The Interesting Chemical Kinetics of a Collapsing Cavitation Bubble 

Preliminary calculations for the thermochemistry of a collapsing cavitation bubble have been recently completed by Madhat Abdel-jawad of Advanced Analysis. Cavitation has been associated with brain damage in veterans displaying symptoms of PTSD.  We carried out the following calculations using  a  chemical kinetics module developed by advanced analysis for the purpose of inclusion into exploCFD. 

 

The reactions modelled include :  

 

H2+O2 <-> 2OH

H2+O2 <-> H+HO2

2OH <-> H+HO2

H2O+O2 <-> OH+HO2

H2O+OH <->H2+HO2

H2+M <-> 2H+M

O2+M <-> 2O+M

H2O+M <-> OH+H+M

OH+M <-> O+H+M

HO2+M <-> H+O2+M

H2O+O <-> 2OH

H2O+H <-> OH+H2

O2+H <-> OH+H

H2+O <-> OH +H

 

 

A single reaction, is modelled as :

 

 

 

 

 

where kf is the reaction rate constant of the forward reaction and kb is the reaction rate constant of the backward reaction. Empirical results have shown (from [2]) that the time rate of formation for C (for example) is:

 

 

 

 

 

 

 

The Arrhenius reaction rate is modelled according to:

 

 

 

 

 


 

 

 

The evolution of the resulting species is shown in the results below and is interesting if somewhat  strange if you are not familiar with these reactions of at these temperatures ( they are quite common in the application of scramjets which I happen to have some experience in. Some interesting features include

 

  1. The bubble dissociates the H2O and some of the species include hydrogen and oxygen ( it basically creates fuel out of water ) You see H2O conc drop and the H conc rise
  2. The temperature at the peak of the pressure spike is too high for this O and H to react but as the bubble rebounds the temperature drops making it cold enough for the hydrogen to burn again  ( ie H and O to recombine into water )  - Now you see the H2O concentration rise and H concentration drop – Not all the water is recovered
  3. OH- and HO2 radicals are also created though the latter is at a very low concentration
  4. Temperatures and Pressures are generally lower ( blue curves are including the reactions ) and the red curves are the original data without the chemical reactions ( called frozen )

 

 

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