Lecture 3 - Properties of pure substances Flashcards
“u” stands for
specific internal energy
In thermodynamics, we are presented with problems as a function of …
pressure and temperature
“v” stands for …
specific volume
”s” stands for …
specific entropy
“h” stands for
specific enthalpy
Properties of pure substances are ..
P, T, s, h, u, v
Two phase systems are …
systems where liquid goes through a phase change to a vapor
A pure substance is one where…
we have fixed chemical composition throughout
In the solid phase, the molecules are ..
arranged in a 3D lattice pattern and are therefore not free to move around.
In the liquid phase, the molecules …
can move and slide over each other, but the molecules are still in a lattice pattern
In the gas phase …
the molecules are far apart from each other and are free to move about and collide.
In a phase change diagram, at constant pressure, the saturation temperature, Ts, is …
Where we go through the phase change of boiling
In phase change diagram, before getting to the saturation temperature, we are in the ______________ region.
the compressed liquid
At constant temperature, the saturation point is the …
boiling point at that pressure.
At the saturation point, we have a ___________.
saturated mixture
In a saturated mixture we have ….
both a liquid and vapor
In the superheated vapor region,
you no longer have a liquid; all you have is vapor
We assume the line for a superheated vapor is …
at a constant pressure
The point at which we go from compressed liquid to saturated mixture is referred to as a …
saturated liquid
The point at which we go from a saturated mixture to a superheated vapor is called ….
a saturated vapor
At boiling, we have _______, and it takes place on the ________.
a liquid and a vapour (liquid and vapor bubbles)
saturated mixture line
Bubbles forming at the bottom of a pan and floating up to the top, but no steam or turbulence at the surface of the water means that we are …
On the compressed liquid line
compressed liquid saturated liquid saturated mixture saturated vapor superheated vapor constant pressure
líquido comprimido líquido saturado mezcla saturada vapor saturado vapor sobrecalentado/recalentado presión constante
At a given (fixed) pressure, the temperature at which a pure substance changes phase is the _________.
saturated temperature (Tsat/Ts)
At the saturation temperature, a pure substances changes from ________ to ________.
liquid to vapor
The table that pertains to a pure substance changing from liquid to vapor at the saturated temperature is …
Tabla 3 (Propiedades del agua saturada [liquido y vapor])
superheated water vapor in spanish
vapor de agua recalentado
Tablas de propiedades termodinámicas del Refrigerante 134a is for …
saturated R134a (pg 84)
At a given temperature, the pressure at which a pure substance changes phase is …
the saturation pressure (Psat/Ps)
At a given temperature, the table we use for a phase change of a pure substance is …
Tabla 3
In Tabla 4, there are different pressures and for each pressure, there is a saturation temperature. This saturation temperature is the temperature at which …
we go through through the phase change
Tabla 3 is only applicable when …
you are going through the phase change process itself.
If you only have a vapor, you have to use Tabla …
4
v’, u’, h’, s’ represent ________ respectively.
specific volume for a saturated liquid
internal energy of a saturated liquid
enthalpy of a saturated liquid
entropy of a saturated liquid
v’’, u’’, h’’, s’’ represent __________ respectively.
specific volume for a saturated vapor
internal energy of a saturated vapor
enthalpy of a saturated vapor
entropy of a saturated vapor
To the left of the saturated region is the ___________.
compressed liquid region.
In the compressed liquid region, we ____________ a phase change process.
have NOT gone into a phase change process
To the right of the two phase region, we have …
the superheated (sobrecalentado/recalentado) region
In the superheated vapor region, we have …
increased the temperature past the saturated temperature.
In Tabla 4, we start at the saturation temperature, and the temperature keeps increasing until …
the temperature at the top of the table.
At the critical point, your …
saturated liquid and saturated vapor state are identical.
At the critical point, you are …
at the top of the T-v diagram
To the left of this andrews curve (∩) is the …
here ___________/
/
compressed liquid phase
Inside this bell curve ∩ is the …
____here____/
/
liquid/vapor phase
To the right of this bell curve ∩ is …
___________/ here
/
the superheated vapor phase
________/ many of these lines on the left can pass
/ through the Andrew’s curve, and each
represents …
the temperature and specific volume of a liquid at constant pressure
∩ on the curve on the left, the critical point is located …
at the top of the curve.
