PDA

View Full Version : Ask it Here



LAURENU2
04-30-2008, 10:54 PM
Heres a Question
I make Tea at times I use a Microwave to heat the water I get from the In-Sink hot water dispenser the last little bit to boiling
The Question
When I take to cup out the water is Not Boiling But as soon as i put the Tea Bag in it starts to Boil Why?
There is No more heat being applied so why dose it wait till the teabag go's in:confused:

Max Dettweiler
05-01-2008, 12:24 AM
Maybe the boiling point of tea is lower than that of pure water? (I don't know, just a guess.)

LAURENU2
05-01-2008, 01:40 AM
The instant boil happens the instant anything touches the water even a spoon or even a drop of new water

jasong
05-01-2008, 01:49 AM
I´d advise Googling it, but I think it has something to do with the smoothness of the bowl. If there are no imperfections in the bowl, than every point of the surface is going to be the same amount of surface tension. When you touch the spoon to the surface, that produces a weak point, which allows some heat to escape, and then after that the boiling is mostly self-sustaining. I mean, what is boiling except the water attempting to give off heat faster than simple radiation will allow? )I may be wrong about this last point)

Please don´t expect me to explain further. As it is, I´m at the limit of my memory. :)

Shish
05-01-2008, 05:10 AM
Microwaves heat any water content by vibrating the molecules and they stay vibrating therefor heating for around 2 minutes after you stop the microwave. Any vaguely metallic object will disturb the molecules frequency and so may cause apparent extra heating.
This is one reason you may get a bad stomach after eating microwaved food as you can actually burn the lining of gullet and stomach by eating food too soon after microwaving.
It is also an extremely inefficient way to heat water to boiling point as it uses a <60% efficient klystron to generate 2.2-2.5Ghz frequency waves.
Good for heating food but get a kettle and put just more than the water you require which will boil very rapidly. Or better still, get one of the new generation tea machines which instantly boil the water as you need it.
Tea should not be made with water from a sink heater or storage heater. It should always be made with fresh water, boiled and just back past boiling into a pre warmed cup or pot. Don't put the milk in until it's brewed as milk stops the tea from brewing properly.
Lot's of other tips for good tea making, see 50's and 60's ads on web (google).
This household are real tea addicts and that includes the dogs and a cockattoo addicted to tea and we buy good old fashioned (tea leaves) and make it properly. I also have to send real tea to friends in Norway and Sweden cos it costs a fortune there.

Paratima
05-01-2008, 02:28 PM
Shish is right on.

Also, if you're making green tea, it's fairly important, taste-wise, to NOT allow the water to get to a rolling boil. If you do, it needs to cool just a bit before hitting the tea leaves.

LAURENU2
05-02-2008, 02:36 PM
Thanks all good insight thats what I love about Free-DC you always get the Info you need:thumbs:
So the Micro's energy gets built up and stored in the heated substance

Shish
05-03-2008, 02:15 AM
Not exactly L. I used to have to explain rf stuff and ac/dc mechanics to trainees and classes but I'm a bit past it nowadays.
Ne'er mind, I'll try.
Imagine the klystron ( a big dirty rf wave generator) was generating a wave which you could see. That wave blows like a wind which makes the molecules vibrate like the string of a kite taut in the wind. The vibration will roughly equal the frequency of the wave (2.4Ghz is 2.4 billion times a second) after some small time (according to how many/much matter you have to absorb the wave energy) and as the energy is absorbed in the matter causing it to vibrate, it heats up the molecules by the friction of them rubbing together. Remove the energy and the molecules will vibrate for some time until they gradually slow down and therefor stop heating. Shaking or moving any matter fast enough in almost any medium (gas/water/matter) by any means will cause friction which heats the matter, just like the space shuttle re-entering the earth's atmosphere smashes gas molecules which make plasma (super heated gas) and the friction against air causes it to heat up until it eventually slows down. Not totally accurate, but you get the picture?:jabber::jabber:
I also had to explain to some people why they couldn't wander around some hi-power radar and microwave sites as even the scatter signal would spark off metal teeth bits or any metal and cause their hearing aids to explode as well as heat their body up enough to cook them from the inside if they were in the wrong place. I know the dangers first hand as I've still got the scars from climbing a live mast and microwave burns are not nice, gimme a flash burn any time. By comparison, 250v AC 50/60hz is just a tickle and 120v I ignore. Life does get serious tho' when japing by leaving a bank of 20kv caps around with no earth strips across the contacts. Every trade has it's rites of passage I guess.Mind you, sparks can be fun too :lmao:

