[conspire] sous vide question.

[Paul Zander]

Ivan,

Any time there are engineers involved, we can find ways to make the problem more complicated. :-)


I agree that water circulation and temperature distribution are factors that might be important.

If one had a big pot with an immersion heater and dropped multiple bags of food on top of each other, one should expect uneven heating, unless something was done to ensure better water movement.


Trying to be practical, I think my best approach is to use the crock-pot as a "proof of concept".  

* Add simple external controller.  For example http://www.instructables.com/id/Sous-vide-cooker-for-less-than-40/

* Determine if available probe can be submerged in the water.
* Use independent thermometer to verify temperature of water.
* Re-position the food a couple of times during the first half-hour, or until temperature seems to be stable.
* Evaluate the results. 


Paul




________________________________
From: Ivan Sergio Borgonovo <mail at webthatworks.it>
To: conspire at linuxmafia.com 
Sent: Wednesday, October 25, 2017 10:22 AM
Subject: Re: [conspire] sous vide question.



On 10/25/2017 06:46 PM, Rick Moen wrote:
> Quoting Ivan Sergio Borgonovo (mail at webthatworks.it):
> 
>> I do work with this stuff. Depending on several factors I witnessed
>> temperature gradients of more than 4C in less than 20cm deep tanks.
> 
> I bow to someone who's actually done the measurements, instead of merely
> owning an accurate thermometer and making shirtsleeve speculations about
> skillets full of water.  ;->

I really didn't have to assure uniform temperature and so I didn't have 
to solve the problem, just be aware of it, since temperature was 
measured indirectly etc...
Actually I was quite surprised myself.

I did many tests with several sensors at a time and if I had to model 
the problem I wouldn't be happy.

What I've learnt is that it depends on too many factors:
- kind of heater (immersion, adhesive on the walls, on the bottom)
- geometry of the tank
- geometry/volume and heater power (speed at which you heat the water)
- stuff you put in and how
- thermal isolation of the tank
- temperature of the water

I think external boilers with pump may be a necessary solution if you've 
larger volumes of water and more precise temperature regulation.

Anyway, I was mostly interested to heat the water fast and be sure the 
temperature didn't drop below a certain level.
Something in the setup made things really worse for temperature 
uniformity: immersion heater and some stuff inside the tank that was 
causing far from ideal convection flow inside the tank.

I'd think in normal cooking pot things should be easier.

I gave a look to sous vide supreme video and they use a grid at the 
bottom to circumvent the problem.

-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it http://www.borgonovo.net



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