Controlling the Sample Temperature
1. For low temperature experiments below 25° C or high temperature experiments above 90° C, switch the filter assembly from house air to nitrogen.
2. Set up your experimental parameters. Recalling standard parameters after this step will set temp='n'.
3. For low temperature experiments below 25° C, you MUST purge nitrogen gas through the heat exchanger coil for AT LEAST 15 minutes. Type temp=20 vtc=25 su.
Warning!!! Failure to purge the exchanger coil will result in ice formation in the coil, followed by rapid increases in gas pressure behind the ice blockage in the coil.
After purging, verify that temp < vtc (type temp? vtc?), and then fill the heat exchanger coolant bucket with liquid nitrogen. DO NOT immerse the exchanger coil in liquid nitrogen without notrogen gas flowing through the coil. DO NOT stop nitrogen gas flow while the exchanger coil is immersed in liquid nitrogen.
WARNING!!! Operating the system with the coolant bucket filled with liquid nitrogen and with temp > vtc or without gas flow results in condensation of liquids inside the exchanger coil. If the exchanger coil is warmed above -210° C or if nitrogen gas is passed through the coil, very cold liquid nitrogen will be forced from the coil and may cause damage to the gas transfer lines, the probe, and your sample.
4. Type temp=<your temp> su (e.g., temp=35 su). Do not change the temperature from the current value by more than 50° C in four minutes or more than 20° C in one minute. Do not change temperatures again until the green light on the hardware VT console stops flashing.
5. After the VT temperature is regulated (green light on hardware VT console stops flashing), wait 5 minutes to allow the sample to equilibrate before acquiring data.
6. When finished with low temperature, drop the exchanger bucket.
7. When you are finished, type temp='n' su.
8. When the temperature > 10°
C and the VT heater is off ( red light on hardware VT console
is off), and the exchanger coil has warmed to room temperature,
switch the filter assembly to house air.
Arrayed Temperature Experiments
Arrayed VT experiments that have a temperature range from above vtc (25° C) to below vtc should be set up starting at the lowest temperature and ending at the highest. When the experiment passes vtc, remove the liquid nitrogen coolant.