Vacuum flasks (OTish)

[Chris French]

In message , Chris French writes

And BTW, if anyone is quoting figures, give the volume of the flask, as it's going to make quite a difference.

[Dave Liquorice]

It certainly does. The stopper on my plastic/glass "Thermos" is hollow, intended to keep sugar/tea/coffee/folding spoon in I think.

Leave it empty and the heat leaks out very quickly, eve with the clip on cups over the top of the stopper. I've cut a bit of 1" thick expanded polystyrene to fit the recess, far far better. B-)

[Davey]

snip

Which is what one needs, after all.

[newshound]

[Reentrant]

I've just filled two 1-litre flasks, one glass and one SS, with boiling water and will check with a lab-grade -10 to 105c mercury thermometer from time to time.

[GB]

Without opening them, I hope? ;)

[Tim+]

Condolences on your fathers demise. Regarding the flask, not sure why you would need an angle grinder. On my SS flask you can easily see that the inner flask is bonded to the outer.

Tim

[RJS]

I have owned a number of SS vacuum flasks over the years, including one made by Stanley but the clear winner is this one:

for the simple reason that the stopper works perfectly insofar as one can pour the drink from the flask and when the stopper is closed there is minimal or no post-pour dribble. This contrasts markedly with every other flask I have.

It also keeps drinks hot for more than 24 hours.

It may hold only 1 litre but the benefit of not having to worry about it dribbling when using it in a car is priceless.

Richard

[Jaffna Dog]

You could have salvaged your drink by filtering it through a piece of cloth - think like a soldier! I usually have some yellow dusters with me anyway, always useful for dealing with spillages etc. As for flasks, I've always u sed the cheap SS ones, they keep tea drinkable for at least six hours.

[Reentrant]

Only briefly! Both flasks were cold at the start ....

SS. Glass

10 mins 93.1. 93.3 1 hr. 90.0 90.0 2 hr. 83.5. 83.2 3 hr. 78.7. 79.5

[Dave Liquorice]

Which shows the glass one is cooling slower than the stainless, not a lot but very clear.

It would be intresting to see the difference after 12 hours and unopened. I'd do the experiment but my glass flask is 1 l and the stainless 1/2 l.

[Tim+]

And according to the measurements at 2 hours suggest that the SS thermos is out performing the glass one, only for the positions to reverse at 3 hours! Obviously thermodynamically hugely unlikely so the measurements must be a bit suspect.

I think my recordings on two 1 litre flasks clearly demonstrate the superiority of glass over SS for heat retention.

Tim

[polygonum]

How do you explain that the glass cooled down *more* quickly between 1hr and 2hr?

It would also be interesting to do the experiment with two flasks which have identical caps so as to eliminate differences due to that.

[Tim Watts]

The 2 hour reading shows acceptable measurement error (for a domestic thermometer).

The 3h one shows a very clear difference that is unlikely to be down to error unless the thermometer is very dodgy.

[Tim Watts]

Measurement error which is actually tiny.

[Reentrant]

Maybe I didn't stir one enough and measured a hotspot. Anyway, final two readings:

SS Glass

4.5 hours: 75.1 76.0

then I went to bed ...

13.5 hours: 60.1 61.3 - and that's the most significant reading.

So I'd say bugger all difference within experimental error. The thermometer is accurate (easily to 0.2 degrees) and the flasks were kept next to each other away from draughts and radiators, However they are slightly different shapes (the SS is squatter so less surface area).

Anyway, if you look at

stainless steel is a poor conductor of heat compared to many other metals, though better than glass. Also the steel is much thinner than the glass in a vacuum flask.

[Tim Watts]

Thank you - that was most interesting.

[Tim+]

Interesting. Clearly not all SS flasks are created equal. I wonder how your's differs from mine?

Tim

[Andrew Gabriel]

My parents have a very large vacuum flask, bought in the mid 1960's in the US. Considering how many picnics, school trips, and the like it went on, it's remarkable that it survived. The lid has a nest of cups in it.

I used to have a standard sized flask which was used to take soup to school as a packed lunch, as did many people at the time. Every few weeks there was the unmistakable sound of one of these landing on the floor and smashing, usually whilst still filled with soup. Mine probably broke a couple of times over the years. I think I still have it somewhere.

[Bill]

In message , Tim+ writes

Thank you.

The hearse got stuck in traffic and was 20 minutes late. If I hear one more comment about being "late for his own funeral" I will scream, there again it did lighten the atmosphere a bit :-)

Why an angle grinder? any excuse to use one and this seemed a good one! I do wonder if there are any spacers of other material in the gap between the inner and outer though.