Combining Cavitation and Thermal Effects?

akash_max · October 24, 2011, 22:19

Hi All,

I am glad to see that you all here solve so many problems and help each other lot. Thanks a lot for all your help.

I am trying to simulate a series flows through an orifice – control volume – orifice. I have fuel as diesel. I am giving an inlet pressure of 2000 bar (total pressure) and outlet pressure 0 bar (Average static pressure). Below are my queries which I would like you all to suggest me on?

· I am presently running this model with cavitation model on. I am finding the cavitation in certain region. I am giving material properties as density and dynamic viscosity at specific temperature. My issue is how to map the variation of density and dynamic viscosity with respect to temperature and pressure into software? What model should I use to plug them into software? or How should I model enthalpy to get this effect?

· Second issue is that my seniors think that the analysis is not enough to just go ahead with results with cavitation only using specific density and dynamic viscosity at particular temperature say 80C. They would like me to check the variation in cavitation along with thermal conditions. I would like to know how I should introduce the thermal model along with cavitation so that I get temperature effects at inlet and outlet and in the default alsof or the fuel running at 80C?

· To check the effect of temperature raise in the orifice leading to increase in cavitation in the model. Will the cavitation increase with introducing the temperature effect and will it develop cavitation in some other regions where we are not seeing now, but experimental testing is showing erosion and cavitation

Kindly suggest me how to model the cavitation along with thermodynamic effect. Should I use total energy model or isothermal model for both diesel and vapour materials.

I would be really glad full to you all here.

Best Regards
Akash

ghorrocks · October 25, 2011, 07:01

Are you asking what density and viscosity to give to the vapour phase? In most cavitation models it is not very important as the density and viscosity difference is so massive between phases that the vapour phase is effectively inviscid and zero density. But you should do a sensitivity study to confirm this in your case.

Your second question would be answered by my first answer - if you do a sensitivity analysis and show the vapour phase properties are not very important then this is irrelevant. But note the vapour pressure will change with temperature, and this is likely to be important.

akash_max · October 25, 2011, 09:08

Hi Glenn,

Thanks for your reply.

I want to perform analysis where in i can see the effect of cavitation and also the temperature effect of fluid. Let say if I give inlet temperature of 212 F for a orifice along with total pressure of 2000 bar as inlet. There is a cavitation in the orifice about 36%.

Now I want to check the effect of hot fluid moving into the orifice, the temepartuer will add up and the fluid gets more hotter as it come out. I want to check the effect of this hot fluid on cavitation leaving out at outlet.

As the fluid change with temperature how should i account this with materials? I have to give density and specific gravity of liquid with respect to temperature and pressure.

Please let me know on this.

Once again thanks for your reply

Best Regards
Akash

ghorrocks · October 25, 2011, 18:42

As I said, the primary effect of temperature is likely to be to change the vapour pressure. It is likely that the effects like changes in density and viscosity in the vapour phase are insignificant. If this is the case you do not need to do thermal analyses, just a sweep of different vapour pressures in an isothermal simulation.

But you should not take my word for it, you should do a sensitivyt analysis and check it for yourself.

CFDtoy · January 19, 2012, 15:09

Hi Akash,

I hope you have already figured out the way to carry out your runs. If not:

- run your incompressible cavitation run along with energy equation. You can use mixture energy modeling. This way not only you specify an inlet (initial T) but also get a distribution of T in the entire domain.

- i am not sure about your "temperature increase" effect. Normally, the temperature in the vicinity of the liquid-vapor interface will be lower since the liquid would have consumed the latent heat while converting to vapor. There are some numerical simulation and experimental results available in literature explaining this.

- To get effect of T on Vapor pressure, pvap should be a function of T..for that specific fuel you can create an equation or link to a database

Let me know how it goes.

Cheers,

CFDtoy

Quote:

Originally Posted by akash_max

Hi All,

I am glad to see that you all here solve so many problems and help each other lot. Thanks a lot for all your help.

I am trying to simulate a series flows through an orifice – control volume – orifice. I have fuel as diesel. I am giving an inlet pressure of 2000 bar (total pressure) and outlet pressure 0 bar (Average static pressure). Below are my queries which I would like you all to suggest me on?

