[Homeroast] Sunbeam Vac pot tuning: a simple solution

Phil Palmintere phil.palmintere at gmail.com
Tue Apr 6 11:59:12 CDT 2010


Hi Allon,

I wasn't thinking about it as a law of nature -- more of a statistical
issue.

If I understand it correctly, a consumer frost-free freezer achieves its
"frost-free-ness" (to make up some words here) by actually heating the
freezer lines of the freezer compartment to above 0 degrees C about every 6
hours to melt the frost off... and that the payload of the freezer goes
through similar although not quite as dramatic freeze/thaw cycles to keep
the frost off them.

Thus, an ice cube's actual temperature, while still below 0 degrees C, might
undergo swings of 20 degrees every 6 hours or so.

And that's assuming the door to the freezer is always closed.  In my house,
it is being opened often to retrieve or store contents, which adds to the
variability of the temp of the ice cube.

In contrast, if the main water supply to most homes goes through miles of
underground pipe, the surrounding earth is a pretty big heat sink to cause
the water to reach a quite consistent temperature when delivered to the tap
(after you've opened the tap & let it run for a minute).

However, off-list someone politely pointed out to me that while the
temperature of the ice cube might indeed vary by 20 or more degrees in a
residential environment, at the end of the day the energy "absorbed" by the
phase change from solid to liquid (melting the ice) is so much higher than
the energy absorbed by first warming the ice from, say, -20 degrees C to 0
degrees C that the only thing that really matters in the real world is the
melting.

So, I guess the initial temperature of the ice cube is pretty much
irrelevant.   

--Phil


> -----Original Message-----
> From: homeroast-bounces at lists.sweetmariascoffee.com [mailto:homeroast-
> bounces at lists.sweetmariascoffee.com] On Behalf Of Allon Stern
> Sent: Tuesday, April 06, 2010 7:34 AM
> To: A list to discuss home coffee roasting. There are rules for this
> list, available at http://www.sweetmarias.com/maillistinfo.html
> Subject: Re: [Homeroast] Sunbeam Vac pot tuning: a simple solution
> 
> 
> On Apr 6, 2010, at 12:49 AM, Phil Palmintere wrote:
> 
> > "...  Icecubes are always the same temperature ...  dan
> >
> > I'm not sure why you say icecubes are always the same temperature.
> 
> Maybe his point is that the ice cubes from his freezer are a consistent
> temperature, versus the tap water which varies between winter and
> summer. I didn't read that as stating that there is a law of nature
> that ice cubes are always some particular temperature.
> 
> -
> allon
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