Update: test results (was Vacuum flasks (OTish))

[Tim+]

>>> You may well be right but until someone explains how their flask is

>>> fundamentally different from my one (perhaps by NOT having a metal to metal >>> thermal bridge to the exterior) I'm still inclined to believe that the >>> traditional glass ones will always be superior for keeping stuff warm. >> >> Have you got your results yet? >> > > > > Right! > > I filled my new one, from Argos and made by Thermos, with boiling water > last night and now, 12 hours later, the water is still too hot to keep my finger in. >

Well after the best part of 24 hrs with a SS flask and a conventional flash filled with boiling water, the temperature of the water in the SS flask was

44C. To drink, it felt decidedly lukewarm.

The conventional flask water temperature was 52C. This felt significantly warmer and an acceptable drinking temperature (just) for tea.

So, it could just be that I have a cheap and nasty SS flask but unless anyone can show me one where the metal does not provide a direct thermal bridge with the outer case, I will continue to believe that conventional flasks out-perform SS ones when it comes to maintaining a constant temperature.

Tim

[Dave W]

Another factor is the thermal characteristics of the stopper. I have a metal flask with a deep cork stopper, and it keeps the water hotter for longer than my cheaper one with a short hollow plastic stopper.

[Chris Holford]

In article , Dave W writes snip a lot of interesting information and opinion!

I've thought about my own collection of SS flasks; One had a dent in it so there was a heat bridge between the inner and outer which would explain why it didn't keep stuff hot (or cold). Another two were cheapies which felt noticeably warm when holding hot stuff; they seemed OK when new.

Thinking about glass; radio valves made in the 40s and earlier are sometimes still usable, so the glass envelope has held it's vacuum for decades. (I know they had getters, but, if the valve had been cold for years in storage, I don't think this would have helped to retain the vacuum.)

I suspect that some SS flasks may have problems with porosity in the welds which would spoil the vacuum over a period of time.

I'm going to try a Thermos or Stanley one next time and also get a glass one for comparison.

Thanks for all the input.

[polygonum]

I agree that porosity could well be a reason. Also, I think that at least some are made by attaching the base to the rest of the flask with glue. Maybe that glue can deteriorate or simply not be up to it?