7kW immersion heater?

[AdamW]

Well, the specific heat capacity of water is 4.2 kJ / kg K if I recall.

So, if you want to heat 1l of water from, say 10 celsius to 100 celsius, with your 25MW heater it would take...

90 degree rise, 1kg of water... requires 378 kJ of energy.
25MW is 25000 kJ of energy per second.
378/25000 = 0.01512 seconds. or 0.063s with the 60MW version

Now, to heat your 200l bath from 10 to 40 celsius, that is...

30 degree rise, 200kg of water, requires 25200kJ of energy.
25200/25000 = one second. or about 0.4s for a 60MW version

That heater is insane: 25MW at 10kV is 2500 amps! and 45 bar?

What is this thing?! The only use i could imagine for something that can kick out 16 litres of boiling water every second would be some chemical plant. And even then I can't help thinking that an electric boiler is a pretty inefficient method!

 

[securespark]

I don't know about that size, but hospitals have them.

 

[AdamW]

when the water in your kettle starts to boil it means that at least some of the water is as hot as it is going to get as a liquid

energy is then being wasted turning the water into useless steam

An interesting fact: apparently if you take a kettle up a mountain and try to make some tea it tastes rubbish. Reason being, the atmospheric pressure at high altitude is sufficiently low that water boils at a measuredly lower temperature and the tea just doesn't work.

Has anyone every tried making tea in a pressure cooker? Then you get the water boiling at 110 degrees or so, perhaps it would taste better?

 

[securespark]

No mate, just stewed.........bleurghhhhhhh!

We tried that when we looked after a scout camp in the late 70's. Some of us got p*ssed and made tea in a pressure cooker, and it was a bag of w*nk.....and I don't even drink the stuff!!

(I'll save some wag a post - now you know why!!)

Don't ask me why the only daring thing we could think of to do was boil up a pressure cooker. It would have been more fun doing the same thing with the pan empty......

Alternatively, there were lots of quadrupeds in the field with us.......

 

[Stod]

That heater is insane: 25MW at 10kV is 2500 amps! and 45 bar?

It's a three phase boiler, so 144 A per phase.

Also, it's a steam boiler, that's the 45 bar. The advantage of an electrode boiler is that you don't have boiler tubes to foul up & it is possible to use untreated feedwater. As scale builds up, the electrodes plunge a little deeper. Eventually, you descale them - much easier than descaling boiler tubes.

 

[Big_Spark]

That heater is insane: 25MW at 10kV is 2500 amps! and 45 bar?

It's a three phase boiler, so 144 A per phase.

It'll be a bit more that 144A per phase Stod, even with a 10Kv supply

 

[AdamW]

Electrode boilers sound like a great idea for domestic hot water, but I can see why they aren't used. When you buy an immersion heater, it is sealed from the factory, risk of earth leakage and electrocution is within acceptable tolerances. But build an electrode boiler that can directly fit into a cylinder where an immersion heater once was and you will get some gimp connecting it up before it is fully installed. Instead of getting singed fingers they would ending up killing themself.

I am thinking, if this particular boiler is a three phase system then surely the easiest way to design it would be to have three separate phase electrodes arranged in a triangle (a delta configuration?) around a neutral electrode. Thus your 25MW @10kV would be 833A per phase.

Of course, I could well be wrong. Stod, how did you get 144A per phase?

 

[Stod]

Of course, I could well be wrong. Stod, how did you get 144A per phase?

By getting the decimal point wrong. It should be 1443 amp.

25000kW /10 kV /sqr(3)

I hope I got it right this time. I'm sure FWL will correct me if I'm wrong.

 

[ban-all-sheds]

No mate, just stewed.........bleurghhhhhhh!

We tried that when we looked after a scout camp in the late 70's. Some of us got p*ssed and made tea in a pressure cooker, and it was a bag of w*nk.....and I don't even drink the stuff!!

That's because you made it in the pressure cooker. It would also be w*nk if you boiled up the tea in an ordinary saucepan for the same time.

Don't ask me why the only daring thing we could think of to do was boil up a pressure cooker. It would have been more fun doing the same thing with the pan empty......

Dunno about daring(1) , and you'd have to have a strange definition of fun(2) , but you could have tried making the tea by boiling just the water in the pressure cooker, and then suddenly releasing the pressure in order to get access to water at 125 deg C....

(1) In this case "daring" means Darwin-proving stupidity

(2) In this case "fun" means 3rd-degree burns

 

[AdamW]

It would also be w*nk if you boiled up the tea in an ordinary saucepan for the same time.

So that's what I have been doing wrong all these years

but you could have tried making the tea by boiling just the water in the pressure cooker, and then suddenly releasing the pressure in order to get access to water at 125 deg C....

Ah, but you can only superheat (i.e. keep liquid above 100 deg C) by putting it under pressure. If you suddenly release the pressure then you will get a lot of almost instantaneous evaporation of the water, so you will get a face full of steam.

Perhaps if you just used a large pressure vessel (such as for testing underwater equipment in a naval laboratory) then you could set up a kettle inside there and a teapot. Now, some whales can dive to depths of around 7000 feet. This gives a pressure of 200 atmospheres. So, let's pump up our vessel to that (obviously you would stand outside and observe via a window/camera). Water will boil at about 290 deg C.

Boil the kettle at 290 degrees, make the tea, then release the pressure. Should taste great!

 

[Big_Spark]

Adam..I'll stick to my trusty kettle thanks...I like tea and coffee..but your method is just too much faffing about!!

 

[ban-all-sheds]

Ah, but you can only superheat (i.e. keep liquid above 100 deg C) by putting it under pressure. If you suddenly release the pressure then you will get a lot of almost instantaneous evaporation of the water, so you will get a face full of steam...

That's what I meant about stupidity and 3rd degree burns....

 

[AdamW]

I dunno, when a beauty salon advertises a face sauna it is hailed to deep cleanse the skin and unclog pores. When it is recreated by half a dozen pi**ed up blokes in a field with a pressure cooker, all of a sudden it is a burning hazard...

Did you know the pressure cooker was actually invented to help make glue? The guy who invented it, Papin, then realised he could use it to cook food instead (well, he was French!) and produced a meal for his fellow members of the Royal Society in London with it.

 

[securespark]

I suppose the dish he served up was chop gluey...followed by sticky toffee pudding......

 

[Stod]

Just get the pressure up to 3206.2 psi and the water won't boil at all. It turns directly into steam at 374 deg C.