Screen J

3 J. Viscosity of Crude Oils Back to Main

This page is used to determine the viscosity of crude oils possessing an API gravity greater than 30º API (g = 0.88), which can be estimated by the equation

Equation (3.25) log m = a – (0.035)(° API)

Where: a = values from table (page 74, volume 1)

° API = (141.5/g ) – 131.5

m = viscosity, cp

To calculate the viscosity of crude oil the Temperature and API Gravity of the crude oil must be entered into the entry spaces. To do so, use the mouse to click the curser in the entry space and input data. Once this has been done, select Run to execute the solution.

The density if crude oil is sometimes shown in ° API. This term is defined by the equation

Equation (3.18)

Equation (3.18)

Where: = relative density (specific gravity)

Temperature is the temperature of the crude oil in SI units, Celsius and Kelvin or in English units, Fahrenheit and Rankin. The Temperature is used to determine the value for "a."

° C = 0.556 (° F - 32), K = ° C + 273, ° F = (1.8)(° C) + 32, ° R = ° F + 460

The answer is given in two units viscosity, cp and viscosity, cs. The basic petroleum viscosity unit has been the poise, or more commonly the centipoise. The poise is a measure of absolute (dynamic) viscosity. It is a derived metric unit: 1 poise = 1 (dyne)(sec) per cm² .

1 centipoise (cp) = 0.01 dyne s/cm² = 0.001Pa·s = 0.000672 lbm/ft – sec

The kinematic viscosity is the absolute viscosity divided by density. The usual unit is the stoke or centistoke.

1 centistoke = 0.01 cm²/s = m²/sec

To convert data values from one unit to another, please refer to Set Auto Convert and Unit Conversion.

Back to Main