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 rawe666 June 27, 2012 04:23

VOF Boiling

Hello friends,
As a part f my project, I simulate HTC with Boiling model. I have experiment results and I am gong to validate the experiment using starccm+ 7.0.2. I have a solid domain which is aluminium and fluid domain water-glycol. Solid domain has a constant temperature which is higher than boiling temperature. Boiling model is going to have a liquid phase as water-glycol mixture and gas phase as a water steam.

I use VOF --> Rohsenow Boiling model. I have two doubts regarding my simulation.

1) Liquid Phase Material Properties
Let's say mixture of T_inlet=90 C and T_boiling= 120 C, V_inlet = 1 m/s at 1 atm in the simulation.
Which temperature I am going to use to determine my material poperties of liquid phase?
What should I use for Standard State Temperature value under properties list?
Gas phase material properties are simply because T_boiling (or T_saturation) is going to be used obviously.

2) I searched literature of Rohsenow boiling. I have good guesses for Exponential Prandl number and C_qw parameter. However, I do not know exactly what HTCxArea means and how can I adjust it for my silmulation. Could someone explain a little bit?

Regarding the issues mentioned above, I kindly request some advice from you. Any help would be appreciated.

Kind regards

 rawe666 July 25, 2012 17:57

Still no reply on HTCxArea ??

 flexi182 August 7, 2012 09:33

HTCxArea: I have tried for the fluid properties p=1 bar at saturation temperature

First I calculate the diameter of a vapour bubble (Bubble Departure Diameter with a contact angle of 45 ° for water)

d= 0.0149 * contact angle * Sqrt((2*surface tension)/(gravity*(Density_liquid - Density_gas)))

Then I calculate the surface and the volume of a ball
Surface / Volume is the contact area per volume [m²/m³]

For the Heat transfer coeffizient I used a Forced convection over a ball.
For Re<0.1 Nusselt Number=2

Where do you find your saturation temperature of water glycol?
What's your guesses for Exponential Prandtl number and C_qw?

 rawe666 August 8, 2012 04:35

Hello Felix,
Thank you for your reply. I am confused, you wrote what you did for your case but you did not mention how (or from which resource) did you calculate HTCxArea value? Could you explain it more? Which value did you use? Default value is given as 5000000.

You can find easily saturated temperature of mixtures from heat transfer books for different mixture rates. Just google it.

For Exponential Prandtl number and C_qw, they are strongly dependent on your materials. Again you need to find them in literature. You can find small table in Incorpera's Heat Transfer Book.

Edit:

I do understand your calcuation. Temperature has a great influence on bubble diameter and heat transfer coefficient.Using field function can be a good idea.

 flexi182 August 9, 2012 01:24

Here's the source book for the Rohsenow model. You can download it for free from MIT!

http://dspace.mit.edu/handle/1721.1/61431

Page 3 diameter of the bubble as it leaves the surface (eqn 3)
Page 4 Bubble Reynolds number and bubble nusselt number (eqn 7 and 8)
Page 5 Contact Angle beta for eqn 3 (eqn 11)

This one the right for c_qw and exponential prandtl number?