tea and toast

I suspect the most efficient way to heat a cup of water is one of those coily immersion heaters, followed by a microwave.

Not that it matters much.

On Friday, July 15, 2016 at 1:09:31 PM UTC-7, Phil Hobbs wrote: ..

...

Aah, but then your next cup wouldn't be fresh brewed.

The water has to be freshly boiled (preferably only the once) then the tea poured from the pot after your brewing time.

cheers

kevin

On Friday, July 15, 2016 at 10:36:32 AM UTC-7, Jeff Layman wrote: ...

...

Yes, but the delta-T across the glass/metal is probably low that it won't make much difference

The heat transfer is probably dominated by the coupling of the container to the air.

kevin

A tea ball is your friend. Just fish it out after 5 minutes or so.

Personally I just strain out the tea leaves with my teeth. ;)

Cheers

Phil Hobbs

...

Not only that but in the US the power is limited to ~1700W that together with modern toasters catering for "thick" bread, or 4 slices, or being a combined toaster oven means that the heat flux is too low to toast effectively.

The bread is dried out before it toasts.

That's not so much of a problem when you can get 3kW out of a wall plug.

I had an old Proctor Silex from 30 years ago that worked well, but my wife threw it out in favour of a more modern Cuisinart that was terrible. I still haven't found a modern one that I like.

cheers

kevin

Not hard to estimate. A spherical tea-kettle of radius R has a volume of 4/3 pi R**3 and a surface area of 4 pi R**2. We assume the contents are well stirred, so that the water is isothermal.

With a wall of thickness d (assumed small compared with R) made from a material of thermal conductivity alpha, a temperature drop of T across the wall will pump

Q dot = 4 pi R**2 T/(d alpha)

watts into the environment. The cooling time constant is then

tau = Q dot / (V rho c_P T)

where rho is the mass density and c_P is the specific heat. For water, rho is 1000 kg/m**3 and c_P is 4.2 kJ/kg/K.

Thus the cooling time for the thermally grounded kettle would be

(d alpha) (4/3 pi R**3 * 1000 * 4200 * T) tau - ------------------------------------- (4 pi R**2) T

tau = 4200000 d alpha R -------------- 3

For an 8-cm radius kettle (about 2 litres), a 4-mm wall thickness (probably about right for glass), a thermally grounded glass kettle with alpha = 1 /W/m/K would have a time constant of

tau = 4200 * 0.004 * 1000 * 0.08 / 3 = 480 seconds, or 8 minutes.

With aluminum, whose alpha is about 200 W/m/K, it would be 2.4 seconds.

The reality is probably about 15 minutes as a SWAG. So the glass kettle walls actually help significantly.

Of course if you're heating it on a stove, it works against you there.

Cheers

Phil Hobbs

I just insert a K-cup ;-) ...Jim Thompson

Why is it important to only have freshly boiled water that has only been boiled once?

Dan

If you boil it twice it tastes burnt. ;)

Cheers

Phil Hobbs

It's the chemicals in NY water. Did you see the recent news item about NY water having unsafe chemicals ?>:-} ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

I'm looking for work... see my website.

It's full of dihydrogen monoxide, for a start. ;)

Cheers

Phil Hobbs

If a pedestrian is in the middle of the road there is a good chance he will get hit. The stats show that running lights reduce accidents.

Wrong.

LEDs? It's the HID lights that a bright. My wife's car has them and we're always getting flashed to turn off the brights, though they're not on.

Running lights, I don't care one way or the other. I prefer a switch on the headlights but my wife always leaves it in the AUTO position.

NYC water is actually quite good. They steal it from the Catskills. ;-)

Not so much evaporates though the glass walls, either.

We steal ours from Hetch Hetchy valley, in the Sierras. Tasty stuff.

It broke John Muir's heart when the dam was built and the valley was flodded.

You must have more sensitive taste buds than I have. What tea brands do you use. My wife buys PC Tips from some internet store. Not the best tea buy better than a lot of teas.

I believe when you boil it the first time you drive out all the dissolved oxygen. And when you boil it again, it is the same as when only boiled once. We use an electric kettle, so it does not get boiled for a long time.

Dan

That's the best part. Then you add the East River sludge >:-} ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

I'm looking for work... see my website.

You must have missed the smiley. ;) ;)

Cheers

Phil Hobbs

You must have missed the smiley. ;) ;)

Cheers

Phil Hobbs