Ch. 3 Properties of Pure, Compressible Substances Flashcards
Quality (X)
only defined in the 2-phase region (undefined in uncooled and superheated regions)
X = 0 saturated liquid
X = 1 saturated vapor
Equation for specific volume (v)
v = X*v[g] + (1-X)v[f]
Enthalpy (H)
[=] kJ
Entropy (S)
[=] kJ/K
Internal energy (U)
[=] kJ
Specific Enthalpy (h)
[=] kJ/kg
Specific Entropy (s)
[=] kJ/(kg*K)
Specific Internal energy (µ)
[=] kJ/kg
Phase
Refers to a quantity of matter that is homogeneous throughout (in both chemical composition and physical structure)
What is a pure substance?
A substance that his uniform and does not very in chemical composition
What is the State principle?
A general rule developed as a guide in determining number of independent properties required to fix the state of a system
What is a simple compressible system?
Commonly encountered pure substances, Such as water or uniform mixture of non-reacting gasses. By the state principal if any to independent intensive properties are specified the values of all other intensive properties will be fixed (one for heat and one for work).
-The term simple system is applied when there’s only one way the system energy can be significantly altered by work as the system undergoes quasiequilibrium processes
What is the intensive state of a closed system at equilibrium?
It’s condition as described by the values of its intensive thermodynamic properties
How are independent intensive properties important in determining the state of the system?
The state can be uniquely determined by giving the values of a subset of the independent intensive properties, and values for all other intensive thermodynamic puppies are determined once this independent subset is specified.
- Volume can have a significant influence on the energy and the only mode of energy transfer by work is associated with the volume change (integral P dV)
What are the two ways energy of a close system can be altered independently?
By heat or by work.
Experiment and observation have shown that pressure is determined as a function of which two independent properties?
Temperature in specific volume are regarded as independent
p = p(T,v)
What is the graph of p = p(T,v) called?
p-v-T surface (a 3-D surface)
What do you the coordinates of a point on the p-v-T surface represent?
The values pressure, specific volume, temperature would assume when the substance is that equilibrium
What is the region called where the state of a system is fixed by any one of the properties: pressure, specific volume, and temperature?
Single-phase region, because all of these are independent when there is a single phase present.
In a single-phase region how many properties are required to fix the state of the system?
Only two (pressure, specific volume, or temperature) because all of these are independent when there is a single phase present
What is the region called where two phases can exist in equilibrium?
Two-phase regions
What is the relationship between pressure and temperature within the two-phase region?
They are not independent, one cannot be changed without changing the other. Therefore, the state cannot be fixed by temperature and pressure alone.
What is required to fix the state within the two-phase region?
Specific volume and either temperature or pressure
What is a saturation state?
A state at which a phase change begins or ends
What is the vapor dome?
The dome-shaped region composed of the two-phase liquid-vapor states
What are the borders of the vapor dome?
The saturated liquid and saturated vapor lines
What is the critical point?
The point at the top of the vapor dome where the saturated liquid and saturated vapor lines meet
What is the critical temperature (T sub c) of a pure substance?
The maximum temperature at which a liquid and vapor phase is 10 coexist in equilibrium
What is the critical pressure and critical specific volume?
The pressure and specific volume at the critical point
What is a phase diagram?
A property diagram formed of the projection of the p-v-T surface onto the pressure-temperature plane. (The two-these regions reduce two lines)
What is the saturation temperature?
The temperature at which a phase change takes place at a given pressure.
What is the saturation pressure?
The pressure at which a phase change takes place at a given temperature.
What is the triple point?
The two dimensional projection of the triple line (three phases exist and equilibrium) onto the phase diagram.
- used as a reference defining temperature scales (The temperature assigned to the triple point of water is 273.16 K, and the pressure is measured to be 0.6113 kPa)
True or false, distinct phases can exist within solids or liquids?
True, in addition to the three phases of solid, liquid, and vapor, it is also possible that distinct phases can exist within solids or liquids (ice has 17 different crystalline structures)
What is the p-v diagram?
The projection of the p-v-T surface onto the pressure-specific volume plane
What are isotherms?
Lines of constant temperature on the p-v diagram
What is the T-v diagram?
Projection of the liquid, two-phase liquid-vapor, and the vapor regions of the p-v-T surface onto the temperature-specific volume plane
What are isobars?
Lines of constant pressure on the T-v diagram
What happens to temperature and pressure in the two-phase region?
They remain constant throughout the region
What is a subcooled liquid region?
Single-phase liquid region to the left of the two-phase region, up to the critical temperature (called subcooled because the temperature at these states is less than the saturation “booking” temperature at the given pressure)
- aka Compressed liquid
What is a compressed liquid state?
Liquid states to the left of the two-phase region (The pressure at each state is higher than the saturation pressure corresponding to the temperature at the state)
-A.k.a. subcooled liquid
What is quality (X)?
The ratio of the mass of vapor To the total mass of a two-phase liquid-vapor mixture (ie. the fraction of the total mass that is in the vapor phase)
X = m(vapor)/{m(liquid) + m(vapor)}
What is a superheated vapor region?
The single-phase vapor region to the right of the two-phase region up to the critical isobar (called superheated because the state of the system is at a temperature greater than the saturation “boiling” temperature corresponding to the given pressure)
What is vaporization?
Phase changes from liquid to vapor
What is condensation?
Phase changes from vapor to liquid
What is melting?
Phase changes from a solid to liquid
What is sublimation?
Phase changes from a solid to vapor
What is deposition?
Phase changes from vapor to solid
What is freezing?
Phase changes from a liquid to solid
What is the supercritical fluid region?
The region above both the critical temperature and critical pressure. (Material in this region has properties somewhat intermediate between what’s thought of as gas and liquid)
What is the difference between the two-phase solid-liquid region and the two-phase vapor-liquid region?
It is analogous except that there is no evidence (as indicated by experiments at high pressures) that it terminates in a critical point
What is the triple line?
The only temperature and pressure at which three phases (solid, liquid, and a vapor) can coexist
-it separates the two-phase vapor-liquid region from the two-phase solid-vapor region
