apy gravity.docx

7/29/2019 APY GRAVITY.docx

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AmericanpetroleumInstitute's invertedscalefor denoting the 'lightness' or 'heaviness' ofcrude

oilsand otherliquidhydrocarbons. Calibrated inAPI degrees(ordegreesAPI), it is used

universally to expresses a crude'srelative densityin an inversemeasurelighter the crude, higher

the API gravity, and vice versa because lighter the crude higher itsmarket value.Oilwith APIgreater than 30 is termed light; between 22 and 30, medium; below 22, heavy; and below 10,

extra heavy.Asphaltonaveragehas an API gravity of 8,Brent Crudeof 35.5, andgasolineof50.Formula: {(141.5 relative density of the crude (at 15.5C or 60F)} - 131.5.

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Density of Fluids - Changing Pressure and

Temperature

Calculating density of fluids when changing pressure andtemperature

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The density of a fluid changes with temperature and pressure. The density of water versustemperature and pressure is indicated in the chart below:

Density and change in Temperature

When temperature is changed the density of a fluid can be expressed as
http://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.htmlhttp://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.htmlhttp://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.htmlhttp://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.htmlhttp://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.htmlhttp://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.html


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1= 0/ (1 + (t1 - t0)) (1)

where

1 = final density (kg/m3)

0 = initial density (kg/m3)

= volumetric temperature expansion coefficient (m3/m

3 oC)

t1 = final temperature (oC)

t0 = initial temperature (oC)

Volumetric Temperature Coefficients -

water: 0.0002 (m

3

/m

3 o

C) at 20

o

C ethyl alcohol : 0.0011 (m3/m3 oC)

Note! - volumetric temperature coefficients varies strongly with temperature.

Density and change in Pressure

When pressure is changed the density of a fluid can be expressed as

1= 0 / (1 - (p1 - p0) / E) (2)

where

E = bulk modulus fluid elasticity (N/m2)

1 = final density (kg/m3)

0 = initial density (kg/m3)

p1 = final pressure (N/m2)

p0 = initial pressure (N/m2)

Bulk Modulus Fluid Elasticity some common Fluids - E

water : 2.15 109 (N/m2) ethyl alcohol : 1.06 109 (N/m2) oil : 1.5 109 (N/m2)

Density of a fluid changing both Temperature and Pressure
http://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlhttp://www.engineeringtoolbox.com/bulk-modulus-elasticity-d_585.htmlhttp://www.engineeringtoolbox.com/bulk-modulus-elasticity-d_585.htmlhttp://www.engineeringtoolbox.com/water-thermal-properties-d_162.html


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The density of a fluid when changing both temperature and pressure can be expressed with (1)

and (2) by substituting0 in eq. 2 with the expression for1in eq. 1.

1 =1(from eq.1) / (1 - (p1 - p0) / E)

=0/ (1 + (t1 - t0)) / (1 - (p1 - p0) / E) (3)

Example - Density of Water at 100 bar and 20oC

density of water 0oC: 999.8 (kg/m3) expansion coefficent of water at 10oC: 0.000088 (m3/m3oC) (average value between 0 and

20oC)

bulk modulus of water: 2.15 109 (N/m2)Density of water can be calculated with (3):

1 = 999.8 (kg/m3

) / (1 + 0.000088 (m3

/m3o

C) (20 (o

C) - 0 (o

C))) / (1 - (100 105

(Pa) - 110

5(Pa)) / 2.15 10

9(N/m

2))

= 998.0 / 0.995

= 1002.7 (kg/m3)

apy gravity.docx

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