# modeling phase change and homogeneous bubbles in many cycles

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 November 29, 2012, 22:39 modeling phase change and homogeneous bubbles in many cycles #1 New Member   Join Date: Nov 2012 Posts: 12 Rep Power: 4 Hi everyone, I have some problem about modeling phase change and homogeneous bubble. 1. According to the Flow-3D tech paper (http://www.flow3d.com/pdfs/tn/FloSci-TN57.pdf) ,I have to first remove a region of fluid as a little bubble and set temperature distribution. It can model a thermal inkjet to eject a droplet. Now I want to let inkjet eject 3 droplets. I want to run simulation for 3 cycles. After the inkjet eject one droplet, can I stop the simulation and remove a region of fluid then set a temperature distribution and continue running the simulation? How can I set the boundery condition? 2. I want to give a constant heat flux at wall boundary as heater to heat the liquid and generate bubble.It didn't work when I set the thermal condition in the wall boundary. How can I set the boundary condition? Hope you can help me solve the problem Thanks, Best regards Tim

 December 4, 2012, 11:12 #2 Member   Join Date: Mar 2012 Posts: 71 Rep Power: 5 For (1) removing the fluid is not really necessary - it is just a convenient initial condition. You can still use the "thermal bubbles with phase change" model without this initial void region by using the "Nucleation" option on the bubble model dialog. (2) can be handled by creating a component in the shape of your heating element and defining it as a heat source in the component properties.

 December 12, 2012, 22:55 #3 New Member   Join Date: Nov 2012 Posts: 12 Rep Power: 4 Dear dmilano, Thanks for your reply. I still have some questions. (1)In the phase change model,there is an item "accommodation coefficient". Does accommodation coefficient affect the bubble formation? And how will it effect the bubble? (2)When I creat a component as a heater,can I decide heating time of the heater?And what boundary condition should I set for the heater? Thanks, Best regards, Tim

 December 13, 2012, 11:04 #4 Member   Join Date: Mar 2012 Posts: 71 Rep Power: 5 The accommodation coefficient adjusts the rate at which the phase change occurs. It is a linear coefficient, so it is pretty intuitive to adjust the rate. Take a look at http://www.flow3d.com/pdfs/tn/FloSci-TN57.pdf for a more thorough explanation. The heat source power can be defined using tabular data, so you have complete control over the input power as a function of time.

 December 14, 2012, 06:34 #5 New Member   Join Date: Nov 2012 Posts: 12 Rep Power: 4 Dear dmilano, Thank you for your reply. I can't find the tabular data in component. Do you mean the tabular data in the boundary condition->thermal information? Can I just create a mesh and define a surface as a wall then setting the power as a heater? Or I have to create a "component" as a heater? Thanks Best regards, Tim

 December 14, 2012, 12:31 #6 Member   Join Date: Mar 2012 Posts: 71 Rep Power: 5 In version 10 the tabular data for the component is under Component #->Component properties->Solid properties->Heat source type. You could certainly specify the thermal power at a mesh boundary but it would put some significant restrictions on the heater geometry.

 December 18, 2012, 08:39 #7 New Member   Join Date: Nov 2012 Posts: 12 Rep Power: 4 Dear dmilano, Thanks for your reply. Can I use it in version 9.3? Thanks Best regards, Tim

 December 19, 2012, 16:34 #8 Member   Join Date: Mar 2012 Posts: 71 Rep Power: 5 The tabular data input isn't in the GUI, but you should be able to do this by adding the parameters tobs and pobs into the prepin.

 December 21, 2012, 10:37 #9 New Member   Join Date: Nov 2012 Posts: 12 Rep Power: 4 Dear dmilano, Thanks for your reply. I still have some question. I want to heat the water to generate a bubble. I use thermal bubble with phase change and heat transfer model . I heat the water to 540 K but it still doesn't generate bubble. How can I let it generate a bubble? Thanks, Best regards Tim

 December 21, 2012, 11:03 #10 Member   Join Date: Mar 2012 Posts: 71 Rep Power: 5 You probably need to activate the cavitation option (ICAV=1) and set CAVRT. There's a nice discussion of what you need to do in the Model Reference->Overview->How do I model?...->Cavitation and bubble formation section of the manual.

 December 21, 2012, 22:53 #11 New Member   Join Date: Nov 2012 Posts: 12 Rep Power: 4 Dear dmilano, Thanks for your reply. I have tried to use cavitation before, but the result didn't match with the experiment data. According to the experiment data ,the heating power is 1.8W. In the simulation, I only can set 0.006 W as heating power. If I set the power over 0.006W, it will not eject droplet properly. Is the physical meaning of the cavitation the same as the heating to generate bubble? Do they have the same mechanism? Thanks, Best regards, Tim

 December 31, 2012, 13:35 #12 Member   Join Date: Mar 2012 Posts: 71 Rep Power: 5 Not sure why that would be, but it sounds like a problem with the fluid properties.

 January 1, 2013, 05:57 droplets injection #13 New Member   parisamp Join Date: Jan 2013 Posts: 2 Rep Power: 0 Hi everyone i am a fluent beginner.i am simulating EVA droplets in PE.i want to inject 200 droplets in a tube and see their deformation and coalescence.i am using vof.how can i do this?please help me .thank you

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