Thermofluids Flashcards
What is the second law of thermodynamics?
The total entropy of an isolated system can only increase with time. “You never get out what you put in”
What is the first law of thermodynamics?
/\U=Q-W
Where U is the internal energy, Q is the heat supplied to the system and W is the work done BY the system
What type of process does a throttle valve represent?
An ISENTHALPIC one.
Define isentropic.
No change in entropy. This is ideal.
Define viscosity.
Viscosity is a quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow
What is the specific volume of a substance?
It is the ratio of a substances volume to it’s mass. Measured in m^3/kg
What is absolute pressure?
Absolute pressure is a comparison between your measured pressure and a vacuum.
What is gauge pressure?
Gauge pressure is a comparison between your pressure and a reference pressure (such as that of the atmosphere).
Name 3 properties of an ideal gas
- Particles are treated as point-masses
- Particles collide elastically with the walls of the container
- Particles may pass through each other. They contain no attractive potential energy
What is the purpose of a U-tub manometer?
To measure the difference between two unknown pressures.
What is Bernoulli’s Equation?
P + pgh + (pC*C)/2 = constant(k)
When does cavitation occur?
When the pressure of the fluid is below the saturated-vapour pressure, cavitation (vapour bubbles) occurs.
What is the critical Reynolds number?
2000
What is incompressible flow?
When the density of a fluid remains constant as it goes through fluid flow.
Define inviscid flow.
A flow where viscous effects do not significantly influence the flow and are this neglected.
What is a Newtonian fluid?
A fluid with a constant viscosity.
What does HCP mean? What is the stacking sequence?
Hexagonal closed packed.
Stacking sequence is ABABABAB
What is atomic packing fraction?
APF=((Number of particles)*(Particle Volume))/(Unit Cell Volume)
How many atoms in a bcc and fcc cubic?
fcc cubic = 4 atoms per unit cell
bcc cubic = 2 atoms per unit cell
What is ionic bonding?
Electrostatic attraction arising from an exchange of electrons to form +ve and -ve species
What is metallic bonding?
+ve ions in a sea of -ve bonding electrons
What is covalent bonding?
Bonding electrons shared between two atoms
What is the equation for bond stiffness?
S=Ea.
a. is the interatomic distances
What is the equation for Poisson’s Ratio?
v=(transverse strain)/(longitudinal strain)
What is the FCC stacking sequence?
ABCABCABC
80 Hb 12/1427/30
Explain this
80 is the hardness Hb is the type of test 12 is the ball diameter 1427 is the load in kgfmm^-2 30 is the load duration in seconds
How many Newtons in 1kgf?
9.81 Newtons =1kgf
What is stress intensity factor (k)?
What is the formula?
The stress intensity factor (K) is used in the field of fracture mechanics. It predicts stress intensity near the tip of a crack caused by a remote load or residual stresses.
Let ó=stress
K=Yó(pi*a)^0.5
a is the crack size
Y is the geometry factor (calculated)
Name the four processes in the Carnot cycle.
Isothermal Expansion 》Isentropic Expansion 》Isothermal Compression 》Isentropic Compression
Define adiabatic.
Relating to or denoting a process or condition in which heat does not enter or leave the system concerned.
“the adiabatic expansion of a perfect gas”
Define Toughness.
A measure of a materials ability to deform plastically without fracturing, as measured by the energy under the stress strain curve
Strength - define it
The measure of a materials resistance to plastic deformation
What are the four types of “impurities” that mean a material can never really reach its theoretical strength?
- Vacancy
- Interstitial Atom
- Interstitial Impurity Atom
- Substitutional Impurity Atom
What is theoretical strength approximately equal to?
E/3
Define stiffness?
The resistance of a material to deformation under an applied force
Define stiffness?
The resistance of a material to deformation under an applied force
What does the Frenkel Model represent?
The frenkel model predicts the critical shear stress of two closed packed planes sliding over each other.
Why is the Frenkel Model too simplistic?
It predicts that the stress can only vary sinusoidally. It doesn’t consider a linear defect separating slipped from unslipped regions. No consideration is given to dislocations.
What are the three main primary bonds? How do they relate to a material’s stiffness?
Covalent - Highest bond stiffness
Metallic - Medium bond stiffness
Ionic - Lower bond stiffness
What is a covalent bond?
Pairs of electrons are shared by two adjacent atoms.
What is a metallic bond?
The sharing of free electrons in a lattice of positively charged ions.
What is ionic bonding?
The bond formed by electrostatic attraction between positively and negatively charged species. Electrons are shared because sharing is caring.
What happens to a shear thinning fluid as a shear stress is applied.
It becomes LESS viscous.
What is a saturated liquid?
A liquid that is on the verge of boiling.
What is a compressed liquid?
A stable liquid that is either at a lower temperature or a higher pressure than a saturated liquid.
What is a saturated vapour?
A vapour that is on the verge of condensing.
What is a superheated vapour?
A stable vapour that is either at a lower pressure or higher temperature than a saturated vapour.
Why does the Carnot cycle have the maximum possible efficiency?
- The rectangle has the maximum possible area for the given temperatures.
- The isentropic processes are impossible to engineer in real life
- All of the heat is added at the maximum temperature
For the Carnot cycle, what is the compressor/turbine order?
- Isothermal Turbine
- Isentropic Turbine
- Isothermal Compressor
- Isentropic Compressor
For an ISENTROPIC feed pump. How do you calculate the change in enthalpy?
dh=v(p2-p1)
True or false, for your true stress strain curve. Your true stress strain equals n (your power).
TRUE
What is the equation for Bulk Modulus.
B=E/3(1-2v)
