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Water Vessel Selection
08/24/2014 at 02:08 • 0 commentsAs I mentioned in the description I am using a standard 10qt aluminum stockpot for the main component of the water vessel. Nothing fancy . . . just a thin pot with no handles and a basic lid. Flimsy by most standards.
But perfect for our purpose. Why? Because its easy to work with, easy to clean, non-reactive, and available literally everywhere for under $10. I've seen sous vide designs using everything from beach coolers to custom built enclosures but there are some real issues with these approaches, especially with the unique methods we're using in this build.
First and foremost we have inlets and outlets for water as opposed to an immersed element and simple agitation pump. Aluminum is easy to work with, drilling a hole or two for a hose barb is a quick job. It is also very conductive to heat, so instead of floating our thermocouples in the liquid we can tape them to the outside of the vessel with kapton tape and still get an excellent reading. This simplifies construction AND cleaning.
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Condensation Issues
08/21/2014 at 04:29 • 0 commentsPeltier modules operate by creating a temperature differential, which means if we're using them to heat our water the other side will get cold. Really cold. When we warm it using a heatsink and fan we're going to get condensation.
Due to this consideration the heatsinks used are straight-finned aluminum, with a drip tray integrated underneath. A small tube then runs to a bottle so condensation can be safely removed. A simple liquid sensor at the top of the bottle will power down the SuperVide in case of overflow.
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Water Additives
08/21/2014 at 04:23 • 0 commentsObviously if we're going to be cooling to sub-freezing temperatures regular old water just won't do. We also want to avoid glycol/etc due to the fact that we'll be putting FOOD in this thing! The solution (its a joke): pickling salt! Pickling salt's fine granules dissolve easily and can lower water's freezing point to below -20C, which is more than sufficient for our purposes. You will of course want to give whatever comes out a quick rinse, but you'd do that anyway!
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Thermal Module Selection
08/21/2014 at 04:18 • 0 commentsAfter exhaustive research I settled on the ThermaTEC Series of Peltier modules from Laird Technologies. Built for cycling applications they can handle the temperatures we desire and are designed to operate in reverse polarity mode on a frequent basis. With a delta T rating of 64C we can achieveeven the highest temperatures that might be wanted for cooking as well as the below freezing temperatures for flash cooling. What's even better is the cost: at $47/unit from Digikey they don't break the bank!
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Initial Feasibility Studies
08/21/2014 at 04:02 • 1 commentUsing a very simple 2A Peltier module salvaged from a minifridge intended for automotive use, I did some testing to determine practicality. With a very minimal test rig (a coffee pot, the module itself with fan and heatsink, and a 12V power supply) I brought a liter of water to hot and cold extremes.
The results were better than I ever could have expected. Despite being a cheap and very underpowered module compared to the Laird ones that will be used in final project it performed wonderfully. It achieved a maximum temperature of 69C and a low of -1C, which is quite impressive given it was never meant for such extremes (The Laird is). As expected it took some time to reach these temperatures given the lack of insulation and low power, but it shows the design is practical.