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Water circulation options for sous vide

 
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PostPosted: Tue Nov 29, 2011 7:52 pm    Post subject: Water circulation options for sous vide Reply with quote

I have read with profit the articles on sous vide on this cool site. I have been playing around with sous vide for several years. I use a very simple set up that features the Auberins PID controller, a garden-variety slow cooker, and a FoodSaver bag system. I am generally happy with this set up except that the only water circulation I get is from the natural thermal circulation. The slow cooker has a heating coil on the bottom that produces hot spots and an unfavorable temperature gradient. I would like to add a submersible water circulation fan/pump. I don't want to pay for a redundant heat source that would be built into a "thermal" circulation device. A simple slow-flow fan is sufficient. My intuition is that a fish tank bubbler is not sufficient. Bubbles rise and presumably this adds a bit of convection, but not really the kind of "slow swirl" I am looking for. The tank of the cooker is oval by the way. So, I started looking around. Few sous vide sites give few options here. I am honing in on using submersible circulation pumps for home aquaria. However, there are questions. Engineering questions. The pumps I found (for example on [/http://www.fish.com]) vary a great deal on the flow rate (from 3 gallons per hour to over 3000). I have no idea what would be best. Plus, I have no way to determine whether a standard aquarium pump (some are described as utility pumps) will operate properly, safely in water that is up to 140 degrees F. Can anyone address either of these concerns?
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gizmographer



Joined: 29 Nov 2011
Posts: 3

PostPosted: Tue Nov 29, 2011 7:55 pm    Post subject: Sorry, I did not register before posting this query Reply with quote

The root message in this thread is from gizmographer. Just learning the ropes.
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Dilbert



Joined: 19 Oct 2007
Posts: 1001
Location: central PA

PostPosted: Tue Nov 29, 2011 8:36 pm    Post subject: Reply with quote

the ready made models usually have some kind of impeller on a shaft.

should be simple enough to rig up a small motor with variable speed control - there is the issue of "space" - something needs to keep the impeller and the bag from becoming one . . .

but on the fish tank idea.... how about a take off on the under gravel filter concept. a perforated plate on the bottom, a glass vertical tube with air bubbling up through the tube to "convey" water - no moving parts so to speak.

given the usual sous vide temps, I suspect any of the cheapie submersibles would take the temps - but as you mentioned, controlling the agitation rate could be problematic - or not - this
http://seattlefoodgeek.com/2010/02/diy-sous-vide-heating-immersion-circulator-for-about-75/
uses a 75 gph pump - higher than I would have expected.
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gizmographer



Joined: 29 Nov 2011
Posts: 3

PostPosted: Wed Nov 30, 2011 12:38 am    Post subject: Reply with quote

Thanks, very helpful. I have seen the 75 dollar circulator rig before and am giving that some thought. Could build the same thing around my PID controller. Has anyone put an engineer's eye to this design? It looks fairly straight forward. Their is a commercial option for the bubbler plate (a fine idea - better than a single point-source bubble emitter): [http://freshmealssolutions.com/] My intuition is that circular movement of the water would be a more efficient means of creating a consistently even heat gradient throughout the tank. But the pumps with motors do take up space (I have seen them about 1.7" x 2" x 2.5" or so. As in quantum physics I am concerned too about strange entanglements between bag and agitator. JB Prince sells a fancy stainless "protective shield" that does this but its huge, not designed for anything but a large square tank and costs more than 5 good aquarium pumps: http://www.jbprince.com/sous-vide-equipment/protective-shield-for-p350.asp. THere is probably a way to improvise a "perforated plate on the bottom of the tank" connected to a little air pump that would work well. Anyone with thoughts or designs?[/url]
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Neil Smith



Joined: 08 Jul 2012
Posts: 2

PostPosted: Sun Jul 08, 2012 7:14 pm    Post subject: Reply with quote

If you're buying a pump, make sure its rated for sous vide temperatures. Aquarium pumps aren't, and melt. You can pick up cheap, high-temperature pumps on eBay that work well. I was using this before I got a commercial kit:

http://www.ebay.com/itm/DC-12V-Electric-Submersible-Water-Pump-95-GPH-P-38B-/250722722452?pt=LH_DefaultDomain_0&hash=item3a603d2294#ht_3344wt_1026

Over on the eGullet forums, several people have reported good results with aquarium bubblers. The advice is to use the air hose directly into the bottom of the tank, without any airstone. You don't need much agitation to circulate the water. I did that for a while when I was between pumps one time, and I had no problems with uneven cooking in a large (~40l) pot.
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PostPosted: Mon May 13, 2013 2:24 pm    Post subject: Reply with quote

Hi,
I have been struggling with this issue for a while. the Idea I am working on at the moment involves taking apart a washing machine pump to seperate the motor from the pump (submerge the pump put the motor above the surface, shaft connecting the two). I have not been able to get much in the way of spec on these but they are raited at around 20 watts which is the right order of magnitude.
I have concerns about running them continuously for 2-4 days as there is no info on duty cycle for these and they usually only run for short periods, but I have a small fan motor from a fridge freezer that might be a better option.
it's all a bit Heath Robinson, and I would be delighted if anyone else has come across low cost low power centrifugal pumps as it seems rather a limited market.
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Dilbert



Joined: 19 Oct 2007
Posts: 1001
Location: central PA

PostPosted: Mon May 13, 2013 5:24 pm    Post subject: Reply with quote

consider: I've never built one, or used one . . .

but however comma and all that, given the needs of sous vide, circulating a large volume of water is likely not required - with the exception of a 300 gallon (ie really really big) "pot"

the heat input to the 'typical' (if there is such a thing) sous vide is not extremely high - it works on maintaining 'the final desired temperature' over a very long period of time. that means "no blast furnace" heat source required....

a simple bubbler system should be adequate to cause circulation in a small container. again considering the rather small temperature differentials of 'thing to be cooked' vs 'cooking water' after the initial 'shock' period, it's not immediately obvious that every circulating molecule of water be of "exactly" the right&proper temperature - the law of minor averages should apply.

the biggest issue appears to be that all the plumbing, piping, components, etc., are able to withstand prolonged exposure to the set point temperatures....
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ralphfcooke



Joined: 05 Feb 2014
Posts: 1
Location: Southampton, England

PostPosted: Wed Feb 05, 2014 3:42 pm    Post subject: Sous Vide water circulation Reply with quote

I also went through the various methods of keeping the water circulating, and eventually returned to my Higher Chemistry classes from many many years ago.
I used a slow speed (about 15rpm) synchronous motor mounted below the crock pot or deep fat fryer ( I have used both) with a strong magnet attached to the shaft. Inside the pot is a lab magnetic stirrer wand that is rotated by magnetic induction. I do use a small stainless perforated cover to ensure the stirrer doesn't get tangled with the food, but other than that this is the simplest way I have found of keeping the water temperature constant throughout the bath.
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