Arrgh.... a <-> b Got the a and b reversed.

Heat a to x degrees above b... 

What I understood you were going to do with method one was heat a to 100'
and let b catch up on its own. That won't work. How you described method 1
just now is basically what I was saying.

---
James.
 
 

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Mario Mendes
> Sent: 2006 Jan 12, Thu 15:06
> To: 'Microcontroller discussion list - Public.'
> Subject: RE: [OT] Need help with some thermodynamics concepts 
> (or source of it)
> Importance: Low
> 
> Hi James,
> 
> I see what you are saying, but (looking at the diagram):
> 
>  |   |      |   |
>  |---|------|---|
>  |   |  b   |   |
>  | a | milk |   | 
>  |   |______|   |
>  |              |
>  |    water     |
>  |______________|
>   ^^^^^^^^^^^^^^ <- heat from stove
> 
> I don't understand what you're trying to explain to me, there 
> is a disconnection between the two of us somewhere.
> 
> 1) How can I heat b to x degrees above a, if I can't directly heat b?
> not only because direct heat from the stove would make the 
> bottom of b's pan a hot spot, but I also can't use a heater 
> immersed in b because as the milk curdles and can't be 
> stirred, the heater itself would become a hot spot, no?
> 2) If a < x = b, even applying heat to a, wouldn't b start to 
> cool until a = x = b and only then start to heat up again as 
> a become hotter than b?
> 
> With the previous option 1, if a = 90 and b = 90, we're ok, 
> then I slowly increase a to 91 and keep it there until b = 
> 91, at which point I then slowly increase a again to 92 and 
> keep it there until b = 92 and so on, until they're both at 
> 100.  I don't see how the 1F/min rule would be violated if I 
> increase a at 0.5F/min.
> 
> Thanks.
> 
> 
> -Mario
> 
> 
> 
> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of James Newtons Massmind
> Sent: Thursday, January 12, 2006 2:24 PM
> To: 'Microcontroller discussion list - Public.'
> Subject: RE: [OT] Need help with some thermodynamics concepts 
> (or source of it)
> 
> 
> > 6. over the period of 30 minutes raise the temperature of 
> the milk to 
> > 100F, and never raise more than 1F/minute.
> 
> Again, method 1 or 2 will violate this rule. As I said before 
> you need to use a third method:
> 
> 3) heat b to a temperature that is x degrees above a and keep 
> increasing b until a hits the target then remove b. This one 
> will give you a straight line temperature increase which will 
> make it easy for you to predict when the target will be 
> reached and adjust x accordingly on the fly. "A" WILL reach 
> the target temp, and will probably overshoot it slightly 
> unless you can remove b instantly.
> 
> You can avoid the overshoot by not increasing the temperature 
> of b past the target temperature so that it curves off like 
> 1) as it approaches the target.
> 
> I have some (minor) experience with this and I know if you 
> try to go from 90 to 100 by floating the curd pan in 100 
> water, the initial temperature change in the curd will exceed 
> 1' per minute.
> 
> As the curd can't be mixed, you must keep it fairly thin and 
> measure its temperature from about half way between the 
> center and the outside edge.
> 
> ---
> James.
>  
> 
> 
> > -----Original Message-----
> > From: piclist-bounces@mit.edu
> > [mailto:piclist-bounces@mit.edu] On Behalf Of James Newtons Massmind
> > Sent: 2006 Jan 11, Wed 15:54
> > To: 'Microcontroller discussion list - Public.'
> > Subject: RE: [OT] Need help with some thermodynamics concepts (or 
> > source of it)
> > 
> > > 1) heat a to the temperature I want b to be heated up to
> > and then keep
> > > a constant there until b reaches the same temperature
> > 
> > I don't see why you need any calculations... This option 
> will bring b 
> > up to temp at a rate dependant on the mass of b and the insulation 
> > between the two assuming they are both mixed to uniform temperature 
> > inside. The temp graph in b will be a curve which will 
> flatten out as 
> > b approaches the target temperature. It will never /actually/ reach 
> > the target but will come very close.
> > 
> > > 2) heat b to a higher temperature than I want b to be at
> > and then let
> > > it cool down while b heats up with the heat given off by a until 
> > > eventually both reach the same temperature
> > 
> > We assume this should have started with "heat /a/ to a higher..."
> > 
> > This one depends on the ratio of masses between a and b and the 
> > insulation... And the mixing...  The curve will be steeper at first 
> > and then flatten out again. Same problems.
> > 
> > 3) heat b to a temperature that is x degrees above a and keep 
> > increasing b until a hits the target then remove b. This 
> one will give 
> > you a straight line temperature increase which will make it 
> easy for 
> > you to predict when the target will be reached and adjust x 
> > accordingly on the fly. "A" WILL reach the target temp, and will 
> > probably overshoot it slightly unless you can remove b instantly.
> > 
> > Feedback removes variables.
> > 
> > ---
> > James.
> >  
> > 
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