The goal with this project was to come up with a cheaper and mess-free alternative to sous vide devices currently on the market. The hope was to introduce a broader audience to sous vide cooking, as well as make it easy to use and easy to clean when done. All sous vide devices on the market require the food to be placed in a vacuum sealed bag. This requires the use of a vacuum sealer, as well as creates waste from the used bags.
Safety was also a factor. Since everything is contained in a bladder in this design, there would be less chance of spilling a large vessel of hot water. 
Finally, the thought was that this might be used in college dorms/housing, in conjunction with something like a George Forman to finish off the food (i.e. grill marks on chicken breast, etc)

I started off by experimenting with heating the water-filled bag from the outside. The simplest thing to use was a clothing iron used by hobbyists (doesn't get too hot), paired with a PID controller. 

Iron with PID controller embedded in plastic bag with high porosity sponges.

PID thermocouple moved to center of bag.
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Slight tilt to help hot water move to the other end of the bag. 
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Trying with sponges again (plastic stand-offs weren't proficient at helping the bladders keep their shape. 

Unit is fully sealed with bleed valve to release air. Air still finds a way to get trapped in the system.
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Added a cam roller to move the water. 
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Sandwiched heating element in between two water filled bags. 

Vertical orientation to let hot water rise to the top (away from the heating element).
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Air getting trapped in top.
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Sous vide egg test (eggs in two different spots to test temp evenness.)
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Double cam rollers with paddles.
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Moved PID to iron due to overheating. 
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No sponge filler; plastic stand-offs. Added agitator and heating element to a C-shaped bladder.

Added structure to top to help compress top piece and remove air. 
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Egg results; similar consistency but timing not same as traditional Sous Vide methods. 

V2 sealed version with bleed valve. 
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Egg test in V2.
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Egg results are closer to traditional Sous Vide but still too soft. 

This concept definitely had possibilities, but there were many obstacles as well. 

1. If this requires a controller and heating element similar to a sous vide stick, it won't be much cheaper. 
2. Would this unit ship pre-filled? If so, that adds cost and complexity, not to mention increases shipping costs. If the user fills it, can we trust them to do it correctly? What happens if they don't bleed out all of the air? What if the water gets contaminated and grows mold? What should be added to the water to prevent this? 
3. Will the heating element and agitator rust since they're constantly immersed in water? Testing of the V2 setup showed some rust on the heating element after a few dozen hours. 
4. If the user pokes a hole in the bag, can they patch it? Is it easier to just replace it? The bladder will most likely be made from silicone, but tests showed that even a thin silicone (sub 1mm) provided quite a bit of insulation, making it harder to transfer heat from the water to the food.