Results not matching for transient thermal natural convection case fluent

suryawanshi_nitin · March 11, 2017, 09:34

Hello All,
I am working on transient thermal problem for which i have carried out experiment at home as explained below,
1. Coke placed at center of room with Coke can temperature 74 Deg. C initially.
2. Ambient temperature of room is 26 deg. C.
3. Started monitoring temp of Coke can for 1 hour which is filled with water & can was closed at top. Thermometer inserted till mid height of can.
4. Temperature of Coke can observed after 1 hour was 44 Deg. C. Hence coke can temperature has dropped from 66 to 44 Deg. C in one hour experimentally.

Then same setup i have created in CFD by creating 3D model of closed room with Coke can at center. Hex mesh created in domain (ICEM block Mesh) & also the boundary layer around can (with Y+<1). Transient, segregated solver selected with SST-kW model turbulence model, also 2nd order scheme for flow equations & also for transient formulation was selected. Density modeled with boussinesq approx. After running transient thermal simulation in Fluent 14.5 version it was observed fluent took more than 3+ hours to drop coke can temperature from 66 to 44 Deg. C.
Hence, why fluent (CFD solvers) taking more time (>3+ hours) than experimental measured time (1 hour) ?

Do i need to use some other settings ?

Thank you in advance.

LuckyTran · March 11, 2017, 15:53

Two sanity checks you can do.

1). Compare the heat transfer coefficient you obtained from your Fluent simulation w/ that observed experimentally (you need to back-calculate it).

2). Solve only the transient heat transfer inside the can with the heat transfer coefficient prescribed equal to the heat transfer coefficient you get from your experiment. If it still takes 3 hours, then you know it's the heat transfer inside the can that is not being correctly modelled and not the natural convection outside the can.

Finally. How are you modelling the water in the can? Is it a fluid or solid? If you model it as a solid, then you don't get convection inside the can which would slow the rate of heat transfer.

March 11, 2017, 09:34	Results not matching for transient thermal natural convection case fluent	#1
suryawanshi_nitin New Member Nitin Suryawanshi Join Date: Mar 2009 Location: Pune, India Posts: 28 Rep Power: 17	Hello All, I am working on transient thermal problem for which i have carried out experiment at home as explained below, 1. Coke placed at center of room with Coke can temperature 74 Deg. C initially. 2. Ambient temperature of room is 26 deg. C. 3. Started monitoring temp of Coke can for 1 hour which is filled with water & can was closed at top. Thermometer inserted till mid height of can. 4. Temperature of Coke can observed after 1 hour was 44 Deg. C. Hence coke can temperature has dropped from 66 to 44 Deg. C in one hour experimentally. Then same setup i have created in CFD by creating 3D model of closed room with Coke can at center. Hex mesh created in domain (ICEM block Mesh) & also the boundary layer around can (with Y+<1). Transient, segregated solver selected with SST-kW model turbulence model, also 2nd order scheme for flow equations & also for transient formulation was selected. Density modeled with boussinesq approx. After running transient thermal simulation in Fluent 14.5 version it was observed fluent took more than 3+ hours to drop coke can temperature from 66 to 44 Deg. C. Hence, why fluent (CFD solvers) taking more time (>3+ hours) than experimental measured time (1 hour) ? Do i need to use some other settings ? Thank you in advance.

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March 11, 2017, 15:53		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	Two sanity checks you can do. 1). Compare the heat transfer coefficient you obtained from your Fluent simulation w/ that observed experimentally (you need to back-calculate it). 2). Solve only the transient heat transfer inside the can with the heat transfer coefficient prescribed equal to the heat transfer coefficient you get from your experiment. If it still takes 3 hours, then you know it's the heat transfer inside the can that is not being correctly modelled and not the natural convection outside the can. Finally. How are you modelling the water in the can? Is it a fluid or solid? If you model it as a solid, then you don't get convection inside the can which would slow the rate of heat transfer.