PURE SUBSTANCES
Pure Substances are substances
that is homogeneous and
invariable in chemical
composition.
When it exists in a multiphase
mixture, the chemical
composition is the same in all
phase.
PURE SUBSTANCES
Phase – any homogeneous part of a
system which is physically distinct and is
separated from other parts of the system
by definite bounding surfaces.
• Solid Phase
Melting
• Liquid Phase
• Vapor or Gaseous Phase
PURE SUBSTANCES
Phase – any homogeneous part of a
system which is physically distinct and is
separated from other parts of the system
by definite bounding surfaces.
• Solid Phase
Freezing
• Liquid Phase
• Vapor or Gaseous Phase
PURE SUBSTANCES
Phase – any homogeneous part of a
system which is physically distinct and is
separated from other parts of the system
by definite bounding surfaces.
• Solid Phase
• Liquid Phase
Vaporization
• Vapor or Gaseous Phase
PURE SUBSTANCES
Phase – any homogeneous part of a
system which is physically distinct and is
separated from other parts of the system
by definite bounding surfaces.
• Solid Phase
• Liquid Phase
Condensation
• Vapor or Gaseous Phase
PURE SUBSTANCES
Phase – any homogeneous part of a
system which is physically distinct and is
separated from other parts of the system
by definite bounding surfaces.
• Solid Phase
Sublimation
• Liquid Phase
• Vapor or Gaseous Phase
Latent heat – the amount of heat needed to change one phase to another.
PURE SUBSTANCES
CRITICAL STAGES:
a. Subcooled or 1 atm
Compressed Liquid:
A liquid that exists at
a temperature which
is lower than the
corresponding
saturation
T < 100°C
temperature at a H2O
given pressure.
Saturation temperature – the temperature where the liquid changes state.
PURE SUBSTANCES
CRITICAL STAGES:
b. Saturated Liquid: 1 atm
A liquid that exists at
a higher temperature
at which it can
remain liquid (critical
point).
T = 100°C
H2O
Saturation temperature – the temperature where the liquid changes state.
PURE SUBSTANCES
CRITICAL STAGES:
c. Mixture of Liquid 1 atm
and Gas:
Part liquid part vapor
at saturation
temperature.
Vapor
T = 100°C
H2O
Saturation temperature – the temperature where the liquid changes state.
PURE SUBSTANCES
CRITICAL STAGES:
d. Saturated Vapor: 1 atm
100% vapor at
saturation
temperature.
Vapor
T = 100°C
H2O
Saturation temperature – the temperature where the liquid changes state.
PURE SUBSTANCES
CRITICAL STAGES:
e. Superheated Vapor: 1 atm
The vapor has a
temperature greater
than the saturation
temperature for a
given pressure.
Vapor
T>
= 100°C
H2O
Saturation temperature – the temperature where the liquid changes state.
PURE SUBSTANCES
CRITICAL PARAMETERS:
1. Quality (x):
The fraction or
percentage by mass mass of vapor
that is vapor or the X=
mass of vapor in the mass of mixture
system divided by
the total system
mass.
PURE SUBSTANCES
CRITICAL PARAMETERS:
2. Percentage of moisture (y):
The fraction or
percentage by mass mass of liquid
that is liquid or the y=
mass of liquid in the mass of mixture
system divided by
the total system
mass.
PURE SUBSTANCES
CRITICAL PARAMETERS:
3. Enthalpy (H):
Note:
fg = change from
H= hf + xhfg
saturated liquid to
saturated vapor.
H= hg - yhfg
f = saturated liquid
g = saturated vapor
Where: hfg = hg - hf
PURE SUBSTANCES
CRITICAL PARAMETERS:
4. Entropy (S):
Note:
fg = change from
S= sf + xsfg
saturated liquid to
saturated vapor.
S= sg - ysfg
f = saturated liquid
g = saturated vapor
Where: sfg = sg - sf
PURE SUBSTANCES
CRITICAL PARAMETERS:
5. Specific Volume (V):
Note:
fg = change from
V= vf + xvfg
saturated liquid to
saturated vapor.
V= vg - yvfg
f = saturated liquid
g = saturated vapor
Where: vfg = vg - vf
EXAMPLES
1. If 2kg of water is at 106 Paa
(10bar), 300°C, find its volume,
enthalpy and entropy.
Sol’n: The water is on superheated stage
a. volume
T (°C) v (m3/kg)
At P = 10bar 280 0.2480
320 0.2678
EXAMPLES
1. If 2kg of water is at 106 Paa
(10bar), 300°C, find its volume,
enthalpy and entropy.
2. A 2kg of water is heated at
constant pressure of 5bar from a
wet state, x = 85%, to 400°C.
Find the change of enthalpy,
entropy and volume.
EXAMPLES
3. Assume 10lb/s of steam undergo a
constant entropy process from 250psia,
700°F to atmospheric pressure. Find
T2, S2, y, ∆H.
4. A 500 liter tank contains a
saturated mixture of steam and
water at 300°C. Determine the a)
mass of each phase if their volumes
are equal. b) volume occupied by
each phase if their masses are equal.
