Micromeritics ASAP 2460, Operator'S Manual

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ASAP 2460 Operator’s Manual Appendix C
246-42800-01 - Aug 2013 C-1
C. CALCULATIONS
This appendix contains the calculations used in the analysis program.
Saturation Pressure
Saturation pressure (Po) is selected on the
Po and Temperature Options
window. It may be entered
or measured in the Po tube. The software uses the following methods to get Po:
1. Po is measured in the Po tube for each isotherm point.
2. The saturation pressure is measured in the sample tube after all adsorption data points have been
collected. This pressure is used as Po for all data points.
3. Po is measured for all points as with #1. After all adsorption points have been taken Po is
measured in the sample tube. The measured Po points are shifted so that the Po measured in the
Po tube matches the Po measured in the sample tube. That is,
Po
i
= Po
i
+ Po
s
- Po
n
where Po
n
is
the Po measured in the Po tube when Po in the sample tube ( Po
s
) was measured.
4. Determine Po from pressure measured over the dosing source. Note that the Adsorptive
Properties must specify dosing from Psat tube, Sample port 3, or Vapor source.
5. The saturation pressure of a gas is measured in the Po tube for each data point. The bath
temperature is found by looking up the temperature for the measured saturation pressure in the
fluid properties. Po of the analysis gas is found from the bath temperature as in #6. If dosing is
done from the Psat tube, Po is determined once at the beginning of the analysis and used for all
data points. Otherwise, Po is measured for each data point.
6. Po is found by looking up the saturation pressure for the entered bath temperature in the fluid
property information.
Lookup of saturation pressure in the fluid properties is done by interpolating the Psat data using
the Clausius-Clapeyron equation, . The constants a and b are determined from
the pressures and temperatures that bound the bath temperature. Temperature lookup is done by
solving for T, , where a and b are determined from the pressures that bound the
given saturation pressure.
7. If entered, Po = user-entered value.
P
 
ln
a
T
---
b + =
T
a
P
 
b – ln
------------------------
=