Vacuum flask test - has anyone at YM got a science GCE?

My sister in law does / did outside catering. She invested in flasks that were expensive but kept the contents very hot for over 20 hours and this was in the winter. No idea of make before anyone asks. I do agree with the comments about the s/s ones for heat retention.
 
Not seen the article so don't know how they represented %ages but:

A fair comparison must be the rate at which energy is lost from the contents to the surroundings. Rate of heat transfer can be related to temperature decrease in whatever temperature units you use per whatever time interval you wish to use. So you could use degrees C decrease per hour as a measure of efficiency of the insulation, or alternately how long it takes to drop a fixed number of temperature units. It doesn't actually matter what linear temperature scale you measure in and you could use farenheit, celsius, kelvin, or fred bloggs units.

The rate of cooling slows down as the temperature difference between the liquid and outside reduces so is not a linear relationship but you are measuring relative heat loss so at any temperature gradient the better insulator allows a lesser amount of total energy loss. The fact it is not linear probably doesn't matter for our purposes as we would measure starting when temperature difference is greatest and only for a small period of time in relation to how long it takes the contents to reach ambient temeprature.

You can therefore do a relative comparison of the rate of cooling as percentage ratio against the best on test so normalising to that, e.g. rate of cooling of flask A is 20% faster than that of Flask B in going from start temperature X to start temperature Y.

So on my basis if Flask A temperature went from 100 to 80 units in an hour and Flask B temperature went from 100 to 90 units in an hour the rate of cooling is 50% greater for Flask A than Flask B so I would consider Flask B to be approx. 50% better at retaining heat than Flask A within the temperature range used.

BSc Applied Physics (Dunelm) unfortuantely a 3rd and 35 years ago so can't remember a thing....
 
guernseyman said:
YM are in good company.

Yesterday, I think, a commentator on BBC news remarked that -70 deg C was twice as cold as -35 deg C.
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Not connected in any way but that yobbish bald bloke who does the Maasterchef has been trailing his Who Do You Think You Are episode.
It's now been dubbed out now, but initially he said he had "done a complete 90° about-face"
 
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As someone said, YM is for sailors, not boffins. However, much yachting material has scientific relevance, such as engineering sails and engines, meteorology and navigation. This is why it can be depressing when media in general put out material purporting to be about science but written by arts folk who lack sufficient curiosity to get their facts right, let alone avoid simple solecisms like "this bacteria".
 
Lakesailor said:
Not connected in any way but that yobbish bald bloke who does the MaSTERCHEF THING HAS BEEN TRAILING HIS Who Do You Think Yo Are episode.
It's now been dubbed out now, but initially he said he had "done a complete 90° about-face"
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Greg Wallace? He is an obnoxious git, gave me great pleasure to read this review;

http://www.telegraph.co.uk/foodandd...reggs-Table-London-SE1-restaurant-review.html

At risk of further thread drift, how come people are reading the October issue and it hasn't arrived on my gizmo?
 
Amulet said:
Not wishing to start a fight, but it doesn't help because it is wrong. If there is a meaningful calculation, then the only defensible basis is to calculate in Kelvin. 100 Celsius is 373.15 Kelvin, and a drop of one degree is an absolute loss of heat stored of about 0.27%, not that this calculation is of any use to anyone.

Or, if you want a practical example, imagine a vacuum flask filled with stuff at -25 Celsius in an ambient temperature of -50 Celsius. Suppose it loses heat and falls to -30 Celsius. What percentage of its stored heat has it lost? The calculation is a scientific nonsense and unnecessary to the article.
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You are of course right. But you are also being pedantic maybe even nerdish. A magazine test report is not a page out of a scientific journal so whilst it might offend your sense of scientific propriety, none of the readers could care a damn what the percentage figure means. All they want to do is to compare one brand of thermos with another. The numbers allow them to do that as far as they wish to go..
 
wotayottie said:
You are of course right. But you are also being pedantic maybe even nerdish. A magazine test report is not a page out of a scientific journal so whilst it might offend your sense of scientific propriety, none of the readers could care a damn what the percentage figure means. All they want to do is to compare one brand of thermos with another. The numbers allow them to do that as far as they wish to go..
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I fundamentally disagree. Quoting the final temperatures alone (given a common start temperature) would have provided the simple comparison required with "highest is best". Introducing the crassly wrong "percentage of heat" idea adds nothing and merely shows up their lack of (really very basic) knowledge.

