The K850 CPD with Thermoelectronic Heatinhg
& Adiabatic Cooling 
Critical
Point Drying (CPD) is so named as it includes, as part of its process,
the occurrence known as the continuity of state for which there is not
apparent difference between the liquid and gas state of a medium, the
surface tension between this interface reducing to zero. This occurs at
a specific temperature and pressure with resulting density, and is known
as the Critical Point. This condition of zero surface tension can be
used to dry Biological Specimens, avoiding the damaging effects of
surface tension.
In biological
specimens we are mainly concerned with the removal of water.
Unfortunately, the critical point of water of +347oC and 3212
p.s.i. is inconvenient, and would cause heat damage to the specimen. The
most common and convenient transitional medium for critical point drying
is Carbon Dioxide CO2, which has its critical point at 31oC
and 1072 p.s.i. However, it is not miscible with water, and therefore we
have to involve a third medium, commonly Acetone, which is termed the
intermediate fluid. We can now convert our transitional fluid, typically
CO2 from liquid to gas without surface tension at the
critical point.
The K850
Critical Point Drier is designed for use with CO2, having
first replaced any water in the specimen by a series of dehydration,
often in the same fluid such as Acetone, which will also be the
intermediate fluid.
(Wet
Specimen) - Water - Acetone - 30% - 100%- CO2 - C.P.D. - (Dry
Specimen)
The specimens
for critical point drying are located in the pressure chamber of the
K850. The chamber is pre-cooled to allow it to be readily filled with
liquid CO2 from a gas cylinder. The chamber is then heated to
just above the critical temperature with subsequent critical pressure
being achieved. The CO2 gas is vented through a needle valve,
to avoid specimen distortion.
The K850 is
fitted with thermoelectronic heating and adiabatic cooling and
temperature control of +5oC cooling and +35oC on
heating. This ensures the critical point is accurately obtained,
avoiding excess pressures or temperatures, or the need to rely on
pressure relief valves to control pressure during the heating cycle. The
chamber is vertical, with top loading, to ensure specimens do not become
uncovered during the drying process, with a side viewing port to locate
the meniscus for the correct level when initially filling the chamber.
Features:
-
Vertical
Chamber with Top Filling and Bottom Draining.
-
Normal
Operating Temperature 35oC Pressure 1350 psi. (Crit.
Temp. 31oC Crit. Press. 1100 p.s.i.
-
Adiabatic
Cooling and Thermoelectric Heating.
-
Fine
Control Needle Valve Pressure Letdown (Flow Gauge Monitor Option)
-
Chamber
with Side Viewing Port and Protective ‘Lexan’ Shield.
-
Stirrer
System for Enhanced Solvent Exchange.
-
Temperature
Monitoring and Control with Thermal Cut-out Protection.
-
Pressure
Monitoring with Safety Cut Out for Over Pressure.
Specifications
of the K850 CPD:
Instrument
Case -450mm W x 350mm D x 175mm H
Weight -12Kg
Specimen Chamber - 32mm Dia x 47mm High Internal
(Tested to 3000 psi)
Temperature Gauge -0-120oC
Thermal Cut-Out -40oC
Pressure Gauge -0-3000 psi
Pressure Safety Cut Out -At 1700 psi
Cooling/Heating - +5oC to +35oC
4 x On/Off Valves -Cool/Fill/Out/Bleed
1 x Needle Valve Letdown -Fine Bleed - (In Series With
Bleed)
Includes: -1 x Specimen Holder Stainless Steel (12
compartments 8mm x 8mm) -10 x PTFE Pourous Specimen Pots (18mm x 14mm
Pack 10)
NOTE: -Flow Guage Monitor option fitted externally in
series with fine bleed.(0-2.2L/Min - CP03266-18)
Services
-CO2 gas cylinder (local supply)
high pressure hose for direct connection (included with Instrument)
Electrical Supply - 230 Volts 50Hz (3 Amp max.)
115 Volts 60Hz (6 Amp max.)
