Pressure drop in a pipe

[guyguy]

hi,

I am trying to evaluate pressure drop in an oil pipe. My problem is that I know that there is also air involved (~ 0.1%). The question is, how does the air influence the pressure drop? (notice i am talking about 0.1% air)
I heard opinions both ways (pressure drop shall fall/rise) but no solid explanation.

please enlighten me...

thanx

guy

 

[guyguy]

bouncing

 

[25362]

The solubility of air in hydrocarbons at 273 K as given by the Ostwald coefficient is 0.095. Meaning that 0.095 volumes of air are dissolved in one volume of hydrocarbon at atmospheric pressure (ie, 9.5%). The method used to measure gas solubilities is described in ASTM D2779-92(2002).

This would imply (although not ensure) that 0.1% v/v air at room conditions would stay dissolved in the oil and not appreciably affect the friction drop as long as pressure doesn't drop too much and the gas is released from solution.

Sometimes air is chemically absorbed by the oil (oxidation) further reducing its availability. The solubility doesn't change much until profound chemical changes warrant a new Ostwald number.

The -as published- effect of temperature, T (absolute) on the Ostwald coefficient C_o (at 273 K), is as follows:

C_T = 0.3 * e^{[0.639(700-T)/T] * (ln 3.333C_o)}​