1. ‫الليبية‬ ‫األكاديمية‬/‫طرابلس‬
A static analytical apparatus for vapour pressure and
(vapour + liquid) phase equilibrium measurements with
an internal stirrer and view windows

2. Outline of Presentation
Introduction
Experiment description and theoretical
models
Materials
Results and discussion

3. 1.Introduction
 Designed a new static analytical apparatus
for reliable vapour pressures and
(vapour+liquid) equilibrium data .
 Design apparatus :-
• Small- scale cell 150ml
• Internal stirrer
• View windows .

4. Introduction (cont’d)
 The composition of phases were analysis by a
gas chromatography connected on line with
TCD detector.
 Operating pressure ranges from (0-3000)kPa.
 Operating temperature ranges from(293- 400)k.

5. Introduction (cont’d)
 Measured of vapour pressure for R245fa
and R600a and VLE of (r600a +r245a)
system for improving thermodynamic
system performance and optimization
of thermodynamics cycles.
 The objected of paper is to provide
anew statical apparatus with internal
stirrer and view windows for reliable
vapour pressures and (vapour +liquid)
equilibrium data of pure and mixed
organic fluids above room temperature

6.  The data of the saturated vapour pressure
were correlated by Wagener type equation .
 The data of VLE were correlated with
thermodynamic model using peng–robinson
EoS (PR EoS) with two different models,
namely the Vander Waals (vDW) mixing
rule, and the HOURON-Vidal (HV) mixing
rule utilizing the random two liquid (NRTL)
activity coefficient model .

7. 2.Experiment description and theoretical
models
1. Equilibrium apparatus
 Equilibrium cell
 Isothermal environment for equilibrium cell
 Pressure, temperature and composition measurements.
A schematic of apparatus is shown in figure”1”

8. Description of apparatus parts
 Equilibrium cell
 Isothermal environment for the equilibrium
cell.
 Pressure, temperature and composition
measurements

9. Equilibrium cell
It is consists of the cell assembly and internal
stirrer. the cell was made of stain steel
(150ml) and enclosed with two Si-Al glasses
each held by mobile flanges.
Two other flanges and charging port on the
cell wall. The upper flange is used to hold
the internal stirrer. The lower flange canting
four different diameter capillaries to inter
the equilibrium cell for sampling.

10. And pressure measurement lines with 0.5mm
inner diameters. The internal stirrer contains
an axis with many blades and two ceramic
bearings, which is controlled by a speed
controller .

11. Isothermal environment for
equilibrium cell
The equilibrium cell is immersed into the iso
thermal liquid bath.
Silicone oil is used as heating medium in liquid
bath for high temperature. The equilibrium
cell is fixed a suitable position within the oil
bath about 50mm of the oil is above the
upper of equilibrium cell to decrease heat
leak.

12. Vacuumed environment and thermal insulation
materials surround thermal bath to over
come heat losses at high temperature.
To monitoring temperature standard platinum
resistance thermostatic(100Ω) is insert into
the bath. Standard platinum resistance
thermometer (25Ω) is used to measured
temperature of equilibrium cell and insert
into cell with a 316 stainless steel casing.

13. The oil bath temperature is controlled by
adjusting the heat loads of cooling water and
an electrical heater using shimaden SR253
digital controllers. A stirrer with a speed
controller is located in the liquid bath to
obtain uniform temperature distributions .

14. A six-port automatic-sample-injection (SPASI)
valve equipped with the GC in which the
sample is loaded through four stainless steel
capillaries with the same 0.35 mm internal
diameters and fine needle valves in the front
of SPASI valve.
The needle valves from Swagelok are turned off
when no sampling is taken. Figure 2 shows a
schematic flow diagram of the SPASI value.
Sampling method

16. The pressure measurement system includes a
digital pressure transducer (Mensor CPT6001)
and sensitive diaphragm pressure transducer
(GE DRUCK).
The diaphragm pressure transducer separates
the sample from an N2 filled system with the
digital pressure transducer.
Pressure temperature and composition
measurement

17. Uncertainty of pressure measurement is
estimated to be within ±500 pa. standard
platinum resistance thermometer 25 Ω is
used for temperature measurements(with
uncertainty of ±5mk(2k)).The compositions
of the phase in equilibrium cell are analyzed
by a Shimadzu GC2014 gas chromatograph
equipped with a thermal conductivity
detector (TCD).

18. The GC must be calibrated with mixtures of
known composition obtained
gravimetrically before the VLE data are
measured.
The uncertainties of vapour and liquid mole
fractions measurements are estimated to be
less than ±0.005.

