I was thinking of what the pressure is when the compressor stops but the freezer is still at -18°. In your scenario my guess is the refrigerant is partly liquid. The instructions say position the thing and leave it 24 hours before switching on, presumably for the liquid to gravitate down. If it were all gas nothing would happen. If that's right, the pressure is the refrigerant vapour pressure at the ambient temperature.
Don't know whether you found these sites Design a Refrigeration System - The Engineering Mindset and Refrigerant R-134a
We're obviously all aware of the fact that such is what is done, but that, in itself, does not mean that such is necessary for the refrigeration cycle to work. I still doubt that it is ('necessary') for the cycle to 'work' after some sort of fashion, since it seems to me that it probably inevitably will 'work' ('after some sort of fashion') when one starts compressing the gas, regardless its pre-compression pressure.
As implied in what I've just written to Sunray, is it not inevitable that a fair proportion of the refrigerant in the system will always be liquid - since, otherwise one would only have a very small amount of refrigerant in the system? ....
The instructions for most domestic fridges and freezers seem have changed over the years, initially down to 4 or so hours and, most recently, I've seen 1-2 hours. Where an 'explanation' is given, it most commonly seems to relate to the need for 'oil' to gravitate from other parts of the system down to the compressor (which, it seems is always 'at the bottom'?)
As I said in #61, I think there is some liquid refrigerant when the whole thing is at ambient temperature. When the compressor has just stopped so the freezer is at -18° more of it will be liquid..
I know how propane tanks work! It's a liquid at storage pressure and the pressure stays constant (at a given temperature) as the contents are used, until the liquid has evaporated. About 8 bara at 20°. Unlike an oxygen (or hydrogen or nitrogen) cylinder where it starts at 200 bar when full and falls steadily as the gas is used.
I said 24 hours from memory, the actual time isn't important. But re-reading my Bosch instructions, it says allow the appliance to sit vertically for about 1/2 hour.
It also says, below minimum design ambient temperature (+10° in my case) "functional irregularities may occur during automatic defrosting of the refrigerator interior". Maybe that's part of the explanation. I think it means the freezer, which has automatic defrost. The fridge has the usual condensate drainage.
Indeed - but, as I said, unless the pressure 'when the whole thing is at ambient temp' is high enough for an appreciable proportion of the refrigerant to be liquid, there would actually be fairly little refrigerant in the system - and does not the ability of the system to 'move' heat efficiently (at least, the rate at which it can do that) depend upon how much (mass) refrigerant there is?
I'm sure you do know how they work, but I suspect that some (including some who may be reading our mutterings!) may not.
Maybe we're partially getting somewhere, since the potential problem they are mentioning is a lot more benign that the "freezer won't work in an outhouse" story we so often hear being thrown about. Mind you, I have a feeling that that story has been around for a lot longer than 'self-defrosting' freezers, so I'm not sure!
Those are much the same as all the others I've seen (there appear to be countless). I'm not sure what they think is the target audience, but I suspect (but, of course, maybe wrong!) that the great majority of non-Physicists who might read it probably don't even know what entropy and enthalpy actually are - and I've yet to come across any of the articles which attempt to explain that!
Oh my giddy aunt, education from 50 years ago and I suspect I've not heard of them since, I suspect this is total bovine excreta but entropy (also spelt entrophy?) something like lack of energy or heat (And I'm struggling for words here) through failure of the process or confusion or something. Enthalpy is something like total energy or heat capacity of a system. B U T P L E A S E don't expect me to have a clue what I'm saying!
Quite so - and you say that you are one of the (I would think very very few) people who have had at least some education about those topics, even if 50 years ago. I would imagine that most people have probably not even heard of the words, ever!
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