FuelsManager Defense
300 Administrator Manual
LPG quantity calculation from liquid density
Calculation of LPG quantity from liquid density at 15°C (LPG °C & LPG °C 1980)
Overall calculation scheme
1. Measure level, average liquid temperature, average vapor temperature,
average pressure in vapor space.
2. Input liquid density at 15°C.
3. Calculate VCF and hence liquid density at tank conditions.
4. Correct measured level for thermal effects and buoyancy. This depends upon
the nature of the gauge.
5. Convert corrected level to liquid volume.
6. Correct liquid volume for tank thermal expansion and pressure effects
7. Convert liquid volume to equivalent volume at 15°C.
8. Calculate liquid mass from liquid volume at 15°C and liquid density at 15°C.
9. Correct total tank volume, for thermal and pressure effects.
10. Calculate vapor volume at measured temperature from corrected total volume
and liquid corrected volume at tank conditions.
11. From liquid density, vapor temperature and vapor space pressure calculate
vapor density.
12. Calculate vapor mass from vapor volume and vapor density at measured
conditions.
13. Calculate total mass as liquid mass plus vapor mass.
14. Calculate weight from total mass and liquid density.
15. Display the required results
Details for each step
Step 1
The Liquid temperature and vapor temperatures should both be weighted
averages to reflect the volume in each vertical section. In the liquid phase there
should be little temperature gradient and a single measurement should be
adequate. In the vapor phase a gradient may be more apparent and the average
of the vapor temperature at the surface and at the top of the tank should be used.
Measured values:
Step 2
Density is to be input by the operator. This should be the liquid density at 15°C,
and should be in units of kg/m
3
.
Input value
H gauge reading of liquid level in mm
TL average liquid temperature °C
TV average vapor temperature °C
P vapor space pressure in bar g.
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