19. Experimental procedure
The experimental system is evacuated using an
oil vacuum pump. Then a certain amount of
the less volatile component is introduced into
the cell. In the experimental process, the
temperature controller is set to the desired
temperature and the internal stirrer is started.

20. When the temperature in the cell reaches the
desired value at least 1h and the fluctuation in
the cell is less than at least 1 h K for at least 10
min, the equ±3 mk for at least 1o min, the
equilibrium state is considered to be achieved.
Then the saturated vapour pressures of the
first component can be obtained. Then the
appropriate more volatile component
is then forced into the cell.

21. Once equilibrium is established, samples of the
vapour and liquid phases are taken. The six way
automatic sampling valve could be used to
clean the capillary and sample quantitatively.
The vapour and liquid mole fractions at the
equilibrium state are measured by the on-line
gas chromatograph. At least 3 samples leading
to a repeatable mole fraction within 0.2% are
taken.

22. VLE data for other compositions are measured
by introducing an adequate amount of the
more volatile component step by step. At
last, the cell is evacuated and the
saturated vapour pressures of the more
volatile pure component are measured.

23. Theoretical models
 Statured vapour pressures.
 (Vapour + liquid) phase equilibrium data
correlations.

24. where p is the pressure, pc is the critical
pressure, Tc is the critical temperature, T
is the temperature, and a0, a1, a2 and a3
are constants of the Wagner equation.
Wagner Type Equation

25. Peng- Robinson (PR)EoS Type Equation

26. where p is the pressure, R is the gas
constant (R = 8.314 J K–1 mol-1), T is
the temperature, v is the molar volume, a
is a function of temperature, b is a
constant, ω is the a centric factor, Tc is
the critical temperature, pc is the critical
pressure.

27. The vDW mixing rule
where kii = 0, kij (=kji) is the
binary interaction parameter and
the
following temperature
dependence of the parameters is
used:
The HV mixing rule
where is the excess Gibbs free energy
at infinite pressure, C is a numerical
constant equal to 0.623225 for the PR
EoS.

29. The NRTL activity coefficient model
Is applied to calculate the
excess Gibbs free energy

30. The minimization of the sum of the absolute relative deviation
between the calculated and experimental pressures is used as the
objective function to correlate the experimental data:
where N is the number of the experiment points measured, and
refers to the pressures from experiment and calculation,
respectively.

31. point test of Van Ness et al.
was performed for the measured VLE data. The proposed standard of
thermodynamic consistent is that the average absolute deviation
(AAD) of vapour composition should be less than 0.01 for the
point test.

32. 3.Materials
mole fraction purity 0.990 for R245Fa and mole fraction purity 0.999 of
R600a Both of the materials were subjected to purity checks detected by
gas chromatography using the thermal conductivity detector (TCD). It was
verified that no significant impurities were found for all materials. Table 1
gives mole fraction purity, critical temperature Tc, critical pressure pc, and a
centric factor ω for R245fa and R600a.

33. 4.Results and discussion
The table 2, 3 represented the experimental
data for R245fa and R600a and VLE system of
(R600a+R245fa) .
Table 4 represent the accuracy data for
apparatus for these material at temperature
range from ( 239.150 to 353)k

34. saturated vapour pressure
Tables and Figures results
 Vapour pressure for R245 fa figure “4”.
 Vapour pressure of binary system table
6,figuer 5,4.

36. VLE measurement
 Deviation of pressure of binary system figure
6,7, table 6,7 and VLE correlation.
 Figure 8 gives comparisons between the data
in the literature and this work using the PR-
HV-NRTL model at three temperatures

37. 5.Conclusions
 The vapour pressure of 1,1,1,3,3-pentafluoropropane
(R245fa) and isobutane (R600a), VLE of (R600a +
R245fa) system from T = (293.150 to 343.880) K using a
new apparatus based on the static-analytic method
with an internal stirrer and view windows.
 The saturated vapour pressures data were correlated
by a Wagner type equation and compared with NIST
REFPROP 9.0 and literature data.

38.  The deviations showed that the experimental
data show good agreement with literature within
temperature range measured.
 The VLE data were regressed with the PR-vdW and
PR-HV-NRTL models The best results were
obtained with the PR-HV-NRTL model.
 The VLE systems also show good thermodynamic
consistency. Good agreement was also obtained for
VLE data of the system between experimental and
literature data.
 The a zeotropic behavior could be found for the
system studied over the temperature ranges studied.

39. Thank you