heat transfer simulation in oven

[Amine A]

hello, we bake aeronautical pieces in an oven.
the piece ( prepreg + nomex ) being in the mold, we put it inside the oven.
a thermocouple is linked to the surface of the mold.
a temperature profile is applied to the oven chamber (ramp up, holding, ramp down).
I want to make a thermal simulation which allows me to know what is the temperature profile given by the thermocouple.
can I do that in Abaqus ? if yes what are the general steps to do it ?
Thanks

 

[FEA way]

Sure, it's possible to simulate this in Abaqus. First you have to prepare the geometry, assign material properties and mesh the model. Choose transient heat transfer analysis step. Then define thermal loads and interactions (including tie constraints between separate parts). You can choose from surface radiation, surface heat flux or temperature boundary condition. Amplitude will allow you to vary the thermal load in time. When you get results, you can measure temperature at selected points using probe tool (or history output request defined before the analysis).

 

[Amine A]

Thank you
but for example if I want to input these steps :
1- ramp up from 0°C to 100°C with rate 1°C/min
2-holding at 100°C for 90min
3-ramp down from 100°C to 0°C with rate 1°C/min
what should I put in load ??

 

[FEA way]

Such changes can be defined using tabular ampltidue which is then assigned to temperature boundary condition. Abaqus multiplies magnitude specified for this BC by amplitude at current time. You can also divide the analysis into 3 separate steps so that different time scale is used for each stage of the process.

 

[Amine A]

Thank you very much
should I do 3 steps and each step has it's amplitude or do only 1 step that has amplitude like this

 

[FEA way]

In this case one step with amplitude like this one should be enough.

 

[Amine A]

Bro, in the oven I put a temperature profile while in abaqus to create a load , I have to put a heat flux which is Q = h A ( To - Tp ) and me I want to determine the temperature in the mold which is Tp.. Do you have any idea about how should I put my loads in abaqus ?

 

[FEA way]

In fact, I think that it would be best to use surface radiation interaction and vary ambient temperature using amplitude as discussed before.

 

[Amine A]

But I think results will differ if the flux in reality is convective. No ??

 

[FEA way]

I was thinking about radiation because that's the most common choice for simulations involving oven heating. But you can use surface film condition interaction if you want. Sink temperature may be varied in time using amplitude like it's done with surface radiation.

 

[Amine A]

oh okay I will try. thank you

 

[Amine A]

Bro , can you tell me what is the difference between the value of sink temperature and the value of sink amplitude ??

 

[FEA way]

Sink amplitude is used when you want to vary sink temperature with time. In such case value defined as sink temperature is multiplied by value specified in amplitude definition for particular moment of time. Here's an example:
- sink temperature: 2°C
- sink amplitude:
0 s --- 10°C
10 s --- 20°C

In this case the resulting sink temperature used in convection interaction will be 20°C for 0 s and 40°C for 10 s. Abaqus will interpolate linearly between these values and use last value if step time exceeds 10 s.

 

[Amine A]

thank you. so if I used only one step for this example then the step time is 10s ?

 

[Amine A]

Bro what is the difference if I used a cfd model and see the temperature in each point of the oven including the mold ?

 

[FEA way]

Time period of this single step should be equal to the duration of the whole process (including some additional time for cooling, if desired).

If you know the temperature distribution on the surface of the body and want to calculate the temperature inside, you can apply temperature boundary condition with distribution defined using mapped field.

 

[Amine A]

So if I want to know the temperature of the thermocouple in the mold what model should I use ? standard model like what I did or cfd model ?

 

[FEA way]

If you have access to Abaqus/CFD (available in older versions of Abaqus - before 2017 release) then you can perform conjugate heat transfer simulation. But regular heat transfer analysis done with Standard solver, as discussed before, should be enough in this case.

 

[Amine A]

because if I have to put 2 pieces for example inside the oven and see what is the temperature in each mold I think I have to use cfd no ?
in fact our problem is when we put 2, 3 or 4 pieces, sometimes we find a non-conforming piece in term of temperature in the mold...
thank you in advance brother ))

 

[FEA way]

The number of pieces in oven is not so important when choosing the analysis type. What really matters is which physical phenomena you want to include. Regular heat transfer simulation will only account for conduction in solid parts while convection and radiation on the surface will be approximated with boundary conditions (interactions). CFD analysis solved in conjugate heat transfer mode allows you to model convection (natural or forced) and radiation in surrounding air but also account for fluid/solid interface phenomena. Of course conduction in solids will be solved too with this type of analysis.