Multiphase bubble size

F/lix · April 14, 2009, 17:54

Hello all,

I am to model a multiphase simulation of an hydraulic turbine (using CFX 11.0) for the first time. To do so, I have to specify the mean bubble diameter, dm, which I find very hard to estimate, especially since the results seem to be very sensitive to this parameter.

Bubble diameter must somehow be related to existing shear stresses and to the surrounding pressure but I don't know how. The only relation I found uses a secret constant parameter "k" multiplying the whole equation and I have no idea of it's order of magnitude, so it's useless.

Does anyone of you have had good experiences modelling bubbles ? How do you estimate their size ? Some people must use these solver capabilities !

Thanks a lot, any help is welcome

Felix

F/lix · April 16, 2009, 16:17

No one has ever tried multiphase in hydro turbines ?

A_Lyaskin · April 17, 2009, 11:43

I remember I've seen some estimations for simple flows (like pipe flows) - I'll try to find a book later.

BTW, CFX also has MUSIG model, which allow you to specify bubble size distribution instead of just one fixed size.

A_Lyaskin · April 17, 2009, 13:24

So the book is "Bubbles, Drops and Particles" by R.Clift, J.R.Grace and M.E.Weber. I'll try to look for other publications - I remember I've seen experimental data for bubble size distribution in pumps, which is more or less similar to your case of hydro turbine

F/lix · April 17, 2009, 13:46

Thanks a lot, I'll try to find the book and have a look at it. The MUSIG model looks interesting but I am still stuck with the distribution size estimation. Specifying a distribution must be more adequate though...

Felix

April 14, 2009, 17:54	Multiphase bubble size	#1
F/lix New Member Join Date: Apr 2009 Posts: 4 Rep Power: 17	Hello all, I am to model a multiphase simulation of an hydraulic turbine (using CFX 11.0) for the first time. To do so, I have to specify the mean bubble diameter, dm, which I find very hard to estimate, especially since the results seem to be very sensitive to this parameter. Bubble diameter must somehow be related to existing shear stresses and to the surrounding pressure but I don't know how. The only relation I found uses a secret constant parameter "k" multiplying the whole equation and I have no idea of it's order of magnitude, so it's useless. Does anyone of you have had good experiences modelling bubbles ? How do you estimate their size ? Some people must use these solver capabilities ! Thanks a lot, any help is welcome Felix

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April 16, 2009, 16:17		#2
F/lix New Member Join Date: Apr 2009 Posts: 4 Rep Power: 17	No one has ever tried multiphase in hydro turbines ?

April 17, 2009, 11:43		#3
A_Lyaskin Member Anton Lyaskin Join Date: Mar 2009 Location: Samara, Russia Posts: 66 Rep Power: 17	I remember I've seen some estimations for simple flows (like pipe flows) - I'll try to find a book later. BTW, CFX also has MUSIG model, which allow you to specify bubble size distribution instead of just one fixed size.

April 17, 2009, 13:24		#4
A_Lyaskin Member Anton Lyaskin Join Date: Mar 2009 Location: Samara, Russia Posts: 66 Rep Power: 17	So the book is "Bubbles, Drops and Particles" by R.Clift, J.R.Grace and M.E.Weber. I'll try to look for other publications - I remember I've seen experimental data for bubble size distribution in pumps, which is more or less similar to your case of hydro turbine

April 17, 2009, 13:46		#5
F/lix New Member Join Date: Apr 2009 Posts: 4 Rep Power: 17	Thanks a lot, I'll try to find the book and have a look at it. The MUSIG model looks interesting but I am still stuck with the distribution size estimation. Specifying a distribution must be more adequate though... Felix