[conspire] sous vide question.

[Ivan Sergio Borgonovo]

On 10/25/2017 06:19 AM, Rick Moen wrote:
> Quoting Ivan Sergio Borgonovo (mail at webthatworks.it):
> 
>>> I will have to think about water circulation, the shape of the pot,
>>> and how the bag(s) might hinder flow.
>>
>> Water circulation is going to raise the cost of everything pretty
>> much and it may not be that useful depending on the size of the pot
>> etc...
>> At that point you'd better start from scratch.
> 
> Water (non-pure) is a reasonably good conductor of heat.  Also, water
> being heated by an element on one side of a container _convects_ heat
> quite well.  I suspect the result is that temperature of said water is
> close enough to uniform as makes no difference.

I do work with this stuff. Depending on several factors I witnessed 
temperature gradients of more than 4C in less than 20cm deep tanks.
Considering most recipes in sous vide are in a reasonably narrow range 
of 30C at most, 4C may be too much.

When you test and calibrate temperature sensors keep in mind that water 
and heater may have a pretty big thermal inertia (thermal inertia of 
sensors is generally negligible).

In a 5L tank with a 2000W immersion heater, I've witnessed 2C delta due 
to thermal inertia of the system. That means that if you turn off the 
heater when you see 50C, you'll reach 52C and if you turn on the heater 
at 50C you'll reach 48C before temperature start to raise again.

You don't have to set up a thermodynamic lab, you just have to graph 
some measure, get an idea, correct via software.

Circulation makes controlling the temperature easier but more expensive 
than writing some extra line of software.

Circulation becomes nearly mandatory for larger volumes and precise 
temperature control but advertising 0.1C precision is mostly a way to 
steal you money for cooking applications.

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