· I am presently running this model with cavitation model on. I am finding the cavitation in certain region. I am giving material properties as density and dynamic viscosity at specific temperature. My issue is how to map the variation of density and dynamic viscosity with respect to temperature and pressure into software? What model should I use to plug them into software? or How should I model enthalpy to get this effect?

· Second issue is that my seniors think that the analysis is not enough to just go ahead with results with cavitation only using specific density and dynamic viscosity at particular temperature say 80C. They would like me to check the variation in cavitation along with thermal conditions. I would like to know how I should introduce the thermal model along with cavitation so that I get temperature effects at inlet and outlet and in the default alsof or the fuel running at 80C?

· To check the effect of temperature raise in the orifice leading to increase in cavitation in the model. Will the cavitation increase with introducing the temperature effect and will it develop cavitation in some other regions where we are not seeing now, but experimental testing is showing erosion and cavitation

Kindly suggest me how to model the cavitation along with thermodynamic effect. Should I use total energy model or isothermal model for both diesel and vapour materials.

I would be really glad full to you all here.

Best Regards
Akash

October 24, 2011, 22:19	Combining Cavitation and Thermal Effects?	#1
akash_max New Member Akash Join Date: Sep 2011 Posts: 12 Rep Power: 15	Hi All, I am glad to see that you all here solve so many problems and help each other lot. Thanks a lot for all your help. I am trying to simulate a series flows through an orifice – control volume – orifice. I have fuel as diesel. I am giving an inlet pressure of 2000 bar (total pressure) and outlet pressure 0 bar (Average static pressure). Below are my queries which I would like you all to suggest me on? · I am presently running this model with cavitation model on. I am finding the cavitation in certain region. I am giving material properties as density and dynamic viscosity at specific temperature. My issue is how to map the variation of density and dynamic viscosity with respect to temperature and pressure into software? What model should I use to plug them into software? or How should I model enthalpy to get this effect? · Second issue is that my seniors think that the analysis is not enough to just go ahead with results with cavitation only using specific density and dynamic viscosity at particular temperature say 80C. They would like me to check the variation in cavitation along with thermal conditions. I would like to know how I should introduce the thermal model along with cavitation so that I get temperature effects at inlet and outlet and in the default alsof or the fuel running at 80C? · To check the effect of temperature raise in the orifice leading to increase in cavitation in the model. Will the cavitation increase with introducing the temperature effect and will it develop cavitation in some other regions where we are not seeing now, but experimental testing is showing erosion and cavitation Kindly suggest me how to model the cavitation along with thermodynamic effect. Should I use total energy model or isothermal model for both diesel and vapour materials. I would be really glad full to you all here. Best Regards Akash

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October 25, 2011, 07:01		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Are you asking what density and viscosity to give to the vapour phase? In most cavitation models it is not very important as the density and viscosity difference is so massive between phases that the vapour phase is effectively inviscid and zero density. But you should do a sensitivity study to confirm this in your case. Your second question would be answered by my first answer - if you do a sensitivity analysis and show the vapour phase properties are not very important then this is irrelevant. But note the vapour pressure will change with temperature, and this is likely to be important.

October 25, 2011, 09:08		#3
akash_max New Member Akash Join Date: Sep 2011 Posts: 12 Rep Power: 15	Hi Glenn, Thanks for your reply. I want to perform analysis where in i can see the effect of cavitation and also the temperature effect of fluid. Let say if I give inlet temperature of 212 F for a orifice along with total pressure of 2000 bar as inlet. There is a cavitation in the orifice about 36%. Now I want to check the effect of hot fluid moving into the orifice, the temepartuer will add up and the fluid gets more hotter as it come out. I want to check the effect of this hot fluid on cavitation leaving out at outlet. As the fluid change with temperature how should i account this with materials? I have to give density and specific gravity of liquid with respect to temperature and pressure. Please let me know on this. Once again thanks for your reply Best Regards Akash

October 25, 2011, 18:42		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	As I said, the primary effect of temperature is likely to be to change the vapour pressure. It is likely that the effects like changes in density and viscosity in the vapour phase are insignificant. If this is the case you do not need to do thermal analyses, just a sweep of different vapour pressures in an isothermal simulation. But you should not take my word for it, you should do a sensitivyt analysis and check it for yourself.