People without understanding of such things will presume a magazine article to be authoritative, and are let down by this sort of sloppiness. I suspect that the magazines were also a major source of that other nonsense - the A/h unit - often tiresomely repeated on these forums by those who don't understand electricity.
 
wotayottie said:
pedantic maybe even nerdish..
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First compliment I've had on the forums.

Scientific understanding matters and having a pseudo scientific investigation talk such nonsense is bad for us. I'm willing to argue that a negative view of science as boffinry or nerdism undermines public understanding of science to the detriment of mankind - you don't want it left in the hands of boffins.

I don't mind being a nerd or a boffin, but there are million things I don't understand. I seek out and welcome those who point them out and put me straight.

If you were a non-sailor writing something which involved sailing you'd get someone who knew about it to read it over before publishing. You'd expect YM to have someone who knew something about science. Someone thought those percentage figures actually meant something. It's true that, if you ignore them you get all the useful information. However, I wouldn't trust a technical test report on a boat, a winch, and echo sounder a radio or anything else if it was carried out by someone with so little scientific understanding - you never know what else they'd get wrong.
 
Amulet said:
I wouldn't trust a technical test report on a boat, a winch, and echo sounder a radio or anything else if it was carried out by someone with so little scientific understanding - you never know what else they'd get wrong.
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This is the reason I cancelled my subscription to Which? Magazine. Once they started reviewing computers, which I know about, I realised it was mostly tosh. I then extrapolated...

There have been a lot of pseudo-technical tests in various IPC magazines over the years: anchors, VHF radios, antennae etc. Some of the the tests require strict conditions, they are rarely adhered to. One test even mentioned that the VHF range tests may have been affected by the height of the tide, well DURR!
 
When David Beckam was at ManU he arrived at the training ground one day with a new vacuum flask. "What's that?" asked his team mates. "It's a vacuum flask" say Becks.

"What does it do" they ask. "Well," says Becks, "you put something hot in it and it keep it hot. You put something cold in it and it keep it cold". "That's incredible" they say in unison, "what have you got in there?"

"Two cups of coffee and a choc-ice".......

Sorry I just though we needed some light relief.....:D
 
Amulet said:
The test in the October issue may make give useful guidance.
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That says it all - it is intended as a guide for yachties - not a treatise on heat capacity migration for scientists.

Of course it's wrong, just as how schools still teach how atoms bond together to form molecules is wrong (well, that is - according to the latest model ...), but sometimes it's necessary to present the information to suit the audience - even if that means being technically incorrect.

Indeed, most higher education is about unlearning the stuff taught earlier in the system - but then, the majority of the population never find themselves in that position.
 
Burnham Bob said:
I know flasks keep hot liquids hot and cold liquids cold, but I've always wondered how they work out which is which and what they need to do........
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It's like mirrors - they invert images from side to side but not top to bottom. How do they know which way is up? Obviously science doesn't know everything.
 
electrosys said:
... but sometimes it's necessary to present the information to suit the audience - even if that means being technically incorrect.....
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There is never a need to be technically "incorrect". Sometimes a good approximation is OK, and certain approximations are conventional in some domains. This is not what is going on here.

Someone writing a technical article decided to compute a number in a way which was meaningless and wrong. It added nothing to the article - it would have been more informative without it. You'd hope that, while there's no reason to suppose that everyone cares about gross scientific misunderstanding, someone writing an article which intentionally conveys an aura of technical expertise would not communicate in such a crassly wrong manner. The article makes apparent sense if you ignore the idiocy, but if you spot the idiocy you wonder what other idiocy you haven't spotted in other tests.

It is about as sensible as saying my boat's maximum speed is 167%.

I'd never write anything about music, but, if I did, I'd be sure to say something completely idiotic - so I'd take it to someone who knew something and get them to check it. I certainly wouldn't say "Not all of us care about a details like whether the time signature is wrong."

The yachting press ought to have the ambition to be technically respected.
 
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