Convection in a hot water tank

Marie13 · February 18, 2013, 12:14

Hi,

I am working on a simplified 2D transient model of a hot water tank. I am using a k-epsilion turbulence model. I have activated buoyancy and gravity and am using the Boussinesq model for density.For boundary conditions I have made the walls adiabatic and fixed the temperature of the heating coil. The water does heat up but it seems like it is only by pure conduction as I am not getting any velocity in the tank. Could someone please help me out?

Thank you.

delaneyluke · February 19, 2013, 15:27

Seems like natural convection, you would have to run an unsteady case in order to capture effects of natural convection.

Regards
Luke

Marie13 · February 19, 2013, 15:58

Thanks Luke. But I did run an unsteady model.

I think it may have to something to do with the density model. The water heats up from 15C to about 80C, which might be the reason for the Boussinesq not to work. I ran the model using the perfect gas density model and this gave me better results; however, I don't think it is right to use that for water.

delaneyluke · February 19, 2013, 16:05

Another point, which I missed earlier.
Your presumption that low water velocity implies conduction could be wrong. Since natural convection is generally a low velocity phenomenon, higher velocities would imply a forced convection.
So convection would be your primary mode of heat transfer even though velocities are low in your domain.

Regards
Luke

MARIO276 · February 19, 2013, 16:45

please someone help me in my post about heat generation rate.

mario276

WilsonLoo · April 2, 2013, 16:39

Quote:

Originally Posted by Marie13

Hi,

I am working on a simplified 2D transient model of a hot water tank. I am using a k-epsilion turbulence model. I have activated buoyancy and gravity and am using the Boussinesq model for density.For boundary conditions I have made the walls adiabatic and fixed the temperature of the heating coil. The water does heat up but it seems like it is only by pure conduction as I am not getting any velocity in the tank. Could someone please help me out?

Thank you.

Hello, I am doing my 3d model of heat sink, could u tell me how to set the walls of the channel to be adiabatic. should i suppress channel in workbench before meshing, setup and so on. thx for reply

February 18, 2013, 12:14	Convection in a hot water tank	#1
Marie13 New Member Join Date: Feb 2013 Location: United Kingdom Posts: 3 Rep Power: 13	Hi, I am working on a simplified 2D transient model of a hot water tank. I am using a k-epsilion turbulence model. I have activated buoyancy and gravity and am using the Boussinesq model for density.For boundary conditions I have made the walls adiabatic and fixed the temperature of the heating coil. The water does heat up but it seems like it is only by pure conduction as I am not getting any velocity in the tank. Could someone please help me out? Thank you.

February 19, 2013, 15:27		#2
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	Seems like natural convection, you would have to run an unsteady case in order to capture effects of natural convection. Regards Luke MARIO276 likes this.

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February 19, 2013, 15:58		#3
Marie13 New Member Join Date: Feb 2013 Location: United Kingdom Posts: 3 Rep Power: 13	Thanks Luke. But I did run an unsteady model. I think it may have to something to do with the density model. The water heats up from 15C to about 80C, which might be the reason for the Boussinesq not to work. I ran the model using the perfect gas density model and this gave me better results; however, I don't think it is right to use that for water.

February 19, 2013, 16:05		#4
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	Another point, which I missed earlier. Your presumption that low water velocity implies conduction could be wrong. Since natural convection is generally a low velocity phenomenon, higher velocities would imply a forced convection. So convection would be your primary mode of heat transfer even though velocities are low in your domain. Regards Luke

February 19, 2013, 16:45		#5
MARIO276 New Member omar Join Date: Feb 2013 Posts: 9 Rep Power: 13	please someone help me in my post about heat generation rate. mario276