LAURENU2
05-03-2008, 03:06 AM
Every trade has it's rites of passage I guess.Mind you, sparks can be fun too
Yea I know that all to well I started in the trades 38 years ago as a electrician
I was pulling a 220 3 phase line off a live breaker panel and shorted my pull line on the high side of the 3 phase line thats 180 V
the pull line blew up in my hands and threw me 10 feet back I blew a big 100A block fuse and shut down all lights down in the sub basement
I thought I was Dead all I could see was the Bright light from the Flash thought it was God calling me

Shish
05-03-2008, 04:20 AM
Well at least you only do that kind of thing once.....mostly :D
I think my biggest was shorting 22Kv power lines which were supposed to be off and having to sit there watching the truck tyres melt with leakage to wet ground until somebody wondered why the Tyne Valley had no power past Corbridge and an engineer radio'd for an emergency disconnect. Just as well we didn't have the linesman who normally came with us to lift the lines with a pole when we crossed the floodbank. Apparently, somebody had got the S. and N. sides of the river confused when generating the disconnect order and when we radio'd control for clearance they just looked at the board and gave us the OK. Surprising how far 22Kv can jump, as well. I can laugh about it now but it took a few shots of brandy to slow my heart down afterwards :eek:

LAURENU2
05-03-2008, 09:28 AM
Hurts don't it if you survive it :cheers:
And no it happened more then once
Thats why I quit and do Plumbing now
The worst that happened now is a lead pot explodes
and I look like a Christmas tree full of tinsel :harhar:

gopher_yarrowzoo
05-03-2008, 05:07 PM
Nice question - yeah I've seen pictures of a glass of water boiled in a microwave nothing happens, no bubbles at all - coffee hit it and BOOM it's boiling over... really weird - inductive heating..
Worst I've done is erm well I survived, the screwdriver didn't - I had the power off or I thought I did, went to separate out a T & E cable to repair it as It was damaged and got between live and Earth - tip melted 30Amp circuit - stupid asshat sparks before me had wired it in to a socket no SPUR :| was well miffed.
The worst I've heard about though was an alarm wired into the "LIVE" side of the main switch :O
You actually use a blow torch on pipes - wow I thought all plumbers used compression fittings, I know a lot about plumbing - my dear dad was a plumber & heating engineer he's dead now but he'd had forgotten more about the stuff than many of the "plumbers" we get around here know.

LAURENU2
05-03-2008, 06:39 PM
You actually use a blow torch on pipes - wow I thought all plumbers used compression fittings,
Ya I'm Old school Still pore lead joints for cast Iron, and Soldier copper pipe
I am one of the few left here that can lead joint a lead pipe together All though I have not run into lead pipes much any more thank god
I can even arch weld a pipe together:jabber:

Shish
05-03-2008, 09:48 PM
Some joints require lead solder such as in pressure heating and some gas if I remember my Corgi correctly. Not allowed to use it for potable water tho' for obvious reasons. UK has had a law against unqualified people messing with gas for some time hence the Corgi quals., but a lot don't realise it also now applies to electrics. As a requirement for some of my jobs in the past I had to do lots of courses and qualifications or at least know about them and their rules and regs.
Another of the fun things to do with newbs and visitors was to take them on a tour thru' the main grid switch area and get control to pop some switching. Always drag an earth lead (still a requirement for vehicles) as well ( before they had special boots for us) and keep everybody close. The bang of the switch going over as the big spark was blown away from it with very high pressure compressed air was only the first fun part. The best bit was watching all their hair stand on end as the static peaked and found it's way to earth. Static can do interesting things to both male and female bodies and was always good for some squeals and blushes.
Never bothered me at all tho' cos my body has negative potential unlike most people's positive. Not immune to shocks, just some of the effects.