Experiment Set-Up - 3B SCIENTIFIC PHYSICS U104001 Instructions D'utilisation

and let in SF till a pressure of approx. 10 bar has
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been attained.
•
Shut the regulating valve.
•
Open the flush valve slightly till the pressure has
dropped to almost 0 bar.
•
Shut the flush valve.
Filling with test gas:
•
After at least four flush cycles, press the MINI-
CAN® gas container against the gas connection fit-
tings. Slowly open the regulating valve and let in
SF till a pressure of approx. 10 bar has been at-
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tained.
•
Shut the regulating valve.
•
Wind the handwheel in the opposite direction till
the piston reaches a position of say 46 mm.
•
Press the MINICAN® gas container against the gas
connection fittings, slowly open the regulating
valve and shut it again when a pressure of 10 bar
has been attained.
7.4 Recommendation for storage lasting for short
periods of time:
One gas filling can remain in the measuring cell for
several days.
If no experiments are being conducted, wind the
handwheel back till the piston is in a position where
it is subjected to the lowest possible pressure – say,
for instance, 46 mm.
If possible the apparatus should always be kept filled
with the thermal medium.
8. Experiments

8.1 Experiment set-up:

Additionally required:
1 Bath/circulating thermostat
1 Dig. quick-response pocket thermometer U11853
1 Type K NiCr-Ni immersion sensor,
-65°C-550°C
2 Silicone tubes, 1 m
1 l Anti-freeze fluid with corrosion-inhibiting additive
for aluminium engines (e.g., Glysantin® G30 ma-
nufactured by BASF)
•
Place the equipment at a suitable height so that it
is convenient to observe the measuring cell. Posi-
tion it so that the safety valve does not point in
the direction of any people who could be injured
or objects that could be damaged.
•
Connect the silicone tubing from the outlet of the
circulation thermostat to the inlet of the heat cas-
ing and from the outlet of the heat casing to the
inlet of the circulation thermostat.
•
Prepare the thermal medium consisting of 2 parts
water to 1 part anti-freeze by volume.
•
Fill the circulated thermostat bath.
8.2 Qualitative observations:
Liquid and gaseous states, dynamic state during phase
transformation, transition points occurring at differ-
ent temperatures.
•
Vary the volume by turning the handwheel and
the temperature by means of the thermostat. Ob-
serve the safety instructions while doing so.
•
Carefully shake the set-up to conduct simple
observations on the boundary between liquid and
gas.
In the vicinity of the critical point, it is also possible to
observe the critical opalescence. Owing to the con-
stant changing of state between liquid and gaseous
states in small regions of the measuring cell, a kind of
"mist" develops and the sulphur hexafluoride appears
to be turbid.
8.3 Measuring isotherms in a p-V diagram:
•
At maximum volume, set the desired temperature
on the circulation thermostat.
•
Gradually reduce the volume in the measuring
cell (in steps down to a position of 10 mm). Wait
till a stationary equilibrium has been attained be-
fore taking pressure readings.
•
Then, beginning with the minimum volume,
gradually increase the volume till the piston posi-
tion is once again at 10 mm. Wait till a stationary
equilibrium has been attained before taking pres-
sure readings.
•
Convert the excess pressure readings into abso-
lute pressure and the piston positions into vol-
ume, as described in chapter 6.
In the low-volume region, stationary equilibrium is
attained more quickly during transition from higher
to lower pressure – i.e. from a lower volume to a
greater volume – since the phase boundary layer for
the phase transition from liquid to gas is created by
vapour bubbles present throughout the liquid. Sta-
tionary equilibrium then takes around 1 to 5 minutes
U14400
to attain, whereby the measurements on the fringe of
the region where both phases exist take longest.
The recommended threshold value of 10 mm refers to
U11854
a filling pressure of 10 bar. Above this value, there
U10146
will certainly be no occurrence of a liquid phase in
the permissible temperature range. The threshold
value shifts to the "right" if the filling pressure is
higher.
8.4 Measuring isochores in a p-T diagram:
•
Set the desired initial temperature. Subsequently
set the desired volume.
•
Gradually allow the temperature to decrease.
•
Wait till a stationary equilibrium has been at-
tained then take the pressure reading.
Measurements where both phases are present can be
plotted to generate a vapour-pressure curve.
Attainment of equilibrium takes up to 20 minutes
after each change of temperature due to the fact that
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