If a fluid is heated beyond the critical point, it looks as follows:
__/ (above the bell curve.)
/ ∩ In this case, we say that we have a ..
supercritical fluid (fluido supercrítico)
The critical point of a superheated fluid is …
the critical point of the Andrew’s curve (at the very top of the curve)
At the critical point of a supercritical fluid, we have …
a critical temperature (Tcr)
The pressure at which we have the critical point and temperature is called …
the critical pressure, Pcr
∩ the left line on this bell curve is called …
the saturated liquid line
∩ the right line on this curve is called …
the saturated vapor line
We calculate properties for mixtures in the two phase region by …
___this region__/
/
v’’ - v’ ; h’’ - h’ ; s’’ - s’ ; u’’ - u’
When performing calculations in the two phase region (where we have a liquid and a vapor), we need a way to calculate the properties because …
we are not at the saturated liquid point nor the saturated vapor point; we are somewhere between the two.
We use a quantity called a quality (título) to …
denote where we are in a two phase region
Quality (título) is denoted as _________ and is defined as _________.
X
X = mass of vapor in our system/total mass
We have a quality (título) of 1 when we are …
on the saturated vapor line
We have a quality (título) of 0 when we are …
on the saturated liquid line
Quality has bounding values of …
0 and 1
In the saturated liquid region, the average value of any intensive property is determined by …
yav = y’ + x*(y’‘-y’)
Average enthalpy in the saturated liquid region is calculated by …
h = h’ + x(h’‘-h’)
Average entropy in the saturated liquid region is calculated by …
s = s’ + x(s’‘-s’)
piston cylinder device in Spanish
dispositivo de cilindro de pistón
piston cylinder in Spanish
cilindro de pistón
1 bar = ____ kPa
100
1 m^3 = ___ dm^3
1000
The mass of the liquid in a two phase region can be found by …
mf = volume of liquid in the problem/volume of liquid at the pressure/temperature in the Table 3
mf = vf/v’
The mass of the vapor in a two phase region can be found by …
mg = volume of vapor in the problem/volume of vapor at the pressure/temperature in the Table 3
mg = vg/v’’
Total mass is found by …
mf + mg
Volume at state 1 or state 2 is found by …
V1 or V2 = total mass * v1 or v2
If the volume in the table corresponds to the volume at state 1 or state 2, we can say that the volume at each state __________
corresponds to a saturated liquid or saturated vapor
At constant temperature, the lines on a P-v diagram look as follows …
\___________
\ and passes through this bell curve, ∩
The following lines represent ______________ on a P-v diagram:
\___________
\
isotherms (constant temperature lines)
___________ can be used to relate pressure and temperature to specific volume (v), specific internal energy (u), specific enthalpy (h), and specific entropy (s) for some substances.
Equations of state; the ideal gas equation
State the ideal gas equation.
PV = mRT
PV = mRT; v = V/m, so from the ideal gas equation, v = …
v = RT/P
The ideal gas equation only works when …
dealing with ideal gases
dealing with liquid/vapor mixtures at high temperature AND pressure
dealing with superheated gases at high temperature AND pressure
THE IDEAL GAS EQUATION ONLY WORKS WHEN:
- liquid/vapor phases quite a ways to the right of the bell curve (at high temperature AND pressure)
- superheated gases way to the right of the bell curve (at high temperature AND pressure)
True
Gases DO NOT deviate significantly from ideal gas behavior at states near the saturation region.
FALSE!
YES THEY DO!
Gases deviate significantly from ideal gas behavior at states near the ____________ and near __________.
saturation region
the critical point
We can use the ideal gas equation near the critical point or near the saturation region.
NO!
Gases deviate from ideal behaviour near the critical point and saturation region.
If dealing with steam and superheated steam, it is wise to use ___________ over the ideal gas equation.
Tables 3 and 4
If you need to work with the ideal gas equation close to the two-phase region, you can account for the non-ideal behavior by …
introducing the compressibility factor, z
using generalized compressibility charts [Figura A-1, A-2 y A-3] (if we know the critical temperature and pressure)
The compressibility factor, z, is equal to ..
z = actual specific volume/ideal specific volume
With the compressibility factor, the ideal gas equation becomes …
Pv = ZRT
