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CAD Simulations: Cooking a Turkey

While I was deciding on an appropriate brine, rub and injection for this years Turkey I was curious how closely a quick and dirty simulation would come to the reality of my smoker out on the deck? So while I was waiting for the bird to thaw I started modeling one up.  Then, to calculate the fowl temperature versus time I used a 4 step process:

1. Gather Data and make Assumptions:

- I'm assuming homogeneous thermal properties.

- Assuming the majority of heat transfer is via convection not accounting for radiation.

- I'm modeling the turkey while cooking dinner so bones are not added. If anyone has a full 3D Turkey skeleton send it on over.

I found some thermal properties for meats here:

http://www.engineeringtoolbox.com/specific-heat-capacity-food-d_295.html

- Most of the standard material properties in Flow are temperature dependant however for this study I'm assuming conductivity and specific heat are basically constant in this temperature range.

- Assuming constant ambient temperature.  When I get a second probe with recording capabilities I will try again with ambient temp(time).  Ideally with the control system on the pellet smoker it's pretty consistent so it's not too big of an assumption.

Step 2. Create a Steady State Flow Simulation of the Smoker:

With Flow I used parametric studies to estimate inlet flow rate and temperature to create a steady state ambient temperature of 325F.  I will use the ambient temperature and convection heat transfer coefficients from Flow rather than estimating them as boundary conditions in thermal.

SOLIDWORKS Simulation
Cut Plot of Ambient Temperature in Flow

 

SOLIDWORKS Simulation
Heat Transfer Coefficient on Surface Note it is NOT uniform

Step 3.  Run transient thermal simulation:

The transient study was run in thermal analysis to reduce tun times.  Running the full smoker model in Flow as a transient would take much longer to run. However we did use Flow to capture the non uniform convection which would be more difficult to apply in thermal.

 

SOLIDWORKS Simulation
Transient Thermal Simulation Using Flow Convection

Now you not may be able to tell from the picture but I was in the holiday "spirit" and forgot to save my temperature probe data from the Turkey.....

SOLIDWORKS Simulation
author trying not to cut off a finger
This gave me a good excuse to smoke some more fowl.  In this case I had fewer guests to feed so I did a slightly more controlled experiment with Cornish hens. Through the beauty of CAD embedded simulation I just scaled down my turkey and then created a new configuration and re-ran with the Hens.
SOLIDWORKS Simulation
Calibrating my model
SOLIDWORKS Simulation
Smoking
SOLIDWORKS Simulation
Finshed!
Step 4:  Conclusion/Comparison:  Time versus temperature calculations 

SOLIDWORKS Simulation
Analysis Compared to Thermal Probe Temperatures over Time

 

Here is a comparison of multiple probe points in the vicinity of the probe on both hens versus time. The actual probe data is in the middle which is a good thing and gives me confidence in my model.  If I was using this turkey to optimize Flow in the smoker this would be good enough to stop here.  If I needed more accuracy I would take into account the following:- Bone thermal mass
- Variation in ambient with time
- Possible variation of conductivity and specific heat with temperature
- Take into account rotating the Hens halfway the smoke.

I hope this give you some insight into the synergy between Flow and Sim Pro thermal and a basic understanding of the assumption that go into a thermal analysis.

Here's a link to some video of the simulations: https://youtu.be/rs7C9d6q6zM

Happy New Year!

-Dave

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