Learning Forum

[Jada]

Hi,

 

I would like to ask a few questions to clarify the way in which a wall boundary is simulated and how the heat transfer rate is calculated in Fluent.

 

I am currently modelling the melting behaviour of a phase change material (PCM) contained in a cubic geometry. A pipe passes through the centre of the geometry, and acts as the heating source- all my simulations are modelled in 2D.

 

There are three boundary conditions: the PCM fluid volume, pipe wall (in the centre of the geometry) and the wall of the container. The wall of the container is modelled as adiabatic, and the pipe wall is modelled with a constant temperature thermal boundary condition, supplying heat to melt the PCM. My questions are as follows:

1. I initially set the material of the pipe wall as copper. However, when I go to check the properties of the pipe wall using the report function i.e., thermal conductivity or density for example, I notice that it gives me the properties of the PCM instead- why is this? I did not apply a thickness to the wall (so 0m)- could this be the reason?
2. How does fluent calculate the heat transfer rate? If the properties of the material assigned to the pipe are not being considered, am I correct in saying that the heat transfer rate report generated by fluent is calculated on the basis of the convective heat transfer only i.e.,  Q=hA(T_(wall)-T(PCM)), where T_wall is constant? I've done a few calculations which seem to support this and there is no radiation heat transfer in my case.  
3. To clarify, the heat transfer rate between the pipe and PCM domain is not calculated on a per unit mass basis like other quantities such as the enthalpy and the internal energy? I would like to compare the thermal energy input from the pipe compared to the energy actually stored by the PCM. 

Any help would be appreciated, thank you. 

 

Kind regards,

Jada

[SVV]

Hi,

I assume the pipe wall is boundary surface and not cell zone. The materials property will be that of the material you defined in the cell zone of which the pipe wall belongs to. The material you define in the wall boundary condition is only used if you are providing a virtual thickness to the wall.

Heat transfer during solidification and melting processes involves the transfer of heat via conduction and convection within the fluid and solid regions of the model. You can refer to the following section in user manual to get more insights. 16.4. Energy Equation (ansys.com)

[Jada]

 

Hi,

Thank you for getting back to me, and apologies for the delayed response. 

Yes, the pipe wall boundary is a surface as a virtual thickness has not been applied to the wall. How would I confirm in fluent the cell zone for which this surface belongs to? Thanks for your help. 

Kind regards,

Jada