the velocity of the system as fluid moves down an isothermal system?
it increases
What happens to the mass velocity of the system as fluid moves down an isothermal system?
it stays the same
What happens to the pressure of the system as fluid moves down an isothermal system?
it decreases
What happens to the Mach number of the system as fluid moves down an isothermal system?
it increases
What is the relationship between the T at choking conditions and at inlet for an isothermal system?
they are equivalent
What is the relationship between the P at choking conditions and at inlet for an isothermal system?
Pch = P1Ma1(sqrt(k))
What is the relationship between the density at choking conditions and at inlet for an isothermal system?
rho(ch) = rho(1)Ma1(sqrt(k))
What is the relationship between the velocity at choking conditions and at inlet for an isothermal system?
u(ch) = (u(1)/(Ma1*sqrt(k)))
What are the units of dynamic viscosity?
kg/(ms) or Pas
What is an example of Bingham Plastic?
toothpaste, peanut butter, butter
What is an example of a dilatant?
quick sand
What kind of shear is dilatant?
thickening (n>1)
What kind of shear is pseudoplastic?
thinning (n<1)
Describe graph of pseudoplastic
starts at origin and eventually curves downward
Describe graph of dilatant
starts at origin and eventually curves upward
Describe graph of Bingham Plastics
is linear and has y-intercept > 0
Describe graph of general plastics
has y-intercept > 0 and eventually curves downward
What type of non-newtonians do we deal with?
time independent
What variable does the velocity eqn of a Bingham plastic contain that the other NN fluids do not?
m
What variable does the velocity eqn of a power law fluid contain that the other NN fluids do not?
K
What variables are in the velocity eqn of a power law fluid that differentiates it from the others?
K and m
What has characteristics of both Bingham Plastics and Power law fluids?
General Plastics
What kind of NNs are power law fluid?
pseudoplastics and dilatants
What does the n in the total stress eqn represent?
plastic viscosity
What NN has a plug like core?
Bingham Plastics
When m≥1 for Bingham plastics, what is true of velocity?
it is 0
When is flow of a Bingham plastic frozen?
when Tau(w)«Tau(not)
What does Tau(w) represent?
Wall stress (Josh thinks)
What is nearly always negligible for a Bingham Plastic mechanical energy balance?
velocity term
For what type of NN do we use Re(gen)?
Power law fluids
