Final Exam Flashcards
(34 cards)
What are equations of state?
Analytical formulations that constitute a third general way of expressing the P-v-T relationship.
Virial equation of state
to relate the P-v-T behavior of a gas to the forces between molecules
z = 1 + B(T)/v + C(T)/v^2 + D(T)/v^3 + …
van der Waals Equation
P = RT/(v-b) - a/v^2
b accounts for volume occupied by the molecules
a/v^2 the forces of attraction between molecules
When can the van der Waals Equation be used?
b)
Derived at crit. temp. point
Inaccurate for substances with z deviating from 0.375 Table A-20
Redlich-Kwong equation (empirical):
P = RT/(v-b) - a/v(v+b)T^(1/2)
No rigorous derivatives a + b are obtained by data fittings
fundamental definition for speed of sound
an intensive property whose value depends on the state of the medium through which the sound propagates. The medium itself may be undergoing any process
The Joule-Thomson coefficient (muj) of an ideal gas is always ___________.
0
Describe how the Joule-Thomson Coefficient can be used for industrial applications.
Provides information on temperature change after the throttling process. Positive Uj is a property of a fluid which can be used to design large-capacity cooling or liquification of gases, such as LNG.
Mixing of ideal gases work and heat (insulated)
Wcv=0
Wcv=0
Therefore Deltau = Qin - Wout = u1-u2 = 0
Energy conservation (mixing of ideal gases)
u1 = NaUa(Ta) + NbUb(Tb) u2 = NaUa(T2) + NbUb(T2)
What is absolute humidity (w)?
The ratio of mass of water vapor at atm to mass of dry air.
Absolute humidity equation
w = mvapor/mair = Pvapor/Pair = vair/vvapor
Ideal gas derivation of absolute humidity
w = 0.622(Pvapor/Pair)
What does 0.622 come from in the ideal gas derivation of absolute humidity?
0.622 = 18/28.9 = (molecular wt. of water)/(molecular weight of air)
Relative humidity equation
Phi = Pr/Pg = (partial pressure of the water vapor)/(saturation pressure of the water vapor at the MIXTURE TEMPERATURE and TOTAL PRESSURE)
Pr equation
Pr = COP/(0.622 + w)
What does relative humidity (phi) pertain to?
Only to the vapor in the atmospheric air, independent of the pressure and density of the dry air in the mixture.
Relation between phi and w
w = (vair/vgas)phi
What is the degree of saturation?
A ratio of the liquid to the total volume of voids in a porous material.
Degree of saturation =
wout/win
What is the dry bulb temperature?
The temperature that would be measured by a thermometer placed in the mixture
What is wet bulb temperature?
Temperature measured by a thermometer whose bulb is enclosed by a wick moistened with water
What is the dew point temperature?
The saturation temperature of the vapor corresponding to its partial pressure in the mixture. It is thus the temp. at which condensation begins if the mixture is cooled at constant vapor pressure.
What is adiabatic saturation temperature?
The temperature that results from adiabatically adding water to the atmospheric air in a steady flow until it becomes saturated.
